Self-Resonant Coil with Series LC Resonance and Electric Field Cancellation

Abstract

A coil structure for near-field wireless power transfer that integrates traditional inductor and external capacitor structures into a single coil to form a series resonance. The series resonance is realized by terminal connection and layering method. The electric field is cancelled by the interleaved structure between the distributed turns. The integrated capacitor can save the cost and space of the resonant capacitor. The electric field cancellation can reduce interference with adjacent components such as touch screens. Other advantages may include low profile and convenience of manufacturing based on RGB technology. This coil could be useful for both consumer electronics and wireless charging of electric vehicles.

Description

[Technical Field]

[0001] Related Applications This application claims priority to and the benefit of U.S. Provisional Patent Application No. 63 / 337,494, filed May 2, 2022, which is incorporated herein by reference in its entirety.

[0002] The presently disclosed subject matter relates to a series self-resonant coil structure for wireless power transfer. [Background technology]

[0003] Wireless power transfer, also known as wireless charging or wireless energy transfer, is a technology that allows electrical devices to be powered without the need for a physical connection between the power source and the device. This technology is becoming increasingly popular in consumer electronics devices such as smartphones, smartwatches, and earphones because it eliminates the need for cables and connectors, making it more convenient for users.

[0004] The basic principle of wireless power transfer is based on the transfer of energy via a magnetic field between two coils: a transmitter coil and a receiver coil. The transmitter generates a magnetic field that induces a current in the receiver coil; this current is then rectified and used to power a device or charge a battery. The efficiency and range of a wireless power transfer system depend on various factors, including the size and geometry of the coil, the distance between the transmitter and receiver, and the frequency and modulation of the magnetic field. Advances in wireless power transfer technology are facilitating the development of new applications in areas such as electric vehicles, medical implants, and industrial automation. Summary of the Invention

[0005] This coil structure for near-field wireless power transfer integrates a conventional inductor and an external capacitor structure into a single coil to form a series resonance. The series resonance is achieved through terminal connections and layering methods. The electric field is canceled by an interleaved structure between the distributed turns. The integrated capacitor saves the cost and space of the resonant capacitor. The electric field cancellation can reduce interference with adjacent components such as touchscreens. Other advantages include a low profile and ease of manufacturing based on PCB technology. This coil could be useful for both consumer electronics and wireless charging of electric vehicles.

[0006] In some examples, a series self-resonant coil structure for wireless power transfer includes a first conductive layer configured in a first planar spiral arrangement, the first conductive layer having a first terminal; a second conductive layer configured in a second planar spiral arrangement, the second conductive layer having a second terminal; and a dielectric layer disposed between the first and second conductive layers. The first conductive layer, the second conductive layer, and the dielectric layer are configured to generate a repeating series LC connection between the first and second terminals. The first conductive layer includes at least one discontinuity, and the second conductive layer is continuous at the location of the at least one discontinuity inverted about the dielectric layer.

[0007] This Summary lists several embodiments of the presently disclosed subject matter, and in many cases, lists variations and permutations of these embodiments. This Summary is merely illustrative of many different embodiments. Mention of one or more representative features of a given embodiment is likewise exemplary. Such embodiments may typically exist with or without the mentioned features; similarly, these features may be applied to other embodiments of the presently disclosed subject matter, whether or not described in this Summary. To avoid excessive repetition, this Summary does not list or suggest all possible combinations of such features. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram of an exemplary wireless power transfer system. [Figure 2A] 1 shows a prototype wireless power transfer system to a laptop with a metal case. [Figure 2B] 1 is a photograph of a commercial coil showing iterative dispersion compensation. [Figure 3A-3C] A comparison of self-resonant coil structures is shown in Figure 3A, 3B, and 3C. Figure 3A shows a series self-resonant coil, a compensated series self-resonant coil, and a symmetrically compensated series self-resonant coil. [Figure 3D] 1 shows the coil structure and current flow diagram for a half-turn compensated version of a series self-resonant coil. [Figure 3E] 1 shows the coil structure and current flow diagram for a symmetrical version of a series self-resonant coil. [Figure 4A-4B] The structure of a square two-turn FSRC is shown in Figure 4. Figure 4A shows the shape of the upper layer as viewed from above, and Figure 4B shows the shape of the lower layer as viewed from above. [Figure 5] Figure 1 shows the current distribution along the longitudinal variation of the coil length, where rI is the fraction of terminal coil current and the position axis is referenced to the number of turns in the coil. [Figures 6A-6B] Figure 6A shows the simulated current density distribution from the top view, and Figure 6B shows the bottom view. [Figures 7A-7B] Figure 7A shows a top view of the HRSC structure. Figure 7B shows a top view using a transparent dielectric. The dashed gray trace represents the lower layer as viewed from above. [Figure 8] 1 illustrates an exemplary coil geometry. [Figure 9A-9B] The flux distributions when a 1 A, 6.78 MHz current is applied are shown in Figure 9A for a conventional coil and in Figure 9B for an exemplary self-resonant coil. [Figure 10] FIG. 1 is a schematic diagram showing a Maxell ferrite simulation. [Figure 11A]1 shows the simulated effect of ferrite on inductance. [Figure 11B] The effect on the induced voltage is shown. [Figures 12A-12B] The calculated coil circuit parameters for a solid wire coil are shown in Figure 12A: LC vs. R (denoted as Q) and Figure 12B: LC vs. Aind (denoted as Vind) in a 20 μT magnetic field. [Figures 13A-13B] The calculated coil circuit parameters are shown in Figure 13A for CSRC and Figure 13B for HRSC. [Figure 13C] The parameters of FSRC are shown below. [Figures 14A-14D] Four coil structures corresponding to the x markers are shown: Figure 14A shows SC, Figure 14B shows CSRC, Figure 14C shows HSRC, and Figure 14D shows FSRC. [Figure 15A] The minimum ESR for each LC combination is shown. [Figure 15B] The corresponding coil type is indicated. [Figure 16] FIG. 1 shows a systematic design showing the loss breakdown of individual voltages. [Figure 17] Schematic diagram of the HFSS simulation. [Figure 18] HFSS simulation chart of impedance. [Figure 19] 10 is a chart showing a comparison of simulated E-fields with a four-turn circular coil. [Figures 20A-20C] A comparison of simulated dielectric losses is shown: Figure 20A shows the scale, Figure 20B shows the CSRC simulation, and Figure 20C shows the FSRC simulation. [Figure 20D] Table I shows a comparison of measured and calculated circuit parameters. [Figure 20E] Table II shows a comparison of measured and calculated circuit parameters. [Figures 21A-21B]The hardware prototype and experimental setup with two receiving coils are shown in Figure 21A. Figure 21B shows the fabricated FSRC coil and the 100W wireless charging station. [Figure 22] 1 is a bar graph showing the calculated loss components contributing to the total conversion loss of a prototype system around 100 W output power. DETAILED DESCRIPTION OF THE INVENTION

[0009] 1 is a block diagram of an exemplary wireless power transfer system 100. The system 100 includes a transmitter 102 and a receiver 104.

[0010] The transmitter 102 includes a power supply 106, a transmit coil 108, and a control circuit 110. The power supply 106 is responsible for providing power to the transmitter 102. The power supply 106 can be a battery or an AC power source, depending on the implementation. The power supply 106 may also include power management circuitry that regulates the input voltage to the transmitter 102.

[0011] The transmit coil 108 generates a magnetic field that is used to wirelessly transfer power to the receive device 104. The transmit coil 108 can be a single coil or an array of multiple coils, depending on the system design. The geometry and placement of the coils may also vary depending on the application.

[0012] The control circuit 110 is configured to control and monitor the wireless power transfer process. The control circuit 110 may include a microcontroller or other electronic components that generate and modulate the magnetic field generated by the transmit coil 108. The control circuit 110 may also monitor the charge state and adjust the output voltage to ensure stable and efficient power transfer. The control circuit 110 may be implemented using various electronic components such as diodes, capacitors, inductors, and transistors.

[0013] The receiving device 104 can be any suitable type of electrical device, such as, for example, a consumer electronic device such as a mobile phone or laptop, or an electric vehicle, or a medical implant device, etc. The receiving device 104 includes a receiving coil 112, a rectifier 114, a regulator 116, a control circuit 118, and a battery 120.

[0014] The receive coil 112 receives the magnetic field generated by the transmit coil 108 and converts the magnetic field into electrical power. The receive coil 112 can be a single coil or an array of multiple coils, depending on the system design. The shape and arrangement of the coils can also vary depending on the application.

[0015] The rectifier 114 converts the AC voltage generated by the receive coil 112 into a DC voltage that can be used to charge the battery 120 or power a device. The rectifier 114 may be implemented using diodes or other electronic components that allow current to flow in one direction.

[0016] Regulator 116 maintains a constant output voltage by regulating the input voltage, which may be useful for powering electronic devices that require a stable power source. Regulator 116 may be implemented using electronic components such as a voltage regulator or a DC-DC converter.

[0017] The control circuit 118 controls the wireless power transfer process, monitors the charging status, and regulates the output voltage. The control circuit 118 may include a microcontroller or other electronic components that communicate with the control circuit 110 of the transmitter 102 to ensure efficient and safe power transfer. The control circuit 118 may also include safety features such as overvoltage protection, overcurrent protection, and temperature sensing.

[0018] The battery 120 stores the electrical energy transferred from the transmitter and provides power to the device 104 when needed. The battery 120 may be a rechargeable battery, such as a lithium-ion battery, that can be wirelessly charged using the wireless power transfer system. The battery 120 may also include battery management circuitry that monitors the battery status and controls the charging process.

[0019] For wireless power transfer in consumer electronics applications such as cell phones or laptops, the on-board receiver coil must be designed to have a low profile and exhibit low stray magnetic fields. The limited space available in compact mobile devices precludes the use of thick, solid copper wire to reduce power losses. Both the operation of the WPT and nearby components are susceptible to stray magnetic and electric fields. Stray magnetic fields can induce eddy currents in adjacent metal or PCB traces, potentially compromising magnetic coupling with the transmitter.

[0020] To alleviate some or all of these problems, the transmit coil 108, the receive coil 112, or both can include a series self-resonant coil structure. For example, the series self-resonant coil structure can be a fully compensated self-resonant coil (FSRC) with series LC resonance and reduced surface electric field for applications in wireless power transfer in consumer electronics. By having repeated series LC connections along the entire coil trace, the series resonant structure simultaneously achieves high Q, low E field, and a thin profile.

[0021] Figure 2A shows a prototype multi-receiver 6.78 MHz wireless charging station. When a 50 W receiver is placed under an aluminum-body laptop, the rectified induced voltage is reduced by a factor of 30 compared to the results without the laptop, preventing charging. To protect against magnetic coupling and reduce interference with adjacent objects, a ferrite shield can be employed on the external coil without requiring patterning of the metal case. Adding ferrite to the system changes the coil induced voltage and self-inductance, which must be taken into account when designing the coil.

[0022] In addition to the stray magnetic field, the electric field generated by the voltage drop along the length of the coil can interact with nearby sensitive electronics, including capacitive touchscreens. The stray electric field can also cause dielectric losses in adjacent materials, such as the coil substrate, adjacent circuitry, and ferrite shielding. To reduce the stray electric field, individual distributed capacitors can be used to compensate the voltage potential of each turn. Current commercial Airfuel receivers use distributed lumped capacitors, which create additional parasitic ESR. The physical size of the capacitors (typically in an 0805 package) significantly increases the height of the coil.

[0023] This paper presents receiver coil and receiver-side designs for, for example, laptop applications. Ferrite effects are modeled and included. An exemplary self-resonant coil is proposed to achieve a low profile, low E-field, and high Q to verify coil operation, modeling, and systematic design.

[0024] Exemplary Coil Structures and Principles of Operation This paper describes a new symmetric, fully compensated self-resonant coil structure to address the need for low-profile coils with compensated electric and shielded magnetic fields.

[0025] Figure 3A shows an exploded view of a circular, three-turn series self-resonant coil (CSRC) with a magnetic shield. The coil is formed by two copper spirals sandwiched between them by a dielectric layer. Terminals A and B of the coil are on opposite layers and opposite ends of the spirals. The AC current path between terminals A and B passes once through the three-turn spiral and once across the dielectric layer.

[0026] Figure 3B shows a half-turn compensated version of the series self-resonant coil. Gaps are provided in each copper spiral so that the current path between the coil terminals crosses the dielectric film multiple times for each half turn of the coil. This repeated crossing of the dielectric creates distributed field compensation. In this design, the terminals are on the same layer but at opposite ends of the spiral. In height-constrained applications, this terminal arrangement presents a challenge because an additional conductor layer is required to connect terminal B back to the outside of the coil and to the power stage.

[0027] Figure 3C shows a symmetrical version of the compensation coil. By aligning the gap with the connection between the turns, this implementation allows both terminals of the device to be located outside the coil.

[0028] 3D shows a coil structure 300 for a half-turn compensated version of a series self-resonant coil and a current flow diagram 320 illustrating current flow in the coil structure 300. The coil structure 300 includes a first conductive layer 302 configured in a first planar spiral arrangement having a first terminal "A." The coil structure 300 includes a second conductive layer 304 configured in a second planar spiral arrangement having a second terminal "B." The coil structure 300 includes a dielectric layer 306 disposed between the first conductive layer 302 and the second conductive layer 304.

[0029] Conductive layers 302 and 304 can have multiple discontinuities, i.e., spirally arranged breaks, with the opposing conductive layer being continuous at locations corresponding to the discontinuities, i.e., locations flipped around dielectric layer 306. For example, first conductive layer 304 has a first number of discontinuities 308 on the left side of the figure, and second conductive layer 304 is continuous at corresponding locations 310 flipped around dielectric layer 306. In another example, second conductive layer 304 has a second number of discontinuities 312 on the right side of the figure, and first conductive layer 302 is continuous at corresponding locations 314 flipped around dielectric layer 306.

[0030] 3E shows a coil structure 350 of a symmetrical version of a series self-resonant coil, and a current flow diagram 370 illustrating the current flow in coil structure 350. The discontinuities in conductive layers 302 and 304 of coil structure 350 result in an interleaved symmetrical structure with repeating series LC connections.

[0031] For example, first conductive layer 304 has a discontinuity where the spiral arrangement comprises a diagonal bridge 352 between two turns of the planar structure, and second conductive layer 304 has a discontinuity where the spiral arrangement comprises a diagonal bridge 354 of an opposite connection of two turns of the planar structure at a location where the spiral arrangement flips around dielectric layer 306. In this example, coil structure 350 also includes opposing diagonal bridges 356 and 358 on different sides of coil structure 350.

[0032] Figure 4 shows further details of a two-turn, square, symmetrical, fully compensated self-resonant coil structure (FSRC). The structure is made using a double-sided copper-clad dielectric laminate. The geometry of the two copper coils is carefully designed to provide resonant inductance. The surface area of ​​the copper and dielectric material is carefully designed to form a resonant capacitor between the two copper layers. Terminals a and b, located in the outer extent of the coil and on opposing layers, are connected to an AC power source (e.g., a WPT inverter).

[0033] Due to the complete separation of the two conductive layers by the dielectric, the coil appears as an open circuit to a DC power source. When an AC power source is applied, current flows from one terminal to the other across the dielectric multiple times, resulting in a repeating series LC connection, and the total capacitance consists of three distributed parasitic capacitances in series. The three parasitic capacitor sections are: 1) from point a to p1, 2) from point p1 to point p2, and 3) from point p2 to point b.

[0034] Similar to a parallel plate capacitor, the current is a displacement current J d =ε r The transition between the two layers takes the form ε0∂E / ∂t, where ε r is the relative permittivity of the dielectric material. As with a conventional uncompensated series self-resonant coil, the electric field between the two copper layers is constant within each capacitor section, resulting in J d is uniformly distributed along the length and width of the trace in each section.

[0035] J for each capacitor section d Because is uniform, the input current transitions linearly from the top input terminal a to the end of the first half turn to point p1 on the bottom layer. At points a and p1, the current in the entire coil flows through one conductor and is zero on the other conductor. In the next section, the current transitions linearly from p1 on the bottom layer to the end of the inner turn to point p2 on the top layer. Then, the current transitions linearly from p2 on the top layer to the end of the outer turn to point b on the bottom layer. At points p2 and b, the current in the entire coil flows through one conductor and is zero on the other conductor.

[0036] The current distribution on the two conductor layers is summarized in Figure 5, showing that the current crosses the dielectric between the top and bottom layers multiple times, resulting in a series LC characteristic with distributed capacitance and reducing nearby fringing E-fields.

[0037] Full-wave FEA simulation is used to verify the current distribution pattern. The results are shown in Figures 6A-6B and are consistent with the analyzed current distribution.

[0038] In Figure 4, each half turn is compensated by a parasitic capacitor, forming a fully compensated self-resonant coil. This structure may be combined with a conventional planar coil to form a new structure in which alternating turns are compensated, i.e., a hybrid self-resonant coil (HSRC). Figures 7A-7B show a three-turn example in which the voltage potentials of the outermost and innermost turns are compensated by parasitic capacitors, but the center turn is not.

[0039] Symmetric FSRCs have additional series capacitance for each half turn of the coil. Therefore, the total equivalent capacitance is small, and geometric constraints can make it difficult to achieve the target capacitance and coil resonant frequency. Compared to other self-resonant coils that do not have repeated series capacitance, FSRCs may require thinner, higher-permittivity dielectric materials to achieve the same resonant frequency. Compared to FSRCs, HSRCs have a reduced number of series capacitances, so for the same dielectric and geometry, the achievable maximum capacitance is greater than FSRCs. Due to the reduced compensation, the leakage electric field of HSRCs is larger than that of FSRCs but smaller than that of conventional coils.

[0040] Coil modeling and design procedure The geometric parameters of the coil are shown in Figure 8. r is the width of each turn, l i is the inner length, l o is the outer length. n s is the number of turns per layer, h r is the thickness of the dielectric layer. t is the thickness of the copper. The dielectric constant and loss tangent are D k and t g is.

[0041] To investigate the performance capabilities, analytical models of inductance, capacitance, and resistance are developed based on literature and FEA-assisted simulation results. L is analyzed based on magnetic field simulation. C and R are analyzed based on comparison with existing self-resonant coils.

[0042] 1. Inductance The top and bottom layers of the proposed coil have the same current flow direction (i.e., from the input terminal to the output terminal). Compared to a conventional PCB coil, the current flow in the proposed coil differs only in that it is perpendicular to the dielectric layers. When the dielectric thickness is small relative to the width, the magnetic flux distributions of the proposed self-resonant coil and the conventional PCB coil are nearly identical. Figures 9A-9B show magnetic field simulations comparing the flux distribution between a conventional single-layer coil (a) and a self-resonant coil (b), assuming both coils carry a 1 A 6.78 MHz current. Due to the identical flux distribution, the two coils have the same inductance.

[0043] The inductance of conventional planar coils has been empirically modeled to an error of less than 3%. TIFF2025515138000002.tif27170, l ro and l ri are the radii of the outer and inner turns, respectively.

[0044] 2. Capacitance Compared to a conventional self-resonant coil, the FSRC has the same parallel plate structure in each capacitor section of each half turn, so the capacitance of each section is modeled using the same method as the CSRC.

[0045] The capacitance of the ith turn of the CSRC is: TIFF2025515138000003.tif33170

[0046] In the case of an FSRC, the total capacitance is the series combination of each half turn and the innermost turn. TIFF2025515138000004.tif15170

[0047] For HSRC, the total capacitance is the series connection of each half-turn with the self-resonant structure, excluding the non-self-resonant turns. For HSRC, if the self-resonant turns are an odd number of turns, the capacitance is: TIFF2025515138000005.tif28170In the formula, k is an integer starting from 3.

[0048] 3. Coil EST The total loss of a self-resonant coil includes copper loss and dielectric loss. Copper loss can be modeled as skin effect loss and proximity effect loss. Skin effect loss is calculated through the integration of the loss density over the entire coil. Proximity loss is due to the calculation of the near field at each turn and then the proximity loss.

[0049] The input current transitions linearly from the top to the bottom spiral over the entire length of each capacitor section, just as in a CSRC. Therefore, the skin-effect ESR of the ith turn, when configured as a self-resonant structure, is: TIFF2025515138000006.tif15170

[0050] If the ith turn is configured as a conventional structure such as an HSRC, the skin effect ESR is: TIFF2025515138000007.tif13170

[0051] Whole Skin Effect ESR The file is TIFF2025515138000008.tif7170.

[0052] In addition to the skin effect, the time-varying H-field around the coil traces causes eddy current losses in the copper foil. Since the H-field of the FSRC coil is nearly identical compared to a conventional coil (see Figure 9), the magnetic field distribution and proximity-related ESR are calculated using the same method as for the CSRC.

[0053] Hc is the H field strength at the center point. H in is the H field strength at the innermost point. H out is the outermost field. The decrease in H field strength at each turn is dH=H in -H out ) / n. As previously shown, TIFF2025515138000009.tif55170

[0054] After obtaining the field distribution information, the proximity effect loss of the ith turn is calculated using the standard equation for eddy currents in the lamination. TIFF2025515138000010.tif13170, V oli is the volume of copper in the ith turn. TIFF2025515138000011.tif7170, l i,in and l i,out are the inner and outer radii of the i-th turn, respectively. Also, B avg,i 2 is the square of the mean peak flux density of the near-field H-field. TIFF2025515138000012.tif44170

[0055] The proximity effect ESR of the ith turn is: TIFF2025515138000013.tif13170

[0056] The total ESR related to the proximity effect is The file is TIFF2025515138000014.tif8170.

[0057] Dielectric loss is the loss tangent t of the dielectric material g It is calculated based on: TIFF2025515138000015.tif12170

[0058] Finally, the total equivalent series resistance (ESR) of the coil is: Rs =R skin +R prox +R c (15)

[0059] magnetic shielding effect Adjacent metal can disrupt magnetic coupling, necessitating ferrite shielding and affecting the inductance and induced voltage of the receive coil. To facilitate the proposed self-resonant coil design, FEA simulations using Ansys Maxwell 2D are used to quantify the effects. The simulated geometry is shown in Figure 10 and includes a transmit coil with a uniform magnetic field.

[0060] Because the magnetic field is uniform, coupling remains constant even if the receive coil is placed at other locations on the transmitter surface or if the transmit coil is configured with other geometries, as long as the field is uniform. Ferrite is a low-loss material at high frequencies, with a permeability of 120. The metal is a 2oz copper layer, representing a two-layer PCB. The coil length is 17.8cm (7 inches) and the maximum height is 1.02mm (0.04 inches).

[0061] The simulation sweeps the coil geometry and ferrite thickness to evaluate the shielding effectiveness of various ferrite thicknesses. The inner radius is swept from 3 cm to 6 cm. The number of turns is swept from 2 to 3. The width is designed for each geometry, leaving a 2 mm gap between adjacent turns. The outer length is fixed at 8.9 cm (3.5 in) based on the available space in the laptop. The inductance and induced voltage are evaluated and compared for two situations: 1) ferrite only, and 2) ferrite + copper. The results are shown in Figures 11A-11B.

[0062] In Figure 11A, the inductance ratio is the inductance L of the ferrite alone. f divided by the inductance of the unshielded coil, L0, or the inductance of the ferrite and copper, L fcuIn Figure 11B, the voltage ratio is the ferrite-only induced voltage V ind,f is the inductance of the unshielded coil, V ind divided by, or the inductance of the ferrite and copper, V ind,fcu V ind is divided by . Without the copper layer, the ferrite shield enhances the magnetic field and therefore increases the coil inductance at all ferrite thicknesses. The ferrite also forms a low impedance loop, allowing more magnetic flux to penetrate the Rx coil, leading to an increase in induced voltage. With the copper layer, some of the magnetic flux passing through the ferrite causes eddy currents, which reduces the inductance and induced voltage for thinner ferrites. As the ferrite thickness increases, the penetration flux into the copper decreases, thus increasing the inductance and induced voltage. A 1mm ferrite has a L fcu / L f is sufficient to reduce the inductance to 5%, resulting in a voltage ratio of 0.95, and the improvement becomes increasingly slower above this thickness. With this in mind, a ferrite thickness of 1 mm was chosen, close to the height limit of 1.02 mm. Both the voltage ratio and the inductance ratio are used in the systematic design.

[0063] Coil Design The FSRC and HSRC coils developed in the previous section are compared with conventional coil geometries in a target 6.78MHz, 50W receiver. Rogers RO3003 dielectric is used for each self-resonant coil. The substrate is 0.13mm thick and D k = 3, and t g = 0.001. Wurth 364003 RF ferrite sheet is used for the magnetic shielding layer.

[0064] For the internal stage design, geometric iterations are used to calculate the coil circuit parameters based on the geometric requirements of the application. Four types of coils are compared: 1) solid copper coil, 2) conventional self-resonant coil (CSRC), 3) HSRC, and 4) FSRC. Modeling of 2) has been reported previously. Geometry was swept within the application requirements, and the circuit parameters designed for the solid coil are shown in Figures 12A-12B. Note that the thickness is limited to 0.2 mm.

[0065] Figure 12A shows the LCR parameters, where R is represented by Q to better understand the quality of the coil. The dashed curve shows the 6.78 MHz LC resonance. One curve is the LC design canceling the reactance of a 50 W rectifier using B340LB diodes. The area of ​​interest for the induced voltage, which is also determined by the rectification stage, is highlighted in a box. Figure 12B shows the induced voltage when the coil is placed in a 20 μT magnetic field.

[0066] The CSRC, HSRC, and FSRC design results are shown in Figures 13A-13B, all of which are the result of geometric iteration. The x symbols in Figures 13A-13B and 12A-12B represent designs with 1.60 μH, 360 pF, and 36 V induction voltage, which meet the requirements of the target application. The corresponding sets of coil circuit diagrams are shown in Figures 14A-14D.

[0067] Due to limited thickness, solid copper only allows for thin wires and limited conductive area, limiting Q. CSRC configures each turn's capacitor in parallel, necessitating limited capacitance from each turn, thus resulting in a thinner design. In comparison, HSRC and FSRC configure each turn's capacitance (if any) in series, magnifying the required capacitance from each turn, resulting in wider traces than CSRC.

[0068] By combining four coils, the resulting LCR design space is shown in Figure 15A, where only the minimum ESR is shown. The coil types are shown in Figure 15B. The numbers 1 through 4 represent SC, CSRC, HSRC, and FSRC.

[0069] The performance capabilities of the complete coil shown in Figure 15A are integrated into a multi-receiver system. The complete end-to-end system-level design results, showing the power dissipation at each individual stage, are shown in Figure 16, similar to the trend seen when thick solid-core ferriteless receivers are used for non-metallic receivers. The optimal design is B = 21 μT, resulting in a power dissipation of 6.94 W when 100 W is transferred to two receivers. Note that the fabricated transmitter is configured with B = 20 μT, resulting in a power dissipation closer to 6.99 W. The receiver is optimized for B = 20 μT, accounting for the slight deviation from the optimum point.

[0070] The design results for the metal-bodied laptop receiver are as follows: s =1.6μH, C s =360pF, ESR=0.18Ω, V o =31.5V. Target V o The receiving coil structure is selected as FSRC, and ri =5.47cm, l ro =8.89cm, w r = 1.23 mm, and n r =2.

[0071] Simulation and experimental verification FEA simulation results The proposed coil is simulated using Ansys HFSS. The top view of the schematic in the simulation is shown in Figure 17. The lower layer viewed from below appears identical to the upper layer due to the symmetrical structure.

[0072] The impedance curve of the FSRC coil is shown in Figure 18, imported directly from HFSS, and shows the series LC resonance. The Y-axis is impedance. The X-axis is the frequency range from 5.5 to 8.5 MHz. The simulated resonant frequency is 6.60 MHz (-0.5%). Another simulation was performed at 1 kHz, and the capacitance was extracted to be 378 pF (+5%). From the simulated resonant frequency and capacitance, the inductance was calculated to be 1.54 μH (-3.8%), demonstrating the accuracy of the modeling. A simulation of just the FSRC coil, with the ferrite and copper removed, was also performed. The results are summarized in Figure 20D and Table I and demonstrate high accuracy. ESR measurements of the FSRC with ferrite are not accurate due to additional ferrite losses that are not modeled.

[0073] In addition to a two-turn rectangular coil that maximizes system efficiency, a four-turn circular geometry has been studied to compare the E-fields for both the FSRC and CSRC. A schematic of the coils and the calculated longitudinal potentials are shown in Figure 19. Based on the calculations, the FSRC exhibits a significantly reduced E-field strength.

[0074] The FEA simulation results are shown in Figures 20A-20C. The FSRC has significantly lower dielectric loss compared to the CSRC, which indicates a reduced E-field within the dielectric.

[0075] Experimental verification To validate the coil design, an FSRC was fabricated using Rogers 3003 low-loss PCB laminate, as shown in Figure 21A. The impedance parameters of the coil were measured using an Agilent 4294A impedance analyzer and compared to the modeled and simulated predictions. As shown in Figure 20D and Table I, the measured results are in good agreement with the FEA simulations.

[0076] Figure 21B shows the experimental setup, where the FSRC is implemented with the proposed rectifier and tested in a 100W 6.78MHz wireless charging station as shown in Figure 21B. The FSRC is implemented with one 50W receiver used to power an aluminum-bodied laptop, and a second 50W receiver used to power a plastic-bodied computer monitor uses a ferrite-free solid-core coil.

[0077] System efficiency is defined as the total DC output power from all receivers divided by the DC input power at the transmitter side. The measured DC voltage and power at the full-load operating point are summarized in Figure 20E and Table II, along with a comparison with the model prediction. The measured power loss was 7.94 W compared to the calculated value of 6.99 W, proving the accuracy of the system modeling and design. Additional losses may be caused by the ferrite. The loss tangent of ferrite is typically less than 2%. However, detailed modeling of how the power loss varies with B is not provided to accurately quantify the ferrite losses. Another possible reason is that ferrite increases the ESR of the FSRC coil, as shown in the simulation.

[0078] The measured system efficiency is 92.7%. The loss breakdown at this operating point is shown in Figure 22.

[0079] conclusion This paper describes a self-resonant coil design for WPT charging of mobile electronic devices such as laptops. The structure achieves high Q, low E field, and a thin profile. The design results are experimentally verified for the proposed FSRC. We detail the systematic design of a multi-receiver system that wirelessly charges both a laptop and a computer monitor, and a complete prototype of the FSRC is experimentally shown to achieve high efficiency.

[0080] It will be understood that various details of the presently disclosed subject matter can be changed without departing from the scope of the presently disclosed subject matter. Further, the foregoing description is for purposes of illustration only, and not limitation.

[0081] References [1] J. Li, R. Qin, J. Sun, and D. Costinett, “Systematic design of a 100W 6.78-MHz wireless charging station covering multiple devices and a large charging area,” IEEE Transactions on Power Electronics, vol. 37, no. 4, pp. 4877-4889, 2022. [2] NS Jeong and F. Carobolante, “Wireless charging of a metal-body device,” IEEE Transactions on Microwave Theory and Techniques, vol. 65, no. 4, pp. 1077-1086, 2017. [3] J.H. Kim and C.-H. Ahn, “Method to reduce metal plate effect between transmitter and receiver in wireless power transfer system,” IEEE Antennas and Wireless Propagation Letters, vol. 17, no. 4, pp. 587-590, 2018. [4] N. S. Jeong, S. Kim, H.-J. Lee, and J. H. Kim, “Wireless charging of a metal-encased device,” IEEE Transactions on Antennas and Propagation, vol. 70, no. 1, pp. 654-663, 2022. [5] S. Yang, J. Narayan, J. Rosenfeld, K. Stevens, and P. Chewning, “Chassis design for wireless-charging coil integration for computing systems,” U.S. Patent US10003218B2, Dec. 20, 2014. [6] S. Yang, E. B. Cooper, E. Elkhouly, J. K. Narayan, and S. Ren, “Low emission coil topology for wireless charging,” United Kingdom Patent GB2533695A, Nov. 23, 2015. [7] A. L. F. Stein, P. A. Kyaw, and C. R. Sullivan, “High-Q self-resonant structure for wireless power transfer,” pp. 3723-3729, 2017. [8] J. Li and D. Costinett, “Analysis and design of a series self-resonant coil for wireless power transfer,” in 2018 IEEE Applied Power Electronics Conference and Exposition (APEC). IEEE, 2018, pp. 1052-1059. [9] R. Qin, J. Li, and D. Costinett, “A 6.6-kw high-frequency wireless power transfer system for electric vehicle charging using multilayer nonuniform self-resonant coil at mhz,” IEEE Transactions on Power Electronics, vol. 37, no. 4, pp. 4842-4856, 2022.

[10] S. S. Mohan, M. del Mar Hershenson, S. P. Boyd, and T. H. Lee, “Simple accurate expressions for planar spiral inductances,” IEEE Journal of Solid-State Circuits, vol. 34, no. 10, pp. 1419-1424, 1999.

[11] C. R. Sullivan and L. Beghou, “Design methodology for a high-Q self-resonant coil for medical and wireless-power applications,” in 14th Workshop on Control and Modeling for Power Electronics (COMPEL). IEEE, 2013, pp. 1-8.

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Claims

1. 1. A series self-resonant coil structure for wireless power transfer, comprising: a first conductive layer configured in a first planar spiral array, the first conductive layer including a first terminal; a second conductive layer configured in a second planar spiral array, the second conductive layer including a second terminal; a dielectric layer disposed between the first conductive layer and the second conductive layer; Equipped with the first conductive layer, the second conductive layer, and the dielectric layer are configured to create a repeating series LC connection between the first terminal and the second terminal; the first conductive layer includes at least one discontinuity, and the second conductive layer is continuous at the at least one discontinuity inverted about the dielectric layer; Coil structure.

2. 2. The coil structure of claim 1, comprising a plurality of parasitic capacitors connected to the first conductive layer and the second conductive layer and configured to compensate a voltage potential of one or more portions of the first planar spiral array and the second planar spiral array.

3. The coil structure of claim 2 , wherein the plurality of parasitic capacitors are disposed on alternating turns of the first conductive layer and the second conductive layer.

4. The coil structure of claim 2 , wherein the plurality of parasitic capacitors are disposed in each half turn of the first conductive layer and the second conductive layer.

5. The coil structure of claim 1 , wherein the first conductive layer and the second conductive layer comprise an alternating symmetrical structure.

6. one or more additional conductive layers arranged in a planar spiral array; one or more additional dielectric layers disposed between the one or more additional conductive layers and adjacent conductive layers; The coil structure of claim 1 , comprising:

7. 10. The coil structure of claim 1, comprising a ferrite shield arranged on a side of the first conductive layer opposite the dielectric layer, the ferrite shield configured to protect against magnetic coupling and reduce interference with adjacent objects.

8. The coil structure of claim 1 comprising an AC power source connected to the first terminal and the second terminal.

9. 1. A system for wireless power transmission, comprising: Power supply, A transmitting coil; a control circuit configured to wirelessly power a receiving device by applying power from the power source to the transmitting coil; and Equipped with The transmitting coil is a first conductive layer configured in a first planar spiral array, the first conductive layer including a first terminal; a second conductive layer configured in a second planar spiral array, the second conductive layer including a second terminal; a dielectric layer disposed between the first conductive layer and the second conductive layer; A series self-resonant coil structure comprising: the first conductive layer, the second conductive layer, and the dielectric layer are configured to create a repeating series LC connection between the first terminal and the second terminal; the first conductive layer includes at least one discontinuity, and the second conductive layer is continuous at the at least one discontinuity inverted about the dielectric layer; system.

10. 10. The system of claim 9, comprising a plurality of parasitic capacitors connected to the first conductive layer and the second conductive layer and configured to compensate a voltage potential of one or more portions of the first planar spiral array and the second planar spiral array.

11. The system of claim 10 , wherein the plurality of parasitic capacitors are disposed on alternating turns of the first conductive layer and the second conductive layer.

12. 11. The system of claim 10, wherein the plurality of parasitic capacitors are disposed in each half-turn of the first conductive layer and the second conductive layer.

13. 10. The system of claim 9, wherein the first conductive layer and the second conductive layer comprise alternating symmetrical structures.

14. one or more additional conductive layers arranged in a planar spiral array; one or more additional dielectric layers disposed between the one or more additional conductive layers and adjacent conductive layers; The system of claim 9 , comprising:

15. 10. The system of claim 9, comprising a ferrite shield arranged on a side of the first conductive layer opposite the dielectric layer, the ferrite shield configured to protect against magnetic coupling and reduce interference with adjacent objects.

16. 10. The system of claim 9, wherein the power source comprises an AC power source connected to the first terminal and the second terminal.

17. 1. A method for wireless power transfer, the method comprising: Detecting an initiation of wireless power transmission to a receiving device; applying power from a power source to a transmitting coil, the transmitting coil comprising: a first conductive layer configured in a first planar spiral array, the first conductive layer including a first terminal; a second conductive layer configured in a second planar spiral array, the second conductive layer including a second terminal; a dielectric layer disposed between the first conductive layer and the second conductive layer; applying power to the series self-resonant coil structure; Including, the first conductive layer, the second conductive layer, and the dielectric layer are configured to create a repeating series LC connection between the first terminal and the second terminal; the first conductive layer includes at least one discontinuity, and the second conductive layer is continuous at the at least one discontinuity inverted about the dielectric layer; method.

18. 20. The method of claim 17, wherein a transmit coil comprises a plurality of parasitic capacitors connected to the first conductive layer and the second conductive layer and configured to compensate a voltage potential of one or more portions of the first planar spiral array and the second planar spiral array.

19. 20. The method of claim 18, wherein the plurality of parasitic capacitors are disposed in alternating turns of the first conductive layer and the second conductive layer.

20. 20. The method of claim 18, wherein the plurality of parasitic capacitors are disposed in each half-turn of the first conductive layer and the second conductive layer.

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