Polyphase wireless electric field power transfer system, transmitter and receiver

Abstract

The transmitter includes a multi-phase RF converter configured to output a plurality of sinusoidal RF power signals, and a multi-phase resonator configured to receive the plurality of sinusoidal RF power signals and resonate a plurality of inductors and capacitive electrodes at a resonant frequency in a plurality of phases to transfer power via resonant electric field coupling.

Description

[Technical field]

[0001] Related Applications This application claims the benefit of U.S. Provisional Patent Application No. 62 / 875,043, filed July 17, 2019, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates generally to wireless power transfer, and more particularly to wireless electric field power transfer systems and transmitters and receivers therefor. [Background technology]

[0003] Various wireless power transfer systems are known. A typical wireless power transfer system includes a power source electrically connected to a wireless power transmitter, and a wireless power receiver electrically connected to a load. In a magnetic induction system, the transmitter has an inductor that transfers electrical energy from the power source to an inductor in the receiver. Power transfer occurs due to magnetic field coupling between the inductors of the transmitter and receiver. The range of those magnetic induction systems is limited, and the inductors of the transmitter and receiver need to be in optimal alignment for effective power transfer. There are also resonant magnetic systems in which power is transferred due to magnetic field coupling between the inductors of the transmitter and receiver. However, in resonant magnetic systems, the inductor is resonated using at least one capacitor. The range of power transfer in resonant magnetic systems is increased through the range of the magnetic induction system, and alignment issues are corrected. Although electromagnetic energy is generated in magnetic induction and resonant magnetic systems, the majority of the power transfer occurs through magnetic fields. Little, if any, power is transferred through electrical induction or resonant electrical induction.

[0004] In an electrical induction system, the transmitter and receiver have capacitive electrodes. Power transfer occurs due to coupling of an electric field between the capacitive electrodes of the transmitter and receiver. Similar to resonant magnetic systems, there are resonant electrical systems in which the capacitive electrodes of the transmitter and receiver are resonated using at least one inductor. Resonant electrical systems increase the range of power transfer compared to electrical induction systems and correct alignment issues. Although electromagnetic energy is generated in electrical induction and resonant electrical systems, the majority of power transfer occurs via electric fields. Little, if any, power is transferred via magnetic induction or resonant magnetic induction. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Pat. No. 9,653,948 [Patent Document 2] U.S. Patent No. 9,979,206 Summary of the Invention [Problem to be solved by the invention]

[0006] Although wireless power transfer techniques are known, improvements are desired. It is therefore an object to provide a novel wireless electric field power transfer system, a transmitter and a receiver therefor, and a method for wirelessly transmitting power. [Means for solving the problem]

[0007] It should be appreciated that this Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description of the Embodiments, and is not intended to be used to limit the scope of the claimed subject matter.

[0008] Thus, in one aspect, a transmitter is provided that includes a multi-phase radio frequency (RF) converter configured to output a plurality of RF power signals, and a multi-phase resonator configured to receive a plurality of sinusoidal RF power signals and resonate a plurality of inductors and capacitive electrodes at a resonant frequency in a plurality of phases to transfer power via resonant electric field coupling.

[0009] In one or more embodiments, the capacitive electrode has multiple-fold rotational symmetry. In one or more embodiments, the axis of multiple-fold rotational symmetry is perpendicular to the major surface of the capacitive electrode about the center of curvature of the capacitive electrode.

[0010] In one or more embodiments, the multi-phase RF converter includes a multi-phase RF inverter including a plurality of transistors, each transistor electrically connected to an inductor of a multi-phase transmit resonator.

[0011] In one or more embodiments, the transmitter further includes a power supply electrically connected to the multi-phase RF converter, the power supply configured to output a direct current (DC) power signal.

[0012] In one or more embodiments, the multi-phase transmit resonator is balanced.

[0013] In one or more embodiments, the multi-phase transmit resonator includes three inductors and three capacitive electrodes.

[0014] In another aspect, a receiver is provided that includes a multi-phase resonator including a plurality of inductors and capacitive electrodes configured to resonate at a resonant frequency to extract power via resonant electric field coupling and output a plurality of sinusoidal radio frequency (RF) power signals, where the plurality of inductors and capacitive electrodes resonate at a plurality of phases; and a multi-phase rectifier configured to receive the plurality of sinusoidal RF power signals and output a direct current (DC) power signal.

[0015] In one or more embodiments, the capacitive electrode has multiple-fold rotational symmetry. In one or more embodiments, the axis of multiple-fold rotational symmetry is perpendicular to the major surface of the capacitive electrode about the center of curvature of the capacitive electrode.

[0016] In one or more embodiments, the multi-phase rectifier includes multiple pairs of diodes, each pair of diodes electrically connected to an inductor of a multi-phase receiver resonator.

[0017] In one or more embodiments, the receiver further includes a load configured to receive the DC power signal output by the multi-phase rectifier.

[0018] In one or more embodiments, the multiphase receiver resonator is balanced.

[0019] In one or more embodiments, the multi-phase receiver resonator includes three inductors and three capacitive electrodes.

[0020] In another aspect, a system is provided that includes a transmitter including a multi-phase RF converter configured to output a plurality of sinusoidal RF power signals; and a multi-phase transmit resonator configured to receive the plurality of sinusoidal RF power signals and resonate a plurality of transmit inductors and transmit capacitive electrodes at a resonant frequency at a plurality of phases to transfer power via resonant electric field coupling; and a receiver including a multi-phase receive resonator including a plurality of receive inductors and receive capacitive electrodes configured to resonate at a resonant frequency to extract power via resonant electric field coupling and output the plurality of sinusoidal RF power signals, the plurality of receive inductors and receive capacitive electrodes resonating at a plurality of phases; and a multi-phase rectifier configured to receive the plurality of sinusoidal RF power signals and output a direct current (DC) power signal.

[0021] In one or more embodiments, the transmit capacitive electrode has multiple-fold rotational symmetry. In one or more embodiments, the axis of multiple-fold rotational symmetry is perpendicular to the major surface of the capacitive electrode about the center of curvature of the capacitive electrode.

[0022] In one or more embodiments, the receiving capacitive electrode has multiple-fold rotational symmetry, hi one or more embodiments, the axis of multiple-fold rotational symmetry is perpendicular to the major surface of the capacitive electrode about the center of curvature of the capacitive electrode.

[0023] In one or more embodiments, the multi-phase RF converter includes a multi-phase RF inverter including a plurality of transistors, each transistor electrically connected to an inductor of a multi-phase transmit resonator.

[0024] In one or more embodiments, the transmitter further includes a power supply electrically connected to the multi-phase RF converter, the power supply configured to output a direct current (DC) power signal.

[0025] In one or more embodiments, the multi-phase transmit resonator is balanced.

[0026] In one or more embodiments, the multi-phase transmit resonator includes three transmit inductors and three transmit capacitive electrodes.

[0027] In one or more embodiments, the multi-phase rectifier includes multiple pairs of diodes, each pair of diodes electrically connected to an inductor of a multi-phase receiver resonator.

[0028] In one or more embodiments, the receiver further includes a load configured to receive the DC power signal output by the multi-phase rectifier.

[0029] In one or more embodiments, the multiphase receiver resonator is balanced.

[0030] In one or more embodiments, the multi-phase transmit resonator includes three transmit inductors and three transmit capacitive electrodes.

[0031] In another aspect, there is provided a method of wirelessly transmitting power via electric field coupling, comprising: converting an input power signal into a multi-sine wave RF power signal at a multi-phase RF converter of any one of the described transmitters; receiving the multi-sine wave RF power signal at a multi-phase resonator of the transmitter; resonating a pair of transmitting inductors and capacitive electrodes of the multi-phase resonator of the transmitter to generate an electric field; and extracting power by a multi-phase RF resonator of any one of the described receivers, the multi-phase RF resonator of the receiver being positioned within the generated electric field.

[0032] In one or more embodiments, the method further includes outputting the received sinusoidal RF power signal to a multi-phase rectifier of the receiver and rectifying the received sinusoidal RF power signal into a rectified signal.

[0033] In one or more embodiments, the rectified signal is a direct current (DC) power signal.

[0034] In one or more embodiments, the input power signal is a DC power signal.

[0035] In one or more embodiments, resonating the pair of transmitting inductors and capacitive electrodes includes resonating the pair at a resonant frequency of a multi-phase resonator of the transmitter.

[0036] In one or more embodiments, resonating the transmitting inductor and capacitive electrode pair includes resonating the i-th transmitting inductor and capacitive electrode pair at (i-1)×360 / n, where n is the number of sinusoidal RF power signals.

[0037] In the described embodiment, exemplary resonant frequencies include 13.56 megahertz and 27.12 megahertz.

[0038] In the described embodiments, the electric field coupling may be strongly (or tightly) or loosely coupled. Loose coupling is when the transmitter and receiver electrodes are separated by air, i.e., there is an air core between the transmitter and receiver.

[0039] The various elements of the described embodiments may be combined in any number of ways as will be appreciated by those of skill in the art.

[0040] Embodiments will now be described more fully with reference to the accompanying drawings. [Brief description of the drawings]

[0041] [Figure 1] FIG. 1 is a block diagram of a wireless power transfer system. [Diagram 2] 1 is a schematic layout of a wireless resonant electric field power transfer system. [Diagram 3] 1 is a block diagram of a wireless power transfer system according to an aspect of the disclosure. [Figure 4] 4 is a schematic layout of the wireless power transfer system of FIG. 3. [Figure 5A] 1 is a schematic layout of a wireless power transfer system in accordance with an aspect of the disclosure. [Figure 5B] 5B is a graph of the load voltage output by the multi-phase rectifier of the wireless power transfer system of FIG. 5A. [Figure 6] FIG. 5B is a plan view of a transmitting capacitive electrode of the wireless power transfer system of FIG. 5A. [Figure 7] FIG. 5B is a plan view of another embodiment of a transmitting capacitive electrode of the wireless power transfer system of FIG. 5A. [Figure 8] 8 is another plan view of the transmit capacitive electrode of FIG. 7. [Figure 9] FIG. 5B is a plan view of another embodiment of the transmitting and receiving capacitive electrodes of the wireless power transfer system of FIG. 5A. [Figure 10] 10 is a graph of radio frequency (RF) efficiency of the wireless power transfer system of FIG. 5A with the transmitting and receiving capacitive electrodes of FIG. [Figure 11]FIG. 5B is a plan view of another embodiment of a transmitting capacitive electrode of the wireless power transfer system of FIG. 5A. [Figure 12] FIG. 1 is a perspective view of a wireless power transfer system according to an aspect of the disclosure. [Figure 13] 13 is a graph of the ratio of current sum to current magnitude as a percentage for 0 to 120 degrees of rotation for the transmitting and receiving capacitive electrodes of the wireless power transfer system of FIG. 12. [Figure 14] 13 is a graph of the phase of the current signal on each receiving segment as a function of the angular position of the wireless power transfer system of FIG. 12. [Figure 15] 13 is a graph of radio frequency (RF) efficiency of the wireless power transfer system of FIG. 12 as a function of angular rotation. [Figure 16] 13 is a graph of the real part of the impedance present at each transmitting capacitive electrode of the wireless power transfer system of FIG. 12 as a function of angular rotation. [Figure 17] 13 is a graph of the imaginary part of the impedance present at each transmitting capacitive electrode of the wireless power transfer system of FIG. 12 as a function of angular rotation. [Figure 18] 13 is a graph of RF efficiency of the wireless power transfer system of FIG. 12 and another wireless power transfer system as a function of vertical separation between the transmit and receive resonators. [Figure 19] FIG. 5B is a plan view of another embodiment of a transmitting capacitive electrode of the wireless power transfer system of FIG. 5A. [Figure 20] FIG. 20 is a plan view of another embodiment of the transmitting capacitive electrode of FIG. 19. [Figure 21] FIG. 1 is a perspective view of a wireless power transfer system according to an aspect of the disclosure. [Figure 22] 22A-E are plan views of other embodiments of the capacitive electrodes of the wireless power transmission system of FIG. [Figure 23] 23A-I are plan views of other embodiments of the capacitive electrodes of the wireless power transmission system of FIG. [Figure 24A] FIG. 6 is a side elevation view of another embodiment of a capacitive electrode of the wireless power transfer system of FIG. [Figure 24B]FIG. 24B is a perspective view of the capacitive electrode of FIG. 24A. [Figure 25A] FIG. 24B is a side elevational view of the capacitive electrodes of FIG. 24A forming the transmit and receive capacitive electrodes. [Figure 25B] FIG. 24B is a side elevational view of the capacitive electrode of FIG. 24A forming another embodiment of the transmit and receive capacitive electrodes. [Figure 26] 6 is a perspective view of another embodiment of a capacitive electrode of the wireless power transfer system of FIG. [Figure 27] 6 is a perspective view of another embodiment of a capacitive electrode of the wireless power transfer system of FIG. [Figure 28A] FIG. 1 is a side elevation view of a wireless power transfer system according to an aspect of the disclosure. [Figure 28B] FIG. 28B is a plan view of the wireless power transfer system of FIG. 28A. [Figure 28C] FIG. 28B is another plan view of the wireless power transfer system of FIG. 28A. [Figure 29A] 29B is a graph of the radio frequency (RF) efficiency of the wireless power transfer system of FIG. 29A as a function of angular rotation. [Figure 29B] 29B is a graph of the received rectified voltage of the wireless power transfer system of FIG. 29A as a function of angular rotation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] The following detailed description of certain embodiments, together with the summary above, will be better understood when read in conjunction with the accompanying drawings. As will be appreciated, the same reference numerals are used to refer to the same elements throughout the description and the drawings. As used herein, an element or feature described in the singular should be understood as not necessarily excluding a plurality of elements or features. Furthermore, reference to "one example" or "one embodiment" is not intended to be interpreted as excluding the existence of additional examples or embodiments that also incorporate the described elements or features of that one example or embodiment. Moreover, unless expressly stated to the contrary, an example or embodiment that "comprises," "has," or "includes" an element or feature or elements or features having a particular property may further include additional elements or features that do not have that particular property. It will also be appreciated that the terms "comprise," "have," and "include" mean "including but not limited to," and the terms "comprise," "have," or "include" have equivalent meanings.

[0043] As used herein, the term "and / or" may include any and all combinations of one or more of the associated listed elements or features.

[0044] When an element or feature is referred to as "on," "attached," "connected," "coupled with," "in contact with," etc., another element or feature, the element or feature may be directly on, attached to, connected to, coupled with, or in contact with the other element or feature, or intermediate elements may be present as well. In contrast, when an element or feature is referred to as "directly on," "directly attached," "directly connected," "directly coupled with," or "in direct contact with" another element or feature, there are no intermediate elements or features present.

[0045] It will be appreciated that spatially related terms such as "lower," "below," "lower," "upper," "upper," "superior," "front," and "rear" may be used herein to facilitate describing the relationship of an element or feature to another element or feature as depicted in the figures. However, spatially related terms may emphasize different orientations in use or operation in addition to the orientation depicted in the figures.

[0046] Reference herein to an example means that one or more features, structures, elements, components, properties, and / or operational steps described in connection with the example are included in the example in at least one embodiment and / or implementation of the subject matter according to this disclosure. Thus, the phrases "one example," "another example," and similar language throughout this disclosure may, but do not necessarily, refer to the same example. Moreover, subject matter characterizing any one example may, but does not necessarily, include subject matter characterizing any other example.

[0047] References herein to "comprised" refer to an actual state of configuration that fundamentally ties an element or feature to the physical characteristics of the element or feature that precedes the term "comprised of."

[0048] Unless otherwise indicated, the terms "first," "second," etc. are used herein merely as labels and are not intended to impose any sequential, positional, or hierarchical requirements on the items to which they refer. Moreover, a reference to a "second" item does not require or preclude the presence of a lower-numbered item (e.g., a "first" item) and / or a higher-numbered item (e.g., a "third" item).

[0049] As used herein, the terms "approximately," "substantially," and "about" refer to an amount close to a stated amount that still performs a desired function or achieves a desired result. For example, the terms "approximately" and "about" may refer to an amount that is within engineering tolerances readily recognized by one of ordinary skill in the art, e.g., less than 10%, less than 5%, less than 1%, less than 0.1%, or less than 0.01% of the stated amount.

[0050] 1 illustrates a wireless power transfer system generally identified by reference numeral 100. The wireless power transfer system 100 includes a transmitter 110 including a power source 112 electrically connected to a transmitting element 114, and a receiver 120 including a receiving element 124 electrically connected to a load 122. Power is transferred from the power source 112 to the transmitting element 114. Power is transferred from the transmitting element 114 to the receiving element 124 via resonant or non-resonant electric or magnetic field coupling. Power is transferred from the receiving element 124 to the load 122.

[0051] In one example embodiment, the wireless power transfer system may take the form of a resonant electric field wireless power transfer system. Figure 2 illustrates a resonant electric field wireless power transfer system, generally identified by reference numeral 200, such as that described in U.S. Patent No. 9,653,948, filed Sep. 7, 2012, by Polu et al., the relevant portions of which are incorporated herein by reference.

[0052] The resonant electric field wireless power transfer system 200 includes a transmitter 210 including a power source 212 electrically connected to a transmit resonator 214. The transmit resonator 214 includes a pair of laterally spaced, elongated transmit capacitive electrodes 216, each of which is electrically connected to the power source 212 via a high quality factor (Q) transmit inductor 218. The system 200 includes a receiver 220 including a receive resonator 224 electrically connected to a load 222. The receive resonator 224 is tuned to the resonant frequency of the transmit resonator 214. The receive resonator 224 includes a pair of laterally spaced, elongated receive capacitive electrodes 226, each of which is electrically connected to the load 222 via a high Q receive inductor 228.

[0053] In this embodiment, inductors 218 and 228 are ferrite core inductors, although one skilled in the art will recognize that other cores are possible.

[0054] In this embodiment, each of the transmit capacitive electrodes 216 and receive capacitive electrodes 226 includes an elongated element formed from a conductive material. The transmit capacitive electrodes 216 are coplanar. The receive capacitive electrodes 226 are coplanar. In this embodiment, the transmit capacitive electrodes 216 and receive capacitive electrodes 226 are in parallel planes. In this embodiment, the transmit capacitive electrodes 216 and receive capacitive electrodes 226 are in the form of generally rectangular, planar plates.

[0055] Although the transmit capacitive electrodes 216 and receive capacitive electrodes 226 have been described as laterally spaced, elongated electrodes, one skilled in the art will recognize that other configurations are possible, including, but not limited to, concentric, coplanar, circular, elliptical, disk, etc. Other suitable electrode configurations are described in U.S. Patent No. 9,979,206, filed September 4, 2015, by Nyberg et al., the relevant portions of which are incorporated herein by reference.

[0056] Although in FIG. 2 inductors 218 and 228 are shown as being connected in series with power source 212 and load 222, respectively, those skilled in the art will recognize that inductors 218 and 228 may also be connected in parallel with power source 212 and load 222, respectively.

[0057] During operation, power is transferred from the power source 212 to the transmit capacitive electrode 216 via the high-Q transmit inductor 218. In particular, the power signal from the power source 212 transmitted to the transmit capacitive electrode 216 via the high-Q transmit inductor 218 excites the transmit resonator 214, causing the transmit resonator 214 to generate an electric field. When a receiver 220, tuned to the same resonant frequency as the transmitter 210, is placed within the resonant electric field, the receive resonator 224 extracts power from the transmit resonator 214 via resonant electric field coupling. The extracted power is then transferred from the receive resonator 224 to the load 222. As the power transfer is highly resonant, the transmit capacitive electrode 216 and the receive capacitive electrode 226, respectively, do not need to be close or aligned together as is the case in non-resonant electric field power transfer systems. Although the transmit resonator may generate a magnetic field, little, if any, power is transferred via magnetic field coupling.

[0058] 3, there is shown a wireless power transfer system according to an embodiment of the disclosure, generally identified by reference numeral 300. The wireless power transfer system 300 includes a transmitter 302 and a receiver 304. The transmitter 302 is configured to transfer power to the receiver 304 via resonant electric field coupling, as described. The receiver 304 is configured to extract power from the transmitter 302 via resonant electric field coupling, as described.

[0059] The transmitter 302 includes a power source 306, a multi-phase RF converter 308, and a multi-phase transmit resonator 310. The power source 306 is electrically connected to the multi-phase RF converter 308. The power source 306 is configured to generate a direct current (DC) power signal. The power source 306 is configured to output the DC power signal to the multi-phase RF converter 308. The multi-phase RF converter 308 is electrically connected to the power source 306. The multi-phase RF converter 308 is electrically connected to the multi-phase transmit resonator 310. The multi-phase RF converter 308 is configured to convert the DC power signal into n sinusoidal RF power signals, where n is a positive integer greater than 2. In this embodiment, the multi-phase RF converter 308 is a multi-phase RF inverter. The sinusoidal RF power signals are shifted out of phase with each other. Each sinusoidal RF power signal is shifted 360 / n degrees out of phase with successive sinusoidal RF power signals. The phases are distributed such that when the first signal is at 0 degrees, the second signal is at 360 / n degrees, the third signal is at 2×360 / n degrees, and the i-th signal is at (i−1)×360 / n degrees. The n sinusoidal RF power signals are output from the multi-phase RF converter 308 to a multi-phase transmit resonator 310. The multi-phase transmit resonator 310 is configured to generate an electric field and transfer power via resonant electric field coupling, as described. A magnetic field may also be generated, but little, if any, power is transferred via resonant or non-resonant magnetic field coupling. The multi-phase transmit resonator 310 includes n electrode / inductor pairs, as described.

[0060] The receiver 304 includes a multi-phase receive resonator 312, a multi-phase rectifier 314, and a load 316. The multi-phase receive resonator 312 is configured to extract power from the multi-phase transmit resonator 310 via resonant electric field coupling, as described. Although a magnetic field may also be present, little, if any, power is extracted via resonant or non-resonant magnetic field coupling. The multi-phase receive resonator 312 is electrically connected to the rectifier 314. The multi-phase receive resonator 312 includes a plurality of capacitive electrode / inductor pairs, as described. The multi-phase receive resonator 312 includes n electrode / inductor pairs. The multi-phase receive resonator 312 is configured to output a plurality of sinusoidal RF power signals to the multi-phase rectifier 314. The multi-phase receive resonator 312 is configured to output n sinusoidal RF power signals to the multi-phase rectifier 314. The sinusoidal RF power signals are shifted out of phase with respect to each other. Each sinusoidal RF power signal is shifted 360 / n degrees out of phase with the other sinusoidal RF power signals. The phases are distributed such that when the first signal is at 0 degrees, the second signal is at 360 / n degrees, the third signal is at 2×360 / n degrees, and the i-th signal is at (i−1)×360 / n degrees. The multi-phase rectifier 314 is configured to convert the received n sinusoidal RF power signals into a DC power signal. The multi-phase rectifier 314 is electrically connected to a load 316. The multi-phase rectifier 314 outputs a DC power signal to the load 316. The load 316 is electrically connected to the multi-phase rectifier 314. The load 316 receives the DC power signal from the multi-phase rectifier 314.

[0061] 4, there is shown a circuit diagram of a wireless power transfer system 300. As previously mentioned, the wireless power transfer system 300 includes a transmitter 302 and a receiver 304. The transmitter 302 includes a power source 306, a multi-phase RF converter 308, and a multi-phase transmit resonator 310.

[0062] As previously mentioned, the power supply 306 is configured to generate a DC power signal. The power supply 306 is configured to output the DC power signal to the multi-phase RF converter 308.

[0063] The multi-phase RF converter 308 is configured to convert the DC power signal into n sinusoidal RF power signals. The multi-phase RF converter 308 includes n pairs of switches 402 and a controller (not shown). The pairs of switches 402 are arranged in parallel. Each pair of switches 402 outputs a sinusoidal RF power signal. Each sinusoidal RF power signal is shifted 360 / n degrees out of phase with the other sinusoidal RF power signals. The phases are distributed such that when the first signal is at 0 degrees, the second signal is at 360 / n degrees, the third signal is at 2×360 / n degrees, and the i-th signal is at (i−1)×360 / n degrees. The n sinusoidal RF power signals are output from the multi-phase RF converter 308 to the multi-phase transmit resonator 310.

[0064] In this embodiment, the switch 402 is a metal oxide semiconductor field effect transistor (MOSFET). In another embodiment, the switch 402 is a wide band gap device (WBD). In one embodiment, the WBD is an eGaN field effect transistor (FET). A controller is configured to control the switching of the switch 402. In this embodiment, the controller is a digital signal processor (DSP). The DSP is configured to send gate signals to the switch 402. The gate signals are phase shifted such that the multi-phase RF converter 308 performs as a multi-phase voltage source with corresponding output voltages. In particular, the i-th gate signal is in phase with (i-1)×360 / n.

[0065] As previously mentioned, the multi-phase transmit resonator 310 is configured to generate an electric field and transfer power via resonant electric field coupling as described. A magnetic field may also be generated, but little, if any, power is transferred via resonant or non-resonant magnetic field coupling. The multi-phase transmit resonator 310 includes n transmit inductors 404 and n transmit capacitive electrodes 406. Each transmit inductor 404 is electrically connected to a transmit capacitive electrode 406. Each transmit inductor 404 is electrically connected between a pair of switches 402 of the multi-phase RF converter 308. In particular, the first transmit inductor 404 is electrically connected to the first transmit capacitive electrode 406. The first transmit inductor 404 is electrically connected between the first pair of switches 402 of the multi-phase RF converter 308. Similarly, the i-th transmit inductor 404 is electrically connected to the i-th transmit capacitive electrode 406. The i-th transmit inductor 404 is electrically connected between the i-th pair of switches 402 of the multi-phase RF converter 308. The i-th transmit capacitive electrode 406 and inductor 404 pair is configured to resonate at the resonant frequency of the multi-phase transmit resonator 310 at a phase of (i-1) x 360 / n degrees to generate an electric field.

[0066] The receiver 304 includes a multi-phase receiving resonator 312, a multi-phase rectifier 314, and a load 316. The multi-phase receiving resonator 312 is configured to extract power from the generated electric field via resonant electric field coupling. Although a magnetic field may also be present, little, if any, power is extracted via resonant or non-resonant magnetic field coupling. The multi-phase receiving resonator 312 includes n receiving capacitive electrodes 410 and n receiving inductors 412. Each receiving inductor 412 is electrically connected to the receiving capacitive electrode 410. Each receiving inductor 412 is electrically connected between a pair of diodes 414 of the multi-phase rectifier 314. In particular, the first receiving capacitive electrode 410 is electrically connected to the first receiving inductor 412. The first receiving inductor 412 is electrically connected between the first pair of diodes 414 of the multi-phase rectifier 314. Similarly, the i-th receiving capacitive electrode 410 is electrically connected to the i-th receiving inductor 412. The i-th receiving inductor 412 is electrically connected between the i-th pair of diodes 414 of the multi-phase rectifier 314. The i-th receiving capacitive electrode 410 and inductor 412 pair are configured to resonate at the resonant frequency of the multi-phase transmitting resonator 310 at a phase of (i-1)×350 / n degrees to extract power from the electric field via resonant electric field coupling. As previously mentioned, the multi-phase rectifier 314 is configured to convert the n sinusoidal RF power signals from the receiving multi-phase resonator 312 into DC power signals. The multi-phase rectifier 314 includes n pairs of diodes 414. The pairs of diodes 414 are arranged in parallel. Each pair of diodes 414 receives a sinusoidal RF power signal. Each sinusoidal RF power signal is shifted 360 / n degrees out of phase with the other sinusoidal RF power signals. The phases are distributed such that when the first signal is at 0 degrees, the second signal is at 360 / n degrees, the third signal is at 2×360 / n degrees, the i-th signal is at (i−1)×360 / n degrees, etc. The n sinusoidal RF power signals are rectified into DC power signals that are output to the load 316.

[0067] As shown in FIG. 4, the capacitance of the i-th transmitting capacitive electrode 406 to ground is given by capacitance C GTiThe capacitance of the ith receiving capacitive electrode 410 to ground is represented by C GRi The capacitance of the i-th transmitting capacitive electrode 406 and the adjacent transmitting capacitive electrodes 406 is represented by C MTi(i+1) The capacitance of the i-th transmitting capacitive electrode 406 and the j-th transmitting capacitive electrode 406 is expressed as C MTij (not shown). The capacitance of the i-th receiving capacitive electrode 410 and the adjacent receiving capacitive electrodes 410 is represented as C MRi(i+1) The capacitance of the i-th receiving capacitive electrode 410 and the j-th receiving capacitive electrode 410 is expressed as C MRij (not shown). The capacitance of the i-th transmitting capacitive electrode 406 and the adjacent i-th receiving capacitive electrode 410 is represented as C MTRii Similarly, the capacitance of the i-th receiving capacitive electrode 410 and the adjacent i-th transmitting capacitive electrode 406 is expressed as C MTRii The capacitance of the i-th transmitting capacitive electrode 406 and the j-th receiving capacitive electrode 410 is expressed as C MTRij (not shown). Similarly, the capacitance of the jth receiving capacitive electrode 410 and the ith transmitting capacitive electrode 406 is represented as C MTRji (not shown). The inductance of the transmitting inductor 404 is represented as L Ti The inductance of the receiving inductor 412 is expressed as L Ri The term i is an integer between 1 and n inclusive, with i+1 at most equal to n. When i is equal to n, i+1 is understood to be 1, such that the labeling is cyclic. The term j is an integer between 1 and n inclusive.

[0068] As explained above, the multi-phase receiving resonator 312 has n pairs of receiving capacitive electrodes 410 and inductors 412. Each pair of receiving capacitive electrodes 410 and inductors 412 carries one of n sinusoidal RF power signals to the multi-phase rectifier 314 and then to the load 316. The wireless power transfer system 300 is balanced when all n pairs of receiving capacitive electrodes 410 and inductors 412 carry currents of the same amplitude and frequency, but with phase differences of 360 / n degrees between successive branches, such that the sum of the currents on all pairs of receiving capacitive electrodes 410 and inductors 412 is zero. If the sum of the currents on all pairs of receiving capacitive electrodes 410 and inductors 412 is not zero, an additional return path to ground must exist. The capacitance C MTRji This non-zero total current is manifested as a current returning through the environment, such that there is no additional physical connection between each of the multi-phase transmit resonators 310 and the multi-phase receive resonators 312. The performance of the system 400 depends on the impedance of the return path. In this embodiment, the performance includes one or more of efficiency, power delivery, electromagnetic interference (EMI), and heating. The impedance of the return path depends on the geometric and electrical properties of any objects in the system's surrounding environment. Furthermore, unbalanced systems may exhibit common mode or ground return currents. Thus, unbalanced systems are less robust because they are more affected by the impedance of objects in the system's surrounding environment than balanced systems.

[0069] The wireless power transfer system 300 has impedances present at its input and output. When transferring power from the power source 306 to the load 316, the impedances present at the input and output of the wireless power transfer system 300 need to be balanced such that all sinusoidal RF power signals output from the multi-phase RF converter 308 encounter substantially the same impedance while entering the multi-phase transmit resonator 310 and while leaving the multi-phase receive resonator 312. If the wireless power transfer system 300 is not balanced, energy will be lost during wireless power transfer such that the energy output from the power source 306 is radiated as heat or sunk to ground. The balanced wireless power transfer system 300 eliminates common mode noise within the wireless power transfer system 300. Assuming a balanced multi-phase RF converter 308 and a balanced load 316 of the wireless power transfer system 400, the wireless power transfer system 400 is balanced when certain requirements are met. In particular, the following conditions need to be met for the wireless power transfer system 400 to be balanced: L T1 =L T2 =…=L Tn C GT1 =C GT2 =…=C GTn C MT12 =C MT23 =…=C MT(n-1)n =C MTn1 C (MT1(1+i)) =C (MT2(2+i)) =…=C MTni L R1 =L R2 =…=L Rn C GR1 =C GR2 =…=C GRn C MR12 =C MR23 =…=C MR(n-1)n =C MRn1 C MR1(1+i) =C MR2(2+i) =…=C MRni C MTR11 =C MTR22 =…=CMTRnn C MTR1(1+i) =C MTR2(2+i) =…=C MTRni C (MTR(1+i)1) =C (MTR(2+i)2) =…=C MTRin

[0070] These conditions are met if the capacitive electrodes 404 and 416 have the same size and configuration, and the inductors 404 and 412 have the same size and configuration.

[0071] During operation, the power supply 306 outputs a DC power signal to the multi-phase RF converter 308. The multi-phase RF converter 308 converts the DC power signal into n sinusoidal RF power signals. The controller sends a gate signal to the switches 402, so that each pair of the switches 402 of the multi-phase RF converter 308 outputs one of the sinusoidal RF power signals to a pair of the transmitting inductors 404 and the capacitive electrodes 406 of the multi-phase transmitting resonator 310. Each pair of the transmitting inductors 404 and the capacitive electrodes 406 resonates at the resonant frequency of the multi-phase transmitting resonator 301 to generate an electric field. In particular, the i-th pair of the transmitting inductors 404 and the capacitive electrodes 406 resonates at a resonant frequency at a phase of (i-1)×360 / n degrees to generate an electric field. When the multi-phase receiving resonator 312 is within the electric field generated by the multi-phase transmitting resonator 310, the electric field excites the multi-phase receiving resonator 312 through resonant electric field coupling. Power is then wirelessly extracted from the multi-phase transmit resonator 310 by the multi-phase receive resonator 314. The multi-phase receive resonator 312 outputs the received sinusoidal RF power signal to a multi-phase rectifier 314. The multi-phase rectifier 314 rectifies the sinusoidal RF power signal into a DC power signal. The DC power signal is then applied to a load 316.

[0072] Compared to the wireless power transfer system 200, a larger number of phases in the wireless power transfer system 300 increases the maximum output power of the multi-phase RF converter 308 (for a given switch 402 and voltage input to the multi-phase RF converter 308) because each phase requires a dedicated pair of switches 402 to handle a limited amount of current and voltage. The maximum output power of the multi-phase RF converter 308 scales linearly with the number of phases. For a transmit multi-phase resonator 310 having a fixed area for the transmit capacitive electrodes 406, increasing the number of transmit capacitive electrodes 406 reduces the area of ​​each transmit capacitive electrode 406. Since the input capacitance of each transmit capacitive electrode 406 depends on the area of ​​the respective transmit capacitive electrode 406, increasing the number of transmit capacitive electrodes 406 reduces the input capacitance of each transmit capacitive electrode 406. The input capacitance is defined as the capacitance seen by looking at each transmit capacitive electrode 406 or capacitance that needs to be compensated by the transmit inductor 404 to achieve resonance at the resonant frequency, and therefore each additional phase requires an additional inductance per transmit capacitive electrode 406. For each additional phase, the multi-phase RF converter 308 requires at least one additional metal-oxide semiconductor field effect transistor (MOSFET) or wideband device (WBD) switch 402, each multi-phase transmit resonator 310 requires at least one additional transmit inductor 404, and the multi-phase rectifier 314 requires at least one additional diode 414.

[0073] The wireless power transfer system 300 may be used to transfer power in a system with, but not limited to, lateral or rotational motion. The wireless power transfer system 300 may also be used to transfer power for various rotating systems, such as through a rotary joint. A rotary joint is defined as a device that includes two or more joints, at least one of which rotates. The wireless power transfer system 300 maintains efficient power transfer throughout a 360 degree rotation.

[0074] Although the wireless power transfer system 300 has been generally described, those skilled in the art will recognize that specific embodiments are possible. FIG. 5A shows a circuit diagram of a wireless power transfer system generally identified by reference numeral 500. The wireless power transfer system 500 is an embodiment of the wireless power system 300 where the integer n is equal to 3. The wireless power transfer system 300 includes a transmitter 502 and a receiver 504. The transmitter 502 is configured to transfer power to the receiver 504 via resonant electric field coupling, as previously described. The receiver 504 is configured to extract power from the transmitter 502 via resonant electric field coupling, as previously described.

[0075] The transmitter 502 includes a power source 506, a multi-phase RF converter 508, and a multi-phase transmit resonator 512. The power source 506 is electrically connected to the multi-phase RF converter 508. The power source 506 is configured to generate a DC power signal. The power source 506 is configured to output the DC power signal to the multi-phase RF converter 508. The multi-phase RF converter 508 is electrically connected to the power source 506. The multi-phase RF converter 508 is electrically connected to the multi-phase transmit resonator 512. The multi-phase RF converter 508 is configured to convert the DC power signal into three (3) sinusoidal RF power signals. The sinusoidal RF power signals are shifted out of phase with each other. Each sinusoidal RF power signal is shifted 360 / 3 degrees out of phase with the successive sinusoidal RF power signals. The phases are distributed such that when the first signal is at 0 degrees, the second signal is at 120 degrees, and the third signal is at 240 degrees. The three sinusoidal RF power signals are output from the multi-phase RF converter 508 to a multi-phase transmit resonator 512 .

[0076] In this embodiment, the multi-phase RF converter 508 is a three-phase RF inverter. The multi-phase RF converter 508 includes three pairs of switches 510 and a controller (not shown). The pairs of switches 510 are arranged in parallel. Each pair of switches 510 outputs a sinusoidal RF power signal. Each sinusoidal RF power signal is shifted 120 degrees out of phase. The three sinusoidal RF power signals are output from the multi-phase RF converter 508 to a multi-phase transmit resonator 512.

[0077] In this embodiment, the switch 510 is a MOSFET. In another embodiment, the switch 510 is a WBD. In one embodiment, the WBD is an eGaN field effect transistor (FET). The controller is configured to send a gating signal to the switch 510 that controls the switching of the switch 510. In this embodiment, the controller is a DSP. The DSP is configured to send a gating signal to the switch 402. The gating signals are phase shifted such that the multi-phase RF converter 308 performs as a multi-phase voltage source with corresponding output voltages. For example, in a three-phase system, the gating signals are at a phase shift of 120 degrees (360 degrees / 3) such that the output voltages of the three-phase converter perform as a three-phase voltage source.

[0078] In this embodiment, the multi-phase transmit resonator 512 is a three-phase transmit resonator. The multi-phase transmit resonator 512 is configured to generate an electric field and transfer power via resonant electric field coupling. A magnetic field may also be generated, but little, if any, power is transferred via resonant or non-resonant magnetic field coupling. The multi-phase transmit resonator 512 includes three transmit inductors 514 and three transmit capacitive electrodes 516. Each transmit inductor 514 is electrically connected to a transmit capacitive electrode 516. Each transmit inductor 514 is electrically connected between a pair of switches 510 of the multi-phase RF converter 508. In this embodiment, each transmit inductor 514 is directly electrically connected to a respective transmit capacitive electrode 516. The first transmit inductor 514 is electrically connected between a first pair of switches 510 of the multi-phase RF converter 508. The first electrically connected pair of transmit inductors 514 and capacitive electrodes 516 are configured to resonate at a resonant frequency of the multi-phase transmit resonator 512 at a phase of 0 degrees to generate an electric field. A second electrically connected pair of transmit inductors 514 and capacitive electrodes 516 are configured to resonate at the resonant frequency of the multi-phase transmit resonator 512 at 120 degrees out of phase to generate an electric field. A third electrically connected pair of transmit inductors 514 and capacitive electrodes 516 are configured to resonate at the resonant frequency of the multi-phase transmit resonator 512 at 240 degrees out of phase to generate an electric field.

[0079] The receiver 504 includes a multi-phase receive resonator 520, a multi-phase rectifier 526, and a load 530. The multi-phase receive resonator 520 is configured to extract power from the multi-phase transmit resonator 512 via resonant electric field coupling. Although a magnetic field may also be present, little, if any, power is extracted via resonant or non-resonant magnetic field coupling. The multi-phase receive resonator 520 is electrically connected to the multi-phase rectifier 526.

[0080] In this embodiment, the multi-phase receiver resonator 520 is a three-phase receiver resonator. The multi-phase receiver resonator 520 is configured to output three sinusoidal RF power signals to the multi-phase rectifier 526. The sinusoidal RF power signals are shifted out of phase with each other. Each sinusoidal RF power signal is shifted out of phase by 120 degrees. The phases are distributed such that when the first signal is at 0 degrees, the second signal is at 120 degrees and the third signal is at 240 degrees. The multi-phase receiver resonator 520 includes three receive capacitive electrodes 522 and three receive inductors 524. Each receive inductor 524 is electrically connected to a receive capacitive electrode 522. In this embodiment, each receive inductor 524 is directly electrically connected to a respective receive capacitive electrode 522. Each receive inductor 524 is electrically connected between a pair of diodes 528 of the multi-phase rectifier 526. The first receive capacitive electrode 522 and inductor 524 pair is configured to resonate at the resonant frequency of the multi-phase transmit resonator 512 at a phase of 0 degrees to extract power from the electric field via resonant electric field coupling. The second receive capacitive electrode 522 and inductor 524 pair is configured to resonate at the resonant frequency of the multi-phase transmit resonator 512 at a phase of 120 degrees to extract power from the electric field via resonant electric field coupling. The third receive capacitive electrode 522 and inductor 524 pair is configured to resonate at the resonant frequency of the multi-phase transmit resonator 512 at a phase of 240 degrees to extract power from the electric field via resonant electric field coupling.

[0081] In this embodiment, the multi-phase rectifier 526 is a three-phase rectifier. The multi-phase rectifier 526 is configured to convert the received three sinusoidal RF power signals into DC power signals. The multi-phase rectifier 526 is electrically connected to a load 530. The multi-phase rectifier 526 outputs the DC power signals to the load 530. The multi-phase rectifier 526 includes three pairs of diodes 528. The pairs of diodes 528 are arranged in parallel. Each pair of diodes 528 receives a sinusoidal RF power signal. Each sinusoidal RF power signal is shifted 120 degrees out of phase. The three sinusoidal RF power signals are rectified into DC power signals that are output to the load 530.

[0082] The load 530 is electrically connected to the multi-phase rectifier 526. The load 530 receives a DC power signal from the multi-phase rectifier 526.

[0083] As shown in FIG. 5, the capacitance of the ith transmitting capacitive electrode 516 to ground is given by capacitance C GTi The capacitance of the i-th receiving capacitive electrode 522 to ground is represented by C GRi The capacitance of the i-th transmitting capacitive electrode 516 and the adjacent transmitting capacitive electrodes 516 is expressed as C MTi(i+1) The capacitance of the i-th transmitting capacitive electrode 516 and the j-th transmitting capacitive electrode 516 is expressed as C MTij (not shown). The capacitance of the i-th receiving capacitive electrode 522 and the adjacent receiving capacitive electrodes 522 is represented as C MRi(i+1) The capacitance of the i-th receiving capacitive electrode 522 and the j-th receiving capacitive electrode 522 is expressed as C MRij (not shown). The capacitance of the i-th transmitting capacitive electrode 516 and the adjacent i-th receiving capacitive electrode 522 is represented as C MTRii Similarly, the capacitance of the i-th receiving capacitive electrode 522 and the adjacent i-th transmitting capacitive electrode 516 is expressed as C MTRii The capacitance of the i-th transmitting capacitive electrode 516 and the adjacent j-th receiving capacitive electrode 522 is expressed as C MTRij (not shown). Similarly, the capacitance of the jth receiving capacitive electrode 522 and the ith transmitting capacitive electrode 516 is represented as C MTRji (not shown). The inductance of the transmitting inductor 510 is represented as L Ti The inductance of the receiving inductor 524 is expressed as L Ri The term i is an integer between 1 and 3, inclusive, with i+1 being at most equal to 3. The term j is an integer between 1 and 3, inclusive.

[0084] As discussed above with reference to the wireless power transfer system 400 along with the balanced multi-phase RF converter 508 and balanced load 530 of the wireless power transfer system 500, the wireless power transfer system 500 is balanced when certain requirements are met. In particular, for the wireless power transfer system 500 to be balanced, the following conditions need to be met: L T1 =L T2 =L T3 C GT1 =C GT2 =C GT3 C MT12 =C MT23 =C MT31 L R1 =L R2 =L R3 C GR1 =C GR2 =C GR3 C MR12 =C MR23 =C MR31 C MTR11 =C MTR22 =C MTR33 C MTR12 =C MTR21 =C MTR23 =C MTR32 =C MTR31 =C MTR13

[0085] These conditions are met if the capacitive electrodes 516 and 522 have the same size and configuration, and the inductors 510 and 524 have the same size and configuration.

[0086] Simulations have been performed to determine the performance of the multi-phase rectifier 526 compared to a conventional single-phase rectifier. Figure 5B is a graph of the load voltage output by the multi-phase rectifier 526 of the wireless power transfer system 500 compared to the load voltage output by a single-phase rectifier. As shown in Figure 5B, the load voltage output by the multi-phase rectifier 526 exhibits less ripple than the load voltage output by the single-phase rectifier.

[0087] As shown in FIG. 6 , in this embodiment of the wireless power transfer system 500, the transmit capacitive electrode 516 of the multi-phase transmit resonator 512 includes three generally elongated planar plates. The plates are coplanar. The plates are generally rectangular. The plates are laterally spaced apart. The plates include a first plate 602, a second plate 604, and a third plate 606. The first plate 602 is spaced apart from and generally parallel to the second plate 604. The second plate 604 is spaced apart from and generally parallel to the first plate 602 and the third plate 606. The third plate 606 is spaced apart from and generally parallel to the second plate 604. The first plate 602 and the third plate 606 are each identical in shape and size. The first plate 602, the second plate 604, and the third plate 606 each have the same length.

[0088] In this embodiment, the first plate 602 and the third plate 606 are electrically connected via a lumped capacitor 608. The lumped capacitor 608 compensates for the weak capacitance between the first plate 602 and the third plate 606.

[0089] As previously mentioned, the mutual capacitance between adjacent plates is represented as capacitance Cmt, and the capacitance of each plate to ground is represented as capacitance Cg. The second plate 604 has a width greater than the width of each of the first plate 602 and the third plate 606. The second plate 604 has a larger width in order for the second plate 604 to maintain the same capacitance to ground Cg as each of the first plate 602 and the third plate 606. Although the transmit capacitive electrode 516 has been described, one skilled in the art will recognize that the receive capacitive electrode 522 may be similarly configured.

[0090] Although the transmit capacitive electrode 516 has been described as having a particular configuration, one skilled in the art will recognize that other configurations are possible. Figures 7 and 8 show another embodiment of the transmit capacitive electrode 516, generally identified as reference character 700. In this embodiment, the transmit capacitive electrode 700 includes n (three) rows of electrodes 702, 704, and 706, one for each phase of the multi-phase transmit resonator 512. Each row of electrodes 702, 704, and 706 includes 3xm+1 (four) plates, where m is a positive integer. In this embodiment, m is 1. The plates are generally elongated planar plates. In this embodiment, the plates are coplanar. The plates are laterally spaced apart. The plates in each row of electrodes 702, 704, and 706 include a first plate 710, a second plate 712, a third plate 714, and a fourth plate 716. The first plate 710 and the fourth plate 716 are identical. The first plate 710 and the fourth plate 716 are generally rectangular. The second plate 712 and the third plate 714 are identical. The second plate 712 and the third plate 714 are generally rectangular. The second plate 712 and the third plate 714 are twice as long as the first plate 710 and the fourth plate 716.

[0091] The first plate 710 is spaced apart from and generally parallel to the second plate 712. The second plate 712 is spaced apart from and generally parallel to the first plate 710 and the third plate 714. The third plate 714 is spaced apart from and generally parallel to the second plate 712 and the fourth plate 716. The fourth plate 716 is spaced apart from and generally parallel to the third plate 714. The first plate 710, the second plate 712, the third plate 714, and the fourth plate 716 each have the same height. The second plate 712 and the third plate 714 have twice the length of the first plate 710 and the fourth plate 716 .

[0092] 7 and 8, the first plate 710, second plate 712, and third plate 714 in the first row of electrodes 702 are each electrically connected to the second plate 712, third plate 714, and fourth plate 716, respectively, of the third row of electrodes 702 via out-of-plane traces. The second plate 712, third plate 714, and fourth plate 716 of the first row of electrodes 702 are each electrically connected to the first plate 710, second plate 712, and third plate 714, respectively, of the second row of electrodes 704 via in-plane traces. The second plate 712, third plate 714, and fourth plate 716 of the second row of electrodes 704 are each electrically connected to the first plate 710, second plate 712, and third plate 714, respectively, of the third row of electrodes 706 via in-plane traces.

[0093] The configuration of the transmit capacitive electrode 700 shown in FIGS. 7 and 8 ensures that the multi-phase transmit resonator 512 is approximately balanced.

[0094] Although a transmitting capacitive electrode 700 has been described, those skilled in the art will recognize that the receiving capacitive electrode 522 may be similarly configured.

[0095] While the embodiments of the transmit capacitive electrode 516 described and shown in Figures 6-8 have been described separately, one skilled in the art will recognize that they may be combined. Turning now to Figure 9, a plan view of another embodiment of a receive capacitive electrode 522 is shown, generally identified by reference numeral 1100. The receive capacitive electrode 1100 includes a first plate 602, a second plate 604, and a third plate 606. In this embodiment, the transmit capacitive electrode 516 is generally identified by reference numeral 1110. The transmit capacitive electrode 1110 includes a row of electrodes 702, 704, and 706 having a first plate 710, a second plate 712, a third plate 714, and a fourth plate 716.

[0096] Simulations have been performed to determine the performance of a wireless power transfer system 300 having a receive capacitive electrode 1100 including a first plate 602, a second plate 604, and a third plate 606, and a transmit capacitive electrode 1110 including a row of electrodes 702, 704, and 706 having a first plate 710, a second plate 712, a third plate 714, and a fourth plate 716. In the simulation, the receive capacitive electrode 1100 has been moved along the horizontal span of the transmit capacitive electrode 1110 from a starting position of 0 millimeters to a final position of 300 millimeters. FIG. 10 is a graph of RF efficiency at a resonant frequency of 13.56 megahertz as a function of the movement of the receive capacitive electrode 1100 along the horizontal span of the transmit capacitive electrode 1110. RF efficiency is defined as the efficiency of wireless power transfer between each of the multi-phase transmit resonators 512 and the multi-phase receive resonators 520. As shown in FIG. 10, RF efficiency remains above 90%.

[0097] Although the exemplary transmit and receive capacitive electrodes have been described as rectangular or square, one skilled in the art will recognize that other configurations are possible. In another embodiment, the transmit capacitive electrode 406 has n identical planar transmit segments. The transmit segments are equally spaced around a center point in the plane. The transmit segments are symmetric about a 360 / n degree rotation around an axis perpendicular to the plane extending from the center point. The transmit segments are separated from each other. In this embodiment, the n transmit capacitive electrodes form a transmit capacitor. During use, the transmit capacitor resonates the reactance of the n transmit inductors 404 at the operating frequency of the RF converter 308. Each transmit inductor 404 resonates with the input capacitance of the corresponding transmit segment.

[0098] The receive capacitive electrode 410 has n identical planar receive segments. The receive segments are equally spaced about a center point in the plane. The receive segments are symmetric about a 360 / n degree rotation about an axis perpendicular to the plane extending from the center point. The receive segments are separated from each other. In this embodiment, the n receive capacitive electrodes form a receive capacitor.

[0099] During use, the multiphase transmit resonator 310 is aligned with the multiphase receive resonator 312 so that the major faces of the transmit and receive segments face each other and the center points of each resonator 310 and 312 lie directly across from each other. The receive segments may be rotated at an angle θ about an axis perpendicular to the plane of the receive segments that passes through the center points of the receive capacitors. When the transmit segments are rotationally aligned with the receive segments, each receive segment is tightly coupled to the corresponding transmit segment. Thus, each receive segment is driven in phase with the corresponding transmit segment. In this position, θ is set to 0. Due to the rotational symmetry of the transmit and receive segments, positions where θ=p×360 / n (where p is any integer) are indistinguishable from positions where θ=0 and therefore indistinguishable from each other.

[0100] Although the transmit capacitive electrode 516 has been described as having a particular configuration, one skilled in the art will recognize that other configurations are possible. FIG. 11 illustrates another embodiment of the transmit capacitive electrode 516, generally identified by reference numeral 1400. In this embodiment, the transmit capacitive electrode 1400 includes three segments 1402. In this embodiment, the segments 1402 are plates. The segments 1402 are coplanar. The segments 1402 are sized identically. The segments 1402 are spaced apart such that they generally form a circle around their circumference. Each segment 1402 spans approximately 120 degrees of a circle. The segments 1402 are equally spaced around a center point in the plane. The segments 1402 have an axis of rotational symmetry that is perpendicular to the major surface of the segments 1402 around the center of curvature of the segments 1402. Although a transmitting capacitive electrode 1400 has been described, those skilled in the art will recognize that the receiving capacitive electrode 522 may be similarly configured.

[0101] Although a wireless power transfer system 500 has been described, one of ordinary skill in the art will recognize that other configurations are possible. Figure 12 shows a partial wireless power transfer system generally identified by reference numeral 1500. The wireless power transfer system 1500 includes a transmitter and a receiver. The transmitter is identical to the previously described transmitter 502 unless otherwise stated. The receiver is identical to the previously described receiver 504 unless otherwise stated.

[0102] In this embodiment, the multiphase transmit resonator 512 includes a transmit capacitive electrode 1502. The transmit capacitive electrode 1502 includes three transmit segments 1504. In this embodiment, the transmit segments 1504 are plates. The transmit segments 1504 are coplanar. The transmit segments 1504 are identically sized. The transmit segments 1504 are spaced apart such that they generally form a circle around their circumference. Each transmit segment 1504 spans approximately 120 degrees of the circle. The transmit segments 1504 are equally spaced around a center point in a plane. The transmit segments 1504 have an axis of three-way rotational symmetry perpendicular to the major surface of the transmit segment 1504 around the center of curvature of the transmit segment 1504. Each transmit segment 1504 is paired with an inductor 514 to ensure that the multiphase transmit resonator 512 is configured to resonate at the resonant frequency of the multiphase transmit resonator 512. The inductors 514 of the multi-phase transmit resonators 512 are identical. Assuming a symmetrical arrangement of the transmit segments 1504, the multi-phase transmit resonators 512 are balanced.

[0103] In this embodiment, each transmit segment 1504 has an outer diameter of 150 millimeters, an inner diameter of 30 millimeters, and a thickness of 0.1 millimeters. Each transmit segment 1504 is separated from adjacent transmit segments 1504 by a gap of 10 millimeters.

[0104] In this embodiment, the multiphase receive resonator 520 includes a receive capacitive electrode 1510. The receive capacitive electrode 1510 includes three receive segments 1512. In this embodiment, the receive segments 1512 are plates. The receive segments 1512 are coplanar. The receive segments 1512 are identically sized. The receive segments 1512 are spaced apart so that they generally form a circle around their circumference. Each receive segment 1512 spans approximately 120 degrees of the circle. The receive segments 1512 are equally spaced around a center point in a plane. The receive segments 1512 have an axis of three-way rotational symmetry perpendicular to the major surface of the receive segment 1512 around the center of curvature of the receive segment 1512. Each receive segment 1512 is paired with an inductor 524 to ensure that the multiphase receive resonator 520 is configured to resonate at a resonant frequency. The multi-phase receive resonator 520 is balanced, assuming a symmetrical arrangement of the receive segments 512. When both the multi-phase transmit resonator 512 and the multi-phase receive resonator 520 are balanced, the wireless power transfer system 1500 is balanced.

[0105] In this embodiment, each receiving segment 1512 has an outer diameter of 150 millimeters, an inner diameter of 30 millimeters, and a thickness of 0.1 millimeters. Each receiving segment 1512 is separated from adjacent receiving segments 1512 by a gap of 10 millimeters.

[0106] In this embodiment, both the transmit inductor 514 and the receive inductor 524 have an inductance of 9.98 μH and a quality factor (Q) of 225, respectively. The transmit capacitive electrode 1502 and the receive capacitive electrode 1510 have the same geometry and are located 50 millimeters apart from each other. The transmit capacitive electrode 1502 and the receive capacitive electrode 1510 have a common axis of three-way rotational symmetry.

[0107] The wireless power transfer system 1500 may be implemented in a rotating structure. The rotating structure may take the form of a slip ring, a helicopter, a rotating chair, etc. When the wireless power transfer system 1500 is implemented in a rotating structure, the transmitting capacitive electrode 1502 and the receiving capacitive electrode 1510 rotate through a 360 degree rotation. Establishing that the leakage current of the wireless power transfer system 1500 is negligible for all angular positions θ from 0 to 120 degrees due to the three-way rotational symmetry of the electrodes 1502 and 1510 proves that the wireless power transfer system 1500 is balanced.

[0108] Simulations have been performed to determine the performance of the wireless power transfer system 1500 and establish that the leakage current of the wireless power transfer system 1500 is negligible for all angular positions θ from 0 to 120 degrees. FIG. 13 is a plot of the ratio of the sum of the currents on each segment 1504 and 1512 to the sum of the current magnitudes on each segment 1504 and 1512 as a percentage for 0 to 120 degrees of rotation for both the transmitting capacitive electrode 1502 and the receiving capacitive electrode 1510, respectively. The sum of the currents on each segment 1504 and 1512 is defined as the common mode current. The ratio in FIG. 13 is given by:

[0109]

number

[0110] i1, i2, and i3 are the currents on the first, second, and third segments 1504 and 1512 of the respective transmitting capacitive electrode 1502 and receiving capacitive electrode 1510, respectively.

[0111] Throughout the 120 degree rotation, the sum of the currents on each segment 1504 and 1512 is less than 0.05% of the root mean square (RMS) of the current. A sum of currents less than 0.05% of the RMS of the current corresponds to a common mode rejection ratio (CMRR) of 66 dB. Thus, leakage current is negligible and the wireless power transfer system 1500 remains balanced under rotation.

[0112] FIG. 14 is a graph of the phase of the current signal on each receive segment 1512 as a function of angular position θ (rotation angle). The phase of the current on each receive segment 1512 decreases approximately linearly from 180 to -180 degrees (or, equivalently, from 0 to 360 degrees) over a 360 degree rotation. Reflecting the structure of the receive capacitive electrode 510, the phase curves sinusoidally away from linearity with a periodicity of 120 degrees. A numerical model of each line in the graph of FIG. 14 is provided in Equations 1A, 1B, and 1C below. Phase1=-θ+offsetA×sin(3×θ+ψ)+0 (Formula 1A) Phase2=-θ+offsetA×sin(3×θ+ψ)+120 (Formula 1B) Phase3=-θ+offsetA×sin(3×θ+ψ)+240 (Formula 1C) A is the amplitude of the sinusoidal oscillation and ψ is the phase constant.

[0113] The modeling parameters for Equations 1A, 1B, and 1C are provided in Table 1 below.

[0114] [Table 1]

[0115] As described by Equations 1A, 1B, and 1C, the phase difference between two adjacent transmit capacitive electrodes 1502 or receive capacitive electrodes 1510 is 120 degrees for any rotation angle, which allows continuous wireless power transfer while the multi-phase receive resonator 512 rotates relative to the multi-phase transmit resonator 520. The periodic phase separation of 120 degrees ensures that the wireless power transfer system 1500 is balanced. Therefore, as established through simulations, the leakage current of the wireless power transfer system 1500 is negligible for all angular positions θ from 0 to 120 degrees.

[0116] Further simulations have been performed to establish the RF efficiency and input impedance of the wireless power transfer system 1500 when implemented in a rotating structure. Through those simulations, it was found that the RF efficiency remained approximately constant during rotation of the transmitting capacitive electrode 1502 and the receiving capacitive electrode 1504 of the wireless power transfer system 1500, thus resulting in predictable performance. However, the input impedance varies significantly during rotation of the transmitting capacitive electrode 1502 and the receiving capacitive electrode 1504 of the wireless power transfer system 1500. In general, during rotation of the transmitting capacitive electrode 1502 and the receiving capacitive electrode 1504 of the wireless power transfer system 1500, the characteristics including the RF efficiency and the input impedance of the wireless power transfer system 1500 oscillate at n times the frequency of rotation of about the average value of the characteristics. The characteristics can be numerically approximated by the form provided in the following Equation 2.

[0117]

number

[0118] g(θ) is a specific characteristic according to the rotation angle of θ degrees,

[0119]

number

[0120] is the average value of the characteristic, and Amp is the extreme and average values.

[0121]

number

[0122] where n is the number of phases and ξ is the phase constant.

[0123] The RF efficiency, real part of the impedance, and imaginary part of the impedance of the wireless power transfer system 1500 are numerically described by using the modeling parameters in Table 2 below in Equation 2. The real and imaginary parts of the wireless power transfer system 1500 are components of the input impedance of the wireless power transfer system 1500.

[0124] [Table 2]

[0125] 15 is a graph of RF efficiency of the wireless power transfer system 1500 at a resonant frequency of 13.56 megahertz as a function of angular rotation through 120 degrees. RF efficiency is defined as the efficiency of wireless power transfer between each of the multi-phase transmit 512 and multi-phase receive resonators 520. The RF efficiency shown in FIG. 15 is characterized by Equation 2 with the modeling parameters in Table 2. The offset parameter is large compared to the amplitude, and therefore the wireless power transfer system 1500 maintains RF efficiency above 94.5% over the 120 degree rotation.

[0126] FIG. 16 is a graph of the real part of the impedance present at each transmitting capacitive electrode 1502 of the wireless power transfer system 1500 as a function of angular rotation through 120 degrees. The input impedance is composed of the real and imaginary parts of the impedance present at each transmitting capacitive electrode 1502. The amplitude of the impedance variation is 44% of the offset. The real part of the impedance shown in FIG. 16 is characterized by Equation 2 with the modeling parameters in Table 2 above.

[0127] 17 is a graph of the imaginary part of the impedance present at each transmitting capacitive electrode 1502 of a wireless power transfer system 1500 as a function of angular rotation through 120 degrees. The imaginary part of the impedance shown in FIG. 17 is characterized by Equation 2 with the modeling parameters of Table 2 above.

[0128] A varying input impedance is loaded to the RF converter 508. Due to the periodic loading, the RF converter 508 therefore outputs a varying amount of power, resulting in a varying amount of power received at the receiver 504.

[0129] FIG. 18 is a graph of the RF efficiency of the wireless power transfer system 1500 and the wireless power transfer system 70 described in U.S. Pat. No. 9,979,206, issued May 22, 2018, relevant portions of which are incorporated herein by reference, at a 13.56 megahertz resonant frequency as a function of the vertical separation between the transmit and receive resonators.

[0130] The wireless power transfer system 70 has a transmit resonator and a receive resonator, each of which includes two disk capacitive electrodes, an outer capacitive electrode, and an inner capacitive electrode. The outer capacitive electrode has an outer diameter R equal to 150 millimeters. out and inner diameter R equal to 120 mm in The inner capacitive electrode has an outer diameter R equal to 110 mm. out and inner diameter R equal to 80 mm inThe inductors of the transmit and receive resonators each have an inductance of 7.37 μH. The wireless power transfer systems 70 and 1500 are tuned to maximize RF efficiency with a longitudinal separation of 300 millimeters between the transmit and receive resonators.

[0131] In FIG. 18, wireless power transfer 70 is identified as "Concentric" and wireless power transfer system 1500 is identified as "Three-Phase." As shown in FIG. 18, wireless power transfer system 1500 has higher RF efficiency at longitudinal separations above approximately 50 millimeters. Wireless power transfer system 70 has higher RF efficiency at longitudinal separations below approximately 50 millimeters. However, this higher RF efficiency at longitudinal separations below approximately 50 millimeters is only an increase of approximately 10.

[0132] Although the transmit capacitive electrode 516 has been described as having a particular configuration, one skilled in the art will recognize that other configurations are possible. FIG. 19 illustrates another embodiment of the transmit capacitive electrode 516, generally identified by reference numeral 2200. In this embodiment, the transmit capacitive electrode 2200 includes three segments 2202. In this embodiment, the segments 2202 are plates. The segments 2202 are in the same plane. The segments 2202 are sized identically. The segments 2202 are spaced apart such that they generally form a circle around their circumference. Each segment 2202 spans approximately 120 degrees of the circle. The segments 2202 are equally spaced around a center point in the plane.

[0133] In this embodiment, the segments 2202 are separated by a logarithmic spiral gap, represented by the dotted lines in FIG. 19 and described by Equation 3 below.

[0134] r(β)=(a / b) β / φ (Formula 3)

[0135] In Equation 3, r(β) is the helical radius for rotation angle β, a is the inner radius, b is the outer radius, h is the outer radius, and φ is the angle swept by the curve.

[0136] The transmit capacitive electrode 2200 provides a more constant input impedance compared to the transmit capacitive electrode 1400, reducing fluctuations in output power and presenting more favorable conditions to the RF converter 508.

[0137] Although a transmitting capacitive electrode 2200 has been described, those skilled in the art will recognize that the receiving capacitive electrode 522 may be similarly configured.

[0138] 20 shows another embodiment of a transmit capacitive electrode 2200 for various values ​​of the angle swept by the curve φ. In particular, the following values ​​have been used: A: φ=30 degrees, B: φ=60 degrees, C: φ=120 degrees, D: φ=180 degrees, and E: φ=360 degrees.

[0139] Although a wireless power transfer system 500 has been described, one of ordinary skill in the art will recognize that other configurations are possible. Figure 21 shows a partial wireless power transfer system generally identified by reference numeral 2400. The wireless power transfer system 2400 includes a transmitter and a receiver. The transmitter is identical to the previously described transmitter 502 unless otherwise stated. The receiver is identical to the previously described receiver 504 unless otherwise stated.

[0140] In this embodiment, the multi-phase transmit resonator 512 includes a transmit capacitive electrode 2402. The transmit capacitive electrode 2402 includes three transmit segments 2404. In this embodiment, the transmit segments 2404 are plates. The transmit segments 2404 are coplanar. The transmit segments 2404 are identically sized. The transmit segments 2404 are spaced apart such that they generally form a circle around their circumference. Each transmit segment 2404 spans approximately 120 degrees of the circle. The transmit segments 2404 are equally spaced around a center point in the plane. The transmit segments 2404 have an axis of three-way rotational symmetry perpendicular to the major surface of the transmit segment 2404 around the center of curvature of the transmit segment 2404. Each transmit segment 2404 is paired with an inductor 514 to ensure that the multi-phase transmit resonator 512 is configured to resonate at the resonant frequency of the multi-phase transmit resonator 512. The inductors 514 of the multi-phase transmit resonators 512 are identical. Assuming a symmetrical arrangement of the transmit segments 2404, the multi-phase transmit resonators 512 are balanced.

[0141] In this embodiment, each transmit segment 2404 has an outer diameter of 150 millimeters, an inner diameter of 30 millimeters, and a thickness of 0.1 millimeters. Each transmit segment 2404 is separated from adjacent transmit segments 2404 by a gap of 10 millimeters.

[0142] In this embodiment, the multi-phase transmit resonator 512 includes a transmit passive electrode 2406. The transmit passive electrode 2406 is described in U.S. Patent Application No. 16 / 138,344, filed September 21, 2018, the relevant portions of which are incorporated herein by reference. In this embodiment, the transmit passive electrode 2406 includes a planar circular plate. The transmit passive electrode 2406 is parallel to the transmit capacitive electrode 2402. The transmit passive electrode 2406 is larger in area than the total area of ​​the transmit capacitive electrode 2402. The center of the transmit passive electrode 2406 is aligned with the center point of the transmit capacitive electrode 2402. The transmit passive electrode 2406 is 50 millimeters from the transmit capacitive electrode 2402.

[0143] In this embodiment, the multiphase receive resonator 520 includes a receive capacitive electrode 2410. The receive capacitive electrode 2410 includes three receive segments 2412. In this embodiment, the receive segments 2412 are plates. The receive segments 2412 are coplanar. The receive segments 2412 are identically sized. The receive segments 2412 are spaced apart so that they generally form a circle around their circumference. Each receive segment 2412 spans approximately 120 degrees of the circle. The receive segments 2412 are equally spaced around a center point in a plane. The receive segments 2412 have an axis of three-way rotational symmetry perpendicular to the major surface of the receive segment 2412 around the center of curvature of the receive segment 2412. Each receive segment 2412 is paired with an inductor 524 to ensure that the multiphase receive resonator 520 is configured to resonate at a resonant frequency. The inductors 524 of the multiphase receive resonators 520 are identical. Assuming a symmetrical arrangement of the transmit segments 2404, the multiphase receive resonators 520 are balanced.

[0144] In this embodiment, each receive segment 2412 has an outer diameter b of 150 millimeters, an inner diameter a of 30 millimeters, a thickness of 0.1 millimeters, and an angle swept by a curve φ of 120 degrees. Each receive segment 2412 is separated from an adjacent receive segment 2412 by a gap of 10 millimeters.

[0145] In this embodiment, the multiphase transmit resonator 512 further includes a receive passive electrode 2414. The receive passive electrode 2414 is described in U.S. Patent Application No. 16 / 138,344, filed September 21, 2018, the relevant portions of which are incorporated herein by reference. In this embodiment, the receive passive electrode 2414 includes a planar circular plate. The receive passive electrode 2414 is coplanar with the receive capacitive electrode 2412. The receive passive electrode 2414 is larger in area than the total area of ​​the receive capacitive electrode 2412. The center of the receive passive electrode 2414 is aligned with the center point of the receive capacitive electrode 2412. The receive passive electrode 2414 is 50 millimeters from the receive capacitive electrode 2412.

[0146] The transmit capacitive electrode 2402 and the receive capacitive electrode 2410 are 50 millimeters apart from each other. The transmit capacitive electrode 1502 and the receive capacitive electrode 1510 have a common axis of three-way rotational symmetry. As both the multi-phase transmit resonator 512 and the multi-phase receive resonator 520 are balanced, the wireless power transfer system 1500 is also balanced.

[0147] Although the passive electrodes 2406 and 2414 can reduce coupling due to the added current return path provided by the mutual capacitance between the active electrodes (i.e., the transmitting capacitive electrode 2402 and the receiving capacitive electrode 2410) and the passive electrodes 2406 and 2414, the passive electrodes 2406 and 2414 can provide advantages. For example, the passive electrodes 2406 and 2414 can add capacitance that reduces both the inductance requirements and the reflected impedance, thus reducing the voltage at the passive electrodes 2406 and 2414. Environmental sensitivity and field emissions can also be reduced. Additionally, the low electric field area opposite the passive electrodes 2406 and 2414 relative to the active electrodes can be suitable for mounting electronics.

[0148] The RF efficiency, real part of the impedance, and imaginary part of the impedance of the wireless power transfer system 2400 are numerically described by using the modeling parameters in Table 3 below in Equation 2. The real and imaginary parts of the impedance of the wireless power transfer system 2400 are components of the input impedance of the wireless power transfer system 2400.

[0149] [Table 3]

[0150] Simulations have been performed to determine the performance of wireless power transfer system 2400 compared to wireless power transfer 1500. Modeling parameters for RF efficiency, the real part of the impedance present at each capacitive electrode of each wireless power transfer system 2400 and 1500, and the imaginary part of the impedance present at each capacitive electrode of each wireless power transfer system 2400 and 1500 are provided in Table 3 above.

[0151] The amplitude of the real part of the impedance of the wireless power transfer system 2400 is the average

[0152]

number

[0153] 36% of the impedance seen by the wireless power transfer system 1500. This represents a significant reduction in impedance variation compared to the wireless power transfer system 1500. Furthermore, as shown in Tables 2 and 3, the average and amplitude of the imaginary part of the impedance of each transmitting capacitive electrode 2302 of the wireless power transfer system 2400 is much smaller than the amplitude of the imaginary part of the impedance of each transmitting capacitive electrode 1502 of the wireless power transfer system 1500. This represents a much more favorable impedance seen by the RF converter 508.

[0154] Further simulations have been performed to determine the performance of the wireless power transfer system 2400 compared to the wireless power transfer system 1500 when varying the angle swept by the curve φ. In general, it appears that increasing the angle swept by the curve φ improves the average RF efficiency (

[0155]

number

[0156] Decreasing the angle φ (fitting parameter) and increasing the amplitude of the efficiency variation under rotation (AMP fitting parameter) decreases the mean and amplitude of the imaginary part of the impedance, decreasing the required inductance of the wireless power transfer system 2400. Simulations have determined that an angle swept by the curve φ from 120 degrees to 180 degrees yields the best overall wireless power transfer system performance.

[0157] Although a multi-phase resonator having three capacitive electrodes has been described, one skilled in the art will recognize that more capacitive electrodes are possible. Figures 22A-22E show other embodiments of capacitive electrodes for use in each of the multi-phase transmit resonator 310 and / or the multi-phase receive resonator 312. In particular, Figure 22A shows three capacitive electrodes arranged in a circle as previously described, Figure 22B shows four capacitive electrodes arranged in a circle, Figure 22C shows five capacitive electrodes arranged in a circle, Figure 22D shows six capacitive electrodes arranged in a circle, and Figure 22E shows twelve capacitive electrodes arranged in a circle.

[0158] Further, although the multi-phase resonators have been described as having capacitive electrodes of particular shapes and configurations, one skilled in the art will recognize that other shapes and configurations are possible. Figures 23A-23I show other embodiments of capacitive electrodes for use in each of the multi-phase transmit resonators 512 and / or receive resonators 520. In particular, Figure 23A shows a capacitive electrode comprising three equally sized segments of a flat circular plate spaced apart by channels.

[0159] Figures 23B and 23C show capacitive electrodes formed from a flat disk with an inner diameter a, an outer diameter b, and channels cut 360 / n degrees apart. In this embodiment, n is 3. The channels extend from the inner diameter a to the outer diameter b along a helical path. In this embodiment, the helical path is logarithmic. Figure 23B shows a capacitive electrode with the helical path arranged counterclockwise. Figure 23C shows a capacitive electrode with the helical path arranged clockwise.

[0160] FIG. 23D shows a capacitive electrode identical to the previously described capacitive electrode 1400 shown in FIG.

[0161] 23E and 23F show capacitive electrodes formed from a flat circular plate with an inner diameter a, an outer diameter b, and channels cut 360 / n degrees apart. In this embodiment, n is 3. The channels extend from the inner diameter a to the outer diameter b along a helical path. In this embodiment, the helical path is archimedian. In another embodiment, the helix is ​​hyperbolic.

[0162] 23G and 23H show a capacitive electrode formed from a flat circular plate with an inner diameter a, an outer diameter b, and channels cut 360 / n degrees apart. In this embodiment, n is 3. The channels extend from the inner diameter a to the outer diameter b along a straight tangent path to the circle formed by the capacitive electrode.

[0163] FIG. 23I shows a capacitive electrode formed from planar rectangular plates formed within a circle, spaced equidistant from each other, such that the plates are aligned with the center of the circle and extend outward from it.

[0164] 23A-23I has been described with three capacitive electrodes, those skilled in the art will recognize that more capacitive electrodes may be possible. Furthermore, those skilled in the art will recognize that the capacitive electrodes shown in Figures 23A-23I may be used in both or only one of the multi-phase transmit and receive resonators.

[0165] Although the multi-phase resonator has been described as having capacitive electrodes of a particular shape and configuration, one skilled in the art will recognize that other shapes and configurations are possible. Fig. 24A is a side elevation view of another embodiment of a capacitive electrode of the wireless power transfer system 500, generally identified by reference character 2800. Fig. 24B is a perspective view of the capacitive electrode 2800. Each capacitive electrode 2800 is a rectangular planar plate 2802. The plates 2802 are arranged at an angle of 120 degrees to each other in a vertical plane, as shown in Fig. 24A. The plates 2802 form triangular prisms at their periphery, as shown in Fig. 24B.

[0166] The plate 2802 may form a portion of at least one of the multi-phase transmit resonator 510 and the receive resonator 520. FIG. 25A is a side elevational view of the plate 2802 forming the transmit capacitive electrode 2902 of the multi-phase transmit resonator 510 and the plate 2802 forming the receive capacitive electrode 2904 of the multi-phase receive resonator 520. In this embodiment, the triangular prism formed on the periphery of the transmit capacitive electrode 2902 subsumes the triangular prism formed on the periphery of the receive capacitive electrode 2904. In this embodiment, the triangular prisms formed on the periphery of the capacitive electrodes 2902 and 2904 have the same orientation. FIG. 25B is a side elevational view of the capacitive electrodes 2902 and 2904 such that the triangular prism formed by the receive capacitive electrode 2904 is inverted relative to the triangular prism formed by the transmit capacitive electrode 2902.

[0167] Although the multi-phase resonator has been described as having capacitive electrodes of a particular shape and configuration, one skilled in the art will recognize that other shapes and configurations are possible. Figure 26 is a perspective view of another embodiment of a capacitive electrode of a wireless power transfer system 500, generally identified by reference character 3000. In this embodiment, the capacitive electrode 3000 includes three segments 3002 that form a hollow tube. Each segment 3002 has the same dimensions.

[0168] Although the multi-phase resonator has been described as having capacitive electrodes of a particular shape and configuration, one skilled in the art will recognize that other shapes and configurations are possible. FIG. 27 is a perspective view of another embodiment of a capacitive electrode of a wireless power transfer system 500, generally identified by reference numeral 3300. The capacitive electrode 3300 is identical to the previously described segment 1402 unless otherwise stated. In this embodiment, the capacitive electrode 3300 includes a transmit segment 3302 forming the transmit capacitive electrode 516 of the multi-phase transmit resonator 512 and a receive segment 3304 forming the receive capacitive electrode 522 of the multi-phase receive resonator 520. The segments 3302 and 3304 are arranged around an axis 3310 such that the axis passes through a center point within a circle formed by the segments 3302 and 3304. In this embodiment, the axis 3310 has a radius of 30 millimeters. The segments 3302 and 3304 have an inner axial displacement from the axis 3310 of 20 millimeters. The segments 3302 and 3304 have an outer axial displacement from the axis 3310 of 120 millimeters. In a simulation of the wireless power transfer system 500 with the segments 3302 and 3304 having an angular position θ of 0 degrees, the RF efficiency of the wireless power transfer system 500 was found to be 87%.

[0169] An experimental wireless power transfer system 4000 has been constructed and is shown in Figures 28A-28C. As shown in Figure 28A, the wireless power transfer system 4000 includes a transmitter 4010 and a receiver 4020. The transmitter 4010 and receiver 4020 are identical to the described transmitter 502 and receiver 504, respectively, unless otherwise noted. Components of the wireless power transfer system 4000, such as a power source and a load, are not shown in Figures 28A-28C.

[0170] The transmitter 4010 and receiver 4020 are configured identically. Therefore, for ease of explanation, only the transmitter 4010 will be described. As clearly depicted in Figures 28A and 28B, the transmitter 4010 includes three (3) capacitive electrodes 4002 and a passive electrode 4004 located opposite the capacitive electrodes 4002 with respect to the receiver 4020. The required electronics for the transmitter 4010 are located on the side of the passive electrodes 4004 opposite the capacitive electrodes 4002 such that emissions due to the passive electrodes 4004 are minimized. In this embodiment, the electronics reside on a printed circuit board (PCB) 4006.

[0171] In this experimental wireless power transfer system 4000, the electrodes 4002 and 4004 were cut from aluminum. The outer and inner diameters of the capacitive electrode 4002 were 100 millimeters and 20 millimeters, respectively. The separation distance between the transmitter 4010 and the receiver 4020 was uniformly 25 millimeters. The separation distance between the transmitter 4010 and the passive electrode 4004 was uniformly 10 millimeters.

[0172] Experimental data has been collected for system 400 to determine system performance. In particular, RF efficiency and received rectified voltage have been determined as a function of rotation angle for various loads, e.g., 50 W, 25 W, and 12.5 W. Turning now to Figures 29A and 29B, the results of those experiments are depicted.

[0173] FIG. 29A is a graph of the RF efficiency of the wireless power transfer system 4000 as a function of angular rotation. The RF efficiency at various loads (50W, 25W, and 12.5W) is depicted. As the load decreases, a more pronounced sensitivity to rotation in the efficiency is observed. At 12.5W, an efficiency minimum occurs at a multiple of 120 due to increased losses from diode communication and inverter hard switching. It is shown that power transfer to a 50W load across a 25 millimeter transmission gap is possible with an average end-to-end efficiency of 73% for all rotations.

[0174] FIG. 29B shows the rectified voltage (V rect ) is a graph of V rect is the unregulated rectified voltage received at the receiver 4020. Similar to FIG. 29A, the rectified voltage is plotted for various loads (50W, 25W, and 12.5W). On average, the maximum and minimum V rect The ratio between has been found to be approximately 1.66. Although the transmit capacitive electrode 406 has been described as having a particular configuration, one skilled in the art will recognize that other configurations are possible. In another embodiment, the transmit capacitive electrode 406 is multi-fold rotationally symmetric. The axis of the multi-fold rotational symmetry is perpendicular to the major surface of the capacitive electrode 406 about the center of curvature of the capacitive electrode 406. Although the transmit capacitive electrode 406 has been described, one skilled in the art will recognize that the receive capacitive electrode 410 may be similarly configured.

[0175] Although a particular wireless power transfer system has been described, one skilled in the art will recognize that other configurations are possible. The wireless power transfer system may further include at least one of a transmitting passive electrode and a receiving passive electrode. Passive electrodes are described in U.S. Patent Application No. 16 / 138,344, filed September 21, 2018, the relevant portions of which are incorporated herein by reference.

[0176] While embodiments have been described above and shown in the accompanying drawings, it will be appreciated that variations and modifications may be made without departing from the scope as defined by the appended claims, which scope is to be accorded the broadest interpretation consistent with this specification as a whole.

Claims

1. a polyphase radio frequency converter configured to output a plurality of sinusoidal radio frequency power signals; a multi-phase transmit resonator configured to receive the plurality of sinusoidal radio frequency power signals and resonate a plurality of inductors and capacitive electrodes at a resonant frequency in a plurality of phases to transfer power via resonant electric field coupling; The transmitter, wherein the multiphase transmit resonator (310, 512) includes three inductors (404, 514) and three capacitive electrodes (406, 516), and a first capacitive electrode (602) is electrically connected to a third capacitive electrode (606) via a lumped capacitor (608).

2. The transmitter of claim 1 , wherein the capacitive electrodes are multi-fold rotationally symmetric.

3. The transmitter of claim 2 , wherein the axis of multi-fold rotational symmetry is perpendicular to a major surface of the capacitive electrode about a center of curvature of the capacitive electrode.

4. 4. The transmitter of claim 1, wherein the multi-phase radio frequency converter comprises a multi-phase radio frequency inverter including a plurality of transistors, each transistor being electrically connected to an inductor of the multi-phase transmitting resonator.

5. 5. The transmitter of claim 1, further comprising a power supply electrically connected to the polyphase radio frequency converter, the power supply configured to output a DC power signal.

6. The transmitter of claim 1 , wherein the multi-phase transmit resonator is balanced.

7. a multi-phase receiver resonator including a plurality of inductors and capacitive electrodes resonating at a plurality of phases, the multi-phase receiver resonator being configured to resonate at a resonant frequency to extract power via resonant electric field coupling and output a plurality of sinusoidal radio frequency power signals; a multi-phase rectifier configured to receive the plurality of sinusoidal radio frequency power signals and to output a DC power signal; A receiver, wherein the multiphase receiving resonator includes three inductors and three capacitive electrodes, a first capacitive electrode being electrically connected to a third capacitive electrode via a lumped capacitor.

8. 8. The receiver of claim 7, wherein the capacitive electrodes are multi-fold rotationally symmetric.

9. 9. The receiver of claim 8, wherein the axis of multi-fold rotational symmetry is perpendicular to a major surface of the capacitive electrode about a center of curvature of the capacitive electrode.

10. 10. The receiver of claim 7, wherein the multi-phase rectifier comprises a plurality of pairs of diodes, each pair of diodes electrically connected to an inductor of the multi-phase receiver resonator.

11. 11. The receiver of claim 7, further comprising a load configured to receive the DC power signal output by the multi-phase rectifier.

12. Receiver according to any one of claims 7 to 11, wherein the multiphase receiver resonator is balanced.

13. A transmitter comprising: a multi-phase radio frequency converter configured to output a plurality of sinusoidal radio frequency power signals; a multi-phase transmit resonator configured to receive the plurality of sinusoidal radio frequency power signals and resonate a plurality of transmit inductors and transmit capacitive electrodes at a resonant frequency in a plurality of phases to transfer power via resonant electric field coupling; A receiver comprising: a multi-phase receiving resonator including a plurality of receiving inductors and receiving capacitive electrodes resonating at the plurality of phases, the multi-phase receiving resonator being configured to resonate at a resonant frequency to extract power via resonant electric field coupling and output the plurality of sinusoidal radio frequency power signals; a multi-phase rectifier configured to receive the plurality of sinusoidal radio frequency power signals and output a DC power signal; the multi-phase transmit resonator includes three transmit inductors and three transmit capacitive electrodes, a first transmit capacitive electrode being electrically connected to a third transmit capacitive electrode via a lumped capacitor; and / or The system, wherein the multiphase receive resonator includes three receive inductors and three receive capacitive electrodes, a first receive capacitive electrode being electrically connected to a third receive capacitive electrode via a lumped capacitor.

14. The system of claim 13 , wherein the transmit capacitive electrodes are multi-fold rotationally symmetric.

15. 15. The system of claim 14, wherein an axis of multi-fold rotational symmetry of the transmit capacitive electrode is perpendicular to a major surface of the transmit capacitive electrode about a center of curvature of the transmit capacitive electrode.

16. 16. The system of claim 13, wherein the receiving capacitive electrodes are multi-fold rotationally symmetric.

17. 17. The system of claim 16, wherein an axis of multi-fold rotational symmetry of the receiving capacitive electrode is perpendicular to a major surface of the receiving capacitive electrode about a center of curvature of the receiving capacitive electrode.

18. 18. The system of claim 13, wherein the multi-phase radio frequency converter comprises a multi-phase radio frequency inverter including a plurality of transistors, each transistor electrically connected to an inductor of the multi-phase transmit resonator.

19. 19. The system of claim 13, wherein the transmitter further comprises a power supply electrically connected to the multi-phase radio frequency converter, the power supply configured to output a DC power signal.

20. 20. The system of claim 13, wherein the multi-phase transmit resonator is balanced.

21. 21. The system of claim 13, wherein the multi-phase rectifier includes a plurality of pairs of diodes, each pair of diodes electrically connected to an inductor of the multi-phase receiver resonator.

22. 22. The system of claim 13, wherein the receiver further comprises a load configured to receive the DC power signal output by the multi-phase rectifier.

23. 23. A system according to any one of claims 13 to 22, wherein the multiphase receiver resonator is balanced.

24. 1. A method for wirelessly transmitting power via electric field coupling, comprising:

7. A multi-phase radio frequency converter for a transmitter according to claim 1, comprising the steps of: converting an input power signal into a plurality of sinusoidal radio frequency power signals; receiving the plurality of sinusoidal radio frequency power signals at a multiphase transmit resonator of the transmitter; resonating a pair of a transmitting inductor and a capacitive electrode of a multi-phase transmitting resonator of the transmitter to generate an electric field; and extracting power by a multiphase receiver resonator of a receiver according to any one of claims 7 to 12, the multiphase receiver resonator being positioned within the generated electric field.

25. outputting a received sinusoidal radio frequency power signal to a polyphase rectifier of the receiver; 25. The method of claim 24, further comprising the step of: rectifying the received sinusoidal radio frequency power signal into a rectified signal.

26. 26. The method of claim 25, wherein the rectified signal is a DC power signal.

27. 27. The method of any one of claims 24 to 26, wherein the input power signal is a DC power signal.

28. 28. The method of claim 24, wherein resonating the pair of transmitting inductor and capacitive electrode comprises resonating the pair at a resonant frequency of a multi-phase resonator of the transmitter.

29. 28. The method of any one of claims 24 to 27, wherein resonating the transmitting inductor and capacitive electrode pair includes resonating the i-th transmitting inductor and capacitive electrode pair at a phase of (i-1) x 360 / n degrees, where n is the number of sinusoidal radio frequency power signals.

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