Abstract:
Exemplary embodiments are directed to wireless power transfer. A wireless power transceiver and device comprise an antenna including a parallel resonator configured to resonate in response to a substantially unmodulated carrier frequency. The wireless power transceiver further comprises a bidirectional power conversion circuit coupled to the parallel resonator. The bidirectional power conversion circuit is reconfigurable to rectify an induced current received at the antenna into DC power and to induce resonance at the antenna in response to DC power.

Description:
CLAIM OF PRIORITY UNDER 35 U.S.C. §119 
     This application claims priority under 35 U.S.C. §119(e) to:
         U.S. Provisional Patent Application 61/093,692 entitled “BIDIRECTIONAL WIRELESS ENERGY TRANSFER” filed on Sep. 2, 2008, the disclosure of which is hereby incorporated by reference in its entirety.   U.S. Provisional Patent Application 61/097,859 entitled “HIGH EFFICIENCY TECHNIQUES AT HIGH FREQUENCY” filed on Sep. 17, 2008, the disclosure of which is hereby incorporated by reference in its entirety.   U.S. Provisional Patent Application 61/104,218 entitled “DUAL HALF BRIDGE POWER CONVERTER” filed on Oct. 9, 2008, the disclosure of which is hereby incorporated by reference in its entirety.   U.S. Provisional Patent Application 61/147,081 entitled “WIRELESS POWER ELECTRONIC CIRCUIT” filed on Jan. 24, 2009, the disclosure of which is hereby incorporated by reference in its entirety.   U.S. Provisional Patent Application 61/218,838 entitled “DEVELOPMENT OF HF POWER CONVERSION ELECTRONICS” filed on Jun. 19, 2009, the disclosure of which is hereby incorporated by reference in its entirety.       

    
    
     BACKGROUND 
     1. Field 
     The present invention relates generally to wireless charging, and more specifically to devices, systems, and methods related to wireless charging systems. 
     2. Background 
     Typically, each powered device such as a wireless electronic device requires its own wired charger and power source, which is usually an alternating current (AC) power outlet. Such a wired configuration becomes unwieldy when many devices need charging. Approaches are being developed that use over-the-air or wireless power transmission between a transmitter and a receiver coupled to the electronic device to be charged. The receive antenna collects the radiated power and rectifies it into usable power for powering the device or charging the battery of the device. 
     Situations may exist where, among several chargeable wireless devices, one wireless chargeable device is depleted of operational charge while another wireless chargeable device has sufficient operational charge. Accordingly, there is a need to allow wireless exchange of power from one wireless chargeable device to another wireless chargeable device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a simplified block diagram of a wireless power transmission system. 
         FIG. 2  illustrates a simplified schematic diagram of a wireless power transmission system. 
         FIG. 3  illustrates a schematic diagram of a loop antenna, in accordance with exemplary embodiments. 
         FIG. 4  illustrates a functional block diagram of a wireless power transmission system, in accordance with an exemplary embodiment. 
         FIG. 5A  and  FIG. 5B  illustrate a bidirectional wireless power device, in accordance with an exemplary embodiment. 
         FIG. 6A  and  FIG. 6B  illustrate various operational contexts for an electronic device configured for bidirectional wireless power transmission, in accordance with exemplary embodiments. 
         FIG. 7  illustrates a block diagram of an electronic device configured for bidirectional wireless power transmission, in accordance with an exemplary embodiment. 
         FIG. 8  illustrates a circuit diagram of a half bridge rectifier. 
         FIG. 9  illustrates a circuit diagram of a wireless power transmission system, in accordance with an exemplary embodiment. 
         FIG. 10  illustrates a circuit diagram of a wireless power transmission system, in accordance with another exemplary embodiment. 
         FIG. 11  illustrates a flowchart of a method for transceiving wireless power, in accordance with an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. 
     The detailed description set forth below in connection with the appended drawings is intended as a description of exemplary embodiments of the present invention and is not intended to represent the only embodiments in which the present invention can be practiced. The term “exemplary” used throughout this description means “serving as an example, instance, or illustration,” and should not necessarily be construed as preferred or advantageous over other exemplary embodiments. The detailed description includes specific details for the purpose of providing a thorough understanding of the exemplary embodiments of the invention. It will be apparent to those skilled in the art that the exemplary embodiments of the invention may be practiced without these specific details. In some instances, well-known structures and devices are shown in block diagram form in order to avoid obscuring the novelty of the exemplary embodiments presented herein. 
     The term “wireless power” is used herein to mean any form of energy associated with electric fields, magnetic fields, electromagnetic fields, or otherwise that is transmitted from a transmitter to a receiver without the use of physical electromagnetic conductors. Power conversion in a system is described herein to wirelessly charge devices including, for example, mobile phones, cordless phones, iPod, MP3 players, headsets, etc. Generally, one underlying principle of wireless energy transfer includes magnetic coupled resonance (i.e., resonant induction) using frequencies, for example, below 30 MHz. However, various frequencies may be employed including frequencies where license-exempt operation at relatively high radiation levels is permitted, for example, at either below 135 kHz (LF) or at 13.56 MHz (HF). At these frequencies normally used by Radio Frequency Identification (RFID) systems, systems must comply with interference and safety standards such as EN 300330 in Europe or FCC Part 15 norm in the United States. By way of illustration and not limitation, the abbreviations LF and HF are used herein where “LF” refers to f 0 =135 kHz and “HF” to refers to f 0 =13.56 MHz. 
     The term “NFC” may also include the functionality of RFID and the terms “NFC” and “RFID” may be interchanged where compatible functionality allows for such substitution. The use of one term or the other is not to be considered limiting. 
     The term “transceiver” may also include the functionality of a transponder and the terms “transceiver” and “transponder” may be interchanged where compatible functionality allows for such substitution. The use of one term over or the other is not to be considered limiting. 
       FIG. 1  illustrates wireless power transmission system  100 , in accordance with various exemplary embodiments. Input power  102  is provided to a transmitter  104  for generating a magnetic field  106  for providing energy transfer. A receiver  108  couples to the magnetic field  106  and generates an output power  110  for storing or consumption by a device (not shown) coupled to the output power  110 . Both the transmitter  104  and the receiver  108  are separated by a distance  112 . In one exemplary embodiment, transmitter  104  and receiver  108  are configured according to a mutual resonant relationship and when the resonant frequency of receiver  108  and the resonant frequency of transmitter  104  are matched, transmission losses between the transmitter  104  and the receiver  108  are minimal when the receiver  108  is located in the “near-field” of the magnetic field  106 . 
     Transmitter  104  further includes a transmit antenna  114  for providing a means for energy transmission and receiver  108  further includes a receive antenna  118  for providing a means for energy reception or coupling. The transmit and receive antennas are sized according to applications and devices to be associated therewith. As stated, an efficient energy transfer occurs by coupling a large portion of the energy in the near-field of the transmitting antenna to a receiving antenna rather than propagating most of the energy in an electromagnetic wave to the far-field. In this near-field, a coupling may be established between the transmit antenna  114  and the receive antenna  118 . The area around the antennas  114  and  118  where this near-field coupling may occur is referred to herein as a coupling-mode region. 
       FIG. 2  shows a simplified schematic diagram of a wireless power transmission system. The transmitter  104 , driven by input power  102 , includes an oscillator  122 , a power amplifier or power stage  124  and a filter and matching circuit  126 . The oscillator is configured to generate a desired frequency, which may be adjusted in response to adjustment signal  123 . The oscillator signal may be amplified by the power amplifier  124  with a power output responsive to control signal  125 . The filter and matching circuit  126  may be included to filter out harmonics or other unwanted frequencies and match the impedance of the transmitter  104  to the transmit antenna  114 . 
     An electronic device  120  couples to or includes the receiver  108 . Receiver  108  may include a matching circuit  132  and a rectifier and switching circuit  134  to generate a DC power output to charge a battery  136  as shown in  FIG. 2  or power host electronics in device  120  coupled to the receiver  108 . The matching circuit  132  may be included to match the impedance of the receiver  108  to the receive antenna  118 . 
     A communication channel  119  may also exist between the transmitter  104  and the receiver  108 . As described herein, the communication channel  119  may be of the form of Near-Field Communication (NFC). In one exemplary embodiment described herein, communication channel  119  is implemented as a separate channel from magnetic field  106  and in another exemplary embodiment, communication channel  119  is combined with magnetic field  106 . 
     As illustrated in  FIG. 3 , antennas used in exemplary embodiments may be configured as a “loop” antenna  150 , which may also be referred to herein as a “magnetic,” “resonant” or a “magnetic resonant” antenna. Loop antennas may be configured to include an air core or a physical core such as a ferrite core. Furthermore, an air core loop antenna allows the placement of other components within the core area. In addition, an air core loop may more readily enable placement of the receive antenna  118  ( FIG. 2 ) within a plane of the transmit antenna  114  ( FIG. 2 ) where the coupled-mode region of the transmit antenna  114  ( FIG. 2 ) may be more effective. 
     As stated, efficient transfer of energy between the transmitter  104  and receiver  108  occurs during matched or nearly matched resonance between the transmitter  104  and the receiver  108 . However, even when resonance between the transmitter  104  and receiver  108  are not matched, energy may be transferred at a lower efficiency. Transfer of energy occurs by coupling energy from the near-field of the transmitting antenna to the receiving antenna residing in the neighborhood where this near-field is established rather than propagating the energy from the transmitting antenna into free space. 
     The resonant frequency of the loop antennas is based on the inductance and capacitance. Inductance in a loop antenna is generally the inductance created by the loop, whereas, capacitance is generally added to the loop antenna&#39;s inductance to create a resonant structure at a desired resonant frequency. As a non-limiting example, capacitor  152  and capacitor  154  may be added to the antenna to create a resonant circuit that generates a sinusoidal or quasi-sinusoidal signal  156 . Accordingly, for larger diameter loop antennas, the size of capacitance needed to induce resonance decreases as the diameter or inductance of the loop increases. Furthermore, as the diameter of the loop antenna increases, the efficient energy transfer area of the near-field increases for “vicinity” coupled devices. Of course, other resonant circuits are possible. As another non-limiting example, a capacitor may be placed in parallel between the two terminals of the loop antenna. In addition, those of ordinary skill in the art will recognize that for transmit antennas the resonant signal  156  may be an input to the loop antenna  150 . 
     Exemplary embodiments of the invention include coupling power between two antennas that are in the near-fields of each other. As stated, the near-field is an area around the antenna in which electromagnetic fields exist but may not propagate or radiate away from the antenna. They are typically confined to a volume that is near the physical volume of the antenna. In the exemplary embodiments of the invention, antennas such as single and multi-turn loop antennas are used for both transmit (Tx) and receive (Rx) antenna systems since most of the environment possibly surrounding the antennas is dielectric and thus has less influence on a magnetic field compared to an electric field. Furthermore, antennas dominantly configured as “electric” antennas (e.g., dipoles and monopoles) or a combination of magnetic and electric antennas is also contemplated. 
     The Tx antenna can be operated at a frequency that is low enough and with an antenna size that is large enough to achieve good coupling efficiency (e.g., &gt;10%) to a small Rx antenna at significantly larger distances than allowed by far-field and inductive approaches mentioned earlier. If the Tx antenna is sized correctly, high coupling efficiencies (e.g., 30%) can be achieved when the Rx antenna on a host device is placed within a coupling-mode region (i.e., in the near-field or a strongly coupled regime) of the driven Tx loop antenna 
     Furthermore, wireless power transmission approaches may be affected by the transmission range including device positioning (e.g., close “proximity” coupling for charging solutions at virtually zero distance or “vicinity” coupling for short range wireless power solutions). Close proximity coupling applications (i.e., strongly coupled regime, coupling factor typically k&gt;0.1) provide energy transfer over short or very short distances typically in the order of millimeters or centimeters depending on the size of the antennas. Vicinity coupling applications (i.e., loosely coupled regime, coupling factor typically k&lt;0.1) provide energy transfer at relatively low efficiency over distances typically in the range from 10 cm to 2 m depending on the size of the antennas. 
       FIG. 4  illustrates a functional block diagram of a wireless power transmission system configured for direct field coupling between a transmitter and a receiver, in accordance with an exemplary embodiment. Wireless power transmission system  200  includes a transmitter  204  and a receiver  208 . Input power P TXin  is provided to transmitter  204  at input port  202  for generating a predominantly non-radiative field with direct field coupling k  206  for providing energy transfer. Receiver  208  directly couples to the non-radiative field  206  and generates an output power P RXout  for storing or consumption by a battery or load  236  coupled to the output port  210 . Both the transmitter  204  and the receiver  208  are separated by a distance. In one exemplary embodiment, transmitter  204  and receiver  208  are configured according to a mutual resonant relationship and when the resonant frequency, f 0 , of receiver  208  and the resonant frequency of transmitter  204  are matched, transmission losses between the transmitter  204  and the receiver  208  are minimal while the receiver  208  is located in the “near-field” of the radiated field generated by transmitter  204 . 
     Transmitter  204  further includes a transmit antenna  214  for providing a means for energy transmission and receiver  208  further includes a receive antenna  218  for providing a means for energy reception. Transmitter  204  further includes a transmit power conversion circuit  220  at least partially functioning as an AC-to-AC converter. Receiver  208  further includes a receive power conversion circuit  222  at least partially functioning as an AC-to-DC converter. 
     Various transmit and receive antenna configurations described herein use capacitively loaded wire loops or multi-turn coils forming a resonant structure that is capable to efficiently couple energy from transmit antenna  214  to the receive antenna  218  via the magnetic field if both the transmit antenna  214  and receive antenna  218  are tuned to a common resonance frequency, f 0 . Accordingly, highly efficient wireless charging of electronic devices (e.g. mobile phones) in a strongly coupled regime is described where transmit antenna  214  and receive antenna  218  are in close proximity resulting in coupling factors typically above 30%. Accordingly, various transmitter and receiver power conversion concepts comprised of a wire loop/coil antenna and power conversion circuits are described herein. 
     While wireless power transmission may occur when one device in a wireless power transmission system includes a transmitter and another device includes a receiver, a single device may include both a wireless power transmitter and a wireless power receiver. Accordingly, such an embodiment could be configured to include dedicated transmit circuitry (e.g., a transmit power conversion circuit and a transmit antenna) and dedicated receiver circuitry (e.g., a receive antenna and a receive power conversion circuit). Since a device is not concurrently configured as a wireless power transmitter and a wireless power receiver, reuse of common circuitry including antennas is desirable. Accordingly, the various exemplary embodiments disclosed herein identify bidirectional power transmission, namely, the capability for a device to both receive wireless power at the device and to transmit wireless power from the device. 
     Various benefits of such a configuration include the ability of a device receive and store wireless power and then to subsequently transmit or “donate” stored power to another receiving or “absorbing” device. Accordingly, such a configuration may also be considered as a “peer-to-peer” “charitable” charging configuration. Such a device-charging arrangement provides considerable convenience in location under which charging occurs (i.e., the receiver or “absorbing” device need not necessarily receive a charge from an inconveniently located or unavailable charging pad). 
       FIG. 5A  and  FIG. 5B  illustrate a bidirectional wireless power device, in accordance with an exemplary embodiment. Bidirectional wireless powering and charging of electronic devices (e.g. mobile phones, head sets, MP3 players, etc.) is disclosed in which electrical energy can be wirelessly transferred, as illustrated in  FIG. 5A , from a power conversion circuit  220  and transmit antenna  214  of a power base  302  (e.g. charging pad) to a bidirectional wireless power transceiver  318  including a transceiver antenna  306  and a bidirectional power conversion circuit  308  of an electronic device  300  as illustrated in  FIG. 5B . Then, as illustrated with reference to  FIG. 5B , the wirelessly transmitted power is stored in a load illustrated as battery  310 . The stored power in battery  310  is then donated through the bidirectional power conversion circuit  308  and transceiver antenna  306  of electronic device  300  to a receive antenna  312  and a power conversion circuit  314  of another electronic device  304  for consumption or storage in load or battery  316 . 
     As described herein, wireless power transfer uses coupled resonance (e.g. 
     capacitively loaded wire loop/coil) that is capable of efficiently coupling energy from a transmitter to a receiver via the magnetic or electric field if both transmitter and receiver are tuned to a common resonance frequency. The various exemplary embodiments described herein include a wireless power transceiver including a resonant antenna  306  and a bidirectional power conversion circuit  308  that can be operated in at least two quadrants, meaning that bidirectional power conversion circuit  308  can either be used as power sink (i.e., positive power flow) or as a power source (i.e., negative power flow). The wireless power transceiver  300  integrated into electronic devices enables wireless exchange of electrical energy among similarly configured electronic devices. The bidirectional power conversion circuit  308  may include a synchronous rectifier as described herein. 
     As stated, electronic device  300  is configured for bidirectional wireless power transmission. With further reference to  FIG. 5A , in a receiving or “absorbing” mode, battery (e.g., power storage device)  310  may be wirelessly charged from an AC mains supplied power base (e.g. charging pad)  302 . With further reference to  FIG. 5B , electronic device  300  may be operated in reverse in a transmit or “donor” mode for transmission of wireless power to another electronic device  304  for operation and storage at a battery  316  that is used to power the electronic device  304 . 
       FIG. 6A  and  FIG. 6B  illustrate various operational contexts for an electronic device configured for bidirectional wireless power transmission, in accordance with exemplary embodiments. Specifically, an electronic device  300  configured for bidirectional wireless power transmission engages in wireless power transmission with a power base  302  wherein electronic device  300  receives wireless power and stores the received power in a battery. Subsequently electronic device  300  is solicited, volunteers or otherwise is enlisted as a donor of stored power. Accordingly, one or more electronic devices  304 A,  304 B receive power from electronic device  300  through a wireless power transmission process. 
     It is contemplated that the wireless transmission process with electronic device  300  operating in donor mode, may be to provide power replenishment e.g. in an urgency, or at least temporary charge, to another device  304 B, or the charging of a micro-power device  304 A, such as headsets, MP3 players, etc. For this purpose, device A is set into donor mode via a user interface or responsive to allowed solicitations. Furthermore, donor electronic device  300  may also perform energy management of its own available power to avoid excessive depletion of stored power within the battery of the donor electronic device  300 . Accordingly, assuming a standardized wireless power interface, devices may be recharged or partially recharged almost everywhere from any wireless power device that can act as donor electronic device and that provides sufficient battery capacity. 
       FIG. 7  illustrates a block diagram of an electronic device configured for bidirectional wireless power transmission, in accordance with an exemplary embodiment. The electronic device  300  includes an antenna  306 , a bidirectional power conversion circuit  308  and a switch  326  for supplying power to the battery  310  or directly to the host device electronics  324 . Bidirectional power conversion circuit  308  includes an active rectifier, an example of which is a synchronous rectifier  320 , and can be operated in at least two quadrants of the VI-plane. 
     Bidirectional power conversion circuit  308  further includes a frequency generation and control circuit  322  for generating the switch waveforms  328  required to operate synchronous rectifier  320  in the desired (transmit or receive) mode and to control the extent to which the electronic device shares its power stored in battery  310  while in donor mode. Frequency generation and control circuit  322  is controlled by control within the host device electronics  324  which also performs battery management and provides a user interface for selection of donor mode. Furthermore, synchronous rectifier  320  may also provide power to frequency generation and control circuit  322  during receive mode when power from battery  310  is depleted or otherwise unavailable. 
     As described, the active rectifier in bidirectional power conversion circuit  306  may be configured as a synchronous rectifier.  FIG. 8  illustrates circuit diagrams of a half bridge rectifier topology  400  including a series resonant magnetic antenna and its dual topology  420  including a parallel resonant magnetic antenna where ‘dual’ refers to the dualism of electrical circuits that is well known in electrical engineering. A synchronous rectifier circuit further described below is based upon a half bridge inverter (push-pull Class D amplifier) topology further arranged in a dual configuration. The dual configuration provides performance benefits at higher frequencies (at HF, e.g. &gt;1 MHz) with respect to switching losses and soft switching and is applicable to transmit and receive power conversion. 
     As illustrated in circuit  400 , conventional half bridge inverter designs include shortcomings relating to switching losses affecting the resonance of antenna  406  caused by junction capacitance of switch transistors. As illustrated in  FIG. 8 , even when soft switching at zero current control is applied, junction capacitance C j    402  needs to be charged and C j′   404  to be discharged or vice-versa at each switching event, causing significant losses at higher frequency. This in contrast to its dual counterpart (i.e., serial-to-parallel conversion) where junction capacitances C j    422  and C j′   424  may be considered merged into a total capacitance comprised of C 1  and junction capacitances C j    422  and C j′   424 . The total capacitance is then adjusted to achieve resonance in the antenna  426  at the desired frequency. 
     The circuit topology of circuit  420  performs with low dV/dt voltage across switches S 1 , S 1′  and enables zero voltage switching, similar to Class E amplifier circuits.  FIG. 9  illustrates a circuit diagram of a wireless power transmission system, in accordance with an exemplary embodiment. A wireless power transmission system  450  includes a bidirectional wireless power transceiver  318 T (where “T” indicates a Transmitter configuration) with a half bridge active rectifier configured with the switching capacitance of switches Q 1  and Q 1′  merged into the resonance capacitance C 1 and a receiver  454 . 
     Bidirectional wireless power transceiver  318 T includes a bidirectional power conversion circuit  308 T and an antenna  306 T. In bidirectional power conversion circuit  308 T, a half bridge active rectifier includes switches Q 1  and Q 1′ , such as a pair of matched Field Effect Transistors (FETs) with adequate voltage and current ratings. The FET switches Q 1  and Q 1′  are driven and accurately controlled by a frequency generation and control circuit  322 T as further monitored by sensors  470  for sensing voltage and current on both FET switches Q 1  and Q 1′ . Furthermore, low loss zero voltage switching, also relies upon accurate tuning of the tank circuit of transmit antenna, L 1  and C 1 , to eliminate any phase shift between tank voltage and the FETs rectangular current waveform. In an exemplary embodiment this tuning may be performed by adjusting the capacitor C 1 . 
     Though even harmonics are potentially suppressed by the symmetric topology (push-pull), odd harmonics filtering in form of a series resonant L-C circuits e.g. tuned to 3 rd  harmonic may additionally be useful. This may be accomplished using additional series resonance, illustrated as harmonic filter  458 T, tuned to harmonic frequencies across the tank circuit of transmit antenna, L 1  and C 1 . 
     In a unidirectional device (receiver)  454  , a half bridge passive diode rectifier  460  is particularly suitable with regard to low voltage/high current charging of a battery  462  (e.g. Li-Ion). Half bridge passive diode rectifier  460  transforms the low load resistance of battery  462  into higher impedance enabling an antenna tank circuit with a realizable L-C ratio for improving receiver efficiency. 
       FIG. 10  illustrates a circuit diagram of a wireless power transmission system, in accordance with another exemplary embodiment. This exemplary embodiment enables exchange of energy from one battery operated device to another battery operated device equally in both directions. A wireless power transmission system  500  includes a bidirectional wireless power transceiver  318 T (where “T” indicates a Transmitter configuration or transmit mode) and a bidirectional wireless power transceiver  318 R (where “R” indicates a Receiver configuration or receive mode). 
     Bidirectional wireless power transceiver  318 T includes a bidirectional power conversion circuit  308 T and an antenna  306 T. In bidirectional power conversion circuit  308 T, a half bridge active rectifier includes switches Q 1  and Q 1′ , such as a pair of matched Field Effect Transistors (FETs) with adequate voltage and current ratings. The FET switches Q 1  and Q 1′  are driven and accurately controlled by a frequency generation and control circuit  322 T as further monitored by sensors  470  for sensing voltage and current on both FET switches Q 1  and Q 1′ . Furthermore, low loss zero voltage switching, also relies upon accurate tuning of the tank circuit of transmit antenna  306 T, L 1  and C 1 , to eliminate any phase shift between tank voltage and the FETs rectangular current waveform. In an exemplary embodiment this tuning may be performed by adjusting capacitor C 1 . 
     Though even harmonics are potentially suppressed by the symmetric topology (push-pull), odd harmonics filtering in form of a series resonant L-C circuits e.g. tuned to 3 rd  harmonic may additionally be useful. This may be accomplished using additional series resonance, illustrated as harmonic filter  458 T, tuned to harmonic frequencies across the tank circuit of transmit antenna, L 1  and C 1 . 
     Bidirectional wireless power transceiver  318 R includes a bidirectional power conversion circuit  308 R and an antenna  306 R. In bidirectional power conversion circuit  308 R, a half bridge active rectifier includes switches Q 2  and Q 2′ , such as a pair of matched Field Effect Transistors (FETs) with adequate voltage and current ratings. The FET switches Q 2  and Q 2′  are driven and accurately controlled by a frequency generation and control circuit  322 R as further monitored by sensors  470  for sensing voltage and current on both FET switches Q 2  and Q 2′ . The drive waveforms may be continuously adjusted in the manner of a phase-locked-loop to reach frequency and phase synchronization with the antenna induced current such to provide maximum or the desired DC power output. As opposed to transmit mode requirements on tuning of the tank circuit of receive antenna, L 2  and C 2 , in receive mode is less critical and some offset from resonance may be tolerated. Thus adjustment e.g. of capacitor C 2  may be less accurate or not be used at all. 
     Though even harmonics are potentially suppressed by the symmetric topology (push-pull), odd harmonics filtering in form of a series resonant L-C circuits e.g. tuned to 3 rd  harmonic may additionally be useful. This may be accomplished using additional series resonance, illustrated as harmonic filter  458 R, tuned to harmonic frequencies across the tank circuit of transmit antenna, L 1  and C 1 . 
     In receive or absorbing mode, the bidirectional power conversion circuit  308  acts as a synchronous rectifier and switches are controlled based on sensed voltage. The exemplary embodiments may also include shunt diodes (not shown) across switches Q 1  and Q 1′ . These switches Q 1  and Q 1′  ensure that the circuit is self recovering in the event the battery is depleted. Specifically, the circuit begins to rectify received high frequency power to provide power to the frequency generation and control circuit  322 . 
       FIG. 11  illustrates a flowchart of a method for transceiving wireless power, in accordance with an exemplary embodiment. Method  600  for transceiving wireless power is supported by the various structures and circuits described herein. Method  600  includes step  602  for receiving an induced current from an antenna resonating in response to a magnetic near-field and rectifying the induced current into DC power through a bidirectional power conversion circuit when the bidirectional power conversion circuit is configured in receive mode. Method  600  further includes step  604  for generating an induced current at a resonant frequency into the antenna from stored DC power through the bidirectional power conversion circuit and generating a magnetic near-field from the antenna when the bidirectional power conversion circuit is configured in transmit mode. 
     Those of skill in the art would understand that control information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. 
     Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, and controlled by computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented and controlled as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the exemplary embodiments of the invention. 
     The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be controlled with a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
     The control steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in Random Access Memory (RAM), flash memory, Read Only Memory (ROM), Electrically Programmable ROM (EPROM), Electrically Erasable Programmable ROM (EEPROM), registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal. 
     In one or more exemplary embodiments, the control functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. 
     The previous description of the disclosed exemplary embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these exemplary embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.