WO2025146654A1

WO2025146654A1 - Near-field transducer

Info

Publication number: WO2025146654A1
Application number: PCT/IB2025/050069
Authority: WO
Inventors: Thomas Darryl MITCHELL; Peter Gerard DORMEHL; Jacques VREY
Original assignee: Erisco Inc
Current assignee: Erisco Inc
Priority date: 2024-01-05
Filing date: 2025-01-03
Publication date: 2025-07-10
Anticipated expiration: 2026-07-05

Abstract

A near-field transducer is provided. The transducer includes a first coil arrangement and a second coil arrangement. The first coil arrangement is stacked on top of the second coil arrangement such that axes of each of the coil arrangements are parallel to one another. The first coil arrangement is offset relative to the second coil arrangement. The first coil arrangement is electrically isolated from the second coil arrangement.

Description

NEAR-FIELD TRANSDUCER

CROSS-REFERENCE(S) TO RELATED APPLICATIONS

This application claims priority from United States provisional patent application number 63/618,194 filed on 5 January 2024, which is incorporated by reference herein.

FIELD OF THE INVENTION

The invention relates to a near-field transducer and in particular, although not exclusively, to a near-field transducer for energy harvesting and/or data transfer.

BACKGROUND TO THE INVENTION

Technologies such as near-field communication (NFC) enable communication between two electronic devices over a short distance (e.g. 4 cm or less). Such technologies are typically based on inductive coupling between two antennas and can allow for wireless transfer of electrical energy and/or data from one device to another. Such technologies often find application in portable electronic devices, such as payment cards, mobile phones, and the like. As such, energy transfer efficiency is an important design criterion as more efficient energy transfer can lower power consumption of an often battery powered host device.

The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application.

SUMMARY OF THE INVENTION

In accordance with an aspect of the invention there is provided a near-field transducer comprising a first coil arrangement and a second coil arrangement, wherein the first coil arrangement is stacked on top of the second coil arrangement such that axes of each of the coil arrangements are parallel to one another, wherein the first coil arrangement is offset relative to the second coil arrangement, and wherein the first coil arrangement is electrically isolated from the second coil arrangement.

Each of the first coil arrangement and second coil arrangement may include one or more rings or spirals. The first coil arrangement may be offset relative to the second coil arrangement by virtue of the rings or spirals of the first coil arrangement being offset from the rings or spirals of the second coil arrangement.

A layer may be interposed between the first coil arrangement and the second coil arrangement so as to electrically separate the first coil arrangement from the second coil arrangement. The layer may be provided by a material having a low dielectric constant at low frequency. The layer may have a dielectric constant of less than or equal to 4 at a frequency of 1 kHz. The layer may have a dielectric constant of less than or equal to 3.7 at a frequency of 1 kHz. The layer may have a dielectric constant of less than or equal to 2.1 at a frequency of 1 kHz. The layer may be an adhesive which adheres the first coil arrangement to the second coil arrangement.

Each of the first coil arrangement and second coil arrangement may include a core. The core may be made from a resistive material. The core may be made from a high volumetric resistive material. The core may be made from a material having a volumetric resistance greater than 10¹² Ohm/cm.

Each of the first coil arrangement and second coil arrangement may include a first conductive coil formed on a first side of a substrate and a second conductive coil formed on a second side of the substrate. The first conductive coil may be connected to the second conductive coil via one or more vias. Each of the first conductive coil and second conductive coil may be provided by a track. At least a portion of the track of the first conductive coil may locate above at least a portion of the track of the second conductive coil such that the first conductive coil is at least partially superimposed on the second conductive coil. The substrate may have a thickness which may be the same as or less than a width of the tracks. At least portions of the tracks of the first coil arrangement may be offset relative to portions of the tracks of the second coil arrangement. The tracks may be offset by a distance which is a function of the width of the tracks. The distance may be equal to the width of the tracks. At least portions of the tracks of the first coil arrangement may be offset relative to portions of the tracks of the second coil arrangement in two dimensions. A width of the tracks may be between 0.5 and 1 .5 mm. A width of the tracks may be between 0.8 and 1 .2 mm. A width of the tracks may be approximately 1 mm.

The rings or spirals may be convex polygon-shaped rings or spirals (such as rectangular, hexagonal or octagonal shaped rings or spirals). For the first coil arrangement, the track of the first conductive coil may be located above the track of the second conductive coil for all sides of the convex polygon-shaped ring or spiral such that the first conductive coil is superimposed on the second conductive coil. For the second coil arrangement, the track of one side of the convex polygon-shaped ring or spiral of the first conductive coil may be offset relative to the track of the same side of the convex polygon-shaped ring or spiral of the second conductive coil. Further, for the second coil arrangement, the track of the first conductive coil may locate above the track of the second conductive coil along remaining sides of the convex polygon-shaped ring or spiral.

A distance between edges of a track of one side of the convex polygon-shaped ring or spiral may be multiple times greater than the track width. A distance between edges of the track of remaining sides of the convex polygon-shaped ring or spiral may be less than the track width.

In accordance with another aspect of the invention there is provided an apparatus comprising the near-field transducer as defined above. The first coil arrangement may be connected to a first contact of a load. The second coil arrangement may be connected to a second contact of the load. The first coil arrangement and second coil arrangement may be connected to the load via a rectifier.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Figure 1A is a schematic diagram which illustrates a top-down view of a near-field transducer according to aspects of the present disclosure and in which tracks of respective coil arrangements are visible;

Figure 1 B is a grey scale version of the schematic diagram of Figure 1 A;

Figure 2 is a top down view of a first side of a first substrate on which a track providing a first coil of a first coil arrangement is formed;

Figure 3 is a top down view of a second side of the first substrate on which a track providing a second coil of the first coil arrangement is formed;

Figure 4 is a top down view of a first side of a second substrate on which a track providing a first coil of a second coil arrangement is formed; Figure 5 is a top down view of a second side of the second substrate on which a track providing a second coil of the second coil arrangement is formed;

Figure 6 is a schematic diagram which illustrates layers of a near-field transducer according to aspects of the present disclosure;

Figure 7A is a top down view of an octagonal shaped ring according to aspects of the present disclosure;

Figure 7B is a top down view of another octagonal shaped ring according to aspects of the present disclosure;

Figure 7C is a top down view of another octagonal shaped ring according to aspects of the present disclosure;

Figure 7D is a top down view of another octagonal shaped ring according to aspects of the present disclosure;

Figure 8 is a circuit diagram which illustrates integration of a near-field transducer into an apparatus according to aspects of the present disclosure; and,

Figure 9 is a circuit diagram which illustrates operation of a near-field transducer integrated into an apparatus according to aspects of the present disclosure in the presence of a powered coil.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

A near-field transducer is provided. The transducer may be a radiofrequency (RF) transducer. The near-field transducer may be a high-efficiency transducer suitable for near-field electrical energy and/or data transfer. The near-field transducer may implement an open coil design for energy harvesting while sustaining sub-carrier communication. The transducer may for example include a first coil arrangement and a second coil arrangement. The first coil arrangement may be stacked on top of the second coil arrangement such that axes of each of the coil arrangements are parallel to one another. The axes in this sense are considered to be axes around which rings or coils of the coil arrangements circle or spiral. The axes may be transverse to planes in which coils of the coil arrangements are formed. The first coil arrangement is offset relative to the second coil arrangement. For example, a ring or spiral, or a centre of the ring or spiral, of the first coil arrangement may be offset relative to a ring or spiral, or the centre of the ring or spiral, of the second coil arrangement. The offset may be in one or two dimensions. For example, if the axes referred to in the foregoing (about which the coils spiral) are considered z-axes, the coil arrangements may be offset from one another in one or both of the x- and y-axes. The first coil arrangement may be electrically isolated from the second coil arrangement. The electrical isolation may be by way of a layer interposed between the first and second coil arrangements. The layer may be an adhesive layer which bonds together substrates providing coils of each of the first and second coil arrangements. The layer may be provided by a material having a low dielectric constant at low frequency (e.g. being less than or equal to 4 at 1 kHz). The layer may have a thickness of about 0.5 mm. Each of the coil arrangements may have a core made from a material having a high volumetric resistance (e.g. being greater than 10¹² Ohm/cm).

When assembled into an apparatus, the first coil arrangement may be electrically connected to a first contact of an electrical load and the second coil arrangement may be electrically connected to a second contact of the electrical load. Connection of the coil arrangements to the respective contacts of the load may be via a diode bridge or another type of rectifier.

Through experimentation, the near-field transducer described herein has been found to achieve higher efficiency than configurations known in the prior art.

The near-field transducer described herein may be implemented in any number of applications where power is transferred electrically. Example applications include using NFC to transfer electrical power and data simultaneously; opening car doors using NFC; interacting with an electronic padlock or door lock using NFC; charging wireless headphones; charging smart watches or other such computing devices, and the like.

An example transducer (10) according to aspects of the present disclosure is illustrated in Figures 1 to 6. The transducer includes a first coil arrangement (12) and a second coil arrangement (14).

Each of the first coil arrangement (12) and the second coil arrangement (14) includes a first conductive coil (16, 18) formed (e.g. disposed, etched, or the like) on a first side of a substrate (20, 22) (such as a printed circuit board (FOB)) and a second conductive coil (24, 26) formed on a second side of the substrate. Each of the conductive coils (16, 18, 24, 26) may be in the form of a ring or spiral formed from a conductive material, such as copper. The ring or spiral may be polygonal (or more specifically convex polygonal) in shape. Example convex polygons implemented according to aspects of the present disclosure include rectangles, hexagons, octagons and the like. For the purposes of terminology, the substrate of the first coil arrangement may be termed the first substrate (20) and the substrate of the second coil arrangement may be termed the second substrate (22).

In the illustrated example, each of the first conductive coil and the second conductive coil of each of the coil arrangements is provided by a track (such as a PCB track). In each of the coil arrangements, the first conductive coil is electrically connected to the second conductive coil via one or more vias, plated through-holes or the like. In the illustrated example, tracks of each coil arrangement are arranged in a rectangular spiral.

The tracks are formed on the respective substrates such that, for each coil arrangement, at least a part of a track of the first conductive coil locates above a track of the second conductive coil. In this manner, for each coil arrangement, at least part of the first conductive coil is superimposed on the second conductive coil. In the illustrated example, for the first coil arrangement, the track of the first conductive coil is located above the track of the second conductive coil for all four sides of the rectangular spiral such that the first conductive coil is superimposed on the second conductive coil. In the illustrated example, for the second coil arrangement, the track of the first conductive coil locates above the track of the second conductive coil along three sides of the rectangular spiral, with the track of the fourth side of the rectangular spiral of the first conductive coil being offset relative to the track of the fourth side of the rectangular spiral of the second conductive coil. In other examples, other arrangements of overlap may be provided.

A width of the tracks may be selected between 0.5 and 1 .5 mm. In some examples, the width of the tracks is selected between 0.8 and 1.2 mm. In some examples, the width of the track is approximately 1 mm. In the illustrated example, the track width is constant. In other examples, different portions of the respective conductive coils may have different track widths. For example, in some examples, sections the track providing a shorter side of a rectangle defined by the rectangular coil may have a greater width than other sections, which may provide better performance in some applications.

A thickness of the tracks may be selected based on an intended frequency of operations, for example 35 urn in the illustrated example. The substrate of each coil arrangement may be formed from a low dielectric constant material. The substrate of each coil arrangement has a thickness which may be the same or is less than a width of the tracks. In some examples, the substrate of each coil arrangement has a thickness which is ±50% of the track width. In some examples, the substrate has a thickness of between 0.1 and 1.5 mm. In some examples, the substrate has a thickness of about 1.2 mm (with an adhesive layer of about 0.5 mm). In other examples, the substrate has a thickness of about 0.4 mm (with an adhesive layer of about 0.5 mm). A distance between edges of the track in the spiral may be a function of the width of the track. The distance between edges of the track of one side of the convex polygon-shaped ring or spiral may in some examples be multiple times greater (e.g., 5 or more times greater) than the width of the track. The distance between edges of a track of remaining sides of the convex polygonshaped spiral may be less than (e.g., 90% of) the track width.

As mentioned, in the illustrated example, tracks of each coil arrangement are arranged in a rectangular spiral (although other examples may implement other convex polygon shapes, such as hexagons, octagons or the like). The distance between edges of the track in the spiral may for example be 90% of the track width for one or more sides of the rectangular spiral. In the illustrated example, the distance between edges of the track of a fourth side of the rectangular spiral is greater than the width of the track (e.g., 5 or more times greater). In the illustrated example, the rectangular spiral tracks have bevelled corners where the tracks change from a horizontal to a vertical direction. “Rectangular”, “hexagonal” or “octagonal” shaped rings or spirals should therefore be taken to mean generally “rectangular”, “hexagonal” or “octagonal” shaped spirals, allowing for features such as bevelled corners, or the like. A “ring” may be an open ring (i.e. having two, spaced apart ends). In other examples, the tracks may be arranged in other shapes (such as circular rings or spirals, other forms of convex polygons and the like).

The first coil arrangement is stacked or placed on top of the second coil arrangement, with a layer (28) interposed therebetween. In other words, the coil arrangements are sandwiched together such that axes of each of the coil arrangements (e.g. z-axes, being axes about which coils of the respective arrangements spiral) are parallel to one another.

The first coil arrangement is stacked or placed on top of the second coil arrangement such that at least portions of tracks of the first coil arrangement are offset relative to corresponding portions of tracks of the second coil arrangement. In this manner, the first coil arrangement is offset relative to the second coil arrangement. More specifically, the first coil arrangement may be offset relative to the second coil arrangement by virtue of the spirals of the first coil arrangement being offset from the spirals of the second coil arrangement.

The portions of tracks which are offset may be offset by a distance which is a function of the width of the tracks. In the illustrated example, the distance is equal to the width of the tracks. The portions of the tracks of the first coil arrangement may be offset relative to the corresponding portions of the tracks of the second coil arrangement in one or two dimensions. For example, the tracks may be offset along one or both of an x-axis and a y-axis. In the illustrated example, the tracks are offset (29) along the x-axis only.

The layer (28) interposed between the first coil arrangement and the second coil arrangement may operate to electrically separate or isolate the first coil arrangement from the second coil arrangement. The layer may be provided by a material having a low dielectric constant at low frequency. For example, the layer may have a dielectric constant of less than or equal to 4 at a frequency of 1 kHz. In some examples, the layer may have a dielectric constant of less than or equal to 3.7 at a frequency of 1 kHz. In some examples, the layer may have a dielectric constant of less than or equal to 2.1 at a frequency of 1 kHz. The layer may be an adhesive which adheres the first coil arrangement to the second coil arrangement. In experimentation, a layer made from the material 3M 468MP was found to be suitable. The layer may have a thickness of about 0.5 mm.

Each of the first coil arrangement and second coil arrangement includes a core (30, 32). The core may be made from a resistive material, such as a high volumetric resistive material (e.g. having a volumetric resistance which is greater than 10¹² Ohm/cm). In experimentation, cores made from polycarbonate were found to be suitable.

A protective coating (34, 36) (e.g. of epoxy or the like) may be provided on either side of the transducer. For example, the protective coating may be provided on external surfaces of the transducer, such as the sides of the substrates (as well as the tracks formed thereon) which are opposite those sides thereof which interface with the layer.

The near-field transducer described herein provides a High Efficiency Open Coil (HEOC) which may achieve a substantial increase in energy harvesting (up to double) across multiple mobile devices. This may reduce the harvesting time and may improve user experience whilst maintaining stable communications. The near-field transducer described herein may provide improved wireless energy transfer. This may be achieved by providing one or both of offset coil arrangements which couple inductively and capacitively and which have high volumetrically resistive cores.

Referring to Figures 7A to 7D, example octagonal shaped rings (116, 118, 124, 126) are shown, which may be connected via vias or the like to provide first and second coil arrangements respectively to provide a near-field transducer as described herein. For example, each of a first coil arrangement and a second coil arrangement may include a first conductive coil (116, 118) formed (e.g. disposed, etched, or the like) on a first side of a substrate and a second conductive coil (124, 126) formed on a second side of the substrate. In other examples the rings may be arranged differently to provide the first and second coil arrangements. Each of the conductive coils (116, 118, 124, 126) may be in the form of a ring formed from a conductive material, such as copper or the like. The example octagonal shaped spirals rings of Figures 7A to 7D may be implemented, mutatis mutandis, in the near-field transducer described above with reference to Figures 1 to 6.

Referring now to Figures 8 and 9, the near-field transducer may be integrated into an apparatus by connecting the transducer (10) to a load (50) via a rectifier (52) (which may for example be provided by a diode bridge) and energy storage capacitor (53). When an energising device (54) including a power source (56) and a powered coil (58) is brought into proximity to the transducer, a coupling capacitor (60) is formed between the coil arrangements and electrical energy and/or data may be transmitted from the energising device to the load via inductive coupling between the powered coil and transducer.

One example of a near-field transducer according to aspects of the present disclosure comprises two offset coil arrangements, not electrically connected to each other, with each coil arrangement being individually connected to either side of a load (and thus meaning there is not a complete electrical circuit). The coils are mechanically bonded with a material (e.g. 3M 468MP) which has a low dielectric constant at a low frequency. The coil arrangements are offset from each other. A material (e.g., polycarbonate) which has a high volumetric resistivity is used for the core of the coils. The near-field transducer described herein includes two separate coil arrangements (Coil A & Coil B). Coil A is electrically connected to load point A. Coil B is electrically connected to load point B. Coil A is not electrically connected to Coil B. A low dielectric constant at low frequency material (e.g., <4 at 1 kHz) is used to form a coupling capacitor between the coils (measured passive capacitance at 200 Hz should be <80 pF). A high volumetric resistive material is used through the core of the two coils, Ohm/cm > 10¹². Coil A is offset from Coil B by the width of the copper track on one or both of the X and Y axes. Thickness of the copper track is 35 urn (10 MHz at 20 urn skin depth of copper). Wider tracks (e.g., between 0.5 - 1.5 mm) with a separation of 10% less than the track width may perform best. Coil offsets in both the X and Y axes appear to perform better. The stack up of the coil arrangements may be important. In some examples, the spacing between the top and bottom layers of each coil should be within 10% of the track thickness of the copper layer. The electrical circuit between the coil arrangements is either: open circuit when no magnetic field is present (e.g., when there is no mobile device attempting an NFC transaction); and, capacitive coupling between the two coil arrangements when there is a magnetic field present (e.g., when there is a mobile device attempting an NFC transaction). Without the magnetic field from the mobile device, there is an open circuit. When an alternating magnetic field is introduced to the electrical circuit it is assumed that a small capacitance is formed between Coil A and Coil B which then provides the improved power harvesting.

Experimentation

Testing was performed on the above-described example of a near-field transducer connected to an Infineon™ NFC chip for energy harvesting and control, a 22mF electrolytic capacitor for energy storage and a DC motor as load. The NFC chip was programmed with Infineon’s sample code which was configured to clamp the storage capacitor voltage at 3.3V and to activate the load once a 3.0V threshold is reached on the storage capacitor. Time to charge the fixed capacitor to 3.0V is used to indicate coil efficiency. Testing was performed with various Android™ and iOS™ devices but, in order to maintain the integrity of the test results, an iPhone™ 12 with iOS™ 16.6.1 was used for all tests recorded herein. iOS™ also allows better control of the activation of the NFC field which facilitates the test procedure. A variety of coils (transducers) were used for the testing, including reference designs from the chip manufacturer (Infineon), TDK and various experimental coils.

The test procedure was as follows:

1 . Connect the transducer under test to the prototype board and attach the oscilloscope probe across the terminals of the storage capacitor. The oscilloscope is configured to measure voltage on the vertical axis and time on the horizontal axis.

2. Place the iPhone™ 12 on the transducer. (Through prior experimentation, ideal positioning of the phone in relation to the different transducers was determined in order to maximise the energy harvested. This varies markedly between the different phone manufacturers and models and transducer types.)

3. Ensure the storage capacitor is discharged by shorting its terminals together.

4. Activate the NFC field (e.g., by pressing the “Unlock" button of the manufacturer’s application executing on the mobile phone).

5. Monitor and record the time it takes for the NFC harvesting chip to charge the storage capacitor to 3.0V and activate the load.

6. Two tests were performed and documented for each transducer that was tested.

The results, in terms of time taken in seconds for the NFC harvesting chip to charge the storage capacitor to 3.0V and activate the load, are as follows:

The Efficient transducer and Efficient transducer window are near-field transducers configured according to aspects of the present disclosure. An analysis of the test results obtained show that the transducer described as being equivalent to the manufacturer’s prototype transducer took approximately 12.8 seconds to charge the storage capacitor to 3.0V whereas the efficient transducer configured according to aspects of the present disclosure took just under 2.9 seconds to charge the storage capacitor to 3.0V. This is a more than fourfold improvement in harvesting time which correlates with the amount of energy harvested. The results, in terms of a rate of energy harvesting in Joule per second, is as follows:

The foregoing description has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure. The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.

Finally, throughout the specification and accompanying claims, unless the context requires otherwise, the word ‘comprise’ or variations such as ‘comprises’ or ‘comprising’ will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

CLAIMS:

1 . A near-field transducer comprising a first coil arrangement and a second coil arrangement, wherein the first coil arrangement is stacked on top of the second coil arrangement such that axes of each of the coil arrangements are parallel to one another, wherein the first coil arrangement is offset relative to the second coil arrangement, and wherein the first coil arrangement is electrically isolated from the second coil arrangement.

2. The transducer as claimed in claim 1 , wherein each of the first coil arrangement and second coil arrangement includes one or more rings or spirals, and wherein the first coil arrangement is offset relative to the second coil arrangement by virtue of the rings or spirals of the first coil arrangement being offset from the rings or spirals of the second coil arrangement.

3. The transducer as claimed in claim 1 or claim 2, wherein a layer is interposed between the first coil arrangement and the second coil arrangement so as to electrically separate the first coil arrangement from the second coil arrangement.

4. The transducer as claimed in claim 3, wherein the layer is provided by a material having a low dielectric constant at low frequency, wherein the layer has a dielectric constant of less than or equal to 4 at a frequency of 1 kHz.

5. The transducer as claimed in claim 3 or claim 4, wherein the layer is an adhesive which adheres the first coil arrangement to the second coil arrangement.

6. The transducer as claimed in any one of the preceding claims, wherein each of the first coil arrangement and second coil arrangement includes a core, wherein the core is made from a resistive material, wherein the core is made from a high volumetric resistive material, and wherein the core is made from a material having a volumetric resistance greater than 10¹² Ohm/cm.

7. The transducer as claimed in any one of the preceding claims, wherein each of the first coil arrangement and second coil arrangement includes a first conductive coil formed on a first side of a substrate and a second conductive coil formed on a second side of the substrate, wherein the first conductive coil is connected to the second conductive coil via one or more vias.

8. The transducer as claimed in claim 7, wherein each of the first conductive coil and second conductive coil is provided by a track.

9. The transducer as claimed in claim 8, wherein at least a portion of the track of the first conductive coil locates above at least a portion of the track of the second conductive coil such that the first conductive coil is at least partially superimposed on the second conductive coil.

10. The transducer as claimed in claim 8 or claim 9, wherein the substrate has a thickness which is the same as or less than a width of the tracks.

11 . The transducer as claimed in any one of claims 8 to 10, wherein at least portions of the tracks of the first coil arrangement are offset relative to portions of the tracks of the second coil arrangement.

12. The transducer as claimed in claim 11 , wherein the tracks are offset by a distance which is a function of a width of the tracks, wherein the distance is equal to the width of the tracks.

13. The transducer as claimed in any one of claims 8 to 12, wherein at least portions of the tracks of the first coil arrangement are offset relative to portions of the tracks of the second coil arrangement in two dimensions.

14. The transducer as claimed in any one of claims 8 to 13, wherein a width of the tracks is between 0.5 and 1 .5 mm.

15. The transducer as claimed in any one of claims 2 to 14, wherein the rings or spirals are convex polygon-shaped rings or spirals.

16. The transducer as claimed in claim 15 when dependent on claim 8, wherein, for the first coil arrangement, the track of the first conductive coil is located above the track of the second conductive coil for all sides of the convex polygon-shaped ring or spiral such that the first conductive coil is superimposed on the second conductive coil.

17. The transducer as claimed in claim 15 when dependent on claim 8, wherein, for the second coil arrangement, the track of one side of the convex polygon-shaped ring or spiral of the first conductive coil is offset relative to the track of the same side of the convex polygon-shaped ring or spiral of the second conductive coil.

18. The transducer as claimed in claim 17, wherein, for the second coil arrangement, the track of the first conductive coil locates above the track of the second conductive coil along remaining sides of the convex polygon-shaped ring or spiral.

19. The transducer as claimed in claim 15 when dependent on claim 8, wherein a distance between edges of a track of one side of the convex polygon-shaped ring or spiral is multiple times greater than the track width, and wherein a distance between edges of the track of remaining sides of the convex polygon-shaped ring or spiral is less than the track width.

20. An apparatus comprising the near-field transducer as claimed in any one of the preceding claims.

21 . The apparatus as claimed in claim 20, wherein the first coil arrangement is connected to a first contact of a load and wherein the second coil arrangement is connected to a second contact of the load, wherein the first coil arrangement and second coil arrangement are connected to the load via a rectifier.