High efficiency resonator coils for large gap wireless power transfer systems

Abstract

High efficiency resonator coils for large gap resonant wireless power transfer (WPT), and a coil design methodology are disclosed. Resonator coils comprise a coil topology defined by coil parameters in which turn dimensions, such as trace widths and spacings of each turn, are configured to reduce or minimize a variance of the z component of magnetic field, over an area of a charging plane at a specified distance, or distance range, from the coil. A Tx resonator coil comprises a capacitor arrangement of tuning and network-matching capacitors for improved coil-to-coil efficiency and end-to-end WPT system performance, e.g. for applications such as through-wall WPT, in the range of tens of watts to at least hundreds of watts. Planar resonator coil topologies are compatible with fabrication using low cost PCB technology, e.g. with multi-layer metal, to reduce losses and improve thermal performance.

1 . A resonator coil for a large gap resonant inductive wireless power transfer (WPT) system comprising:
 a dielectric substrate;   conductive traces patterned to define a coil topology comprising a plurality of n turns providing a specified inductance L, and   a capacitor arrangement comprising first and second series tuning capacitors C 2   a  and C 2   b  in first and second feed lines of the coil, a series matching capacitor C 1  at a mid-point of the coil, and a shunt capacitor C 3  connected across the feed lines between the series tuning capacitors C 2   a  and C 2   b  and turns of the coil.   
     
     
         2 . The resonator coil of  claim 1 , wherein:
 values of capacitors C 1 , C 2   a  and C 2   b  and C 3  are selected to provide a specified resonant frequency and input impedance.   
     
     
         3 . The resonator coil of  claim 1 , wherein the resonator coil is a transmitter coil, and values of capacitors C 1 , C 2   a  and C 2   b  and C 3  are selected to optimize: an efficiency of a power amplifier of the WPT system; a coil-to-coil efficiency for transmitter and receiver coils of the WPT system, and an end-to-end system efficiency. 
     
     
         4 . The resonator coil of  claim 1 , wherein the resonator coil is a transmitter coil and the values of capacitors C 1 , C 2   a  and C 2   b  and C 3  are selected for operation of the PA at or above a minimum required efficiency, or, to maximize efficiency of the PA. 
     
     
         5 . The resonator coil of  claim 1 , wherein the resonator coil is a transmitter coil, and the values of capacitors C 1 , C 2   a  and C 2   b  and C 3  are selected to reduce or optimize input reflection coefficient S 11 . 
     
     
         6 . The resonator coil of  claim 1 , wherein the resonator coil has a first input impedance Z TX   1  with C 2   a  and C 2   b  only, and a second input impedance Z TX   2  with C 1 , C 2   a  and C 2   b  and C 3 , wherein Z TX 2>Z TX   1  to reduce or minimize an input reflection coefficient S 11 . 
     
     
         7 . The resonator coil of  claim 1 , wherein the resonator coil has a first input impedance Z TX   1  with C 2   a  and C 2   b  only, and a second input impedance Z TX   2  with C 1 , C 2   a  and C 2   b  and C 3 , wherein Z TX 2>Z TX   1  to obtain a best efficiency point of operation of a power amplifier of the WPT system. 
     
     
         8 . The resonator coil of  claim 1 , wherein the inductance L is provided by first and second parts of the coil having inductances L 1  and L 2 , where L 1 +L 2 =L, and C 1  is placed between the first and second parts of the coil. 
     
     
         9 . The resonator coil of  claim 8 , wherein L 1 =L 2 . 
     
     
         10 . The resonator coil of  claim 1 , wherein the coil has a coil area A and each turn has turn dimensions comprising a conductive trace length, width and turn spacing;
 the turn dimensions being configured to provide a variance of the vertical magnetic field distribution over a target area of a charging plane spaced a distance D gap  from the plane of the coil, said variance being less than a reference variance;   wherein the reference variance is defined as a variance of the vertical magnetic field distribution over the target area of the charging plane spaced D gap  from the plane of a reference coil of corresponding coil area A, having a reference coil topology comprising n turns of uniform trace width and turn spacing.   
     
     
         11 . A resonator coil topology for a large gap resonant inductive wireless power transfer (WPT) system comprising:
 a coil of coil area A comprising a plurality of n turns, each turn having turn dimensions comprising a conductive trace length, width and turn spacing;   the turn dimensions being configured to provide a variance of the vertical magnetic field distribution over a target area of a charging plane spaced a distance D gap  from the plane of the coil, said variance being less than a reference variance;   wherein the reference variance is defined as a variance of the vertical magnetic field distribution over the target area of the charging plane spaced D gap  from the plane of a reference coil of corresponding coil area A, having a reference coil topology comprising n turns of uniform trace width and turn spacing; and   the turn dimensions of at least one turn differ from turn dimensions of the reference coil.   
     
     
         12 . A resonator coil for a large gap resonant inductive wireless power transfer (WPT) system comprising:
 a dielectric substrate;   conductive traces patterned to define a coil topology comprising a plurality of n turns over a coil area A;   each turn having turn dimensions comprising a conductive trace length, width and turn spacing;   the turn dimensions being configured to provide a variance of the vertical magnetic field distribution over a target area of a charging plane spaced a distance D gap  from the plane of the coil, said variance being less than a reference variance;   wherein the reference variance is defined as a variance of the vertical magnetic field distribution over the target area of the charging plane spaced D gap  from the plane of a reference coil of a corresponding coil area A, having a reference coil topology comprising n turns of uniform trace width and turn spacing.   
     
     
         13 . The resonator coil topology of  claim 12 , wherein the turn dimensions of at least one turn are configured to provide a coil topology that differs from the reference coil topology. 
     
     
         14 . The resonator coil topology of  claim 12 , wherein the turn dimensions of at least one turn are configured to provide a coil topology comprising at least one of non-uniform trace widths and non-uniform turn spacings. 
     
     
         15 . The resonator coil topology of  claim 12 , wherein the turn dimensions of each turn are individually configured to provide a coil topology comprising at least one of non-uniform trace widths and non-uniform turn spacings. 
     
     
         16 . The resonator coil topology of  claim 12 , wherein the turn dimensions of each turn are individually configured to minimize said variance. 
     
     
         17 . The resonator coil topology of  claim 12 , wherein said variance is ≤15%. 
     
     
         18 . The resonator coil topology of  claim 12 , wherein said variance is a relative standard deviation of ≤15%. 
     
     
         19 . The resonator coil topology of  claim 12 , configured for D gap  in a range of 50 mm to 500 mm. 
     
     
         20 . The resonator coil of  claim 12 , configured for D gap  in a range of −200 mm. 
     
     
         21 . The resonator coil of  claim 12 , configured for D gap  in a range of 200 mm±10%. 
     
     
         22 . The resonator coil of  claim 12 , configured for through-wall WPT. 
     
     
         23 . The resonator coil of  claim 12 , configured for through-wall WPT of power in a range of tens of watts to at least hundreds of watts. 
     
     
         24 . A resonator coil for a large gap resonant inductive wireless power transfer (WPT) system comprising:
 a dielectric substrate;   conductive traces patterned to define a coil topology comprising a plurality of n turns over a coil area A;   each turn having turn dimensions comprising a conductive trace length, width and turn spacing;   the turn dimensions being non-uniform and configured to provide a variance of the vertical magnetic field distribution over a target area of a charging plane spaced a distance D gap  from the plane of the coil, said variance being ≤15%.   
     
     
         25 . The resonator coil of  claim 24 , comprising a capacitor arrangement comprising first and second series tuning capacitors C 2   a  and C 2   b  in first and second feed lines of the coil, a series matching capacitor C 1  at a mid-point of the coil, and a shunt capacitor C 3  connected across the feed lines between the series tuning capacitors C 2   a  and C 2   b  and turns of the coil. 
     
     
         26 . The resonator coil of  claim 12 , wherein turns of the reference coil are substantially square or rectangular, with rounded corners. 
     
     
         27 . A transmitter (Tx) for a resonant inductive wireless transfer (WPT) system comprising a power amplifier (PA) and a Tx resonator coil;
 wherein the Tx resonator coil comprises a dielectric substrate and conductive traces patterned to define a coil topology of a specified inductance L, and   at least one of:   a) a capacitor arrangement comprising first and second series tuning capacitors C 2   a  and C 2   b  at first and second feed ports of the coil, a series matching capacitor C 1  at a mid-point of the coil, and a shunt capacitor C 3  connected across feed lines between the series tuning capacitors C 2   a  and C 2   b  and turns of the coil; wherein:   values of capacitors C 1 , C 2   a  and C 2   b  and C 3  provide a specified resonant frequency and input impedance for operation of the PA at a required (or maximum) efficiency of the PA; and   b) the resonator coil topology comprises a coil area A comprising a plurality of n turns, each turn having turn dimensions comprising a conductive trace length, width and turn spacing;   the turn dimensions being configured to provide a variance of the vertical magnetic field distribution over a target area of a charging plane spaced a distance D gap  from the plane of the coil, said variance being less than a reference variance;   wherein the reference variance is defined as a variance of the vertical magnetic field distribution over the target area of the charging plane spaced D gap  from the plane of a reference coil of corresponding area A, having a reference coil topology comprising n turns of uniform trace width and turn spacing.   
     
     
         28 . The transmitter of  claim 27 , wherein the capacitor arrangement is tuned for operation of the PA at a point of maximum efficiency. 
     
     
         29 . The transmitter of  claim 27 , wherein the capacitor arrangement is tuned for operation of the PA at ≥90% efficiency. 
     
     
         30 . The transmitter of  claim 27 , wherein said variance is ≤15%. 
     
     
         31 . The transmitter of  claim 27 , configured for through-wall WPT. 
     
     
         32 . The transmitter of  claim 27 , configured for through wall WPT over a gap distance D gap  in a range from 50 mm to 500 mm. 
     
     
         33 . The transmitter of  claim 27  configured for through wall WPT in a power range from tens of watts to at least hundreds of watts. 
     
     
         34 . The transmitter of  claim 27 , wherein the PA is implemented with GaN transistors and is capable of operating at ≥90% efficiency. 
     
     
         35 . A resonant inductive wireless transfer (WPT) system comprising a power amplifier (PA) and a Tx resonator coil as defined in  claim 27 , and a Rx resonator coil, the Rx resonator coil having the same coil topology as the Tx resonator coil. 
     
     
         36 . A method of configuring the capacitor arrangement for the resonator coil of  claim 1  comprising:
 selecting a value of C 1  to make C 1  and the inductance L of the Tx coil resonate at the required frequency; 
 setting C 2   a  and C 2   b  to be equal and have a value C 2   a =C 2   b= 2*C 1 ; 
 using an Rx coil, tuning the value of C 3  a target specification such as a best efficiency point of the power amplifier (PA) of the transmitter; 
 measuring an S 11  parameter (i.e. input reflection coefficient); 
 tuning C 3  and C 2   a , C 2   b  so that the Tx coil resonates at the required frequency and so that the Tx impedance Z Tx  is in range for operation of the PA at an efficiency in a range from a is minimum required efficiency to a maximum efficiency. 
 
     
     
         37 . A method of configuring a resonator coil, comprising:
 obtaining a population of parameters (a 1 , b 1 , . . . a n , b n ) initial  defining an initial (reference) coil topology to be optimized,   the population of parameters (a 1 , b 1  . . . a n , b n ) initial  comprising: a maximum coil dimension, a number of turns, a minimum spacing between turns, a minimum trace width, et al. for each turn;   obtaining a target specification, comprising:   selecting a gap distance D gap  from the coil to a charging surface;   selecting a charging area Area charging  of the charging surface relative to an area of the coil Area coil ;   selecting a Figure of Merit (FOM) which is derived from a vertical magnetic field distribution H z  over the charging area Area charging  of the charging surface at gap distance D gap  from the coil;
 a) for the initial population of parameters (a 1 , b 1  . . . a n , b n ), computing the vertical magnetic field distribution H z  over the charging plane; 
 b) computing the FOM based on a fitness function F(H z ) over said area of the charging plane; and 
 c) systematically changing the population of parameters, and for each of a plurality of m populations of parameters (a 1 , b 1  . . . a n , b n ) m  where m=2 to m=M, computing H z  over the charging plane and computing the fitness function F(H z ) m  over the charging plane; 
 d) when the value of the fitness function F(H z ) for an mth population of parameters (a 1 , b 1  . . . a n , b n ) m  meets a target specification, storing the mth population of parameters (a 1 , b 1  . . . a n , b n ) m  as a target population of parameters; 
 e) outputting the set of parameters (a 1 , b 1  . . . a n , b n ) m  corresponding to the target value of the fitness function F(H z ), to define a coil topology meeting the target specification having a coil distribution comprising said dimensions, trace widths and spacings of each of the n turns. 
   
     
     
         38 . The method of  claim 37  wherein the FOM is a variance of the vertical magnetic field distribution H z  over a target area of a charging plane spaced a distance D gap  from the plane of the coil. 
     
     
         39 . The method of  claim 38  wherein the target specification comprises minimum value of said variance.