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WO2020040639A2 - An electrical stimulation device for body tissue - Google Patents

An electrical stimulation device for body tissue Download PDF

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Publication number
WO2020040639A2
WO2020040639A2 PCT/NL2019/050542 NL2019050542W WO2020040639A2 WO 2020040639 A2 WO2020040639 A2 WO 2020040639A2 NL 2019050542 W NL2019050542 W NL 2019050542W WO 2020040639 A2 WO2020040639 A2 WO 2020040639A2
Authority
WO
WIPO (PCT)
Prior art keywords
energy
electrode unit
pulse generator
approx
pulses
Prior art date
Application number
PCT/NL2019/050542
Other languages
French (fr)
Other versions
WO2020040639A3 (en
Inventor
Hubert Martens
Daniël SCHOBBEN
Antonius Driessen
Original Assignee
Salvia Bioelectronics B.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Salvia Bioelectronics B.V. filed Critical Salvia Bioelectronics B.V.
Publication of WO2020040639A2 publication Critical patent/WO2020040639A2/en
Publication of WO2020040639A3 publication Critical patent/WO2020040639A3/en

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Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N1/00—Electrotherapy; Circuits therefor
    • A61N1/18—Applying electric currents by contact electrodes
    • A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
    • A61N1/36—Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
    • A61N1/372—Arrangements in connection with the implantation of stimulators
    • A61N1/378—Electrical supply
    • A61N1/3787—Electrical supply from an external energy source
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N1/00—Electrotherapy; Circuits therefor
    • A61N1/18—Applying electric currents by contact electrodes
    • A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
    • A61N1/36—Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
    • A61N1/372—Arrangements in connection with the implantation of stimulators
    • A61N1/37211—Means for communicating with stimulators
    • A61N1/37217—Means for communicating with stimulators characterised by the communication link, e.g. acoustic or tactile
    • A61N1/37223—Circuits for electromagnetic coupling

Definitions

  • the present disclosure relates to an electrical stimulation device, an implantable pulse generator unit and an implantable electrode unit.
  • Implantable devices require a protection method, both to protect the body from implant contamination and the implant electronics from corrosion. Encapsulation is a critical component for the design of a medical device implant - it acts as a barrier between the active electronics and the inside of the human body. The function of this barrier is to prevent electrical current and materials leakage from the device into the body and to protect the electronics from human body fluids in order to prevent the degradation process of the implant electronics.
  • IPG implantable pulse generators
  • US application US 2016/0158562 describes systems and methods to create a magnetic field from an elongated transmission coil of an external stimulator and expose an elongated receiver coil of a magnetic driver to the magnetic field.
  • the systems and methods generate at the magnetic driver a pulse forming a stimulation waveform in response to a remote magnetic field.
  • the systems and methods deliver the stimulation waveform to a target peripheral nerve through an electrode from the magnetic driver.
  • US application US 2018/0093099 describes a microstimulator with an energy harvesting circuit configured to receive an input signal from a remote transmitter and generate an electrical signal based on the received input signal.
  • the microstimulator further comprises a diode rectifier in series with the energy harvesting circuit.
  • the diode rectifier is configured to rectify the electrical signal.
  • the energy harvesting circuit and the diode rectifier can be encapsulated within a biocompatible electrically insulating material. Additionally, in some cases, an electrical interface is exposed through the biocompatible electrically insulating material.
  • US application US 2012/0095531 describes a system and method for energy transfer between a transmitting unit and a receiving unit, over relatively large distances.
  • the transmitting unit has a transmitting antenna circuit having a first resonant frequency and a high quality factor.
  • an electrical stimulation device comprising a treatment pulse generator unit and an implantable electrode unit;
  • the treatment pulse generator unit comprising: a controller for producing treatment energy pulses; one or more energy transmitters, configured and arranged to wirelessly transmit the treatment energy pulses;
  • the implantable electrode unit comprising: an electrode unit encapsulation layer, configured and arranged to resist the ingress of fluids from a human or animal body into at least a portion of the electrode unit; one or more energy receivers, configured and arranged to wirelessly receive at least a portion of the treatment pulsed energy from an associated energy transmitter through the encapsulation layer when the associated energy transmitter is proximate; one or more stimulation electrodes, each configured to receive treatment pulsed energy from an associated energy receiver, and further configured to transmit the treatment pulsed energy received to human or animal tissue as electrical pulses; wherein the implantable electrode unit is configured and arranged to be rigidly attached to the treatment pulse generator unit such that one or more energy transmitters are proximate the associated energy transmitter.
  • the encapsulation layer is configured and arranged to allow, in use, the portion of treatment pulsed energy to be received wirelessly through the encapsulation layer.
  • the electrode unit may be separately optimized for implantability.
  • the dimensions of the implantable electrode unit may also be minimized as the functionality is divided between the electrode unit and the pulse generator unit.
  • the rigid attachment may provide improved retention of alignment and/or proximity - this may improve the stability and reproducibility of the one or more energy transfer channels.
  • Known devices use wireless energy transfer to allow energy transfer over relatively large distances, and to avoid physical connections.
  • the devices in this disclosure use wireless transfer when the transmitter and receiver are relatively close - this allows a high efficiency of energy transfer through an encapsulation layer, allowing the encapsulation layer to be optimized to a high degree to reduce the risk of ingress while improving the reproducibility of the energy transfer within a stimulation channel.
  • the device is further configured such that the separation between the one or more energy receivers and the associated energy transmitter is lOmm or less, preferably 7mm or less, more preferably 5mm or less, even more preferably 3mm or less, most preferably 2mm or less.
  • the power of the transmitted treatment energy pulses may be reduced. This may allow lower powers to be used and/or provide a longer lifetime in the case that the pulse generator unit comprises a power source.
  • the device is further configured and arranged such that the treatment pulse generator and the implantable electrode unit are separable by dermis or skin.
  • the implantable electrode unit is configured and arranged to be rigidly attached to the treatment pulse generator unit such that one or more energy transmitters are aligned to the associated energy transmitter.
  • Proximity may be predetermined to a high degree, as well as alignment.
  • the device further comprises mechanical means, such as a pin or a magnet, configured and arranged to provide alignment.
  • the device is further configured and arranged such that the rigid attachment is configured and arranged to be detachable.
  • the device is further configured and arranged to wirelessly transmit the treatment pulse energy as magnetic pulses, light pulses, electromagnetic pulses, RF pulses, microwave pulses, acoustic pulses, electrical field pulses, and any combination thereof.
  • the one or more energy receivers and the one or more energy transmitters are configured and arranged to provide one or more non-galvanic couplings for the treatment pulsed energy.
  • the device further comprises: one or more reference conductor, configured and arranged to provide an electrical reference value for one or more stimulation electrodes.
  • Providing a reference conductor may provide a higher degree of control of the stimulation required. This may be provided as a separate electrode, and/or use one of the electrodes provided in the electrode unit.
  • the implantable electrode unit further comprises: one or more circuit components, configured and arranged to transfer the pulsed energy from one or more energy receiver to the one or more associated stimulation electrodes as electrical pulses; wherein the one or more circuit components are predominantly passive.
  • the one or more energy transmitters each comprise a first conductor, electrically connected to the controller, configured and arranged to wirelessly transmit the energy pulses;
  • the one or more energy receivers each comprise a second conductor, electrically connected to one or more associated electrodes; the one or more second conductors being configured to wirelessly receive at least a portion of the pulsed energy from the associated first conductor when the associated first conductor is proximate.
  • energy pulse may be wirelessly transmitted in different configurations and arrangements, it may be advantageous to use electrical conductors as these may allow the electrode unit to be further simplified, as the received pulse energy is converted to electrical energy, which is provided to the stimulation electrodes.
  • the one or more first conductors may optionally form coils with one or more windings.
  • adjacent coils may be separated by a distance substantially equal to the diameter of the coils. This may provide a reduction in electrode unit dimensions without greatly increasing crosstalk.
  • the first coils may have substantially the same diameter as the second coils. This may provide a higher degree of alignment accuracy.
  • Minimizing of the dimensions of the electrode unit may be further improved by providing one or more of the coils with a diameter of between 1 to 3 millimeters.
  • the treatment pulse generator unit may also be advantageous to configure and arrange the treatment pulse generator unit to be implantable by the treatment pulse generator unit comprising a pulse generator encapsulation layer, configured and arranged to resist the ingress of fluids from a human or animal body into at least a portion of the treatment pulse generator unit.
  • the reliability may be improved by the device further comprising a stimulation device encapsulation layer, configured and arranged to resist the ingress of fluids from a human or animal body into the treatment pulse generator unit and/or the electrode unit.
  • the device may be further configured and arranged to be implantable.
  • This may be particularly advantageous as the voltages and currents that may make the stimulation device more susceptible to galvanic corrosions are in general higher in the treatment pulse generator unit than in electrode unit.
  • the DC voltages and currents may be much higher.
  • the treatment pulse generator generally comprises active (non-passive) components, and may comprise a power source, such as a battery, which may further increase the susceptibility to galvanic corrosion.
  • FIG. 1 depicts schematically an implantable electrical stimulation device, such as an implantable pulse generators (IPG);
  • IPG implantable pulse generators
  • FIG. 2 schematically depicts an improved electrical stimulation device comprising two units - an implantable pulse generator unit and an implantable electrode unit;
  • FIG. 3 depicts a further example of an improved electrical stimulation device, comprising a further pulse generator unit and a further electrode unit;
  • FIG. 4A depicts another improved electrical stimulation device, comprising the pulse generator and the implantable electrode unit depicted in FIG 3;
  • FIG. 4B depicts an alternative alignment and proximity of the device depicted in FIG. 3;
  • FIG. 5 depicts schematically a configuration for resonant inductive coupling;
  • FIG. 6 depicts an alternative model for determining configurations suitable for resonant inductive coupling
  • FIG. 7 depicts the magnetic field produced when a current of 1 mA passes through a preferred first coil with diameters lmm, 2mm and 3mm and having one (1) winding;
  • FIG. 8 depicts the variation in the coupling factor (the quality of the energy transfer) over a separation distance between a first and second coils with diameters lmm, 2mm and 3mm;
  • FIG. 9 shows the efficiency of power transfer over a separation distance between a first and second coil with a coil diameter of 1 mm and a transmission frequency of 10 kHz;
  • FIG. 10 shows the efficiency of power transfer over a separation distance between a first and second coil with a coil diameter of 1 mm and a transmission frequency of 150 kHz;
  • FIG. 11 shows the efficiency of power transfer over a separation distance between a first and second coil with a coil diameter of 2 mm and a transmission frequency of 10 kHz;
  • FIG. 12 shows the efficiency of power transfer over a separation distance between a first and second coil with a coil diameter of 2 mm and a transmission frequency of 150 kHz;
  • FIG. 13 shows the efficiency of power transfer over a separation distance between a first and second coil with a coil diameter of 3 mm and a transmission frequency of 10 kHz;
  • FIG. 14 shows the efficiency of power transfer over a separation distance between a first and second coil with a coil diameter of 3 mm and a transmission frequency of 150 kHz;
  • FIG. 1 depicts schematically an implantable electrical stimulation device 700, such as an implantable pulse generators (IPG).
  • the implantable device 700 comprises a power supply 750, such as a battery, configured and arranged to provide power to a controller 720.
  • the battery may be rechargeable and/or non-rechargeable.
  • the controller 720 is electrically connected to one or more stimulation electrodes 760 and at least one reference electrode 770 - each stimulation electrode 720 provides energy relative to the at least one reference electrode 770.
  • the controller 720 may be software programmable, firmware programmable, hard-wired and any combination thereof.
  • the implantable device 700 is configured and arranged to be implantable such that a suitable amount of energy may be provided to a region of human or animal tissue proximate the one or more stimulation electrodes 720 after implantation.
  • Implantation may be partial or complete - at least a portion of the device comprising the one or more stimulation electrodes 760 may be implanted.
  • encapsulation 710 is provided such as a hermetic titanium can or case. Additionally or alternatively, the encapsulation 710 may be configured to reduce the chance of leakage of fluids or other substances from the implantable device 700 into the human or animal body. The encapsulation 710 is further configured to allow electrical stimulation to be applied to tissue using the electrodes 760, 770.
  • the controller 720 is further configured and arranged to provide energy through the electrodes 760, 770 in the form of one or more electrical pulses.
  • the controller 720 may be further configured and arranged to control parameters of the pulses, such as intensity, duration, waveform shape, frequency, and repetition rate.
  • Ingress of fluids into the implantable device 700 may reduce the performance of the device 700, or even reduce the operation lifetime of the device 700. This may be disadvantageous, particularly when the implantable device 700 requires a surgical procedure, or the intervention of a healthcare professional, for implantation and explantation / replacement.
  • US patent 9,333,339 discloses such an IPG device, configured and arranged to provide Peripheral Nerve Stimulation (PNS) for pain relief.
  • the IPG device comprises a stimulation lead 14 as depicted in FIGURES 4, 14,15, 17, 18, 19 and described in the relevant parts of the description.
  • the use of a stimulation lead 14 may be advantageous as the position of stimulation electrode may be determined more accurately, and smaller leads may be used for tissue regions where smaller dimensions are more suitable.
  • suitable pulse parameters for an IPG include: 0.5 - 4.0 Volt amplitude, 90 - 200 microseconds pulse width and 50 - 400 Hz repetition rate.
  • FIGURES 17, 18, 19 implantation of the pulse generator (IPG) 16 is depicted in FIGURES 17, 18, 19 and described in the relevant parts of the description.
  • IPG 16 and possibly part of the lead must be encapsulated.
  • Particular attention must be paid to the connection of the electrode lead (stimulation lead) to the pulse generator (IPG).
  • the risk of ingress around this connection point may be reduced by including a header portion in the pulse generator (IPG) using an electrical feedthrough that is sealed.
  • FIG. 2 schematically depicts an improved electrical stimulation device 100 comprising two units - an optionally implantable (or partially implantable) treatment pulse generator unit 200 and an implantable (or partially implantable) electrode unit 300.
  • Implantable means being suitable for implantation under the skin in a human or animal body, preferably in a living body and preferably for extended periods of time.
  • Implantation depth may vary depending on the tissue to receive the electrical stimulation - for example:
  • the treatment pulse generator unit 200 and the electrode unit 300 may be combined into one device 100 by, for example, encapsulating them together.
  • the energy transfer between the treatment pulse generator unit 200 and the electrode unit 300 is configured and arranged according to the invention.
  • both units 200, 300 are configured and arranged to be implantable (or partially implantable) as one device 100 together.
  • the electrode unit 300 may be inserted (or partially inserted) into the pulse generator unit 200, configured and arranged to provide energy transfer between them according to the invention.
  • the electrode unit 300 is configured and arranged to be implantable.
  • the treatment pulse generator unit 200 may be configured to be implantable as well.
  • the pulse generator unit 200 may be configured and arranged to be an external unit, for example, a trans-dermal electrical stimulation device 100
  • the electrode unit 300 and pulse generator unit 200 are configured and arranged to be separate, distinct devices, configured and arranged to provide energy transfer between them according to the invention.
  • the electrode unit 300 is configured and arranged to be implantable.
  • the pulse generator unit 200 may be configured to be implantable as well. Alternatively, the pulse generator unit 200 may be configured and arranged to be an external unit, for example, a trans-dermal electrical stimulation device 100
  • the treatment pulse generator unit 200 comprises:
  • a power supply 250 which may be any type of power source suitable for use with an implantable device.
  • a power source suitable for use with an implantable device.
  • AC and/or DC voltages may be used in the pulse generator unit 200, and DC may be provided from the power supply 250 to the rest of the pulse generator unit 200.
  • controller 220 for producing treatment energy pulses.
  • This may be a suitably configured and programmed processor, controlling one or more parameters of the energy pulses, such as intensity, duration, waveform shape, frequency, and repetition rate using one or more software methods. It may operate in a stand-alone mode, or it may be in regular communication with an external controller, or some combination thereof.
  • one or more treatment energy transmitters configured and arranged to wirelessly transmit the treatment energy pulses.
  • the device is optimized for the transfer of treatment energy pulses. This is different to known systems where energy is transferred wirelessly for power purposes - although the energy being transfer may be alternating, the energy transferred during power transfer is used to power a treatment pulse generator.
  • the devices comprise treatment pulse generators at the transmission part of the device.
  • Any suitable treatment energy transmitter may be used, such as:
  • one or more coils 230 configured and arranged to convert the energy pulses to magnetic pulses for transmission;
  • one or more lasers, LED’s or laser diodes configured and arranged to convert the energy pulses to light pulses for transmission;
  • inductive coils configured and arranged to convert the energy pulses to electromagnetic pulses for transmission
  • electromagnetic transducers configured and arranged to convert the energy pulses to electromagnetic radiation pulses for transmission, such as RF (radio-frequency) or microwaves;
  • acoustic transducers configured and arranged to convert the energy pulses to acoustic pulses for transmission, such as ultrasound;
  • one or more electrical capacitive conductors configured and arranged to convert the energy pulses to electrical field pulses for transmission.
  • the transmitter components may be miniaturized using modern manufacturing technology. These technologies comprise at least one conductor.
  • the treatment pulse generator 200 may comprise an encapsulation layer 210.
  • This layer 210 is configured and arranged to resist the ingress of fluids from a human or animal body into the pulse generator unit 200.
  • the implantable electrode unit 300 comprises:
  • one or more energy receivers 340 configured and arranged to wirelessly receive at least a portion of the pulsed energy from an associated energy transmitter 230 when the associated energy transmitter 230 is proximate.
  • Any suitable energy receivers may be used, including the types indicated as examples of energy transmitters.
  • the same or a similar type is used to provide a high degree of efficiency in the
  • photo-diodes may be used to convert incoming photons to electrical energy
  • coils may be used to convert magnetic energy to electrical energy
  • piezo-sensitive element may be used to convert acoustic energy to electrical energy.
  • These technologies comprise at least one conductor.
  • one or more stimulation electrodes 360, 370 each configured to receive pulsed energy from an associated energy receiver 340, and further configured to transmit the pulsed energy received to human or animal tissue as electrical pulses.
  • an electrode unit encapsulation layer 310 configured and arranged to resist the ingress of fluids from a human or animal body into at least a portion of the electrode unit 300.
  • the encapsulation layer 310 is configured and arranged to allow, in use, the portion of pulsed energy to be received wirelessly through the encapsulation layer 310.
  • the example in Figure 2 depicts a first conductor 235 configured to be used as an energy transmitter 230 - in this case, a first coil 230.
  • the first conductor 235 is electrically connected to the controller 220, and the controller 220 is electrically connected to the power supply 250.
  • the controller 220 generates electrical pulses which change the electrical potential and/or current applied to the first conductor 235, causing energy to be wirelessly transmitted.
  • the example in Figure 2 further depicts a second conductor 345, associated with the first conductor 235, and configured to be used as an energy receiver 340.
  • the second conductor 345 is a second coil 340, and the coils are configured and arranged to provide inductive coupling between the first coil 230 of the pulse generator unit 200 and the second coil 340 of the implantable electrode unit 300.
  • the second conductor 345 is electrically connected to one or more electrodes 360, 370.
  • the second conductor 345 is a coil 340, and it is connected to two electrodes - as stimulation electrode 360 and a reference electrode 370.
  • the second conductor 345 receives at least a portion of the energy transmitted by the energy transmitter 230, and passes this to the electrodes 360, 370 as electrical pulses.
  • the electrical pulses are applied by the electrodes 360, 370 in use to body tissue proximate the electrodes 360, 370.
  • the portion of energy received by the receiver 340 depends on parameters such as the type of second conductor 345 used, the alignment between the first 235 and second 345 conductors, the distance between the first 235 and second 345 conductors, and the materials between the first 235 and second 345 conductors.
  • one or more stimulation channels are provided - Figure 2 depicts an example of a single electrical stimulation channel, configured such that, in use, pulses generated by the controller 220 are applied as electrical pulses by the electrodes 360, 370 to body tissue.
  • a wireless link is provided between the energy transmitter 230 and the energy receiver 340. This wireless link advantageously may allow:
  • the implantable electrode unit 300 to be reduced in size, making implantation easier and increasing the possible body locations where the improved electrical stimulation device 100 may be used;
  • the electrode unit 300 may be configured and arranged to comprise only passive components. Passive components (or passive devices) are incapable of controlling current by means of another electrical signal, such as resistors, capacitors, inductors, transformers, and even diodes;
  • the implantable electrode unit 300 to be configured and arranged to comprise substantially no internal power source.
  • the electrode unit (300) is substantially inactive when the pulse generator unit 200 is inactive for an extended period. This may further reduce complexity and may further increase reliability and lifetime.
  • the implantable electrode unit 300 (and the pulse generator unit 200 if also configured and arranged to be implantable) may be encapsulated 310 to a higher degree - in other words, to resist to a higher degree the ingress of ingress of fluids from a human or animal body into the electrode unit 300.
  • Encapsulating layers such as the electrode unit encapsulation layer 310, may comprise materials such as a silicone rubber, a silicone elastomer, a latex rubber, a glass, a ceramic, parylene, liquid crystalline polymer (LCP), a biocompatible polymer, a biocompatible elastomer, or any combination thereof.
  • conductive surfaces may also be required - in that case, a metal, an alloy, titanium, stainless steel, cobalt-chromium maybe used.
  • Atomic layer deposition or PECVD may be used for layers with thicknesses in the nanometers range.
  • the multilayers and the processes described in EP patent EP 24646421B1 may also be used.
  • Silicone rubbers, such MED-6215 may be used with a layer thickness in the 0.1 to 1 millimeter range. Preferably a thickness of approximately 0.2mm may be used. Any convenient process may be used, such as dip coating or molding.
  • Encapsulating layers may also be used to mold a particular shape - for example to make smooth edges, a curvature or a shape that helps with the implantation procedure. Encapsulation may further increase reliability and lifetime. The degree to which encapsulation resists ingress may be measured experimentally by subjecting the device 100 and/or units 200, 300 to appropriate testing;
  • the electrode unit encapsulation layer 310 to extend between one or more energy transmitters 230 and one or more associated energy receivers 340.
  • the degree of encapsulation may be substantially greater in a region between one or more energy transmitters 230 and one or more associated energy receivers 340.
  • the electrode unit encapsulation layer 310 is preferably further configured to allow the energy to be transmitted through the layer 310 to a high degree to optimize the energy which may reach the one or more energy receivers 340;
  • the implantable electrode unit 300 to be implanted at a different distance below the skin (different depth) or in a different bodily cavity compared to the pulse generator unit 200.
  • the hostility of body conditions for implants may vary greatly - it may therefore be advantageous to separate the units 200, 300 by a small distance.
  • typical separations may range from a few tens of microns to a few hundred microns, from a few hundred microns to a few millimeters, from a few millimeters to a few centimeters.
  • the pulse generator unit 200 is substantially not implanted - the units may be separated by 1 to 3 millimeters of dermis (skin).
  • the pulse generator unit 200 may be partially implanted - for example, percutaneous and/or subcutaneous conductors 230 may be used to reduce the distance over which the energy pulses are wirelessly transmitted.
  • a further advantage may be that the pulse generator unit 200 and implantable electrode unit 300 may be configured and arranged to have different reliability and lifetimes because the replacement of the pulse generator unit 200 may be simplified. In some cases, it may be user replaceable or only require a minimally invasive procedure. This may reduce the cost of the improved device 100
  • Energy transfer between the pulse generator 200 and the implantable electrode unit 300 is preferably through one or more non-galvanic couplings. In other words, no direct electrical contact is made between the pulse generator unit 200 and the electrode unit 300 - the pulse energy is transferred wirelessly.
  • the transmission of the pulsed energy to human or animal tissue as electrical pulses preferably uses the one or more electrodes 360 to fonn one or more direct electrical contact with tissue.
  • This may provide one or more galvanic (or partially non-galvanic) charge transfer couplings with the tissue.
  • a reference conductor 370 may be optionally provided, either using one of the electrodes 360, 370 or a separate conductor, to provide an electrical reference value for the one or more stimulation electrodes 360.
  • a further percutaneous or subcutaneous electrode may also be used, or a conductive surface making contact with an outer surface of skin.
  • at least a portion of the implantable electrode unit housing may also comprise a reference conductor 370 - for example, by including a conducting material in the encapsulation layer 310 such as a conductive ceramic layer, a metal-in-glass feedthrough, or a hermetically-sealed metal cap.
  • the degree of stimulation applied by an electrode 360 depends on parameters such as the pulse parameters, a voltage applied, a current applied, the distance between the electrode 360 and the reference conductor 370, surface areas of the electrode 360 and the reference conductor 370, the tissue between the electrode 360 and the reference electrode 370.
  • a single reference conductor 370 may be used with all the stimulation electrodes 360, or more than one reference conductors 370 may be provided.
  • Figure 3 depicts a further example of an improved electrical stimulation device 101, comprising a further pulse generator unit 201 and a further electrode unit 301.
  • the further pulse generator unit 201 comprises:
  • a power supply 250 comprising a coil 255, configured and arranged to provide power directly to the components and devices comprised in the further pulse generator unit 201, and indirectly to the further electrode unit 301.
  • coil-based power supplies are well-known in the art, allowing devices to be powered using, for example,
  • the power supply 250 typically comprises components and devices to generate DC power using the energy received by the coil 255.
  • controller 220 powered by the power supply 250 in use
  • the one or more first conductors 235 form electrical coils with one or more windings. They are depicted in a 1 -dimensional array. Note that 2-d and 3-d arrays may also be used, depending on factors such as the type of tissue to be stimulated, the dimensions of the units 201, 301 and the amount of room available at the implantation site.
  • the conductors 235 may be provided as coils having at least one winding - the efficiency of energy transfer may increase with more turns.
  • Providing the conductors 235 as a pad may also be advantageous and may work for higher frequencies of radio frequencies.
  • the pulse generator unit 200 is configured and arranged to be implantable, it further comprises a pulse generator encapsulation layer 210, configured and arranged to resist the ingress of fluids from a human or animal body into at least a portion of the pulse generator unit 200.
  • a pulse generator encapsulation layer 210 configured and arranged to resist the ingress of fluids from a human or animal body into at least a portion of the pulse generator unit 200. Materials may be used similar to those mentioned for the electrode unit encapsulating layer 310 above.
  • one of the first conductors 235 is configured to represent, in use, a reference value. As depicted, it is the most left of the first conductors 235.
  • the controller 220 is configured and arranged to provide up to four stimulation channels of pulsed energy with respect to the reference value. In practice any number of stimulation channels may be provided, depending on factors such as the type of tissue to be stimulated, the dimensions of the units 201, 301 and the amount of room available at the implantation site. After implantation of at least the further electrode unit 301, up to four stimulation channels may be used. Alternatively or additionally, a selection may be made of one or more stimulation channels that provide the desired stimulation effect, compensating for possible inaccuracies during positioning.
  • the further implantable electrode unit 301 comprises:
  • one or more energy receivers 340 each comprising a second conductor 345, each electrically connected to an associated electrode 360, 370, and each configured to wirelessly receive at least a portion pulsed energy from an associated first conductor 235 when the associated first conductor 235 is proximate.
  • the one or more second conductors 345 are configured and arranged to co-operate with one or more first conductors 235 to allow transfer of energy pulses.
  • the one or more second conductors 345 form electrical coils with one or more windings. They are depicted in a 1 -dimensional array. In general, the second conductors 345 may have similar or the same dimensions and/or spacings as the array of first conductors 235.
  • the second conductors 345 may be provided as coils having at least one winding - the efficiency of energy transfer may increase with more turns. Providing the conductors 345 as a pad may also be advantageous and may work for higher frequencies of radio frequencies
  • - five stimulation electrodes 360, 370 each configured to receive pulsed energy from an associated second conductor 345. They are also further configured to transmit the pulsed energy received to human or animal tissue as electrical pulses. These may be any suitable electrode known in the art for this purpose. They are depicted in a 1- dimensional array. However, 2-d and 3-d arrays may also be used, depending on factors such as the type of tissue to be stimulated, the dimensions of the units 201, 301 and the amount of room available at the implantation site. In general, the number, dimensions and/or spacings of the stimulating electrodes 360 may be selected and optimized separately from the wireless transfer channels 230, 235, 340, 345. After implantation of at least the further electrode unit 301, up to five stimulation electrodes 360, 370 may be used in this embodiment to provide up to five electrical stimulations to tissue.
  • a selection may be made of one or more stimulation electrodes 360, 370 that provide the desired stimulation effect, compensating for possible inaccuracies during positioning.
  • the energy from a single stimulation channel 230, 235, 340, 345 may be converted to one or more stimulation electrodes 360, 370.
  • a single electrode 360, 370 may receive pulsed energy through one or more wireless transfer channels.
  • the number of stimulation electrodes 360 is assumed to be the same as the number of stimulation channels 230, 340.
  • rectifiers 350 each electrically connected between an associated electrode 360, 370 and an associated energy receiver 340 such as a second conductor 345.
  • rectifiers 350 may be needed to provide the correct form of wavelength, for example converting alternating pulses received through the second conductors 345 to a unidirectional pulse.
  • the device is configured to provide AC electrical pulses through the stimulation electrodes 360.
  • an electrode unit encapsulation layer 310 configured and arranged to resist the ingress of fluids from a human or animal body into the electrode unit 300.
  • one of the stimulation electrodes 360, 370 is configured and arranged to function as a reference conductor 370 or reference electrode 370. As depicted, it is the most left of the electrodes 370. From the four stimulation channels used for the wireless power transfer 230, 340, four electrical pulses are available from the four stimulation electrodes 360 with respect to the reference electrode 370. As depicted, the reference electrode 370 is electrically connected to each of the other four electrodes 360 to provide the reference level.
  • the further pulse generator unit 201 is disposed such that the first conductors 235 are proximate the second conductors 345 and correctly aligned.
  • the portion of energy transferred will be higher with a correct alignment and/or closer proximity - alignment and/or proximity may be achieved, for example, by appropriate mechanical means, such a pins or magnets, or using a suitable electric sensor.
  • the pulse generator unit 201 may be rigidly attached to the pulse generator unit 301 to retain the alignment and/or proximity.
  • the pulse generator unit 201 may be configured to be detachable to simplify replacement.
  • the power supply After providing suitable energy to the power coil 255, the power supply provides DC power to the components and devices of the further pulse generator unit 201, including the controller 220.
  • the controller 220 may then activate one or more of the stimulation channels 230, 340 by producing energy pulses in the form of electrical pulses, which are passed to the one or more conductors 230.
  • Each conductor 230 receiving an electrical pulse transmits the energy pulses wirelessly away from the pulse generator unit 201.
  • the second conductors 345 are sufficiently proximate and sufficiently aligned, they receive at least a portion of the pulsed energy, and convert it to electrical pulses.
  • the electrical pulses pass through the rectifier 350, creating unidirectional electrical pulses at each of the active electrodes 360, 370.
  • the electrical stimulation signal applied, in use to the tissue corresponds to the electrical pulse at each active stimulation electrode 360 compared to the reference signal 370.
  • regular operation of the device 101 may be started immediately.
  • the positioning of the stimulation electrodes may need to be checked, and if necessary, adapted or fine-tuned.
  • the position of the stimulating electrodes 360 and the reference electrode 370 may be changed by moving the electrodes 360, 370 and/or the unit 301.
  • the position of the electrical stimulation in use may be modified by the controller 220 selecting one or more of the stimulation channels 230, 340 to be fully or partially active.
  • the tissue stimulated is proximate this active stimulation electrode 360.
  • electrical pulses are provided at the stimulation electrode 360 associated with this stimulation channel, and the tissue stimulated is proximate this active stimulation electrode 360.
  • two adjacent stimulation channels 230, 340 are fully active, electrical pulses are provided at two adjacent stimulation electrodes 360 associated with these two stimulation channels, and the tissue stimulated is proximate these two active stimulation electrodes 360, which includes the region of tissue disposed between the two active electrodes 360.
  • the region of tissue stimulated may be reduced by reducing the amount of energy sent by the controller 220 through the active stimulation channels, and
  • the - two or more energy receivers 340 configured and arranged to wirelessly receive at least a portion of the treatment pulsed energy from an associated energy transmitter 230 through the encapsulation layer 310 when the associated energy transmitter 230 is proximate;
  • stimulation electrodes 360, 370 each configured to receive treatment pulsed energy from an associated energy receiver 340;
  • implantable electrode unit 300 is configured and arranged to be rigidly attached to the treatment pulse generator unit 200 such that two or more energy transmitters 340 are proximate the associated energy transmitter 230.
  • Up to four stimulation channels may be used in this example.
  • a selection may be made of one or more stimulation channels that provide the desired stimulation effect, compensating for possible inaccuracies during positioning
  • the device 101 of Figure 3 may optionally be configured to provide up to five stimulation channels 230, 340 and up to five electrical pulses from five electrodes 360, 370 by configuring and arranging the reference electrode 370 depicted as a stimulation electrode 360 (in this case, at least disconnecting any electrical connections between the reference electrode 370 and the other electrodes 360) and providing a separate reference conductor as explained above.
  • the parameters of the electrical pulses applied to the tissue through the stimulation electrodes 360 may be optimized separately from the energy pulses transmitted wirelessly from the pulse generator unit 301.
  • some forms of wireless transmission may more efficient at higher frequencies, but in many treatment applications lower frequencies are preferred.
  • therapy (treatment) pulses may be 100 microsecond to 1 millisecond wide, and repeated with 40 to 1000 Hz.
  • the energy pulse wireless transmission may use a frequency of 3 kHz to 150kHz, for example.
  • the components and devices in the implantable electrode unit 301 may configured and arranged to modify the signals, for example:
  • a low pass filter may be included to block or reduce high frequency components
  • a high pass filter may be included to block or reduce low frequency components
  • a notch filter may be included to selectively pass a desired range of frequency components
  • - resistive components may be used to reduce amplitudes
  • - rectifiers may be used to convert AC signals to unidirectional signals
  • Five stimulation channels 230, 340 are depicted in Figure 3, configured to provide four electrical stimulation channels 360 with respect to the reference electrode 370. However, the skilled person will easily modify this example to provide the required number of electrical stimulation channels:
  • one stimulation channel may be provided by deactivating all stimulation channels except one using the controller 220.
  • an implantable electrode unit may be provided comprising one energy receiver 340 connected to one electrode 360. This may provide an implant with small dimensions, simplifying implantation. However, fine-tuning of the electrical stimulation during use may be limited to modifying one or more of the energy pulse parameters and/or moving the position of the one electrode 360.
  • two stimulation channels may be provided by deactivating all stimulation channels except two using the controller 220.
  • an implantable electrode unit may be provided comprising two energy receivers 340 connected to two associated electrodes 360. This may provide an implant with smaller dimensions than the configuration depicted in Figure 3.
  • two or more stimulation channels may be advantageous due to the high degree of flexibility and adjustment capabilities.
  • the number of stimulation channels 230, 340 is the same as the number of stimulating electrodes 360, two or more stimulating electrodes 360 may also be provided.
  • the improved electrical stimulation device 100, 101 may be configured and arranged for different uses, such as for stimulating one or more nerves, one or more muscles, one or more organs, spinal cord tissue, and any combination thereof.
  • the invention provides a highly configurable device 100, 101, which may be optimized for very different types of neurostimulations - for example, the heart (pacemaker) to a single facial nerve.
  • it may be used to treat headaches, primary headaches, incontinence, occipital neuralgia, sleep apnea, limb pain, leg pain, back pain, lower back pain, phantom pain, chronic pain, epilepsy, overactive bladder, poststroke pain, obesity, and any combination thereof
  • Electrodes 760, 770 must always be present, providing an electrical contact from the inner electronics to the outside. It is therefore difficult to completely encapsulate the region around the electrode 760, 770.
  • the invention is based on the insights that the reliability of implantable electrical stimulation devices may be improved 100, 101 by separating the electrode functionality from the pulse generator functionality into separate pulse generator 200, 201 and electrode 300, 301 units:
  • the pulse generator unit separating the functionality allows the pulse generator unit to be more completely encapsulated and/or moved to a position where ingress of fluids is less likely. In some cases, the pulse generator does not need to be implanted.
  • the construction of the electrode unit 300, 301 may be simplified, as the controller 220 and many high power components are comprised in the pulse generator unit 200, 201. In some cases, only passive components may be used, reducing the period of time that voltages are present close to the stimulation electrodes 360 to the periods when electrical stimulation is provided.
  • the electrode unit 300, 301 may further improve reliability and lifetime.
  • the electrode unit 300, 301 may be designed such that predominantly AC voltages and currents are used.
  • FIG 4A depicts another improved electrical stimulation device 102, comprising the pulse generator 201 and the implantable electrode unit 301 depicted in Figure 3, and described above.
  • This device 102 differs in that:
  • the pulse generator 201 and implantable electrode unit 301 are not separable - they are rigidly attached such that the one or more energy transmitters 230 (in this case one or more first conductors 235) are aligned and/or proximate the associated one or more energy receivers 340 (in this case one or more second conductors 345).
  • the alignment and degree of proximation is sufficient for acceptable energy transfer, and acceptable electrical stimulation.
  • the pulse generator 201 is implantable, and comprises a pulse generator encapsulation layer 210;
  • this device 102 comprises a device encapsulation layer 110, configured and arranged to resist the ingress of fluids from a human or animal body into the device 102.
  • the device 102 of Figure 4 A is configured and arranged to be implantable - however, where convenient, it may also be configured and arranged to be only partially implanted.
  • both the pulse generator unit 201 and electrode unit 301 are provided with two encapsulation layers to further improve the lifetime and reliability.
  • Each encapsulation layer 110, 210, 310 may be separately optimized as indicated above in the description of the electrode unit encapsulation layer 310.
  • the pulse generator encapsulation layer 210 and/or electrode encapsulation layer 310 may be reduced in thickness in the region of the energy transmitters 230 and energy receivers 340 to optimize the wireless coupling (in other words, to optimize the portion of energy received by the one or more energy receivers 340).
  • the thickness in these regions may be less than li n. Less than O. lmm may be even more preferred.
  • the device encapsulation layer 110 may be silicone rubber, and the electrode unit encapsulation layer 310 and/or pulse generator encapsulation layer 210 may be a thin layer (or multilayer) applied with atomic layer deposition or PECVD.
  • Figure 4A depicts a separation between the row of energy transmitters and the row of energy receivers, but that is not required - the electrode unit encapsulation layer 310 may be in physical contact with the pulse generator encapsulation layer 210.
  • the degree of proximity is determined by the distance between the transmitters and the receivers in the plane of the paper, and the degree of alignment is determined along an axis approximately perpendicular to the plane of the paper.
  • Figure 4B depicts an alternative alignment and proximity - as in Figure 4A, another improved electrical stimulation device 102 is shown comprising the pulse generator 201 and the implantable electrode unit 301.
  • the desired degree of alignment and proximity is achieved by positioning the first 235 and second 345 conductors such that they are approximately parallel planar and“overlapping”. This may be advantageous if, for example, the first 235 and second 345 conductors each form a pad or a relatively“flat” (low in height) coil.
  • the device 102 may be constructed such that the total height of the device (as depicted, height is in the direction
  • the degree of alignment is determined in the plane of the paper, and the degree of proximity is determined by the distance between the transmitters and the receivers along an axis approximately perpendicular to the paper.
  • the wireless coupling between the one or more first conductors 235 and the one or more second conductors 345 is preferably based on resonant inductive coupling, although the invention may be operated with any degree of inductive coupling.
  • a configuration for resonant inductive coupling for an improved electrical stimulation device 100, 101, 102 is depicted schematically in Figure 5, as a circuit model of the pulse generator 200, 201 depicted on the left hand side, and the circuit model of the electrode unit 300, 301 depicted on the right hand side.
  • the controller 220 comprises the energy pulse source VI - this produces the necessary signal for electrical stimulation.
  • the controller 220 is electrically connected across the first conductor 235.
  • the controller 220 may be an ASIC.
  • the first conductor 235 is modelled in Figure 5 as a resistor Rl, capacitor Cl and inductor Ll connected in series. Resistor Rl influences the output current of the controller 220. Capacitor Cl is preferably used for matching. Matching is preferred to convert most of the apparent power into real power instead of reactive power since reactive power is not usable for the electrode unit 300, 301.
  • Inductor Ll is the main wireless power transfer component since it creates a magnetic field if current passes through it. This magnetic field couples to the inductor L2 in the electrode unit 300, 301.
  • a high frequency is preferred to optimize the transfer of energy from the first conductor 235 to the second conductor 345.
  • the second conductor 345 is modelled in Figure 5 as an inductor L2, capacitor C2 and resistor R2 connected in parallel.
  • the capacitor C2 has a similar function to the capacitor Cl. It may be configured to maximize the real power from the received apparent power.
  • a diode Dl is connected in series with the second conductor 345, and a capacitor C3 is connected in parallel with the second conductor 345.
  • Components Dl and C3 combine to form an optional rectifier 350, which may be required to convert the received energy pulses into a unidirectional waveform, which is preferred for some electrical stimulation uses.
  • the frequency of the electrical pulses to be applied to the tissue is lower than the frequency of the energy pulses transferring between the first conductor 245 and the second conductor 345 - the rectifier 350 may be configured to reduce the frequency of the electrical pulses passed to the stimulation electrode 360.
  • the model further comprises two resistors R3 and R4 in series connected across capacitor C3.
  • Resistor R3 is used to optimize the energy transfer to the resistor R4.
  • R4 represents the stimulation electrode 360 and the interface that it makes with tissue during operation. For example, it may represent tissue in the proximity of a peripheral nerve.
  • the model depicted in Figure 6 may be used for determining configurations suitable for resonant inductive coupling.
  • the first 235 and second 345 conductors are modelled differently to simplify the calculations by concentrating on the portion of energy pulses transferred wirelessly from the first conductor 235 to the second conductor 345. Compared to the model of Figure 5, the differences are:
  • the rectifier 350 comprising Diode D1 and Capacitor C3, is omitted as they may be neglected for this simplified efficiency calculation.
  • the stimulating electrode 360 in use comprising Resistor R3 and Resistor R4 have been omitted, as they may be neglected for this simplified efficiency calculation.
  • Ll-Lm in series with Lm represents the coil of the energy transmitter 230 (in other words, the inductance of the first conductor 235);
  • L2-Lm in series with Lm represents the coil of the energy receiver 340 (in other words, the inductance of the second conductor 345);
  • - Inductor Lm represents the energy lost when the efficiency of the wireless coupling between the first 235 and second 345 conductor is less than one hundred percent.
  • the efficiency may be calculated using
  • the source providing the energy pulses is comprised in the controller 220, and delivers pulses with a power of roughly 1 or 10 mW - these are typical values for neurostimulation for treatments of, for example, headaches, primary headaches, incontinence, occipital neuralgia, sleep apnea, limb pain, leg pain, back pain, lower back pain, phantom pain, chronic pain, epilepsy, overactive bladder, poststroke pain, obesity, or any combination thereof.
  • the coil inductances of the first 235 and second 345 conductors depend on parameters.
  • the conductors 235, 345 (coils) preferred for neurostimulation have:
  • Diameter of the coils used typically 1, 2, or 3 mm
  • Frequency typically, in the range 10 - 150 kHz
  • Wire thickness for the coils typically 50 microns (micrometers)
  • coils 235, 345 of lmm diameter or less may greatly reduce the size of the device 100 to be implanted - in particular, it may greatly reduce the size of the electrode unit 200, 201.
  • the optimization information provided, including the efficiency plots, are based on realistic assumptions regarding the boundary conditions for the size of the coils 235, 345, their distance to each other and the number of windings in each coil 235, 345.
  • the resistors Rl and R2 may be configured to provide maximum power transfer via matching. It may be advantageous to configure the minimum resistance to be equal to the sole (or Ohmic) resistance of the coils 235, 245 themselves This reduces the possible efficiency calculation to the set of all plausible values. Resistance values can be as low as possible, even 0 (zero) ohm, but they can also be extremely large, such as 1 mega Ohm (10 6 ) or even larger. However it helpful to know the boundaries of the resistance values since that reduces the pool of possible resistance values.
  • the value of the resistance could be set to zero, but that is not physically realistic since there will always be a minimal resistance provided by the coils 235, 345. So this should be taken into account when setting up the equations for the calculation.
  • the optimal resistor values can be found in [1 ⁇ ] milliohm. This chosen set reduces the possibility of short circuiting due to the reduced set of possible resistance values. This complements the idea of having a minimal resistance equal to that of the coil 235. In other words, Rl and Cl in Figures 5 and 6 being equal to zero
  • z is the distance variable between the first 235 and second 345 coils, measured in meters.
  • I is the current through the coil in Amperes r is the coil radius in meters.
  • the area of the second coil 345 is indicated by Acoil, which is expressed in m2 m is the permeability of the material in H/m.
  • the capacitor values may be selected according to the following equation
  • the coupling factor is preferably taken into account as it represents a first indication for efficiency. This coupling factor ranges from -1 up to 1. Having a coupling factor of -1 or 1 indicates good coupling while a coupling factor of 0 is no coupling.
  • the coupling factor may be calculated via
  • Figure 7 depicts the magnetic field produced when a current of 1 mA passes through a preferred first coil 235 with diameters lmm, 2mm and 3mm and having one (1) winding.
  • the magnetic field strength is plotted logarithmically on the vertical axis over a range of 10 8 to 10 2 A/m.
  • Distance is plotted logarithmically on the horizontal axis over a range of 10 2 (0.01) to 10 2 (100) millimeters (mm). Distance is measured perpendicular to the mid-point of the coil 235 plane.
  • the International Commission on Non-Ionizing Radiation Protection (ICNIRP) provides guidelines for limiting exposure to time-varying electric, magnetic and electromagnetic fields.
  • ICNIRP International Commission on Non-Ionizing Radiation Protection
  • the maximum magnetic field strength is 5 A/m, and this is also shown on Figure 7 as a horizontal line.
  • the wireless coupling may provide the highest field strength of all the fields in the improved device 100, 101, 102, this should be determined for each configuration.
  • This graph curves down to approx. 4 x 10 1 (0.4) A/m at 10° (1 mm), approx. 6 x 10 4 A/m at 10 1 (10) mm and approx. 6 x 10 7 A/m at 10 2 (100) mm.
  • This graph curves down to approx. 10° (1) A/m at 10° (1 mm), approx. 2.5 x 10 ! A/m at 10 1 (10) mm and approx. 2.5 x lO 6 A/m at 10 2 (100) mm.
  • This graph curves down to approx. 10° (1) A/m at 10° (1 mm), approx. 5 x l0 J A/m at 10 1 (10) mm and approx. 5.5 x I O 6 A/m at 10 2 (100) mm.
  • the field strength is relatively constant below a distance of about 0.5 x 10 1 (0.5) mm.
  • the field strength decreases rapidly. This is also advantageous because adjacent coils 235 may be spaced at distances comparable to the coil diameters without increasing the risk of interference or cross-talk.
  • the rapid drop in field strength means that at even higher field strengths proximate the coil 235, the field strength away from the coil 235 (where tissue contacts the outer housing or encapsulation layer of implant) will not easily exceed the ICNIRP guidelines.
  • Figure 8 depicts the variation in the coupling factor (the quality of the energy transfer) over a separation distance between the first 235 and second 345 coils with diameters lmm, 2mm and 3mm.
  • the coupling factor is plotted logarithmically on the vertical axis over a range of 10 x to 10° (1).
  • Distance is plotted logarithmically on the horizontal axis over a range of 10 2 (0.01) to 10 2 (100) millimeters (mm).
  • Distance is measured perpendicular to the mid-point of the coil 235 plane. It is assumed that the first 235 and second 345 coils are substantially the same diameter, they are plane parallel and optimally aligned with each other.
  • This graph curves down to approx. 5 x 10 2 (0.05) at 10° (1 mm), approx. 6.5 x 10 3 at 10 1 (10) mm and approx. 7 x 10 8 at 10 2 (100) mm.
  • This graph curves down to approx. 1.5 x 10 1 (0.15) at 10° (1 mm), approx. 4 x 10 4 at 10 1 (10) mm and approx. 4.5 x 10 7 at 10 2 (100) mm.
  • This graph curves down to approx. 2 x 10 1 (0.2) at 10° (1 mm), approx. 1.5 x 10 3 at 10 1 (10) mm and approx. 1.25 x 10 6 at 10 2 (100) mm.
  • the maximum coupling of 0.4 may be obtained from coils with diameter 1 mm.
  • the coils with the larger diameters outperform the 1 mm diameter coil with respect to coupling factor over longer distances than 200 microns (micrometers) or 0.2 millimeters.
  • the separation distance between the first 235 and second 345 coils should preferably be less than 1 mm for an optimal coupling factor.
  • Figure 9 shows the efficiency of power transfer over a separation distance between the first 235 and second 345 coil with a coil diameter of 1 mm and a
  • Graphs are plotted for 1, 2, 3 and 4 turns on the coil 235, 345.
  • the efficiency in % is plotted logarithmically on the vertical axis over a range of 10 6 to 10° (1), so 1 on the graph is equal to 1%.
  • Distance is plotted linearly on the horizontal axis over a range of 0 to 10 millimeters (mm). Distance is measured perpendicular to the mid-point of the coil 235 plane. It is assumed that the first 235 and second 345 coils are substantially the same diameter, they are plane parallel and optimally aligned with each other. The optimal resistance has been selected for the energy receiver 340 (the receiver coil 345) for the modelling.
  • the graph of one (1) turn is depicted as a solid line. It starts at approx efficiency 2 x 10 4 at distance 0.1 mm. It rises to about 1 x 10 3 at 1 mm, and it remains at approx. 1 x 10 3 until about 3mm. After that, it drops to approx. 2.5 x 1 O 4 at 5 mm, approx. 4.5 x 10° at 7 mm and approx. 5 x 10 6 at 10 mm.
  • the graph of two (2) turns is depicted as a dashed line. It starts at approx efficiency 3 x 10 3 at distance 0.1 mm. It rises to about 1.7 x 10 2 at 1 mm, and it remains at approx. 1.7 x 10 2 until about 2mm. After that, it drops to approx. 5 x 10 3 at 3 mm, approx. 3.5 x 10 4 at 5 mm, approx. 4.5 x 10 3 at 7 mm and approx. 5 x 10 6 at 10 mm.
  • the graph of three (3) turns is depicted as a dotted line. It starts at approx efficiency 1.7 x 10 2 at distance 0.1 mm. It rises to about 7.5 x 10 2 at 1 mm, and it remains at approx. 7.5 x 10 2 until about l.25mm. After that, it drops to approx. 4 x 10 2 at 2mm, 7 x l0 3 at 3 mm, approx. 3.5 x 10 4 at 5 mm, approx. 4.5 x 10 5 at 7 mm and approx. 5 x 10 6 at 10 mm.
  • the graph of four (4) turns is depicted as a dashed-dotted line. It starts at approx efficiency 5 x 10 2 at distance 0.1 mm. It rises to about 0.2 x 10 1 at 0.8 mm, and it remains at approx. 0.2 x 10 4 until about l. lmm. After that, it drops to approx. 6 x 10 2 at 2mm, 7 x 10 3 at 3 mm, approx. 3.5 x 10 4 at 5 mm, approx. 4.5 x 10 5 at 7 mm and approx. 5 x 10 6 at 10 mm.
  • the maximum efficiency peak value increases with the number of turns.
  • Figure 10 shows the efficiency of power transfer over a separation distance between the first 235 and second 345 coil with a coil diameter of 1 mm and a
  • Graphs are plotted for 1, 2, 3 and 4 turns on the coil 235, 345.
  • the efficiency in % is plotted logarithmically on the vertical axis over a range of 10 6 to 10 2 (100), so 100 on the graph is equal to 100%.
  • Distance is plotted linearly on the horizontal axis over a range of 0 to 10 millimeters (mm). Distance is measured perpendicular to the mid-point of the coil 235 plane. It is assumed that the first 235 and second 345 coils are substantially the same diameter, they are plane parallel and optimally aligned with each other. The optimal resistance has been selected for the energy receiver 340 (the receiver coil 345) for the modelling.
  • the graph of one (1) turn is depicted as a solid line. It starts at approx efficiency 5 x 10 2 at distance 0.1 mm. It rises to about 2 x 10 4 (0.2) at 0.8mm, and it remains at approx. 0.2 until about 1. limn. After that, it drops to approx. 5.5 x 10 2 at 2mm, approx. 7 x 10 3 at 3mm, approx. 3.5 x 10 4 at 5 mm, approx. 5 x 10 5 at 7 mm and approx. 5.5 x 10 6 at 10 mm.
  • the graph of two (2) turns is depicted as a dashed line. It starts at approx efficiency 7 x 10 (0.7) at distance 0.1 mm. It rises to about 2.5 x 10° (2.5) at 0.5mm, and it remains at approx. 2.5 until about 0.7mm. After that, it drops to approx. 5.5 x 10 2 at 2mm, approx. 7 x 10 3 at 3mm, approx. 3.5 x 10 4 at 5 mm, approx. 5 x l0 5 at 7 mm and approx. 5.5 x 1 O 6 at 10 mm.
  • the graph of three (3) turns is depicted as a dotted line. It starts at approx efficiency 3.5 x 10° (3.5) at distance 0.1 mm. It rises to about 2 x 10 1 (20) at 0.3mm, and it remains at approx. 20 until about 0.5mm. After that, it drops to approx. 5.5 x 10 2 at 2mm, approx. 7 x 10 3 at 3mm, approx. 3.5 x 10 4 at 5 mm, approx. 5 x 10° at 7 mm and approx. 5.5 x 1 O 6 at 10 mm.
  • the graph of four (4) turns is depicted as a dashed-dotted line. It starts at approx efficiency 1 x 10 1 (10) at distance 0.1 mm. It rises to about 8.5 x 10° (8.5) at 0.4mm, and it remains at approx. 8.5 until about 0.6mm. After that, it drops to approx. 5.5 x 10 2 at 2mm, approx. 7 x 10 3 at 3mm, approx. 3.5 x 10 4 at 5 mm, approx. 5 x 10° at 7 mm and approx. 5.5 x 10 6 at 10 mm.
  • the maximum efficiency peak value increases with the number of turns.
  • So 4-turns provides a maximum of 18.6% using a frequency of energy pulses of 150 kHz.
  • Figure 11 shows the efficiency of power transfer over a separation distance between the first 235 and second 345 coil with a coil diameter of 2 mm and a
  • the graph of one (1) turn is depicted as a solid line. It starts at approx efficiency 7 x 10 3 at distance 0 mm. It rises to about 1.5 x 10 2 at 1.5 nun, and it remains at approx. 1.5 x 10 2 until about 2.75mm. After that, it drops to approx. 4 x 10 3 at 5 mm, approx. 8 x 10 4 at 7 mm and approx. 1 x 1 O 4 at 10 mm.
  • the graph of two (2) turns is depicted as a dashed line. It starts at approx efficiency 1.2 x lO 1 (0.12) at distance 0 mm. It rises to about 2 x 10 4 (0.2) at 1 mm, and it remains at approx. 0.2 until about l .8mm. After that, it drops to approx. 7 x 10 2 at 3mm, approx. 6 x 1 O 3 at 5 mm, approx. 8 x 1 O 4 at 7 mm and approx. 1 x 10 4 at 10 mm.
  • the graph of three (3) turns is depicted as a dotted line. It starts at approx efficiency 6 x 10 1 (0.6) at distance 0 mm. It rises to about 9.5 x 10 1 (0.95) at 0.8 mm, and it remains at approx. 0.95 until about l .3mm. After that, it drops to approx. 1 x 10 4 (0.1) at 3mm, approx. 6 x 10 3 at 5 mm, approx. 8 x 10 4 at 7 mm and approx. 1 x 10 4 at 10 mm.
  • the graph of four (4) turns is depicted as a dashed-dotted line. It starts at approx efficiency 1.8 x 10° (1.8) at distance 0 mm. It rises to about 2.5 x 10° (2.5) at 0.65 mm, and it remains at approx. 2.5 until about 1 mm. After that, it drops to approx. 1 x 10 4 (0.1) at 3mm, approx. 6 x 10 3 at 5 mm, approx. 8 x 10 4 at 7 mm and approx. 1 x 10 4 at 10 mm.
  • Figure 12 shows the efficiency of power transfer over a separation distance between the first 235 and second 345 coil with a coil diameter of 2 mm and a
  • Graphs are plotted for 1, 2, 3 and 4 turns on the coil 235, 345.
  • the efficiency in % is plotted logarithmically on the vertical axis over a range of 10 5 to 10 2 (100), so 100 on the graph is equal to 100%.
  • Distance is plotted linearly on the horizontal axis over a range of 0 to 10 millimeters (mm). Distance is measured perpendicular to the mid-point of the coil 235 plane. It is assumed that the first 235 and second 345 coils are substantially the same diameter, they are plane parallel and optimally aligned with each other. The optimal resistance has been selected for the energy receiver 340 (the receiver coil 345) for the modelling.
  • the graph of one (1) turn is depicted as a solid line. It starts at approx efficiency 1.7 x 10° (1.7) at distance 0 mm. It rises to about 2.1 x 10° (2.1) at 0.7 mm, and it remains at approx. 2.1 until about 1.1 mm. After that, it drops to approx. 1 x 10 4 (0.1) at 3mm, approx. 6 x 10 3 at 5 mm, approx. 8.5 x 10 4 at 7 mm and approx. 1 x 10 4 at 10 mm .
  • the graph of two (2) turns is depicted as a dashed line. It starts at approx efficiency 1.7 x 10 1 (17) at distance 0 mm. It stays at about 17 until 0.6 mm. After that, it drops to approx. 9.5 x 10° (9.5) at lmm, approx. 1 x 10 4 (0.1) at 3mm, approx. 6 x 10 3 at 5 mm, approx. 8.5 x 10 4 at 7 mm and approx. 1 x 10 4 at 10 mm.
  • the graph of three (3) turns is depicted as a dotted line. It starts at approx efficiency 3.5 x 10 1 (35) at distance 0 mm. It stays at about 35 until 0.2 mm. After that, it drops to approx. 1.1 x 10 1 (11.1) at lmm, approx. 1 x 10 4 (0.1) at 3mm, approx. 6 x 10 3 at 5 mm, approx. 8.5 x 10 4 at 7 mm and approx. 1 x 10 4 at 10 mm.
  • the graph of four (4) turns is depicted as a dashed-dotted line. It starts at approx efficiency 4.5 x 10 1 (45) at distance 0 mm. It stays at about 45 until 0.1 mm. After that, it drops to approx. 1.1 x 10 1 (11.1) at lmm, approx. 1 x 10 4 (0.1) at 3mm, approx. 6 x 10 3 at 5 mm, approx. 8.5 x 10 4 at 7 mm and approx. 1 x 10 4 at 10 mm.
  • the maximum efficiency peak value increases with the number of turns.
  • So 4-turns provides a maximum of 44.4% using a frequency of energy pulses of 150 kHz.
  • Figure 13 shows the efficiency of power transfer over a separation distance between the first 235 and second 345 coil with a coil diameter of 3 mm and a
  • the graph of one (1) turn is depicted as a solid line. It starts at approx efficiency 5.5 x 10 3 at distance 0 mm. It rises to about 1.2 x 10 2 at 2 mm, and it remains at approx. 1.2 x 10 2 until about 2.8mm. After that, it drops to approx. 4.5 x 10 3 at 5 mm, approx. 9 x 10 4 at 7 mm and approx. 1.2 x 10 4 at 10 mm.
  • the graph of two (2) turns is depicted as a dashed line. It starts at approx efficiency 9 x 10 2 at distance 0 mm. It rises to about 1.8 x 10 4 (0.18) at 1.3 mm, and it remains at approx. 0.18 until about 1.9 mm. After that, it drops to approx. 7.5 x 10 2 at 3mm, approx. 7.5 x 10’ at 5 mm, approx. 1 x 10 3 at 7 mm and approx. 1.2 x 10 4 at 10 mm.
  • the graph of three (3) turns is depicted as a dotted line. It starts at approx efficiency 4.5 x 10 1 (0.45) at distance 0 mm. It rises to about 7.5 x 10 4 (0.75) at 1 mm, and it remains at approx. 0.75 until about 1.4 mm. After that, it drops to approx. 7.5 x 10 2 at 3mm, approx. 7.5 x 10 ⁇ ’ at 5 mm, approx. 1 x l0 3 at 7 mm and approx. 1.2 x 10 4 at 10 mm.
  • the graph of four (4) turns is depicted as a dashed-dotted line. It starts at approx efficiency 1.5 x 10° (1.5) at distance 0 mm. It rises to about 2 x 10° (2) at 0.75 mm, and it remains at approx. 2 until about 1.2 mm. After that, it drops to approx. 7.5 x 10 2 at 3mm, approx. 7.5 x 10 3 at 5 mm, approx. 1 x 10 4 at 7 mm and approx. 1.2 x 10 4 at 10 mm.
  • the maximum efficiency peak value increases with the number of turns.
  • Figure 14 shows the efficiency of power transfer over a separation distance between the first 235 and second 345 coil with a coil diameter of 3 mm and a
  • the graph of one (1) turn is depicted as a solid line. It starts at approx efficiency 1.2 x 10° (1.2) at distance 0 mm. It rises to about 2 x 10° (2) at 0.75 mm, and it remains at approx. 2 until about 1.2 mm. After that, it drops to approx. 1.1 x 10 1 (0.11) at 3mm, approx. 7 x 10 3 at 5 mm, approx. 1 x 10 ⁇ ’ at 7 mm and approx. 1.2 x 10 4 at 10 mm.
  • the graph of two (2) turns is depicted as a dashed line. It starts at approx efficiency 1.5 x 10 1 (15) at distance 0 mm. It remains about 15 until about 0.7 mm. After that, it drops to approx. 1 x 10° (1) at 2mm, approx. 1.1 x lO 1 (0.11) at 3mm, approx. 7 x 10 3 at 5 mm, approx. 1 x 10 3 at 7 mm and approx. 1.2 x 10 4 at 10 mm.
  • the graph of three (3) turns is depicted as a dotted line. It starts at approx efficiency 3.5 x 10 1 (35) at distance 0 mm. It remains about 35 until about 0.25 mm. After that, it drops to approx. 1.5 x 10 1 (15) at lmm, approx. 1 x 10° (1) at 2mm, approx. 1. 1 x 10 1 (0.11) at 3mm, approx. 7 x 10’ at 5 mm, approx. 1 x 10 3 at 7 mm and approx. 1.2 x 10 4 at 10 mm.
  • the graph of four (4) turns is depicted as a dashed-dotted line. It starts at approx efficiency 4.5 x 10 1 (45) at distance 0 mm. It remains about 45 until about 0.2 mm. After that, it drops to approx. 1.5 x 10 1 (15) at lmm, approx. 1 x 10° (1) at 2mm, approx. 1.1 x 10 (0.11) at 3mm, approx. 7 x lO 3 at 5 mm, approx. 1 x 10 3 at 7 nun and approx. 1.2 x 10 4 at 10 mm.
  • the maximum efficiency peak value increases with the number of turns.
  • So 4-turns provides a maximum of 46.4% using a frequency of energy pulses of 150 kHz.
  • first 235 and second 345 coil When using a first 235 and second 345 coil, smaller diameter coils are preferred as this may allow the dimensions of the improved device 100, 101, 102 to be reduced. In particular, the dimensions of the implantable electrode unit 300, 301 may be reduced. Coils with diameters less than lOnnn are preferred, diameters less than 2mm are more preferred.
  • an energy receiver 340 may receive a portion of the pulsed energy from the associated energy transmitter 230 and a portion of the pulsed energy from an energy transmitter 230 adjacent to the associated transmitter 230.
  • adjacent coils 235, 345 are separated by a distance substantially equal to the diameter of the coils 235, 345.
  • Figures 15 and 16 depict examples of nerves that may be stimulated using a suitably configured improved electrical stimulation device 100, 101, 102 to provide neurostimulation to treat, for example, headaches or primary headaches.
  • Figure 15 depicts the left supraorbital nerve 910 and right supraorbital nerve 920 which may be electrically stimulated using a suitably configured device.
  • Figure 16 depicts the left greater occipital nerve 930 and right greater occipital nerve 940 which may also be electrically stimulated using a suitably configured device.
  • a suitable location is determined to provide the electrical stimulation required for the treatment.
  • Approximate implant locations for the part of the stimulation device comprising the stimulation electrodes 360, 370 are depicted as regions:
  • these will be the approximate locations 810, 820, 830, 840 for the implantable electrode unit 300, 301.
  • a separate stimulation device 100, 101, 102 may be used for each implant location. Where implant locations 810, 820, 830, 840 are close together, or even overlapping a single stimulation device 100, 101, 102 may be configured to stimulate at more than one implant location 810, 820, 830, 840.
  • a plurality of stimulation devices 100, 101, 102 may be operated separately, simultaneously, sequentially or any combination thereof to provide the required treatment.
  • processor should be understood to encompass a single processor or two or more processors in communication with each other.
  • one or more energy receivers for wirelessly receiving pulsed energy

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Abstract

Implantable devices require a protection method, both to protect the body from implant contamination and the implant electronics from corrosion. Encapsulation is a critical component for the design of a medical device implant –it acts as a barrier between the active electronics and the inside of the human body. Currently, bulky feedthroughs and headers must be incorporated in the design of medical devices, such as implantable pulse generators (IPG), to reduce the risk of water ingress. This means that efforts to miniaturize such implantable devices are hindered. An electrical stimulation device is provided comprising a treatment pulse generator unit and an implantable electrode unit; the treatment pulse generator unit being configured and arranged to wirelessly transmit the treatment energy pulses; the implantable electrode unit comprising an electrode unit encapsulation layer, configured and arranged to resist the ingress of fluids from a human or animal body; and being configured and arranged to wirelessly receive at least a portion of the treatment pulsed energy from an associated energy transmitter through the encapsulation layer when the associated energy transmitter is proximate. The electrode unit further comprises one or more stimulation electrodes,and is configured and arranged to be rigidly attached to the treatment pulse generator unit such that one or more energy transmitters are proximate the associated energy transmitter. By providing a separate electrode unit comprising an encapsulation layer and transmitting the signals wirelessly to the electrode unit through the encapsulation layer, the electrode unit may be separately optimized for implantability. In addition, the dimensions of the implantable electrode unit may also be minimized as the functionality is divided between the electrode unit and the pulse generator unit. In addition, the rigid attachment may provide improved retention of alignment and/or proximity –this may improve the stability and reproducibility of the one or more energy transfer channels.

Description

AN ELECTRICAL STIMULATION DEVICE FOR BODY TISSUE
FIELD
The present disclosure relates to an electrical stimulation device, an implantable pulse generator unit and an implantable electrode unit.
BACKGROUND
Implantable devices require a protection method, both to protect the body from implant contamination and the implant electronics from corrosion. Encapsulation is a critical component for the design of a medical device implant - it acts as a barrier between the active electronics and the inside of the human body. The function of this barrier is to prevent electrical current and materials leakage from the device into the body and to protect the electronics from human body fluids in order to prevent the degradation process of the implant electronics.
Currently, bulky feedthroughs and headers must be incorporated in the design of medical devices, such as implantable pulse generators (IPG), to reduce the risk of water ingress. The electronics are often packed into hermetic titanium cans or cases, which are bulky. This means that efforts to miniaturize such implantable devices are hindered.
US application US 2016/0158562 describes systems and methods to create a magnetic field from an elongated transmission coil of an external stimulator and expose an elongated receiver coil of a magnetic driver to the magnetic field. The systems and methods generate at the magnetic driver a pulse forming a stimulation waveform in response to a remote magnetic field. The systems and methods deliver the stimulation waveform to a target peripheral nerve through an electrode from the magnetic driver.
US application US 2018/0093099 describes a microstimulator with an energy harvesting circuit configured to receive an input signal from a remote transmitter and generate an electrical signal based on the received input signal. The microstimulator further comprises a diode rectifier in series with the energy harvesting circuit. The diode rectifier is configured to rectify the electrical signal. The energy harvesting circuit and the diode rectifier can be encapsulated within a biocompatible electrically insulating material. Additionally, in some cases, an electrical interface is exposed through the biocompatible electrically insulating material.
US application US 2012/0095531 describes a system and method for energy transfer between a transmitting unit and a receiving unit, over relatively large distances. The transmitting unit has a transmitting antenna circuit having a first resonant frequency and a high quality factor.
It is an object of the invention to provide improved protection of the implantable medical device against water ingress while allowing such devices to be reduced in size.
GENERAL STATEMENTS
According to a first aspect of the present disclosure, there is provided an electrical stimulation device comprising a treatment pulse generator unit and an implantable electrode unit; the treatment pulse generator unit comprising: a controller for producing treatment energy pulses; one or more energy transmitters, configured and arranged to wirelessly transmit the treatment energy pulses; the implantable electrode unit comprising: an electrode unit encapsulation layer, configured and arranged to resist the ingress of fluids from a human or animal body into at least a portion of the electrode unit; one or more energy receivers, configured and arranged to wirelessly receive at least a portion of the treatment pulsed energy from an associated energy transmitter through the encapsulation layer when the associated energy transmitter is proximate; one or more stimulation electrodes, each configured to receive treatment pulsed energy from an associated energy receiver, and further configured to transmit the treatment pulsed energy received to human or animal tissue as electrical pulses; wherein the implantable electrode unit is configured and arranged to be rigidly attached to the treatment pulse generator unit such that one or more energy transmitters are proximate the associated energy transmitter.
The encapsulation layer is configured and arranged to allow, in use, the portion of treatment pulsed energy to be received wirelessly through the encapsulation layer. By providing a separate electrode unit comprising an encapsulation layer and transmitting the signals wirelessly to the electrode unit through the encapsulation layer, the electrode unit may be separately optimized for implantability. In addition, the dimensions of the implantable electrode unit may also be minimized as the functionality is divided between the electrode unit and the pulse generator unit. In addition, the rigid attachment may provide improved retention of alignment and/or proximity - this may improve the stability and reproducibility of the one or more energy transfer channels. Known devices use wireless energy transfer to allow energy transfer over relatively large distances, and to avoid physical connections. However, the devices in this disclosure use wireless transfer when the transmitter and receiver are relatively close - this allows a high efficiency of energy transfer through an encapsulation layer, allowing the encapsulation layer to be optimized to a high degree to reduce the risk of ingress while improving the reproducibility of the energy transfer within a stimulation channel.
According to a further aspect of the current disclosure, the device is further configured such that the separation between the one or more energy receivers and the associated energy transmitter is lOmm or less, preferably 7mm or less, more preferably 5mm or less, even more preferably 3mm or less, most preferably 2mm or less.
By using wireless energy transfer over such relatively short distances, the power of the transmitted treatment energy pulses may be reduced. This may allow lower powers to be used and/or provide a longer lifetime in the case that the pulse generator unit comprises a power source.
According to a still further aspect of the current disclosure, the device is further configured and arranged such that the treatment pulse generator and the implantable electrode unit are separable by dermis or skin.
This may reduce the risks associated with implantation, such as infection.
According to another aspect of the current disclosure, the implantable electrode unit is configured and arranged to be rigidly attached to the treatment pulse generator unit such that one or more energy transmitters are aligned to the associated energy transmitter.
This may provide a further increase in stability of the one or more energy transfer channels. Proximity may be predetermined to a high degree, as well as alignment.
According to yet another aspect of the current disclosure, the device further comprises mechanical means, such as a pin or a magnet, configured and arranged to provide alignment. According to still another aspect of the current disclosure the device is further configured and arranged such that the rigid attachment is configured and arranged to be detachable.
This may simplify replacement.
According to another aspect of the current disclosure, the device is further configured and arranged to wirelessly transmit the treatment pulse energy as magnetic pulses, light pulses, electromagnetic pulses, RF pulses, microwave pulses, acoustic pulses, electrical field pulses, and any combination thereof.
According to a further aspect of the current disclosure, the one or more energy receivers and the one or more energy transmitters are configured and arranged to provide one or more non-galvanic couplings for the treatment pulsed energy.
In other words, no direct electrical contact is made between the pulse generator unit and the electrode unit - the pulse energy is transferred wirelessly. This may be advantageous in reducing the susceptibility to galvanic corrosion, particularly for the implantable electrode unit.
According to another aspect of the current disclosure, the device further comprises: one or more reference conductor, configured and arranged to provide an electrical reference value for one or more stimulation electrodes.
Providing a reference conductor may provide a higher degree of control of the stimulation required. This may be provided as a separate electrode, and/or use one of the electrodes provided in the electrode unit.
According to yet another aspect of the current disclosure, the implantable electrode unit further comprises: one or more circuit components, configured and arranged to transfer the pulsed energy from one or more energy receiver to the one or more associated stimulation electrodes as electrical pulses; wherein the one or more circuit components are predominantly passive.
This may further reduce complexity and may further increase reliability and lifetime. In addition, it allows the electrode unit dimensions to be further reduced. These advantages may be further optimized by configuring and arranging the electrode unit to comprise only passive components.
In a still further aspect of the current disclosure, the one or more energy transmitters each comprise a first conductor, electrically connected to the controller, configured and arranged to wirelessly transmit the energy pulses; the one or more energy receivers each comprise a second conductor, electrically connected to one or more associated electrodes; the one or more second conductors being configured to wirelessly receive at least a portion of the pulsed energy from the associated first conductor when the associated first conductor is proximate.
Although energy pulse may be wirelessly transmitted in different configurations and arrangements, it may be advantageous to use electrical conductors as these may allow the electrode unit to be further simplified, as the received pulse energy is converted to electrical energy, which is provided to the stimulation electrodes. The one or more first conductors may optionally form coils with one or more windings.
Optionally, adjacent coils may be separated by a distance substantially equal to the diameter of the coils. This may provide a reduction in electrode unit dimensions without greatly increasing crosstalk.
Optionally, the first coils may have substantially the same diameter as the second coils. This may provide a higher degree of alignment accuracy.
Minimizing of the dimensions of the electrode unit may be further improved by providing one or more of the coils with a diameter of between 1 to 3 millimeters.
It may also be advantageous to configure and arrange the treatment pulse generator unit to be implantable by the treatment pulse generator unit comprising a pulse generator encapsulation layer, configured and arranged to resist the ingress of fluids from a human or animal body into at least a portion of the treatment pulse generator unit.
This provides an optimum degree of flexibility, allowing the encapsulation of each unit to be optimized separately, dependent on the site of the implantation of each unit. In some configurations, the reliability may be improved by the device further comprising a stimulation device encapsulation layer, configured and arranged to resist the ingress of fluids from a human or animal body into the treatment pulse generator unit and/or the electrode unit.
Optionally, the device may be further configured and arranged to be implantable. This may be particularly advantageous as the voltages and currents that may make the stimulation device more susceptible to galvanic corrosions are in general higher in the treatment pulse generator unit than in electrode unit. In particular, the DC voltages and currents may be much higher. In addition, the treatment pulse generator generally comprises active (non-passive) components, and may comprise a power source, such as a battery, which may further increase the susceptibility to galvanic corrosion.
BRIEF DESCRIPTION OF THE DRAWINGS
Features and advantages of some embodiments of the present invention, and the manner in which the same are accomplished, will become more readily apparent upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings, which illustrate preferred and exemplary embodiments, and which are not necessarily drawn to scale, wherein:
FIG. 1 depicts schematically an implantable electrical stimulation device, such as an implantable pulse generators (IPG);
FIG. 2 schematically depicts an improved electrical stimulation device comprising two units - an implantable pulse generator unit and an implantable electrode unit;
FIG. 3 depicts a further example of an improved electrical stimulation device, comprising a further pulse generator unit and a further electrode unit;
FIG. 4A depicts another improved electrical stimulation device, comprising the pulse generator and the implantable electrode unit depicted in FIG 3;
FIG. 4B depicts an alternative alignment and proximity of the device depicted in FIG. 3; FIG. 5 depicts schematically a configuration for resonant inductive coupling;
FIG. 6 depicts an alternative model for determining configurations suitable for resonant inductive coupling;
FIG. 7 depicts the magnetic field produced when a current of 1 mA passes through a preferred first coil with diameters lmm, 2mm and 3mm and having one (1) winding;
FIG. 8 depicts the variation in the coupling factor (the quality of the energy transfer) over a separation distance between a first and second coils with diameters lmm, 2mm and 3mm;
FIG. 9 shows the efficiency of power transfer over a separation distance between a first and second coil with a coil diameter of 1 mm and a transmission frequency of 10 kHz;
FIG. 10 shows the efficiency of power transfer over a separation distance between a first and second coil with a coil diameter of 1 mm and a transmission frequency of 150 kHz;
FIG. 11 shows the efficiency of power transfer over a separation distance between a first and second coil with a coil diameter of 2 mm and a transmission frequency of 10 kHz;
FIG. 12 shows the efficiency of power transfer over a separation distance between a first and second coil with a coil diameter of 2 mm and a transmission frequency of 150 kHz;
FIG. 13 shows the efficiency of power transfer over a separation distance between a first and second coil with a coil diameter of 3 mm and a transmission frequency of 10 kHz;
FIG. 14 shows the efficiency of power transfer over a separation distance between a first and second coil with a coil diameter of 3 mm and a transmission frequency of 150 kHz;
DETAILED DESCRIPTION
In the following detailed description, numerous non-limiting specific details are given to assist in understanding this disclosure. It will be obvious to a person skilled in the art that the software methods may be implemented on any type of suitable controllers, memory elements, and/or computer processors.
FIG. 1 depicts schematically an implantable electrical stimulation device 700, such as an implantable pulse generators (IPG). The implantable device 700 comprises a power supply 750, such as a battery, configured and arranged to provide power to a controller 720. The battery may be rechargeable and/or non-rechargeable. The controller 720 is electrically connected to one or more stimulation electrodes 760 and at least one reference electrode 770 - each stimulation electrode 720 provides energy relative to the at least one reference electrode 770. The controller 720 may be software programmable, firmware programmable, hard-wired and any combination thereof.
The implantable device 700 is configured and arranged to be implantable such that a suitable amount of energy may be provided to a region of human or animal tissue proximate the one or more stimulation electrodes 720 after implantation.
Implantation may be partial or complete - at least a portion of the device comprising the one or more stimulation electrodes 760 may be implanted.
To reduce the chance of ingress of fluids, such as water, from the body into the implantable device 700, encapsulation 710 is provided such as a hermetic titanium can or case. Additionally or alternatively, the encapsulation 710 may be configured to reduce the chance of leakage of fluids or other substances from the implantable device 700 into the human or animal body. The encapsulation 710 is further configured to allow electrical stimulation to be applied to tissue using the electrodes 760, 770.
The controller 720 is further configured and arranged to provide energy through the electrodes 760, 770 in the form of one or more electrical pulses. The controller 720 may be further configured and arranged to control parameters of the pulses, such as intensity, duration, waveform shape, frequency, and repetition rate.
Ingress of fluids into the implantable device 700 may reduce the performance of the device 700, or even reduce the operation lifetime of the device 700. This may be disadvantageous, particularly when the implantable device 700 requires a surgical procedure, or the intervention of a healthcare professional, for implantation and explantation / replacement. US patent 9,333,339 discloses such an IPG device, configured and arranged to provide Peripheral Nerve Stimulation (PNS) for pain relief. The IPG device comprises a stimulation lead 14 as depicted in FIGURES 4, 14,15, 17, 18, 19 and described in the relevant parts of the description. The use of a stimulation lead 14 may be advantageous as the position of stimulation electrode may be determined more accurately, and smaller leads may be used for tissue regions where smaller dimensions are more suitable. As described in column 8, suitable pulse parameters for an IPG include: 0.5 - 4.0 Volt amplitude, 90 - 200 microseconds pulse width and 50 - 400 Hz repetition rate.
However, implantation of the pulse generator (IPG) 16 is depicted in FIGURES 17, 18, 19 and described in the relevant parts of the description. This means that the IPG 16 and possibly part of the lead must be encapsulated. Particular attention must be paid to the connection of the electrode lead (stimulation lead) to the pulse generator (IPG). The risk of ingress around this connection point may be reduced by including a header portion in the pulse generator (IPG) using an electrical feedthrough that is sealed. However, this limits the degree to which pulse generators may be reduced in size.
FIG. 2 schematically depicts an improved electrical stimulation device 100 comprising two units - an optionally implantable (or partially implantable) treatment pulse generator unit 200 and an implantable (or partially implantable) electrode unit 300. Implantable means being suitable for implantation under the skin in a human or animal body, preferably in a living body and preferably for extended periods of time.
Implantation depth may vary depending on the tissue to receive the electrical stimulation - for example:
- just below the dermis at a depth of 1 to 3mm from the surface;
- subcutaneous at a depth of 1 to 3 cm from the surface;
- in a bodily cavity;
As will be described in more detail below, the treatment pulse generator unit 200 and the electrode unit 300 may be combined into one device 100 by, for example, encapsulating them together. The energy transfer between the treatment pulse generator unit 200 and the electrode unit 300 is configured and arranged according to the invention. By encapsulating them together, both units 200, 300 are configured and arranged to be implantable (or partially implantable) as one device 100 together.
Alternatively, the electrode unit 300 may be inserted (or partially inserted) into the pulse generator unit 200, configured and arranged to provide energy transfer between them according to the invention. The electrode unit 300 is configured and arranged to be implantable. The treatment pulse generator unit 200 may be configured to be implantable as well. Alternatively, the pulse generator unit 200 may be configured and arranged to be an external unit, for example, a trans-dermal electrical stimulation device 100
The electrode unit 300 and pulse generator unit 200 are configured and arranged to be separate, distinct devices, configured and arranged to provide energy transfer between them according to the invention. The electrode unit 300 is configured and arranged to be implantable. The pulse generator unit 200 may be configured to be implantable as well. Alternatively, the pulse generator unit 200 may be configured and arranged to be an external unit, for example, a trans-dermal electrical stimulation device 100
The treatment pulse generator unit 200 comprises:
- a power supply 250, which may be any type of power source suitable for use with an implantable device. For example, one or more rechargeable batteries, one or more non-rechargeable batteries, a wireless power receiver, or some combination thereof. AC and/or DC voltages may be used in the pulse generator unit 200, and DC may be provided from the power supply 250 to the rest of the pulse generator unit 200.
- a controller 220 for producing treatment energy pulses. This may be a suitably configured and programmed processor, controlling one or more parameters of the energy pulses, such as intensity, duration, waveform shape, frequency, and repetition rate using one or more software methods. It may operate in a stand-alone mode, or it may be in regular communication with an external controller, or some combination thereof.
- one or more treatment energy transmitters, configured and arranged to wirelessly transmit the treatment energy pulses.
The device is optimized for the transfer of treatment energy pulses. This is different to known systems where energy is transferred wirelessly for power purposes - although the energy being transfer may be alternating, the energy transferred during power transfer is used to power a treatment pulse generator. In this disclosure, the devices comprise treatment pulse generators at the transmission part of the device.
Any suitable treatment energy transmitter may be used, such as:
- one or more coils 230, as depicted in Figure 2, configured and arranged to convert the energy pulses to magnetic pulses for transmission;
- one or more lasers, LED’s or laser diodes, configured and arranged to convert the energy pulses to light pulses for transmission;
- one or more inductive coils, configured and arranged to convert the energy pulses to electromagnetic pulses for transmission;
- one or more electromagnetic transducers, configured and arranged to convert the energy pulses to electromagnetic radiation pulses for transmission, such as RF (radio-frequency) or microwaves;
- one or more acoustic transducers, configured and arranged to convert the energy pulses to acoustic pulses for transmission, such as ultrasound;
- one or more electrical capacitive conductors, configured and arranged to convert the energy pulses to electrical field pulses for transmission.
Combinations of these transmitter types may also be used. The transmitter components may be miniaturized using modern manufacturing technology. These technologies comprise at least one conductor.
Optionally, if the treatment pulse generator 200 is configured and arranged to be implantable, it may comprise an encapsulation layer 210. This layer 210 is configured and arranged to resist the ingress of fluids from a human or animal body into the pulse generator unit 200.
The implantable electrode unit 300 comprises:
- one or more energy receivers 340, configured and arranged to wirelessly receive at least a portion of the pulsed energy from an associated energy transmitter 230 when the associated energy transmitter 230 is proximate. Any suitable energy receivers may be used, including the types indicated as examples of energy transmitters. Preferably, the same or a similar type is used to provide a high degree of efficiency in the
transmission of the pulsed energy. For example, photo-diodes may be used to convert incoming photons to electrical energy, coils may be used to convert magnetic energy to electrical energy, piezo-sensitive element may be used to convert acoustic energy to electrical energy. These technologies comprise at least one conductor.
- one or more stimulation electrodes 360, 370, each configured to receive pulsed energy from an associated energy receiver 340, and further configured to transmit the pulsed energy received to human or animal tissue as electrical pulses.
- an electrode unit encapsulation layer 310, configured and arranged to resist the ingress of fluids from a human or animal body into at least a portion of the electrode unit 300. The encapsulation layer 310 is configured and arranged to allow, in use, the portion of pulsed energy to be received wirelessly through the encapsulation layer 310.
The example in Figure 2 depicts a first conductor 235 configured to be used as an energy transmitter 230 - in this case, a first coil 230. The first conductor 235 is electrically connected to the controller 220, and the controller 220 is electrically connected to the power supply 250. In use, the controller 220 generates electrical pulses which change the electrical potential and/or current applied to the first conductor 235, causing energy to be wirelessly transmitted.
The example in Figure 2 further depicts a second conductor 345, associated with the first conductor 235, and configured to be used as an energy receiver 340. In this case, the second conductor 345 is a second coil 340, and the coils are configured and arranged to provide inductive coupling between the first coil 230 of the pulse generator unit 200 and the second coil 340 of the implantable electrode unit 300.
The second conductor 345 is electrically connected to one or more electrodes 360, 370. In this example, the second conductor 345 is a coil 340, and it is connected to two electrodes - as stimulation electrode 360 and a reference electrode 370. In use, the second conductor 345 receives at least a portion of the energy transmitted by the energy transmitter 230, and passes this to the electrodes 360, 370 as electrical pulses. The electrical pulses are applied by the electrodes 360, 370 in use to body tissue proximate the electrodes 360, 370. The portion of energy received by the receiver 340 depends on parameters such as the type of second conductor 345 used, the alignment between the first 235 and second 345 conductors, the distance between the first 235 and second 345 conductors, and the materials between the first 235 and second 345 conductors.
In general, one or more stimulation channels are provided - Figure 2 depicts an example of a single electrical stimulation channel, configured such that, in use, pulses generated by the controller 220 are applied as electrical pulses by the electrodes 360, 370 to body tissue. At a convenient point in each stimulation channel, a wireless link is provided between the energy transmitter 230 and the energy receiver 340. This wireless link advantageously may allow:
- the implantable electrode unit 300 to be reduced in size, making implantation easier and increasing the possible body locations where the improved electrical stimulation device 100 may be used;
- the number of components in the implantable electrode unit 300 to be minimized, which may increase reliability and lifetime;
- circuit components to be used in the electrode unit 300 to provide the electrical pulses which are predominantly passive. This may further reduce complexity and may further increase reliability and lifetime. In addition, it allows the electrode unit dimensions to be further reduced. Optionally, the electrode unit 300 may configured and arranged to comprise only passive components. Passive components (or passive devices) are incapable of controlling current by means of another electrical signal, such as resistors, capacitors, inductors, transformers, and even diodes;
- the implantable electrode unit 300 to be configured and arranged to comprise substantially no internal power source. In other words, the electrode unit (300) is substantially inactive when the pulse generator unit 200 is inactive for an extended period. This may further reduce complexity and may further increase reliability and lifetime.
- the implantable electrode unit 300 (and the pulse generator unit 200 if also configured and arranged to be implantable) may be encapsulated 310 to a higher degree - in other words, to resist to a higher degree the ingress of ingress of fluids from a human or animal body into the electrode unit 300. Encapsulating layers, such as the electrode unit encapsulation layer 310, may comprise materials such as a silicone rubber, a silicone elastomer, a latex rubber, a glass, a ceramic, parylene, liquid crystalline polymer (LCP), a biocompatible polymer, a biocompatible elastomer, or any combination thereof. Additionally, conductive surfaces may also be required - in that case, a metal, an alloy, titanium, stainless steel, cobalt-chromium maybe used. Atomic layer deposition or PECVD may be used for layers with thicknesses in the nanometers range. The multilayers and the processes described in EP patent EP 24646421B1 may also be used. Silicone rubbers, such MED-6215, may be used with a layer thickness in the 0.1 to 1 millimeter range. Preferably a thickness of approximately 0.2mm may be used. Any convenient process may be used, such as dip coating or molding. Encapsulating layers may also be used to mold a particular shape - for example to make smooth edges, a curvature or a shape that helps with the implantation procedure. Encapsulation may further increase reliability and lifetime. The degree to which encapsulation resists ingress may be measured experimentally by subjecting the device 100 and/or units 200, 300 to appropriate testing;
- the electrode unit encapsulation layer 310 to extend between one or more energy transmitters 230 and one or more associated energy receivers 340. Alternatively or additionally, the degree of encapsulation may be substantially greater in a region between one or more energy transmitters 230 and one or more associated energy receivers 340.
The electrode unit encapsulation layer 310 is preferably further configured to allow the energy to be transmitted through the layer 310 to a high degree to optimize the energy which may reach the one or more energy receivers 340;
- the implantable electrode unit 300 to be implanted at a different distance below the skin (different depth) or in a different bodily cavity compared to the pulse generator unit 200. Depending on the tissue to be electrically stimulated, the hostility of body conditions for implants may vary greatly - it may therefore be advantageous to separate the units 200, 300 by a small distance. Depending on the transmitter types and energies used, typical separations may range from a few tens of microns to a few hundred microns, from a few hundred microns to a few millimeters, from a few millimeters to a few centimeters. Advantageously, the pulse generator unit 200 is substantially not implanted - the units may be separated by 1 to 3 millimeters of dermis (skin). This may reduce the risks associated with implantation, such as infection. Alternatively or additionally, the pulse generator unit 200 may be partially implanted - for example, percutaneous and/or subcutaneous conductors 230 may be used to reduce the distance over which the energy pulses are wirelessly transmitted. A further advantage may be that the pulse generator unit 200 and implantable electrode unit 300 may be configured and arranged to have different reliability and lifetimes because the replacement of the pulse generator unit 200 may be simplified. In some cases, it may be user replaceable or only require a minimally invasive procedure. This may reduce the cost of the improved device 100
Energy transfer between the pulse generator 200 and the implantable electrode unit 300 is preferably through one or more non-galvanic couplings. In other words, no direct electrical contact is made between the pulse generator unit 200 and the electrode unit 300 - the pulse energy is transferred wirelessly.
In contrast, the transmission of the pulsed energy to human or animal tissue as electrical pulses preferably uses the one or more electrodes 360 to fonn one or more direct electrical contact with tissue. This may provide one or more galvanic (or partially non-galvanic) charge transfer couplings with the tissue.
A reference conductor 370 may be optionally provided, either using one of the electrodes 360, 370 or a separate conductor, to provide an electrical reference value for the one or more stimulation electrodes 360. A further percutaneous or subcutaneous electrode may also be used, or a conductive surface making contact with an outer surface of skin. Alternatively or additionally, at least a portion of the implantable electrode unit housing may also comprise a reference conductor 370 - for example, by including a conducting material in the encapsulation layer 310 such as a conductive ceramic layer, a metal-in-glass feedthrough, or a hermetically-sealed metal cap.
The degree of stimulation applied by an electrode 360 depends on parameters such as the pulse parameters, a voltage applied, a current applied, the distance between the electrode 360 and the reference conductor 370, surface areas of the electrode 360 and the reference conductor 370, the tissue between the electrode 360 and the reference electrode 370. Depending on the degree of control required, a single reference conductor 370 may be used with all the stimulation electrodes 360, or more than one reference conductors 370 may be provided.
Figure 3 depicts a further example of an improved electrical stimulation device 101, comprising a further pulse generator unit 201 and a further electrode unit 301.
The further pulse generator unit 201 comprises:
- a power supply 250 comprising a coil 255, configured and arranged to provide power directly to the components and devices comprised in the further pulse generator unit 201, and indirectly to the further electrode unit 301. Such coil-based power supplies are well-known in the art, allowing devices to be powered using, for example,
RF energy. The power supply 250 typically comprises components and devices to generate DC power using the energy received by the coil 255.
- a controller 220, powered by the power supply 250 in use;
- five energy transmitters 230 each comprising a first conductor 235, electrically connected to the controller 220, configured and arranged to wirelessly transmit energy pulses inductively. They are configured and arranged to co-operate with the associated one or more second conductors 345 provided in the electrode unit, which is described below. As depicted in this example, the one or more first conductors 235 form electrical coils with one or more windings. They are depicted in a 1 -dimensional array. Note that 2-d and 3-d arrays may also be used, depending on factors such as the type of tissue to be stimulated, the dimensions of the units 201, 301 and the amount of room available at the implantation site. The conductors 235 may be provided as coils having at least one winding - the efficiency of energy transfer may increase with more turns.
Providing the conductors 235 as a pad may also be advantageous and may work for higher frequencies of radio frequencies.
- optionally, if the pulse generator unit 200 is configured and arranged to be implantable, it further comprises a pulse generator encapsulation layer 210, configured and arranged to resist the ingress of fluids from a human or animal body into at least a portion of the pulse generator unit 200. Materials may be used similar to those mentioned for the electrode unit encapsulating layer 310 above.
In this configuration, one of the first conductors 235 is configured to represent, in use, a reference value. As depicted, it is the most left of the first conductors 235. The controller 220 is configured and arranged to provide up to four stimulation channels of pulsed energy with respect to the reference value. In practice any number of stimulation channels may be provided, depending on factors such as the type of tissue to be stimulated, the dimensions of the units 201, 301 and the amount of room available at the implantation site. After implantation of at least the further electrode unit 301, up to four stimulation channels may be used. Alternatively or additionally, a selection may be made of one or more stimulation channels that provide the desired stimulation effect, compensating for possible inaccuracies during positioning.
The further implantable electrode unit 301 comprises:
- one or more energy receivers 340 each comprising a second conductor 345, each electrically connected to an associated electrode 360, 370, and each configured to wirelessly receive at least a portion pulsed energy from an associated first conductor 235 when the associated first conductor 235 is proximate. The one or more second conductors 345 are configured and arranged to co-operate with one or more first conductors 235 to allow transfer of energy pulses. As depicted in this example, the one or more second conductors 345 form electrical coils with one or more windings. They are depicted in a 1 -dimensional array. In general, the second conductors 345 may have similar or the same dimensions and/or spacings as the array of first conductors 235.
However, it may also be advantageous to provide different numbers of conductors and/or different layouts - this may, for example, provide additional adjustment and setting possibilities, redundancy to improve reliability, allow different electrode units to operate with a standardized pulse generator, or allow different pulse generator units to operate with a standardized electrode unit. The second conductors 345 may be provided as coils having at least one winding - the efficiency of energy transfer may increase with more turns. Providing the conductors 345 as a pad may also be advantageous and may work for higher frequencies of radio frequencies
- five stimulation electrodes 360, 370, each configured to receive pulsed energy from an associated second conductor 345. They are also further configured to transmit the pulsed energy received to human or animal tissue as electrical pulses. These may be any suitable electrode known in the art for this purpose. They are depicted in a 1- dimensional array. However, 2-d and 3-d arrays may also be used, depending on factors such as the type of tissue to be stimulated, the dimensions of the units 201, 301 and the amount of room available at the implantation site. In general, the number, dimensions and/or spacings of the stimulating electrodes 360 may be selected and optimized separately from the wireless transfer channels 230, 235, 340, 345. After implantation of at least the further electrode unit 301, up to five stimulation electrodes 360, 370 may be used in this embodiment to provide up to five electrical stimulations to tissue.
Alternatively or additionally, a selection may be made of one or more stimulation electrodes 360, 370 that provide the desired stimulation effect, compensating for possible inaccuracies during positioning. The energy from a single stimulation channel 230, 235, 340, 345 may be converted to one or more stimulation electrodes 360, 370. Similarly, a single electrode 360, 370 may receive pulsed energy through one or more wireless transfer channels. For the explanation of this example, the number of stimulation electrodes 360 is assumed to be the same as the number of stimulation channels 230, 340.
- optionally one or more rectifiers 350, each electrically connected between an associated electrode 360, 370 and an associated energy receiver 340 such as a second conductor 345. Depending on the use, rectifiers 350 may be needed to provide the correct form of wavelength, for example converting alternating pulses received through the second conductors 345 to a unidirectional pulse. In many cases, the device is configured to provide AC electrical pulses through the stimulation electrodes 360.
- an electrode unit encapsulation layer 310, configured and arranged to resist the ingress of fluids from a human or animal body into the electrode unit 300.
In this example, one of the stimulation electrodes 360, 370 is configured and arranged to function as a reference conductor 370 or reference electrode 370. As depicted, it is the most left of the electrodes 370. From the four stimulation channels used for the wireless power transfer 230, 340, four electrical pulses are available from the four stimulation electrodes 360 with respect to the reference electrode 370. As depicted, the reference electrode 370 is electrically connected to each of the other four electrodes 360 to provide the reference level.
After implantation of at least the further electrode unit 301, the further pulse generator unit 201 is disposed such that the first conductors 235 are proximate the second conductors 345 and correctly aligned. In general, the portion of energy transferred will be higher with a correct alignment and/or closer proximity - alignment and/or proximity may be achieved, for example, by appropriate mechanical means, such a pins or magnets, or using a suitable electric sensor. Optionally, the pulse generator unit 201 may be rigidly attached to the pulse generator unit 301 to retain the alignment and/or proximity. The pulse generator unit 201 may be configured to be detachable to simplify replacement.
After providing suitable energy to the power coil 255, the power supply provides DC power to the components and devices of the further pulse generator unit 201, including the controller 220. The controller 220 may then activate one or more of the stimulation channels 230, 340 by producing energy pulses in the form of electrical pulses, which are passed to the one or more conductors 230. Each conductor 230 receiving an electrical pulse transmits the energy pulses wirelessly away from the pulse generator unit 201. If the second conductors 345 are sufficiently proximate and sufficiently aligned, they receive at least a portion of the pulsed energy, and convert it to electrical pulses. The electrical pulses pass through the rectifier 350, creating unidirectional electrical pulses at each of the active electrodes 360, 370. The electrical stimulation signal applied, in use to the tissue, corresponds to the electrical pulse at each active stimulation electrode 360 compared to the reference signal 370.
In some cases, regular operation of the device 101 may be started immediately. In many cases, the positioning of the stimulation electrodes may need to be checked, and if necessary, adapted or fine-tuned. For example, the position of the stimulating electrodes 360 and the reference electrode 370 may be changed by moving the electrodes 360, 370 and/or the unit 301. Additionally or alternatively, the position of the electrical stimulation in use may be modified by the controller 220 selecting one or more of the stimulation channels 230, 340 to be fully or partially active.
For example, if only one stimulation channel 230, 340 is fully active, electrical pulses are provided at the stimulation electrode 360 associated with this stimulation channel, and the tissue stimulated is proximate this active stimulation electrode 360. If two adjacent stimulation channels 230, 340 are fully active, electrical pulses are provided at two adjacent stimulation electrodes 360 associated with these two stimulation channels, and the tissue stimulated is proximate these two active stimulation electrodes 360, which includes the region of tissue disposed between the two active electrodes 360. The region of tissue stimulated may be reduced by reducing the amount of energy sent by the controller 220 through the active stimulation channels, and
consequently the electrical pulse energy provided by the associated active electrodes 360.
It may therefore be advantageous to provide: - two or more energy transmitters 230, comprised in the treatment pulse generator
200;
- two or more energy receivers 340, configured and arranged to wirelessly receive at least a portion of the treatment pulsed energy from an associated energy transmitter 230 through the encapsulation layer 310 when the associated energy transmitter 230 is proximate;
- two or more stimulation electrodes 360, 370, each configured to receive treatment pulsed energy from an associated energy receiver 340;
wherein the implantable electrode unit 300 is configured and arranged to be rigidly attached to the treatment pulse generator unit 200 such that two or more energy transmitters 340 are proximate the associated energy transmitter 230.
Up to four stimulation channels may be used in this example. Alternatively or additionally, a selection may be made of one or more stimulation channels that provide the desired stimulation effect, compensating for possible inaccuracies during positioning
The device 101 of Figure 3 may optionally be configured to provide up to five stimulation channels 230, 340 and up to five electrical pulses from five electrodes 360, 370 by configuring and arranging the reference electrode 370 depicted as a stimulation electrode 360 (in this case, at least disconnecting any electrical connections between the reference electrode 370 and the other electrodes 360) and providing a separate reference conductor as explained above.
The parameters of the electrical pulses applied to the tissue through the stimulation electrodes 360 may be optimized separately from the energy pulses transmitted wirelessly from the pulse generator unit 301. For example, some forms of wireless transmission may more efficient at higher frequencies, but in many treatment applications lower frequencies are preferred. For example, therapy (treatment) pulses may be 100 microsecond to 1 millisecond wide, and repeated with 40 to 1000 Hz. The energy pulse wireless transmission may use a frequency of 3 kHz to 150kHz, for example.
The components and devices in the implantable electrode unit 301 may configured and arranged to modify the signals, for example:
- a low pass filter may be included to block or reduce high frequency components;
- a high pass filter may be included to block or reduce low frequency components;
- a notch filter may be included to selectively pass a desired range of frequency components;
- resistive components may be used to reduce amplitudes; and
- rectifiers may be used to convert AC signals to unidirectional signals;
Five stimulation channels 230, 340 are depicted in Figure 3, configured to provide four electrical stimulation channels 360 with respect to the reference electrode 370. However, the skilled person will easily modify this example to provide the required number of electrical stimulation channels:
- one stimulation channel may be provided by deactivating all stimulation channels except one using the controller 220. Alternatively or additionally, an implantable electrode unit may be provided comprising one energy receiver 340 connected to one electrode 360. This may provide an implant with small dimensions, simplifying implantation. However, fine-tuning of the electrical stimulation during use may be limited to modifying one or more of the energy pulse parameters and/or moving the position of the one electrode 360.
- two stimulation channels may be provided by deactivating all stimulation channels except two using the controller 220. Alternatively or additionally, an implantable electrode unit may be provided comprising two energy receivers 340 connected to two associated electrodes 360. This may provide an implant with smaller dimensions than the configuration depicted in Figure 3. As fine-tuning of the electrical stimulation during use is available by varying one or more energy pulse parameters in each stimulation channel, two or more stimulation channels may be advantageous due to the high degree of flexibility and adjustment capabilities. In the case that the number of stimulation channels 230, 340 is the same as the number of stimulating electrodes 360, two or more stimulating electrodes 360 may also be provided.
The improved electrical stimulation device 100, 101 may be configured and arranged for different uses, such as for stimulating one or more nerves, one or more muscles, one or more organs, spinal cord tissue, and any combination thereof. The invention provides a highly configurable device 100, 101, which may be optimized for very different types of neurostimulations - for example, the heart (pacemaker) to a single facial nerve.
For example, it may be used to treat headaches, primary headaches, incontinence, occipital neuralgia, sleep apnea, limb pain, leg pain, back pain, lower back pain, phantom pain, chronic pain, epilepsy, overactive bladder, poststroke pain, obesity, and any combination thereof
One of the main causes of failure of conventional implants 700 (as depicted in Figure 1) is due to ingress of bodily fluids through the region around the electrodes 760, 770. For electrical stimulation, and in particular for neurostimulation, electrodes 760, 770 must always be present, providing an electrical contact from the inner electronics to the outside. It is therefore difficult to completely encapsulate the region around the electrode 760, 770.
In addition, without wishing to be bound by theory, it appears that the use of DC voltages makes the implant 700 much more susceptible to galvanic corrosion. As described in“Effect of bias voltage and temperature on lifetime of wireless neural interfaces with A1 2O3 and parylene bilayer encapsulation”, Xie, Rieth et. al, Biomed Microdevices 2015 Feb; l7(l): l (DOI l0.l007/sl0544-0l4-9904-y), application of a five volt DC continuous voltage appears to be one of the factors in increasing the aging factor. For these wireless neural interfaces, the reduction in equivalent lifetime to 140 equivalent days was acceptable, as with a use of three hours per days, this represents an acceptable three years of lifetime. For the authors of this paper, improving the encapsulation by using a bilayer comprising alumina deposited by Atomic Layer Deposition (ALD) and parylene C compared to the standard parylene-only encapsulation provided the greatest improvement in lifetime.
The invention is based on the insights that the reliability of implantable electrical stimulation devices may be improved 100, 101 by separating the electrode functionality from the pulse generator functionality into separate pulse generator 200, 201 and electrode 300, 301 units:
- the higher DC power voltages, typically found in the pulse generator, are moved further away from the stimulating electrodes 360;
- separating the functionality allows the pulse generator unit to be more completely encapsulated and/or moved to a position where ingress of fluids is less likely. In some cases, the pulse generator does not need to be implanted.
- the construction of the electrode unit 300, 301 may be simplified, as the controller 220 and many high power components are comprised in the pulse generator unit 200, 201. In some cases, only passive components may be used, reducing the period of time that voltages are present close to the stimulation electrodes 360 to the periods when electrical stimulation is provided.
- without wishing to be bound by theory, it is believed that avoiding the use of DC voltages and currents in the electrode unit 300, 301 may further improve reliability and lifetime. By using a non-galvanic coupling with the pulse generator 200, 201, the electrode unit 300, 301 may be designed such that predominantly AC voltages and currents are used.
Figure 4A depicts another improved electrical stimulation device 102, comprising the pulse generator 201 and the implantable electrode unit 301 depicted in Figure 3, and described above. This device 102 differs in that:
- the pulse generator 201 and implantable electrode unit 301 are not separable - they are rigidly attached such that the one or more energy transmitters 230 (in this case one or more first conductors 235) are aligned and/or proximate the associated one or more energy receivers 340 (in this case one or more second conductors 345). The alignment and degree of proximation is sufficient for acceptable energy transfer, and acceptable electrical stimulation.
- the pulse generator 201 is implantable, and comprises a pulse generator encapsulation layer 210;
- this device 102 comprises a device encapsulation layer 110, configured and arranged to resist the ingress of fluids from a human or animal body into the device 102.
The device 102 of Figure 4 A is configured and arranged to be implantable - however, where convenient, it may also be configured and arranged to be only partially implanted.
By providing three encapsulation layers 110, 210, 310, both the pulse generator unit 201 and electrode unit 301 are provided with two encapsulation layers to further improve the lifetime and reliability. Each encapsulation layer 110, 210, 310 may be separately optimized as indicated above in the description of the electrode unit encapsulation layer 310.
By providing a device encapsulation layer 110, the pulse generator encapsulation layer 210 and/or electrode encapsulation layer 310 may be reduced in thickness in the region of the energy transmitters 230 and energy receivers 340 to optimize the wireless coupling (in other words, to optimize the portion of energy received by the one or more energy receivers 340). For example, when using silicone aibber, it may be advantageous to reduce the thickness in these regions to less than li n. Less than O. lmm may be even more preferred. In a further example, the device encapsulation layer 110 may be silicone rubber, and the electrode unit encapsulation layer 310 and/or pulse generator encapsulation layer 210 may be a thin layer (or multilayer) applied with atomic layer deposition or PECVD.
Figure 4A depicts a separation between the row of energy transmitters and the row of energy receivers, but that is not required - the electrode unit encapsulation layer 310 may be in physical contact with the pulse generator encapsulation layer 210. As depicted, the degree of proximity is determined by the distance between the transmitters and the receivers in the plane of the paper, and the degree of alignment is determined along an axis approximately perpendicular to the plane of the paper.
Figure 4B depicts an alternative alignment and proximity - as in Figure 4A, another improved electrical stimulation device 102 is shown comprising the pulse generator 201 and the implantable electrode unit 301. However, here, the desired degree of alignment and proximity is achieved by positioning the first 235 and second 345 conductors such that they are approximately parallel planar and“overlapping”. This may be advantageous if, for example, the first 235 and second 345 conductors each form a pad or a relatively“flat” (low in height) coil. Typically, the device 102 may be constructed such that the total height of the device (as depicted, height is in the direction
perpendicular to the page) is approximately 1.6 mm before encapsulation.
In other words, the degree of alignment is determined in the plane of the paper, and the degree of proximity is determined by the distance between the transmitters and the receivers along an axis approximately perpendicular to the paper.
The wireless coupling between the one or more first conductors 235 and the one or more second conductors 345 is preferably based on resonant inductive coupling, although the invention may be operated with any degree of inductive coupling.
A configuration for resonant inductive coupling for an improved electrical stimulation device 100, 101, 102, is depicted schematically in Figure 5, as a circuit model of the pulse generator 200, 201 depicted on the left hand side, and the circuit model of the electrode unit 300, 301 depicted on the right hand side.
The controller 220 comprises the energy pulse source VI - this produces the necessary signal for electrical stimulation. The controller 220 is electrically connected across the first conductor 235. The controller 220 may be an ASIC.
The first conductor 235 is modelled in Figure 5 as a resistor Rl, capacitor Cl and inductor Ll connected in series. Resistor Rl influences the output current of the controller 220. Capacitor Cl is preferably used for matching. Matching is preferred to convert most of the apparent power into real power instead of reactive power since reactive power is not usable for the electrode unit 300, 301. Inductor Ll is the main wireless power transfer component since it creates a magnetic field if current passes through it. This magnetic field couples to the inductor L2 in the electrode unit 300, 301.
In general, a high frequency is preferred to optimize the transfer of energy from the first conductor 235 to the second conductor 345.
The second conductor 345 is modelled in Figure 5 as an inductor L2, capacitor C2 and resistor R2 connected in parallel. The capacitor C2 has a similar function to the capacitor Cl. It may be configured to maximize the real power from the received apparent power.
A diode Dl is connected in series with the second conductor 345, and a capacitor C3 is connected in parallel with the second conductor 345. Components Dl and C3 combine to form an optional rectifier 350, which may be required to convert the received energy pulses into a unidirectional waveform, which is preferred for some electrical stimulation uses. In general, the frequency of the electrical pulses to be applied to the tissue is lower than the frequency of the energy pulses transferring between the first conductor 245 and the second conductor 345 - the rectifier 350 may be configured to reduce the frequency of the electrical pulses passed to the stimulation electrode 360.
The model further comprises two resistors R3 and R4 in series connected across capacitor C3. Resistor R3 is used to optimize the energy transfer to the resistor R4. R4 represents the stimulation electrode 360 and the interface that it makes with tissue during operation. For example, it may represent tissue in the proximity of a peripheral nerve.
Alternatively, the model depicted in Figure 6 may be used for determining configurations suitable for resonant inductive coupling. The first 235 and second 345 conductors are modelled differently to simplify the calculations by concentrating on the portion of energy pulses transferred wirelessly from the first conductor 235 to the second conductor 345. Compared to the model of Figure 5, the differences are:
- The rectifier 350, comprising Diode D1 and Capacitor C3, is omitted as they may be neglected for this simplified efficiency calculation.
- The stimulating electrode 360 in use, comprising Resistor R3 and Resistor R4 have been omitted, as they may be neglected for this simplified efficiency calculation.
- Inductor Ll-Lm in series with Lm represents the coil of the energy transmitter 230 (in other words, the inductance of the first conductor 235);
- Inductor L2-Lm in series with Lm represents the coil of the energy receiver 340 (in other words, the inductance of the second conductor 345);
- Inductor Lm represents the energy lost when the efficiency of the wireless coupling between the first 235 and second 345 conductor is less than one hundred percent.
The efficiency may be calculated using
Figure imgf000028_0001
or
Figure imgf000028_0002
The following factors should be taken into account when determining the efficiency:
- The source providing the energy pulses is comprised in the controller 220, and delivers pulses with a power of roughly 1 or 10 mW - these are typical values for neurostimulation for treatments of, for example, headaches, primary headaches, incontinence, occipital neuralgia, sleep apnea, limb pain, leg pain, back pain, lower back pain, phantom pain, chronic pain, epilepsy, overactive bladder, poststroke pain, obesity, or any combination thereof.
- The coil inductances of the first 235 and second 345 conductors depend on parameters. The conductors 235, 345 (coils) preferred for neurostimulation have:
• Number of turns: typically coils with 1, 2, 3, or 4 turns may be used
• Diameter of the coils used: typically 1, 2, or 3 mm
• Frequency: typically, in the range 10 - 150 kHz
• Wire thickness for the coils: typically 50 microns (micrometers)
It may be advantageous to use coils 235, 345 of lmm diameter or less, as this may greatly reduce the size of the device 100 to be implanted - in particular, it may greatly reduce the size of the electrode unit 200, 201. The optimization information provided, including the efficiency plots, are based on realistic assumptions regarding the boundary conditions for the size of the coils 235, 345, their distance to each other and the number of windings in each coil 235, 345.
- The resistors Rl and R2 may be configured to provide maximum power transfer via matching. It may be advantageous to configure the minimum resistance to be equal to the sole (or Ohmic) resistance of the coils 235, 245 themselves This reduces the possible efficiency calculation to the set of all plausible values. Resistance values can be as low as possible, even 0 (zero) ohm, but they can also be extremely large, such as 1 mega Ohm (106) or even larger. However it helpful to know the boundaries of the resistance values since that reduces the pool of possible resistance values.
The only boundary found at this moment in the calculation is the minimum value, since this is dictated by the parameters of the preferred coils 245, 345, which are in the order of 1 milliohm because they are so small. Therefore, the possible resistance values may be reduced.
Theoretically, the value of the resistance could be set to zero, but that is not physically realistic since there will always be a minimal resistance provided by the coils 235, 345. So this should be taken into account when setting up the equations for the calculation. Thus, the optimal resistor values can be found in [1 ¥] milliohm. This chosen set reduces the possibility of short circuiting due to the reduced set of possible resistance values. This complements the idea of having a minimal resistance equal to that of the coil 235. In other words, Rl and Cl in Figures 5 and 6 being equal to zero
- An additional inductor, Lm, is included in Figure 6 - this represents the mutual inductance. This mutual inductance is obtained via two equations
Figure imgf000030_0001
where z is the distance variable between the first 235 and second 345 coils, measured in meters. I is the current through the coil in Amperes r is the coil radius in meters. The area of the second coil 345 is indicated by Acoil, which is expressed in m2 m is the permeability of the material in H/m.
It is assumed that the area of the first 235 and second 345 coil are the same (or symmetric), therefore only one Acoil is defined.
- The capacitor values may be selected according to the following equation
Figure imgf000030_0002
Where w is the radial frequency in rad/s.
- In addition, the coupling factor is preferably taken into account as it represents a first indication for efficiency. This coupling factor ranges from -1 up to 1. Having a coupling factor of -1 or 1 indicates good coupling while a coupling factor of 0 is no coupling. The coupling factor may be calculated via
Figure imgf000030_0003
Figure 7 depicts the magnetic field produced when a current of 1 mA passes through a preferred first coil 235 with diameters lmm, 2mm and 3mm and having one (1) winding. The magnetic field strength is plotted logarithmically on the vertical axis over a range of 108 to 102 A/m. Distance is plotted logarithmically on the horizontal axis over a range of 102 (0.01) to 102 (100) millimeters (mm). Distance is measured perpendicular to the mid-point of the coil 235 plane.
The International Commission on Non-Ionizing Radiation Protection (ICNIRP) provides guidelines for limiting exposure to time-varying electric, magnetic and electromagnetic fields. For the preferred wireless transmission frequency range of 3 kHz to 150 kHz, the maximum magnetic field strength is 5 A/m, and this is also shown on Figure 7 as a horizontal line. As the wireless coupling may provide the highest field strength of all the fields in the improved device 100, 101, 102, this should be determined for each configuration.
The graph of D = lmm (diameter = lmm) is depicted as a dashed line. It starts at approx field strength 5 A/m at distance 10 2 (0.01) mm. It remains at 5 A/m, coinciding with the maximum value according to the ICNIRP guideline until about 10 1 (0.1) mm, where the field strength starts to drop in value. This graph curves down to approx. 4 x 10 1 (0.4) A/m at 10° (1 mm), approx. 6 x 104 A/m at 101 (10) mm and approx. 6 x 10 7 A/m at 102 (100) mm.
The graph of D = 2mm (diameter = 2mm) is depicted as a dotted line. It starts at approx field strength 2.5 A/m at distance 102 (0.01) mm. It remains at 2.5 A/m, until approx. 2 x 10 1 (0.2) mm, where the field strength starts to drop in value. This graph curves down to approx. 10° (1) A/m at 10° (1 mm), approx. 2.5 x 10 ! A/m at 101 (10) mm and approx. 2.5 x lO 6 A/m at 102 (100) mm.
The graph of D = 3mm (diameter = 3mm) is depicted as a dash-dotted line. It starts at approx field strength 1.8 A/m at distance 102 (0.01) mm. It remains at 1.8 A/m, until approx. 3 x 10 1 (0.3) mm, where the field strength starts to drop in value. This graph curves down to approx. 10° (1) A/m at 10° (1 mm), approx. 5 x l0 J A/m at 101 (10) mm and approx. 5.5 x I O 6 A/m at 102 (100) mm.
These measurements all stayed under the ICNIRP guidelines - the D=lmm graph came the closest, but it did not exceed 5 A/m, even very close to the coil 235. For all diameters, the field strength is relatively constant below a distance of about 0.5 x 10 1 (0.5) mm. For distances greater than 10° (1) mm, the field strength decreases rapidly. This is also advantageous because adjacent coils 235 may be spaced at distances comparable to the coil diameters without increasing the risk of interference or cross-talk. In addition, the rapid drop in field strength means that at even higher field strengths proximate the coil 235, the field strength away from the coil 235 (where tissue contacts the outer housing or encapsulation layer of implant) will not easily exceed the ICNIRP guidelines.
Figure 8 depicts the variation in the coupling factor (the quality of the energy transfer) over a separation distance between the first 235 and second 345 coils with diameters lmm, 2mm and 3mm. The coupling factor is plotted logarithmically on the vertical axis over a range of 10 x to 10° (1). Distance is plotted logarithmically on the horizontal axis over a range of 10 2 (0.01) to 102 (100) millimeters (mm). Distance is measured perpendicular to the mid-point of the coil 235 plane. It is assumed that the first 235 and second 345 coils are substantially the same diameter, they are plane parallel and optimally aligned with each other.
The graph of D = lmm (diameter = lmm) is depicted as a dashed line. It starts at approx field strength 5 x 10 1 (0.5) at distance 7 x 10 2 (0.07) mm. It remains at 0.5 until about 1.5 x 10 1 (0.15) mm, where the coupling starts to drop in value. This graph curves down to approx. 5 x 102 (0.05) at 10° (1 mm), approx. 6.5 x 10 3 at 101 (10) mm and approx. 7 x 10 8 at 102 (100) mm.
The graph of D = 2mm (diameter = 2mm) is depicted as a dotted line. It starts at approx field strength 4 x 10 1 (0.4) at distance 7 x 10 2 (0.07) mm. It remains at 0.4 until about 3 x 10 1 (0.3) mm, where the coupling starts to drop in value. This graph curves down to approx. 1.5 x 10 1 (0.15) at 10° (1 mm), approx. 4 x 10 4 at 101 (10) mm and approx. 4.5 x 10 7 at 102 (100) mm.
The graph of D = 3mm (diameter = 3mm) is depicted as a dashed-dotted line. It starts at approx field strength 4 x 10 1 (0.4) at distance 7 x 10 2 (0.07) mm. It remains at 0.4 until about 4 x 10 1 (0.4) mm, where the coupling starts to drop in value. This graph curves down to approx. 2 x 10 1 (0.2) at 10° (1 mm), approx. 1.5 x 10 3 at 101 (10) mm and approx. 1.25 x 10 6 at 102 (100) mm. The maximum coupling of 0.4 may be obtained from coils with diameter 1 mm. The coils with the larger diameters outperform the 1 mm diameter coil with respect to coupling factor over longer distances than 200 microns (micrometers) or 0.2 millimeters. The separation distance between the first 235 and second 345 coils should preferably be less than 1 mm for an optimal coupling factor.
Figure 9 shows the efficiency of power transfer over a separation distance between the first 235 and second 345 coil with a coil diameter of 1 mm and a
transmission frequency of 10 kHz. Graphs are plotted for 1, 2, 3 and 4 turns on the coil 235, 345. The efficiency in % is plotted logarithmically on the vertical axis over a range of 10 6 to 10° (1), so 1 on the graph is equal to 1%. Distance is plotted linearly on the horizontal axis over a range of 0 to 10 millimeters (mm). Distance is measured perpendicular to the mid-point of the coil 235 plane. It is assumed that the first 235 and second 345 coils are substantially the same diameter, they are plane parallel and optimally aligned with each other. The optimal resistance has been selected for the energy receiver 340 (the receiver coil 345) for the modelling.
The graph of one (1) turn is depicted as a solid line. It starts at approx efficiency 2 x 104 at distance 0.1 mm. It rises to about 1 x 103 at 1 mm, and it remains at approx. 1 x 103 until about 3mm. After that, it drops to approx. 2.5 x 1 O4 at 5 mm, approx. 4.5 x 10° at 7 mm and approx. 5 x 106 at 10 mm.
The graph of two (2) turns is depicted as a dashed line. It starts at approx efficiency 3 x 10 3 at distance 0.1 mm. It rises to about 1.7 x 102 at 1 mm, and it remains at approx. 1.7 x 102 until about 2mm. After that, it drops to approx. 5 x 103 at 3 mm, approx. 3.5 x 104 at 5 mm, approx. 4.5 x 10 3 at 7 mm and approx. 5 x 106 at 10 mm.
The graph of three (3) turns is depicted as a dotted line. It starts at approx efficiency 1.7 x 10 2 at distance 0.1 mm. It rises to about 7.5 x 102 at 1 mm, and it remains at approx. 7.5 x 102 until about l.25mm. After that, it drops to approx. 4 x 102 at 2mm, 7 x l0 3 at 3 mm, approx. 3.5 x 104 at 5 mm, approx. 4.5 x 10 5 at 7 mm and approx. 5 x 106 at 10 mm.
The graph of four (4) turns is depicted as a dashed-dotted line. It starts at approx efficiency 5 x 102 at distance 0.1 mm. It rises to about 0.2 x 10 1 at 0.8 mm, and it remains at approx. 0.2 x 104 until about l. lmm. After that, it drops to approx. 6 x 102 at 2mm, 7 x 10 3 at 3 mm, approx. 3.5 x 104 at 5 mm, approx. 4.5 x 10 5 at 7 mm and approx. 5 x 106 at 10 mm.
The maximum efficiency peak value increases with the number of turns.
So 4-turns provides a maximum of 0.22% using a frequency of energy pulses of 10 kHz.
Figure 10 shows the efficiency of power transfer over a separation distance between the first 235 and second 345 coil with a coil diameter of 1 mm and a
transmission frequency of 150 kHz. Graphs are plotted for 1, 2, 3 and 4 turns on the coil 235, 345. The efficiency in % is plotted logarithmically on the vertical axis over a range of 106 to 102 (100), so 100 on the graph is equal to 100%. Distance is plotted linearly on the horizontal axis over a range of 0 to 10 millimeters (mm). Distance is measured perpendicular to the mid-point of the coil 235 plane. It is assumed that the first 235 and second 345 coils are substantially the same diameter, they are plane parallel and optimally aligned with each other. The optimal resistance has been selected for the energy receiver 340 (the receiver coil 345) for the modelling.
The graph of one (1) turn is depicted as a solid line. It starts at approx efficiency 5 x 102 at distance 0.1 mm. It rises to about 2 x 104 (0.2) at 0.8mm, and it remains at approx. 0.2 until about 1. limn. After that, it drops to approx. 5.5 x 102 at 2mm, approx. 7 x 103 at 3mm, approx. 3.5 x 104 at 5 mm, approx. 5 x 10 5 at 7 mm and approx. 5.5 x 106 at 10 mm.
The graph of two (2) turns is depicted as a dashed line. It starts at approx efficiency 7 x 10 (0.7) at distance 0.1 mm. It rises to about 2.5 x 10° (2.5) at 0.5mm, and it remains at approx. 2.5 until about 0.7mm. After that, it drops to approx. 5.5 x 102 at 2mm, approx. 7 x 103 at 3mm, approx. 3.5 x 104 at 5 mm, approx. 5 x l0 5 at 7 mm and approx. 5.5 x 1 O 6 at 10 mm.
The graph of three (3) turns is depicted as a dotted line. It starts at approx efficiency 3.5 x 10° (3.5) at distance 0.1 mm. It rises to about 2 x 101 (20) at 0.3mm, and it remains at approx. 20 until about 0.5mm. After that, it drops to approx. 5.5 x 102 at 2mm, approx. 7 x 10 3 at 3mm, approx. 3.5 x 104 at 5 mm, approx. 5 x 10° at 7 mm and approx. 5.5 x 1 O 6 at 10 mm.
The graph of four (4) turns is depicted as a dashed-dotted line. It starts at approx efficiency 1 x 101 (10) at distance 0.1 mm. It rises to about 8.5 x 10° (8.5) at 0.4mm, and it remains at approx. 8.5 until about 0.6mm. After that, it drops to approx. 5.5 x 10 2 at 2mm, approx. 7 x 10 3 at 3mm, approx. 3.5 x 104 at 5 mm, approx. 5 x 10° at 7 mm and approx. 5.5 x 106 at 10 mm.
The maximum efficiency peak value increases with the number of turns.
So 4-turns provides a maximum of 18.6% using a frequency of energy pulses of 150 kHz.
Figure 11 shows the efficiency of power transfer over a separation distance between the first 235 and second 345 coil with a coil diameter of 2 mm and a
transmission frequency of 10 kHz. Graphs are plotted for 1, 2, 3 and 4 turns on the coil 235, 345. The efficiency in % is plotted logarithmically on the vertical axis over a range of 10 5 to 101 (10), so 10 on the graph is equal to 10%. Distance is plotted linearly on the horizontal axis over a range of 0 to 10 millimeters (mm). Distance is measured perpendicular to the mid-point of the coil 235 plane. It is assumed that the first 235 and second 345 coils are substantially the same diameter, they are plane parallel and optimally aligned with each other. The optimal resistance has been selected for the energy receiver 340 (the receiver coil 345) for the modelling.
The graph of one (1) turn is depicted as a solid line. It starts at approx efficiency 7 x 10 3 at distance 0 mm. It rises to about 1.5 x 10 2 at 1.5 nun, and it remains at approx. 1.5 x 10 2 until about 2.75mm. After that, it drops to approx. 4 x 10 3 at 5 mm, approx. 8 x 104 at 7 mm and approx. 1 x 1 O 4 at 10 mm.
The graph of two (2) turns is depicted as a dashed line. It starts at approx efficiency 1.2 x lO 1 (0.12) at distance 0 mm. It rises to about 2 x 104 (0.2) at 1 mm, and it remains at approx. 0.2 until about l .8mm. After that, it drops to approx. 7 x 10 2 at 3mm, approx. 6 x 1 O 3 at 5 mm, approx. 8 x 1 O 4 at 7 mm and approx. 1 x 104 at 10 mm.
The graph of three (3) turns is depicted as a dotted line. It starts at approx efficiency 6 x 10 1 (0.6) at distance 0 mm. It rises to about 9.5 x 10 1 (0.95) at 0.8 mm, and it remains at approx. 0.95 until about l .3mm. After that, it drops to approx. 1 x 104 (0.1) at 3mm, approx. 6 x 10 3 at 5 mm, approx. 8 x 104 at 7 mm and approx. 1 x 104 at 10 mm.
The graph of four (4) turns is depicted as a dashed-dotted line. It starts at approx efficiency 1.8 x 10° (1.8) at distance 0 mm. It rises to about 2.5 x 10° (2.5) at 0.65 mm, and it remains at approx. 2.5 until about 1 mm. After that, it drops to approx. 1 x 104 (0.1) at 3mm, approx. 6 x 10 3 at 5 mm, approx. 8 x 104 at 7 mm and approx. 1 x 104 at 10 mm.
The maximum efficiency peak value increases with the number of turns. So 4-turns provides a maximum of 2.4% using a frequency of energy pulses of 10 kHz
Figure 12 shows the efficiency of power transfer over a separation distance between the first 235 and second 345 coil with a coil diameter of 2 mm and a
transmission frequency of 150 kHz. Graphs are plotted for 1, 2, 3 and 4 turns on the coil 235, 345. The efficiency in % is plotted logarithmically on the vertical axis over a range of 10 5 to 102 (100), so 100 on the graph is equal to 100%. Distance is plotted linearly on the horizontal axis over a range of 0 to 10 millimeters (mm). Distance is measured perpendicular to the mid-point of the coil 235 plane. It is assumed that the first 235 and second 345 coils are substantially the same diameter, they are plane parallel and optimally aligned with each other. The optimal resistance has been selected for the energy receiver 340 (the receiver coil 345) for the modelling.
The graph of one (1) turn is depicted as a solid line. It starts at approx efficiency 1.7 x 10° (1.7) at distance 0 mm. It rises to about 2.1 x 10° (2.1) at 0.7 mm, and it remains at approx. 2.1 until about 1.1 mm. After that, it drops to approx. 1 x 104 (0.1) at 3mm, approx. 6 x 10 3 at 5 mm, approx. 8.5 x 104 at 7 mm and approx. 1 x 104 at 10 mm .
The graph of two (2) turns is depicted as a dashed line. It starts at approx efficiency 1.7 x 101 (17) at distance 0 mm. It stays at about 17 until 0.6 mm. After that, it drops to approx. 9.5 x 10° (9.5) at lmm, approx. 1 x 104 (0.1) at 3mm, approx. 6 x 10 3 at 5 mm, approx. 8.5 x 104 at 7 mm and approx. 1 x 104 at 10 mm.
The graph of three (3) turns is depicted as a dotted line. It starts at approx efficiency 3.5 x 101 (35) at distance 0 mm. It stays at about 35 until 0.2 mm. After that, it drops to approx. 1.1 x 101 (11.1) at lmm, approx. 1 x 104 (0.1) at 3mm, approx. 6 x 10 3 at 5 mm, approx. 8.5 x 104 at 7 mm and approx. 1 x 104 at 10 mm.
The graph of four (4) turns is depicted as a dashed-dotted line. It starts at approx efficiency 4.5 x 101 (45) at distance 0 mm. It stays at about 45 until 0.1 mm. After that, it drops to approx. 1.1 x 101 (11.1) at lmm, approx. 1 x 104 (0.1) at 3mm, approx. 6 x 10 3 at 5 mm, approx. 8.5 x 104 at 7 mm and approx. 1 x 104 at 10 mm.
The maximum efficiency peak value increases with the number of turns.
So 4-turns provides a maximum of 44.4% using a frequency of energy pulses of 150 kHz.
Figure 13 shows the efficiency of power transfer over a separation distance between the first 235 and second 345 coil with a coil diameter of 3 mm and a
transmission frequency of 10 kHz. Graphs are plotted for 1, 2, 3 and 4 turns on the coil 235, 345. The efficiency in % is plotted logarithmically on the vertical axis over a range of 104 to 101 (10), so 10 on the graph is equal to 10%. Distance is plotted linearly on the horizontal axis over a range of 0 to 10 millimeters (mm). Distance is measured perpendicular to the mid-point of the coil 235 plane. It is assumed that the first 235 and second 345 coils are substantially the same diameter, they are plane parallel and optimally aligned with each other. The optimal resistance has been selected for the energy receiver 340 (the receiver coil 345) for the modelling.
The graph of one (1) turn is depicted as a solid line. It starts at approx efficiency 5.5 x 10 3 at distance 0 mm. It rises to about 1.2 x 102 at 2 mm, and it remains at approx. 1.2 x 102 until about 2.8mm. After that, it drops to approx. 4.5 x 10 3 at 5 mm, approx. 9 x 104 at 7 mm and approx. 1.2 x 104 at 10 mm.
The graph of two (2) turns is depicted as a dashed line. It starts at approx efficiency 9 x 102 at distance 0 mm. It rises to about 1.8 x 104 (0.18) at 1.3 mm, and it remains at approx. 0.18 until about 1.9 mm. After that, it drops to approx. 7.5 x 102 at 3mm, approx. 7.5 x 10’ at 5 mm, approx. 1 x 10 3 at 7 mm and approx. 1.2 x 104 at 10 mm.
The graph of three (3) turns is depicted as a dotted line. It starts at approx efficiency 4.5 x 10 1 (0.45) at distance 0 mm. It rises to about 7.5 x 104 (0.75) at 1 mm, and it remains at approx. 0.75 until about 1.4 mm. After that, it drops to approx. 7.5 x 102 at 3mm, approx. 7.5 x 10 ·’ at 5 mm, approx. 1 x l0 3 at 7 mm and approx. 1.2 x 104 at 10 mm.
The graph of four (4) turns is depicted as a dashed-dotted line. It starts at approx efficiency 1.5 x 10° (1.5) at distance 0 mm. It rises to about 2 x 10° (2) at 0.75 mm, and it remains at approx. 2 until about 1.2 mm. After that, it drops to approx. 7.5 x 102 at 3mm, approx. 7.5 x 103 at 5 mm, approx. 1 x 104 at 7 mm and approx. 1.2 x 104 at 10 mm.
The maximum efficiency peak value increases with the number of turns.
So 4-turns provides a maximum of 2.2% using a frequency of energy pulses of 10 kHz.
Figure 14 shows the efficiency of power transfer over a separation distance between the first 235 and second 345 coil with a coil diameter of 3 mm and a
transmission frequency of 150 kHz. Graphs are plotted for 1, 2, 3 and 4 turns on the coil 235, 345. The efficiency in % is plotted logarithmically on the vertical axis over a range of 104 to 102 (100), so 100 on the graph is equal to 100%. Distance is plotted linearly on the horizontal axis over a range of 0 to 10 millimeters (mm). Distance is measured perpendicular to the mid-point of the coil 235 plane. It is assumed that the first 235 and second 345 coils are substantially the same diameter, they are plane parallel and optimally aligned with each other. The optimal resistance has been selected for the energy receiver 340 (the receiver coil 345) for the modelling.
The graph of one (1) turn is depicted as a solid line. It starts at approx efficiency 1.2 x 10° (1.2) at distance 0 mm. It rises to about 2 x 10° (2) at 0.75 mm, and it remains at approx. 2 until about 1.2 mm. After that, it drops to approx. 1.1 x 10 1 (0.11) at 3mm, approx. 7 x 10 3 at 5 mm, approx. 1 x 10 ·’ at 7 mm and approx. 1.2 x 104 at 10 mm.
The graph of two (2) turns is depicted as a dashed line. It starts at approx efficiency 1.5 x 101 (15) at distance 0 mm. It remains about 15 until about 0.7 mm. After that, it drops to approx. 1 x 10° (1) at 2mm, approx. 1.1 x lO 1 (0.11) at 3mm, approx. 7 x 10 3 at 5 mm, approx. 1 x 10 3 at 7 mm and approx. 1.2 x 104 at 10 mm.
The graph of three (3) turns is depicted as a dotted line. It starts at approx efficiency 3.5 x 101 (35) at distance 0 mm. It remains about 35 until about 0.25 mm. After that, it drops to approx. 1.5 x 101 (15) at lmm, approx. 1 x 10° (1) at 2mm, approx. 1. 1 x 10 1 (0.11) at 3mm, approx. 7 x 10’ at 5 mm, approx. 1 x 10 3 at 7 mm and approx. 1.2 x 104 at 10 mm.
The graph of four (4) turns is depicted as a dashed-dotted line. It starts at approx efficiency 4.5 x 101 (45) at distance 0 mm. It remains about 45 until about 0.2 mm. After that, it drops to approx. 1.5 x 101 (15) at lmm, approx. 1 x 10° (1) at 2mm, approx. 1.1 x 10 (0.11) at 3mm, approx. 7 x lO 3 at 5 mm, approx. 1 x 10 3 at 7 nun and approx. 1.2 x 104 at 10 mm.
The maximum efficiency peak value increases with the number of turns.
So 4-turns provides a maximum of 46.4% using a frequency of energy pulses of 150 kHz.
When using a first 235 and second 345 coil, smaller diameter coils are preferred as this may allow the dimensions of the improved device 100, 101, 102 to be reduced. In particular, the dimensions of the implantable electrode unit 300, 301 may be reduced. Coils with diameters less than lOnnn are preferred, diameters less than 2mm are more preferred.
For similar reasons, the separation between adjacent coils 235, 345 is also kept a small as possible. However, if the separation is too small, undesired cross-talk may occur. In other words, an energy receiver 340 may receive a portion of the pulsed energy from the associated energy transmitter 230 and a portion of the pulsed energy from an energy transmitter 230 adjacent to the associated transmitter 230. Preferably, adjacent coils 235, 345 are separated by a distance substantially equal to the diameter of the coils 235, 345.
Figures 15 and 16 depict examples of nerves that may be stimulated using a suitably configured improved electrical stimulation device 100, 101, 102 to provide neurostimulation to treat, for example, headaches or primary headaches.
Figure 15 depicts the left supraorbital nerve 910 and right supraorbital nerve 920 which may be electrically stimulated using a suitably configured device. Figure 16 depicts the left greater occipital nerve 930 and right greater occipital nerve 940 which may also be electrically stimulated using a suitably configured device.
Depending on the size of the region to be stimulated and the dimensions of the part of the device to be implanted, a suitable location is determined to provide the electrical stimulation required for the treatment. Approximate implant locations for the part of the stimulation device comprising the stimulation electrodes 360, 370 are depicted as regions:
- 810 for a left supraorbital implant
- 820 for a right supraorbital implant
- 830 for a left occipital implant
- 840 for a right occipital implant
In many cases, these will be the approximate locations 810, 820, 830, 840 for the implantable electrode unit 300, 301.
For each implant location, 810, 820, 830, 840 a separate stimulation device 100, 101, 102 may be used. Where implant locations 810, 820, 830, 840 are close together, or even overlapping a single stimulation device 100, 101, 102 may be configured to stimulate at more than one implant location 810, 820, 830, 840.
A plurality of stimulation devices 100, 101, 102 may be operated separately, simultaneously, sequentially or any combination thereof to provide the required treatment. As used herein and in the appended claims, the term "processor" should be understood to encompass a single processor or two or more processors in communication with each other.
The flow charts and descriptions thereof herein should not be understood to prescribe a fixed order of performing the method steps described therein. Rather the method steps may be performed in any order that is practicable. Similarly, the coding examples are used to explain the algorithm, and are not intended to represent the only implementations of these algorithms - the person skilled in the art will be able to conceive many different ways to achieve the same functionality as provided by the embodiments described herein.
Although the present invention has been described in connection with specific exemplary embodiments, it should be understood that various changes, substitutions, and alterations apparent to those skilled in the art can be made to the disclosed embodiments without departing from the spirit and scope of the invention as set forth in the appended claims.
REFERENCE NUMBERS USED IN DRAWINGS
100 an improved electrical stimulation device
101 a further improved electrical stimulation device
102 another improved electrical stimulation device
110 stimulation device encapsulation layer
200 pulse generator unit
201 a further pulse generator unit
210 pulse generator encapsulation layer
220 controller for producing energy pulses
230 one or more energy transmitters for wirelessly transmitting pulsed energy
235 one or more first conductors for wirelessly transmitting pulsed energy
250 power supply
255 main coil
300 implantable electrode unit
301 a further implantable electrode unit
310 electrode unit encapsulation layer
340 one or more energy receivers for wirelessly receiving pulsed energy
345 one or more second conductors for wirelessly receiving pulsed energy
350 one or more rectifiers
360 one or more stimulation electrodes
370 reference electrode for stimulation
700 an implantable electrical stimulation device
710 encapsulation
720 controller
750 power supply
760 one or more stimulation electrode
770 reference electrode for stimulation
810 Left supraorbital implant location
820 Right supraorbital implant location
830 Left occipital implant location
840 Right occipital implant location
910 Left supraorbital nerve Right supraorbital nerve Left greater occipital nerve Right greater occipital nerve

Claims

CLAIMS:
1. An electrical stimulation device (100, 101) comprising a treatment pulse generator unit (200) and an implantable electrode unit (300);
the treatment pulse generator unit (200) comprising:
- a controller (220) for producing treatment energy pulses;
- one or more energy transmitters (230), configured and arranged to wirelessly transmit the treatment energy pulses;
the implantable electrode unit (300) comprising:
- an electrode unit encapsulation layer (310), configured and arranged to resist the ingress of fluids from a human or animal body into at least a portion of the electrode unit (300);
- one or more energy receivers (340), configured and arranged to wirelessly receive at least a portion of the treatment pulsed energy from an associated energy transmitter (230) through the encapsulation layer (310) when the associated energy transmitter (230) is proximate;
- one or more stimulation electrodes (360, 370), each configured to receive treatment pulsed energy from an associated energy receiver (340), and further configured to transmit the treatment pulsed energy received to human or animal tissue as electrical pulses; wherein the implantable electrode unit (300) is configured and arranged to be rigidly attached to the treatment pulse generator unit (200) such that one or more energy transmitters (340) are proximate the associated energy transmitter (230).
2. The device according to claim 1, wherein:
- the separation between the one or more energy receivers (340) and the associated energy transmitter (230) is lOmm or less, preferably 7mm or less, more preferably 5mm or less, even more preferably 3mm or less, most preferably 2mm or less.
3. The device according to claim 1 or claim 2, wherein the device (100, 101) is further configured and arranged such that the treatment pulse generator (200) and the implantable electrode unit (300) are separable by dermis or skin.
4. The device according to any preceding claim, wherein the implantable electrode unit (300) is configured and arranged to be rigidly attached to the treatment pulse generator unit (200) such that one or more energy transmitters (340) are aligned to the associated energy transmitter (230).
5. The device according to claim 4, wherein the device (100, 101) further comprise mechanical means, such as a pin or a magnet, configured and arranged to provide alignment.
6. The device according to any preceding claim, wherein the device (100, 101) is further configured and arranged such that the rigid attachment is configured and arranged to be detachable.
7. The device according to any preceding claim, wherein the device (100, 101) is further configured and arranged to wirelessly transmit the treatment pulse energy as magnetic pulses, light pulses, electromagnetic pulses, RF pulses, microwave pulses, acoustic pulses, electrical field pulses, and any combination thereof.
8. The device according to any preceding claim, wherein:
- the one or more energy receivers (340) and the one or more energy transmitters (230) are configured and arranged to provide one or more non-galvanic couplings for the treatment pulsed energy.
9. The device according to any preceding claim, wherein the device further comprises:
- one or more reference conductor (370), configured and arranged to provide an electrical reference value for one or more stimulation electrodes (360).
10. The device according to any preceding claim, wherein the implantable electrode unit (300) further comprise:
- one or more circuit components, configured and arranged to transfer the pulsed energy from one or more energy receivers (340) to the one or more associated stimulation electrodes (360, 370) as electrical pulses;
wherein the one or more circuit components are predominantly passive.
11. The device according to any preceding claim, wherein:
- the one or more energy transmitters (230) each comprise a first conductor (230), electrically connected to the controller (220), configured and arranged to wirelessly transmit the energy pulses;
- the one or more energy receivers (340) each comprise a second conductor (340), electrically connected to one or more associated electrodes (360, 370);
the one or more second conductors (340) being configured to wirelessly receive at least a portion of the pulsed energy from the associated first conductor (230) when the associated first conductor (230) is proximate.
12. The device according to claim 11, wherein:
- the one or more first conductors (230) form coils with one or more windings.
13. The device according to claim 11 or 12, wherein:
- the one or more second conductors (340) form coils with one or more windings.
14. The device according to claim 12 or claim 13, wherein:
- adjacent coils (230, 235, 340, 345) are separated by a distance substantially equal to the diameter of the coils (230, 235, 340, 345).
15. The device according to claims 12 to claim 14, wherein:
- the first coils (230, 235) have substantially the same diameter as the second coils (340, 345).
16. The device according to claims 12 to 15, wherein one or more of the coils (230, 340) has a diameter of between 1 to 3 millimeters.
17. The device according to any preceding claim, wherein the electrode unit (300) further comprises: - one or more rectifiers (350), each electrically connected between an associated electrode (360, 370) and an associated energy receiver (340).
118. The device according to any preceding claim, wherein:
- the treatment pulse generator (220) is configured to produce, in use, energy pulses having a frequency between 3 kHz and 150kHz.
19. The device according to any preceding claim, wherein:
- the treatment pulse generator unit (200) is implantable;
and further comprises a pulse generator encapsulation layer (210), configured and arranged to resist the ingress of fluids from a human or animal body into at least a portion of the treatment pulse generator unit (200).
20. The device according to any preceding claim, wherein:
- the device (100, 101) further comprising a stimulation device encapsulation layer (110), configured and arranged to resist the ingress of fluids from a human or animal body into the treatment pulse generator unit (200) and/or the electrode unit (300).
21. The device according to any preceding claim, wherein:
- the device (100, 101) is further configured and arranged to be implantable.
22. The device according to any preceding claim, wherein:
- one or more encapsulation layers (110, 210, 310) comprises a material selected from the group:
- a silicone rubber, a silicone elastomer, a latex aibber, a glass, a metal, an alloy, titanium, stainless steel, cobalt-chromium, a ceramic, parylene, LCP, a
biocompatible polymer, a biocompatible elastomer, or any combination thereof.
23. Use of the device according to claim 1 to claim 22 for stimulating:
- one or more nerves, one or more muscles, one or more organs, spinal cord tissue, and any combination thereof.
24. Use of the device according to claim 1 to 22 for treatment of: - headaches, primary headaches, incontinence, occipital neuralgia, sleep apnea, limb pain, leg pain, back pain, lower back pain, phantom pain, chronic pain, epilepsy, overactive bladder, poststroke pain, obesity, and any combination thereof.
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