KR102446465B1 - Wireless power transmission system using a small quad-band antenna - Google Patents

Abstract

A wireless power transmission system according to an embodiment of the present invention includes a WPT (Wireless Power Transfer) transmitter located outside of a body tissue; and a wireless body transplant device capable of being implanted inside the body tissue, wherein the wireless body transplant device includes: a quad band implant antenna for receiving radio frequency power radiated from the WPT transmitter; and a rectifier comprising a two-step voltage doubler for converting the received radio frequency power into usable direct current, wherein the quad band implant antenna has a slot ground plane, a substrate layer, a radiating patch, and a superstrate. It has a layered structure, and a shunt capacitor is used at the open end of the slot ground plane.

Description

Wireless power transmission system using a small quad-band antenna {EFFICIENT WIRELESS POWER TRANSFER SYSTEM WITH A MINIATURIZED QUAD-BAND IMPLANTABLE ANTENNA}

The present invention relates to a body-implantable wireless power transmission system using a small quad-band antenna, and more particularly, it is possible to efficiently transmit power through a miniaturized quad-band antenna, a wireless power transmission transmitter, and a voltage doubler having high conversion efficiency. It relates to an implantable wireless power transmission system.

In the era of the 4th industrial revolution, autonomous wireless implantable medical devices are taking place at a rapid pace in human life. This is developing at a faster rate as the use of Bluetooth frequency for wireless medical devices has become commonplace through smartphone applications in real life. Recently, as individuals can control wireless medical devices and check data without temporal and spatial restrictions, the demand for wireless medical devices is increasing. Conventionally, wireless medical devices perform functions through body patches or attachments, rather than being inserted into the body. However, as the biocompatibility of the wireless medical device is ensured, a body implantable medical device that can be directly inserted into the body has also emerged.

For implantable medical devices, smooth operation inside the body and efficient wireless power supply are of the utmost importance. Therefore, the operability in a multifaceted tissue environment determines the performance of implantable medical devices.

Regarding power supply, conventional wireless implantable medical devices are powered by a lithium ion battery. However, in the case of lithium ion batteries, there are disadvantages in that the size is large, the capacity is dependent on the size, and surgery is required to replace the battery. Therefore, in order to solve these shortcomings, there is a need for an efficient and miniaturized wireless power transmission system that can be inserted into the body. Furthermore, it is necessary to develop an implantable wireless medical device capable of performing various functions with minimal implantation due to the special tissue environment of the human body.

The present invention is to solve the above problems, and to provide a wireless power transmission device capable of quad-band operation such as telemetry at 403 and 915 MHz, wireless power transmission in an intermediate band of 1470 MHz, and a control signal at 2.4 GHz. do.

An object of the present invention is to provide a wireless power transmission device that uses an implantable antenna implantable inside a body tissue, not one, but a plurality of operating frequency bands.

An object of the present invention is to provide a wireless power transmission device using a wireless power transmission transmitter for power concentration in body tissues.

An object of the present invention is to provide a wireless power transmission system that provides high power efficiency through a WPT transmitter operable at 1470 MHz.

An object of the present invention is to provide a wireless power transfer system that provides high power efficiency through a wireless power transfer (WPT) transmitter capable of operating at 1470 MHz.

A wireless power transmission system according to an embodiment of the present invention includes a WPT (Wireless Power Transfer) transmitter located outside of a body tissue; and a wireless body transplant device capable of being implanted inside the body tissue, wherein the wireless body transplant device includes: a quad band implant antenna for receiving radio frequency power radiated from the WPT transmitter; and a rectifier comprising a two-step voltage doubler for converting the received radio frequency power into usable direct current, wherein the quad band implant antenna has a slot ground plane, a substrate layer, a radiating patch, and a superstrate. It has a layered structure, and a shunt capacitor is used at the open end of the slot ground plane.

According to an embodiment of the present invention, by providing a quad-band implant antenna that can be operated in all of 403, 915, 1470, and 2400 MHz, it is possible to provide a wireless power transmission system that can be operated in all four bands.

According to an embodiment of the present invention, a body capable of efficiently operating in a body tissue environment by reducing the charging time of an implanted medical device inside the human body and maintaining high power transfer efficiency (PTE) through the WPT transmitter An implantable medical device may be provided.

According to an embodiment of the present invention, an object of the present invention is to provide a wireless power transmission system having a high-efficiency power conversion effect from input power through a rectifier including a two-step voltage doubler.

1 is a diagram for explaining a wireless power transmission system according to an embodiment of the present invention.
2 is a diagram for explaining a wireless body transplantation apparatus including a quad-band antenna according to an embodiment of the present invention.
3 is a view for explaining a quad-band implant antenna according to an embodiment of the present invention.
4 is a diagram for explaining a WPT transmitter of a wireless power transmission system according to an embodiment of the present invention.
5 is a diagram showing experimental design and results for a WPT transmitter according to an embodiment of the present invention.
6 is a view for explaining a rectifier of a wireless power transmission system according to an embodiment of the present invention.
7 is a diagram for explaining an experimental design related to the performance of a wireless power transmission system according to an embodiment of the present invention.
8 is a view for explaining an experimental result according to the design of the quad-band implant antenna according to an embodiment of the present invention.
9 is a diagram illustrating a current distribution of a quad-band implant antenna system according to an embodiment of the present invention.
10 is a diagram for explaining an experimental result of a wireless power transmission system according to an embodiment of the present invention.
11 is a diagram for explaining an experimental result on the WPT transmitter performance of the wireless power transmission system according to an embodiment of the present invention.
12 is a diagram showing experimental results for ML according to an embodiment of the present invention.
13 is a diagram showing experimental results on the performance of a two-stage voltage doubler of a wireless power transmission system according to an embodiment of the present invention.
14 is a view showing experimental design and results of a rectifier including a WPT transmitter and a two-stage voltage doubler according to an embodiment of the present invention.
15 is a diagram for confirming the biosafety of the wireless power transmission system according to an embodiment of the present invention.
16 is a diagram for explaining the performance of a wireless power transmission system according to an embodiment of the present invention.

The above-described objects, features and advantages will be described below in detail with reference to the accompanying drawings, and accordingly, those skilled in the art to which the present invention pertains will be able to easily implement the technical idea of the present invention. In describing the present invention, if it is determined that a detailed description of a known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description will be omitted.

In the drawings, the same reference numerals are used to refer to the same or similar elements, and all combinations described in the specification and claims may be combined in any manner. And unless otherwise specified, it is to be understood that references to the singular may include one or more, and references to the singular may also include the plural.

The terminology used herein is for the purpose of describing specific exemplary embodiments only and is not intended to be limiting. As used herein, singular expressions may also be intended to include plural meanings unless the sentence clearly indicates otherwise. The term “and/or,” “and/or” includes any and all combinations of the items listed therewith. The terms "comprises", "comprising", "comprising", "comprising", "having", "having" and the like have an implicit meaning, so that these terms refer to their described features, integers, It specifies steps, operations, elements, and/or components and does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The steps, processes, and acts of the method described herein should not be construed as necessarily performing their performance in such a specific order as discussed or exemplified, unless the order of performance thereof is physically determined. . It should also be understood that additional or alternative steps may be used.

In addition, each component may be implemented as a hardware processor, respectively, the above components may be integrated into one hardware processor, or the above components may be combined with each other and implemented as a plurality of hardware processors.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a diagram for explaining a wireless power transmission system according to an embodiment of the present invention.

Referring to FIG. 1 , a wireless power transmission system 100 according to an embodiment of the present invention may include a wireless body transplant device 110 , a WPT transmitter 300 , and a rectifier 400 . The WPT transmitter 300 can be optimized to focus power at 1470 MHz with a size of 6 cm x 6 cm. The rectifier 400 may include a two-stage voltage doubler, and the two-stage voltage doubler may function to convert radio frequency input power into usable direct current. The two-stage voltage doubler can have a high efficiency of 90% at a conversion efficiency of 2-dBm. The wireless body recognition device 110 may include a quad-band implant antenna. The quad-band implant antenna can have a small size of 8.43mm ³ and can support quad-band operation such as telemetry at 403 and 915MHz, wireless power transfer in the band of 1470MHz, and control signals at 2.4GHz. Furthermore, the operating band of the quad-band implant antenna of the present invention is not interpreted as being limited to the aforementioned frequency band, and the operating band may be four or more depending on the function and purpose of the wireless body transplant device.

The description of the wireless body implantation device will be described in detail with reference to FIG. 2 to be described later.

2 is a diagram for explaining a wireless body transplantation apparatus including a quad-band antenna according to an embodiment of the present invention. The wireless body transplant device 110 can be divided into two types, a capsule type and a flat type, depending on the field of application of the wireless power transmission system. FIG. 2(a) shows a capsule type wireless body transplant device, and FIG. 2(b) shows a flat type wireless body transplant device. In the case of the capsule type, it can be widely applied to capsule endoscopes or pacemakers. In the case of a flat type, it can be used for existing pacemaker deep brain stimulators (DBS) and SCS.

Hereinafter, the internal device of the wireless body transplant device will be described with reference to FIGS. 2A and 2B .

The capsule-type wireless body transplant device may have a diameter of 8 mm, a length of 18 mm. In the case of a flat-type wireless body transplant device, the length may correspond to 18 mm, the width is 7.5 mm, and the height is 4 mm. A quad-band implant antenna 200 that can operate at 403, 915, 1470 MHz, and 2.4Ghz for both the capsule-type wireless body transplant device and the flat-type wireless body transplant device, an electronic integrated circuit (hereinafter referred to as 'electronic IC') ( 113 ) may include a mounted printed circuit board (Printed Circuit Board, hereinafter referred to as 'PCB'), two batteries 111 , and a battery holder 112 .

In the case of the capsule-type wireless body transplant device, it may further include a lens 114 equipped with an LED.

In the case of a flat-type wireless body transplant device, referring to FIG. 2B , a sensor 116 may be further included. The battery 111 that fits into both the capsule type and the flat type may have a diameter of 4.8 mm and a height of 1.65 mm.

Since the wireless body transplant device needs to be implanted inside the body, it must have a biocompatible material suitable for the transplanted body tissue. Therefore, both the capsule type and the flat type wireless transplant device can be encapsulated outside by biocompatible alumina with a thickness of 0.25 mm with dielectric constant = 9.8 and tangent loss, tan δ = 0.006. In the case of the capsule type, the outside may be packed through the cap 117 .

The capsule type wireless body transplant device and the flat type wireless body transplant device may have volumes of 770.74 mm ³ and 521.71 mm ³ , respectively.

The function of the quad-band implant antenna 200 in relation to wireless power transmission is pivotal for both the capsule type wireless body transplant device and the flat type wireless body transplant device, and will be described in detail below with reference to FIG. 3 .

3 is a view for explaining a quad-band implant antenna according to an embodiment of the present invention.

The conventional implant antenna is a broadband helical antenna, which is used only for telemetry at 915 MHz. It was also unsuitable for modern small wireless implants such as pacemakers. The quad-band implant antenna 200 of the present invention may perform a function so that the wireless body transplant device can perform multi-task processing of two-way data communication, control signals, and wireless power supply.

Figure 3 (a) is a front view of the quad band implant antenna, Figure 3 (b) is a perspective view of the quad band implant antenna, Figure 3 (c) is a side view of the quad band implant antenna, Figure 3 (d) is a quad band implant A schematic diagram of the structure of the antenna is shown.

The quad band implant antenna 200 may include a segment-cut circular meander radiating patch 201 and a slotted ground plane 202 . A substrate layer 204 may be positioned between the slot ground plane 202 and the radiating patch 201 . A superstrate layer 203 may be positioned on the radiation patch 201 . Accordingly, the slot ground plane 202, the substrate layer 204, the radiation patch 201, and the superstrate layer 203 may be layered to form a structure.

The substrate layer 204 may be a Rogers substrate RO3010 having a dielectric constant of 10.2 and a tangent loss of 0.0035 loss tangent. A substrate layer 204 may be sandwiched between the radiating patch 201 and the slot ground plane 202, and the thickness may be 0.25 mm. The radiation patch 201 may have a planar helicoid structure. The planar helicoid shape can extend the electrical length and current path, thereby reducing the size of the quad-band implant antenna.

A shorting pin via 205 and a coaxial feed 206 are used between the radiating patch 201 and the slot ground plane 202 so that the current path can be longer and the operating frequency can be lowered.

In addition, an open-end ground slot, which is a combination of two S1 slots 208 and S2 slots 209 , is added to provide a miniaturization and additional resonance generation effect of the quad-band implant antenna 200 .

A shunt capacitor 207 may be used at the open end of the slot ground plane 201 . The shunt capacitor 207 may be used at the open end of the slot ground plane 201 to stabilize the impedance in the resonant frequency band, improve the impedance bandwidth, and provide an additional size reduction effect.

In the case of the radiating patch 201, it is packed with a 0.025 mm thick biocompatible super straight polyamide layer with a dielectric constant of 4.3 and a loss tangent of 0.004 to insulate the antenna from the surrounding tissue and contribute to the miniaturization of the antenna.

Hereinafter, various parameter values of the radiation patch 201 will be described with reference to the table 210 .

The radiating patch 201 may have W ₁ , W ₂ , W ₃ , 1 ₁ , 1 ₂ , 1 ₃ , 1 ₄ , and 1 ₅ parameter values in a planar helicoid structure. W ₁ , W ₂ , W ₃ , l ₁ , l ₂ , l ₃ , l ₄ , l ₅ parameter values may be confirmed with reference to the table 210 .

In Fig. 3(b), the slot ground plane 202 of the quad-band implant antenna has a radius D and l ₆ , l ₇ , l ₈ , l ₉ , l _{10 ,} l ₁₁ , l ₁₂ , l ₁₃ , l ₁₄ , l ₁₅ , l ₁₆ , l ₁₇ , can have parameter values. The parameter value may be confirmed with reference to the table 210 .

Referring to the side view of FIG. 3C , the values of h ₁ and h ₂ may be the values of h by adding parameter values.

The values of h ₁ , h ₂ and h values may also be confirmed with reference to the table 201 .

Accordingly, the quad-band implant antenna 200 may have a horizontal length of 7 mm and a thickness of 0.275 mm.

The quad band implant antenna 200 can be optimized through the location, slot length and design of the coaxial feed 206 and the via 205 that is the shorting pin, proper design of the shunt capacitor 207 value, the radiating patch 201 design, etc. have. Therefore, the quad-band implant antenna 200 of the present invention can operate in the 403, 915, 1470 MHz, 2.4 GHz bands. Here, the 403 MHz band corresponds to the medical implant communication system band, the industrial scientific and medical bands correspond to 915 MHz and 2.4 GHz, and 1470 MHz corresponds to the medium band. Furthermore, the operating frequency band of the quad-band implant antenna of the present invention is not limited and interpreted, and may be changed according to the type and purpose of the wireless body transplant device. In addition, the operating frequency band of the quad-band implant antenna of the present invention is limited to four and may not be interpreted and may be more.

4 is a diagram for explaining a WPT transmitter of a wireless power transmission system according to an embodiment of the present invention.

The WPT transmitter 300 performs the function of tracking the medical device and releasing most of the force to the tissue.

4(a) is a front view of the WPT transmitter, FIG. 4(b) is a rear view of the WPT transmitter, and FIG. 4(c) is a side view of the WPT transmitter.

The WPT transmitter has a patch 301 with four patterns, and its backside may have a complete ground plane 302 . Furthermore, power may be concentrated to a port having four directions. FIG. 4(b) shows a case in which the ground plane 302 includes two ports P1 and P2. In addition, a center circle 304 may be positioned at the center of the four pattern patches 301 .

A substrate layer 303 may be positioned between the pattern patch 301 and the ground plane 302 .

The WPT transmitter 300 of the present invention may be formed of a low-loss Teflon material. The Teflon material may have a thickness of 1.6 mm, a dielectric constant of 2.1, and a tangent loss of 0.001.

The concentration of radiated power can be adjusted by appropriately allocating the phase of each port 301 .

When the wireless body implant device is encapsulated and moves a lot, it can be used for power tracking by considering various phase combinations of the four ports at the same time. Alternatively, only ports with two 180 degree phase shifts may be considered if the mobility of the wireless body implant is low.

The WPT transmitter 300 of the present invention can focus radiated power to tissue. This may be possible through the patterned patch 301 of the WPT transmitter 300 providing a narrow path in the center, thereby accelerating current flow, and confining the magnetic field to that location.

Referring to FIG. 4(d), due to the rear ground plane 302, the center of the antenna and maximum radiation may occur at the center of the patch.

Furthermore, compared to the case in which the antenna is not systemized, the WPT transmitter 300 may be able to operate near tissue having a high dielectric constant.

However, it is necessary to conduct a simulation experiment that can actually confirm the performance of the WPT transmitter in the internal environment of the body.

Hereinafter, with reference to FIG. 5, a description of the simulation experiment of the WPT transmitter will be described later.

5 is a diagram showing experimental design and results for a WPT transmitter according to an embodiment of the present invention.

WPT transmitters should be verified for their performance when implanted in humans. Therefore, referring to FIG. 5 , an experiment is designed by positioning the WPT transmitter at a distance of 5 mm from the muscle box, which is a position where the WPT transmitter is viewed from the wireless body transplantation device, within the wireless power transmission system including the WPT transmitter. Experiments can be broadly analyzed at 1470 MHz.

Looking at the experimental results, it can be seen that the larger the radius of the patch center circle of the WPT transmitter, the higher the resonant frequency band. Therefore, it can be seen that operation is possible at all frequencies in the range of 1.3 to 2.5 GHz depending on the value of the radius of the center circle of the WPT transmitter.

Therefore, such a WPT transmitter can perform a wideband operation function and can be used with other wireless power transmission systems.

6 is a diagram for explaining a rectifier of a wireless power transmission system according to an embodiment of the present invention.

The rectifier 400 performs a function of converting RF energy into DC voltage to supply power to a wireless power transmission system or to charge a battery. A simple rectifier is not suitable for low-power applications, and a rectifier with a certain level of voltage may be required for the wireless power transfer system of the present invention to operate.

The rectifier 400 of the present invention may use a modified two-stage voltage doubler model 402 . Referring to FIG. 6 , a modified two-step voltage doubler model 402 can be identified.

A pair of commercial RF Schottky diodes, SMS7630, may be used for the modified two-stage voltage doubler model 402 . The diode may have an Rs value of 20 ohms, a Cy value of 0.18pF, and a Bv value of 2V.

In the case of the DICKSON model, the one-step voltage doubler 401, the circuit may be composed of two diodes D1 and D2 and two capacitors C3 and C4.

In the case of the two-step voltage doubler 402, the circuit may be composed of an inductor L4, two additional capacitors C2 and C5, and diodes D3 and D4.

The working principle of the one-step voltage doubler 401 is that the negative half-period diode D2 is forward biased and can charge C3. At this time, the positive half-cycle diode D2 has a forward bias, and D1 has a reverse bias to block the discharge of C3, and can be fully charged with a negative half-cycle.

With C3 fully charged, the same amount of voltage is input to C4 and can be charged. This may have the effect that the output voltage is doubled.

In the case of a two-stage voltage doubler 402, the doubled output voltage may be passed to the next stage to charge the capacitor C2. Furthermore, the doubled output voltage passed to the next stage can further increase the peak of the rectified voltage and raise it to the required level.

The efficiency of converting RF energy into DC voltage can be determined by input power, input impedance, and output load.

In order to match the input impedance of the rectifier 400 and the input impedance of the antenna, a rectifying circuit may be required. Conventionally, a method of conjugating the input impedance of the antenna using a simple inductor and removing the imaginary part of the input impedance of the rectifier has been generally used.

However, as mentioned above, the efficiency of converting RF energy into DC voltage is very sensitive to the input power. Accordingly, in the rectifier 400 of the present invention, a rectifier circuit function may be performed using the two-step voltage doubler 402 . Through this, there is an effect that the efficiency of the rectifier 400 can be isolated from a change in input power.

In the case of the rectifier 400 using the two-stage voltage doubler 402 of the present invention, the efficiency of converting RF energy to DC voltage at 2 dBm is achieved 90%, and the function of the rectifier of the present invention can be performed in a wide range of input power. have.

Hereinafter, with reference to FIGS. 7 to 16, experimental design and results for the performance of the wireless power transmission system, the performance of the quad-band implanted antenna system, the performance of the wireless power transmission system including the quad-band implanted antenna, and the performance of the WPT transmitter to explain

7 is a diagram for explaining an experimental design related to the performance of a wireless power transmission system according to an embodiment of the present invention.

The quad-band implant antenna of the present invention can be deviced to design a wireless body transplantation device prototype, and the prototype can be tested within the same human skin tissue using the ANSYS high-frequency structure simulator (HFSS).

Furthermore, experiments can be conducted using Sim4Life based on finite differential time domain (FDTD) in realistic DUKE human models.

Referring to FIG. 7( a ), in the radiation box composed of 400 mm x 400 mm x 400 mm, a 100 mm x 100 mm x 100 mm homogeneous muscle box exists in the human skin tissue environment, and experiments can be carried out in the homogeneous muscle box.

A homogeneous muscle box can be set up so that its electrical properties can be frequency dependent. In this homogeneous muscle tissue, a wireless body transplantation device prototype is implanted, and the experiment is carried out using HFSS.

Referring to FIG. 7(b), it is shown that an experiment is performed based on FDTD in a realistic DUKE human model. The prototype 501 can be made into two types: a capsule type and a flat type.

In the case of the capsule type, it may be implanted in the small intestine to proceed with the experiment, and in the case of the flat type, it may be implanted in the head and heart to proceed with the experiment.

A prototype 501 manufactured for actual experimental measurements may be connected to a vector network analyzer (VNA) using a micro connector to measure performance. As the experimental environment, an ASTM model filled with a saline solution and minced pork muscle tissue 504 may be used.

It is also possible to connect the two ports of the WPT transmitter to the two output ports of the hybrid coupler operating as a 180° phase shift and power divider to measure the performance of the WPT transmitter (502).

VNA port 1 is connected to the D port of the hybrid coupler so that the incident power can be split into two equal amplitudes but 180° phase. As shown in Figure 7, the WPT transmitter is placed next to a container filled with minced pork muscle tissue and a 3D head model filled with saline and S-parameters can be measured (504).

To estimate the PTE of a WPT transmitter, a wireless body implant prototype can be built, the prototype and the WPT transmitter can be combined into a wireless power transfer system and inserted into a box filled with saline solution (506) and minced pork tissue in the box. .

It can be connected to port 1 of the VNA. The WPT transmitter setup can attach a quad band implant antenna to the tissue wall and connect to port 2 of the VNA as shown in FIG. 7 (503).

The distance between the WPT transmitter and the prototype is 5 cm, and the transmission coefficient S21 and reflection coefficient S11 can be measured.

8 is a view for explaining an experimental result according to the design of the quad-band implant antenna according to an embodiment of the present invention.

Several steps can be taken to design a quad-band implant antenna. For the step for designing the antenna, reference may be made to FIG. 8( a ), and through FIG. 8( b ), the experimental result of confirming the resonant frequency band of the antenna according to the step of designing the antenna can be seen.

In step 1, a spiral-shaped radiating patch is placed on the cylindrical ground plane of a segment cut with a diameter of 7 mm. It can be seen that the antenna system that has gone through step 1 resonates at frequencies of 2.3 GHz and 895 MHz.

Accordingly, in step 2, the slot S2 may be cut and positioned at the edge of the ground plane. It can be seen that the impedance is improved at 2.4GHz and 895MHz due to slot S2 and additionally resonates at 1.45GHz.

In step 3, a resonance may be generated at a frequency of 403 MHz through the S1 slot. Additionally, it can be seen that resonance occurs at 950, 1470 MHz, and 2.4 GHz.

In step 4, a modified slot may be formed by combining the S1 slot and the S2 slot. This shows good impedance matching in the 403 MHz frequency band and the 403 and 915 MHz bands. However, the frequency resonance in the midfield band and in the higher frequency band was not good. In addition, it is necessary to exhibit a resonance effect in the 2.7 GHz band and to exhibit good impedance matching in a lower frequency band.

Therefore, by placing the radiation patch of step 1 in step 5 in the S1 slot and S2 slot combination of step 4 together, it is possible to design a final quad-band implant antenna.

Furthermore, referring to FIG. 8(c) , the results of the resonance frequency band experiment according to the value of the shunt capacitor can be confirmed.

The quad-band implant antenna of the present invention may be designed by connecting a shunt capacitor to the ground plane in order to improve the downward movement of resonance and additionally improve impedance matching.

In the case of a shunt capacitor, it is possible not only to improve impedance matching in all four bands, but also to shift the resonance band to a higher resonant frequency band. For the performance of the quad-band implanted antenna system, proper placement and appropriate value of the shunt capacitor can be considered.

Referring to FIG. 8(c) , it can be seen that the experimental analysis is performed according to the value of the shunt capacitor. As the value of the shunt capacitor increases, it can be seen that the impedance matching in the frequency band is improved and the impedance BW is improved. The impedance matching improvement effect of the frequency band is maintained until the value of the shunt capacitor is increased to 4.2pF, but when the value is 4.2pF or higher, the left shift of the frequency resonance band is confirmed in the 1470MHz and 403MHz bands.

Hereinafter, the current distribution of the quad-band implant antenna system will be described with reference to FIG. 9 .

9 is a diagram illustrating a current distribution of a quad-band implant antenna system according to an embodiment of the present invention. 9 shows the current distribution in the patch and the ground plane of the quad-band implant antenna at 403, 915, 1470, and 2400 MHz. At 403 MHz, which is a low frequency in FIG. 9( a ), the current may have the same current direction in the patch and the ground plane. This allows the antenna system to be in monopole mode. Fig. 9(c) shows that the current is reversed once in the patch. This indicates that it can be in half-wave monopole mode at 1470 MHz.

9(b) and (d) show that the current reverses its direction several times. This indicates that it resonates in full-wavelength antenna mode at 915 MHz and 2.4 GHz.

Hereinafter, an experimental design and results regarding the performance of the wireless power transmission system and the quad-band implant antenna will be described with reference to FIGS. 10 to 16 .

10 is a diagram for explaining an experimental result of a wireless power transmission system according to an embodiment of the present invention. The simulation model using HFSS in the human skin tissue environment, the model simulated in the DUKE human model, the ASTM model filled with saline solution, and the actual system measurement values in minced pork muscle tissue can be compared. That is, the result values for the four cases can be confirmed through FIG. 10 .

Looking at the experimental results of FIG. 10( a ), it can be confirmed that all four cases have sufficient bandwidth in four frequency bands. Furthermore, radiation patterns can be identified in the minced pork muscle tissue. The four frequency bands are 403, 915, 1470, and 2400 MHz frequency bands. The table of Fig. 10(b) shows the comparison result between the measured actual value and the simulated prototype. 10( c ) is a graph comparing HFSS simulation, Sim4Life simulation, and actual measured values. The measured actual values correspond to -34, -29.6, -28.2, and -22.4dBi at 403, 915, 1470, and 2400 MHz, respectively.

11 is a diagram for explaining an experimental result on the WPT transmitter performance of the wireless power transmission system according to an embodiment of the present invention. Figure 11 (a) shows the experimental results of the simulation of the performance of the WPT transmitter in the DUKE human model. 11(b) shows the results of testing the performance of the WPT transmitter in an ASTM model filled with saline solution and minced pork muscle tissue environment. Both the WPT transmitter and implant antenna are matched, resonating at 1470 MHz, indicating that they are in the Gihahertz sub-midfield radio range. The maximum PTE value may be calculated using the measured transmission coefficient S21 and reflection coefficient S11. The reflection coefficient is less than -25 dB at 1470 MHz, which means that the PTE value is greater than 99%. The power given to the WPT transmitter is radiated towards the quad band implant antenna. When reflected back to the WPT transmitter due to a very small force, the reflection coefficient S11 is ignored. The measured transmission coefficient S21 of the WPT transmitter corresponds to -36 dB.

However, since the permittivity value of the tissue is 55 and the permittivity value of air is 1, the PTE may be reduced due to the discrepancy. Due to dielectric mismatch, some of the main radiated power may be reflected back to the WPT transmitter. This can negatively affect PTE. To solve this problem, the wireless power transmission system may use a matching layer having a high dielectric constant (Matching Layer, hereinafter referred to as 'ML'). Experimental results for ML having a high dielectric constant will be described with reference to FIG. 12 .

12 is a diagram showing experimental results for ML according to an embodiment of the present invention. Fig. 12(a) shows the experimental results without using ML having a high permittivity, and Fig. 12(b) shows the experimental results using ML having a high permittivity. As the tissue's electromagnetic field is greatly increased to minimize dielectric mismatch, ML can be used. ML may have a dielectric constant of 78 and a tangent loss value of 0.0004. Through this, the value of S21 can be -21.7dB, and the experimental results confirmed that the maximum PTE was 0.2% and 0.67%, respectively, depending on the presence or absence of ML.

13 is a diagram showing experimental results on the performance of a two-stage voltage doubler of a wireless power transmission system according to an embodiment of the present invention. For a two-stage voltage doubler, a 50 sub-miniature A (SMA) connector can be connected to the manufactured prototype input. Efficiency at different power levels can be measured at 1470 MHz. Referring to FIG. 13( a ), a comparison of simulated and measured RF-DC conversion efficiencies for different power levels at 1470 MHz may be shown. It can be seen that the peak conversion efficiency corresponds to 90% at 3dBm and 90% at 2dBm in simulation and measurement, respectively. Through this, the two-stage voltage doubler can provide high efficiency and a relatively wide input power level compared to the conventional RF rectifier.

Wireless power transfer systems may include microprocessors and other ICs. A high voltage may be required for smooth operation of these electronic devices. For example, the high voltage may be 3-5V DC voltage. However, a simple diode rectifier topology is problematic in that it does not provide this voltage range at low power. The two-stage voltage doubler of the present invention has the effect of providing a voltage greater than 3V at 0dBm. Figure 13(b) shows the simulated and measured output voltage of the rectifier at different power levels (-20 to 10 dBm). The two-stage voltage doubler of the present invention can provide a milliwatt range greater than 3V in the milliwatt range in both simulated and measured values. After measuring each component individually, it can be integrated with a wireless body transplant equipped with a quad-band implant antenna to demonstrate and verify system performance.

In addition, the experimental design and results for confirming the performance of the rectifier including the WPT transmitter and the two-stage voltage doubler will be described with reference to FIG. 14 .

14 is a view showing experimental design and results of a rectifier including a WPT transmitter and a two-stage voltage doubler according to an embodiment of the present invention. The WPT transmitter is connected to an RF power amplifier with a hybrid coupler and is powered by an RF signal generator (MS2830A, Anritsu). Referring to FIG. 14( a ), for the experiment, the WPT transmitter can be implanted with a wireless power transmission system in minced pork muscle tissue. To measure the output voltage and current, a digital multimeter (Hioki3239 Digital HiTester, Hioki) can be connected through a wire to the load resistance of the rectifier. The WPT transmitter was given 1W, and a voltage of 3.14V was measured at the output of the rectenna as shown.

Fig. 14(b) shows the WPT transmitter setup (antenna + hybrid coupler). As shown in Fig. 14(c), in the wireless power transmission system, the load resistance (RL) of the rectenna of the rectenna may be replaced with a green LED, and it can be placed in a container filled with a saline solution to a depth of 4-5 cm. At least 2.1V is required to turn on the LED, so if the output voltage of the rectifier is greater than 3V, you can see that the LED turns green. It can be confirmed that the WPT transmitter of the present invention can emit light with good intensity from the LED when 1W is given. It can be seen that the wireless power transmission system can deliver 4-6.7 mW power at a depth of 5 cm or more in the tissue, and provide a voltage of 3 V or more. Even without 4-6.7mW power and a 3V battery, this could be enough voltage to run the device.

15 is a view for confirming the biosafety of the wireless power transmission system according to an embodiment of the present invention.

To evaluate the compliance of the wireless power transfer system with Federal Communications Commission (FCC) and International Commission on Non-Ionizing Radiation Protection (ICNIRP) safety guidelines, the WPT transmitter was placed at least 5 mm on the chest using Sim4Life of a real human Duke model and Conduct an experiment. Each port of the WPT transmitter is supplied with 1W power, and analysis for a specific absorption rate (SAR) can be performed. The highest SAR values of the WPT transmitter averaged 0.187 and 0.15 W/kg for 1 and 10 g of tissue, respectively. The normalized 1-g / 10-g SAR distribution can be seen in Figure 15 (a) and (b).

The simulated 1g SAR distribution in FIG. 15(a) is normalized to 1.6 W/kg, and the 10-g SAR distribution in FIG. 15(b) is normalized to 2 W/kg. Based on the simulated maximum SAR values (0.187 W/kg for 1 g and 0.15 W/kg for 10 g) at an input power of 1 W, the maximum allowable power values of 8.6 and 13.3 W are calculated.

It can be confirmed that the maximum allowable power value of the wireless power transmission system of the present invention is a safe value. Even when the WPT transmitter is powered up to 8.6 and 13.3W, it remains safe. Current lead-free pacemakers use a 120mAh battery and have a battery life of 7-10 years. The capsule endoscope uses a 55-mAh battery and has a lifespan of 8-10 hours. For implants such as capsules, a receive power of 6.7 mW may be sufficient.

16 is a diagram for explaining the performance of a wireless power transmission system according to an embodiment of the present invention.

Referring to the table of Figure 16, the wireless power transmission system of the present invention may include a quad-band implant antenna that can operate at 403, 915, 1470, 2400 MHz. The size of the implant antenna may have a volume of 8.43 mm ³ , and the patch of the implant antenna may have a serpentine line shape.

The WPT transmitter of the wireless power transmission system of the present invention may be operable at 1470 MHz, and the PTE efficiency may have a value of 0.67%. The rectifier of the present invention may have a modified two-stage voltage doubler, and the efficiency of the rectifier may have a conversion efficiency of about 90% at 2dBm.

In relation to conventional medical devices, when the capsule endoscope and the lead-free pacemaker are charged using a battery, the charging times correspond to 25 hours and 54 hours, respectively. For a lead-free pacemaker, charging for 54 hours and 30 minutes over 7 years could double the lifespan, and while using the capsule endoscope on battery, recharging the battery at 6.7 mW for 8 hours could increase device life by 32% .

However, when the medical device is inserted into the human body, there may be restrictions on the charging time. The longer the charging time for a medical device inserted into the human body, the more likely it is to have a significant impact on a patient's life. Further, in terms of temperature, the temperature of the tissue increases to 37.565C during the exposure time of 1 hour. The harmless range of temperature increases in body tissues corresponds to 2C. When the body tissue temperature rises from 37° C. to 37.565° C., during the first 4 minutes of exposure, there is a temperature rise, and after 4 minutes, no further increase in temperature occurs.

The WPT transmitter of the present invention can safely provide transmitted power. According to the FCC, the maximum effective isotropic radiated power (EIRP) near-field, point-to-point link can be increased to 36 dBm while meeting safety standards.

Furthermore, increasing the performance of the WPT transmitter has the effect of reducing the charging time. If the power of the WPT transmitter is tripled (3W) and the charging voltage is maintained at 3.1V, the charging time is 8 hours 30 minutes for the capsule endoscope and 18 hours 30 minutes for the lead-free pacemaker. It can be seen that the performance of the WPT transmitter of the present invention is effective compared to the battery charging time of 25 hours for a capsule endoscope and 54 hours for a lead-free pacemaker in conventional medical devices.

Embodiments of the present invention disclosed in the present specification and drawings are merely provided for specific examples in order to easily explain the technical contents of the present invention and help the understanding of the present invention, and are not intended to limit the scope of the present invention. It will be apparent to those of ordinary skill in the art to which the present invention pertains that other modifications based on the technical spirit of the present invention can be implemented in addition to the embodiments disclosed herein.

Claims (11)

Wireless Power Transfer (WPT) transmitters located outside of body tissue; and
a wireless body transplant device capable of being implanted inside the body tissue;
The wireless body transplant device
a quad-band implant antenna for receiving radio frequency power radiated from the WPT transmitter; and
A rectifier comprising a two-step voltage doubler for converting the received radio frequency power into usable direct current,
The quad band implant antenna is
A slot ground plane, a substrate layer, a radiation patch, and a superstrate layer have a layered structure,
A shunt capacitor is used at the open end of the slot ground plane.
wireless power transfer system.
The method of claim 1,
The wireless body transplant device is a capsule type or a flat type,
The wireless body transplant device includes at least one of a printed circuit board (PCB) on which one or more electronic ICs are mounted, one or more batteries, a battery holder, a lens equipped with an LED, and a sensor
wireless power transfer system.
The method of claim 1,
The quad band implant antenna is
It supports two-way data communication, control signal, wireless power supply function, and has multiple operating bands.
wireless power transfer system.
2. The method of claim 1
The radiation patch of the quad-band implant antenna has a planar helicoid structure.
wireless power transfer system.
2. The method of claim 1
The slot ground plane of the quad-band implant antenna is
It is an open ground slot in which a first slot formed inside the slot ground plane and a second slot formed along the periphery of the slot ground plane are combined,
wherein the shunt capacitor is disposed at a position where the first slot and the second slot meet.
wireless power transfer system.
The method of claim 1,
The WPT transmitter is
It has a structure in which a ground plane including four ports, a substrate layer, and four pattern patches are sequentially stacked.
wireless power transfer system.
7. The method of claim 6,
A central circle is located at the center of the four pattern patches,
The four pattern patches have a shape that becomes narrower as it approaches the central circle,
The four ports are respectively located between the four pattern patches,
Power is concentrated to the four ports
wireless power transfer system.
8. The method of claim 7,
Adjusting the radius value of the center circle to move the resonant frequency band
wireless power transfer system.
2. The method of claim 1
In order to prevent a decrease in power transfer efficiency (PTE) due to a mismatch between the permittivity value of the tissue and the permittivity value of air, a matching layer disposed between the WPT transmitter and the tissue including more,
The permittivity value of the matching layer is higher than the permittivity value of the tissue.
wireless power transfer system.
2. The method of claim 1
The two-stage voltage doubler is
a one-step voltage doubler consisting of a circuit using two diodes and two capacitors; and
It consists of a circuit connected to the first stage voltage doubler using two additional diodes and two additional capacitors.
wireless power transfer system.
11. The method of claim 10,
In the second-stage voltage doubler, any capacitor of the first-stage voltage doubler is charged with voltage and
Characterized in that the charged voltage is the input voltage of the other capacitor of the circuit connected to the first-stage voltage doubler
wireless power transfer system.

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