Patent Publication Number: US-2022224168-A1

Title: Wireless Power Delivery Systems and Methods of Delivering Wireless Power

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of and priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application Ser. No. 63/136,159, entitled “Long Distance Wireless Power Delivery to a Battery Free Device” and filed Jan. 11, 2021, which is incorporated herein by reference in its entirety for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to wireless power delivery systems and methods of delivering wireless power. 
     BACKGROUND 
     Non-proximity wireless power transmission at a distance through use of radio frequency (RF) and mm-wave beam forming and focusing may enable and enhance a plethora of new applications such as powering and charging of portable and standalone devices wirelessly. For example, the proliferation of internet of things (IoT) devices and sensors can be substantially accelerated by delivering power to them wirelessly and eliminating need for extra wiring during installation of such devices or frequent replacement or charging of batteries. Another example of practical usage of such devices is continuous background wireless powering and charging of portable personal devices, such as smartphones and tablets that may significantly enhance their usability and in the long run reduce the demand on the amount of energy that needs to be carried by such devices (e.g., as in a battery), due the ubiquity and availability of long-range wireless power transfer and wireless charging. In addition to these devices many other smaller devices such as wireless mouse and keyboard to thermostats and security sensors and cameras may benefit from wireless power transfer, which may eliminate the need to plug them in or change the battery. 
     SUMMARY OF THE INVENTION 
     Various embodiments are directed to a wireless power delivery system including: a wireless power generation unit (GU) including: a GU antenna array; and a GU wireless communication circuit; and one or more recovery units (RUs), where each RU comprises: an RU antenna array; and an RU wireless communication circuit, where the GU antenna array is configured to use volumetric refocusing to scan the area for the one or more RUs by sweeping a wireless scan signal to be captured by the RU antenna array, where when the RU antenna array receives the wireless scan signal, the RU wireless communication unit is configured to transmit a wireless signal back to the GU wireless communication unit, where the GU is configured to record the focal coordinates of each RU based upon the signal received by the GU from each RU, and where the GU is configured to emit a wireless power signal to the recorded focal coordinates of each RU to be received by each RU antenna array. 
     In various other embodiments, the GU records the focal coordinates of each RU further based upon when the wireless signal is received by the GU and the beam direction of the wireless scan signal at that time. 
     In still various other embodiments, the GU further includes: a processor; and memory including machine readable instructions executable by the processor to: control the GU antenna array to sweep the wireless scan signal; record the focal coordinates of each RU; and control the GU antenna array to emit the wireless power signal to the focal coordinates of each RU. 
     In still various other embodiments, at least one of the one or more RUs is a passive device configured to wake up when the wireless scan signal is received and transmit the wireless signal to the GU. 
     In still various other embodiments, at least one of the one or more RUs further includes an energy storage component capable of powering the RU wireless communication circuit and an RU controller. 
     In still various other embodiments, the RU controller is configured to control the RU wireless communication circuit to transmit the wireless signal back to the GU wireless communication unit. 
     In still various other embodiments, the at least one of the one or more RUs further includes a power detector which is configured to wake up the RU controller when the wireless scan signal is captured by the RU antenna array. 
     In still various other embodiments, the RU further includes a power management integrated circuit which is configured to deliver the power received from the wireless power signal to a powered device. 
     In still various other embodiments, the wireless power signal includes a start signal and a stop signal. 
     In still various other embodiments, the start signal includes transitioning from a high amplitude signal to a low amplitude signal. 
     In still various other embodiments, the stop signal includes transitioning to the low amplitude signal. 
     In still various other embodiments, the low amplitude signal is lower in amplitude than an intermediate ongoing switching. 
     In still various other embodiments, the intermediate ongoing switching includes beam switching or time-division multiplexing. 
     In still various other embodiments, volumetric refocusing includes dynamically moving the focal point of the GU antenna array by applying different phase settings to the wireless scan signal. 
     In still various other embodiments, volumetric refocusing further includes utilizing a phase table obtained by focusing into a known location and re-calculating the phase settings to refocus the wireless scan signal to a different point in space. 
     In still various other embodiments, the re-calculated phase settings include a phase adjustment of: 
     
       
         
           
             
               
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     where antenna m, n in the GU antenna array is used to refocus the wireless scan signal to location {right arrow over (R)} 1  from a calibration point {right arrow over (R)} 0 , and ΔL mn ({right arrow over (R)} 0 {right arrow over (R)} 1 ) is the length difference of antenna m, n in the array to the calibration point {right arrow over (R)} 0  and the location {right arrow over (R)} 1 . 
     Various embodiments are further directed to a method for delivery wireless power, the method including: scanning, using volumetric refocusing, a wireless scan signal from a wireless power generation unit (GU) to one or more recovery units (RUs); when the RUs receive the wireless scan signal, each of the RUs is configured to transmit a wireless signal back to the GU; recording the focal coordinates of each RU based upon the signal received by the GU from each RU; and emitting a wireless power signal from the GU to the recorded focal coordinates to be received by each RU. 
     In various other embodiments, at least one of the one or more RUs is a passive device configured to wake up when receiving the wireless scan signal and transmit the wireless signal to the GU. 
     In still various other embodiments, at least one of the one or more RUs includes an energy storage component and a power detector which is configured to detect the wireless scan signal and wake up the RU to transmit the wireless signal to the GU. 
     In still various other embodiments, the wireless power signal includes a start signal and a stop signal. 
     In still various other embodiments, the start signal includes transitioning from a high amplitude signal to a low amplitude signal. 
     In still various other embodiments, the stop signal includes transitioning to the low amplitude signal. 
     In still various other embodiments, the low amplitude signal is lower in amplitude than an intermediate ongoing switching. 
     In still various other embodiments, the intermediate ongoing switching includes beam switching or time-division multiplexing. 
     In still various other embodiments, volumetric refocusing includes dynamically moving the focal point of the GU antenna array by applying different phase settings to the wireless scan signal. 
     Various embodiments are further directed to a wireless power generation unit (GU) including: a GU antenna array; a GU wireless communication circuit; and a computing unit, where the GU antenna array is configured to use volumetric refocusing to scan the area for one or more recovery units (RUs) by sweeping a wireless scan signal to be captured by each of the RUs, where the GU wireless communication circuit is configured to receive a signal transmitted back from each of the RUs after the RU receives the wireless scan signal, where the computing unit is configured to record the focal coordinates of each RU based upon the signal received from each RU, and where the GU antenna array is further configured to emit a wireless power signal to the recorded focal coordinates of each RU to be received by each RU. 
     In various other embodiments, the wireless power GU further includes a hardware controller configured to control the GU antenna array. 
     In still various other embodiments, the wireless power signal comprises a start signal and a stop signal. 
     In still various other embodiments, the start signal includes transitioning from a high amplitude signal to a low amplitude signal. 
     In still various other embodiments, the stop signal comprises transitioning to the low amplitude signal. 
     In still various other embodiments, the low amplitude signal is lower in amplitude than an intermediate ongoing switching. 
     In still various other embodiments, the intermediate ongoing switching includes beam switching or time-division multiplexing. 
     In still various other embodiments, volumetric refocusing includes dynamically moving the focal point of the GU antenna array by applying different phase settings to the wireless scan signal. 
     In still various other embodiments, volumetric refocusing further includes utilizing a phase table obtained by focusing into a known location and re-calculating the phase settings to refocus the wireless scan signal to a different point in space. 
     In still various other embodiments, the re-calculated phase settings include a phase adjustment of: 
     
       
         
           
             
               
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             , 
           
         
       
     
     where antenna m, n in the GU antenna array is used to refocus the wireless scan signal to location {right arrow over (R)} 1  from a calibration point {right arrow over (R)} 0 , and ΔL mn ({right arrow over (R)} 0 {right arrow over (R)} 1 ) is the length difference of antenna m, n in the array to the calibration point {right arrow over (R)} 0  and the location {right arrow over (R)} 1 . 
     Various embodiments are further directed to a recovery unit (RU) including: an RU antenna array; an RU wireless communication circuit; and a controller, where the RU antenna array is configured to: receive a wireless scan signal from a wireless power generation unit (GU); after the RU antenna array receives the wireless scan signal, wake up the controller which turns on the RU wireless communication circuit to broadcast a signal back to the GU; and receive a wireless power signal from the GU. 
     In various other embodiments, the RU is a passive device configured to wake up when receiving the wireless scan signal and broadcast the wireless signal back to the GU. 
     In still various other embodiments, the RU further includes an energy storage component which powers the RU wireless communication circuit and an RU controller. 
     In still various other embodiments, the RU controller is configured to control the RU wireless communication circuit to transmit the wireless signal back to the GU. 
     In still various other embodiments, the RU further includes a power detector which is configured to wake up the RU controller when the wireless scan signal is captured by the RU antenna array. 
     In still various other embodiments, the RU further includes a power management integrated circuit which is configured to deliver the power received from the wireless power signal to a powered device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The description will be more fully understood with reference to the following figures and data graphs, which are presented as various embodiment of the disclosure and should not be construed as a complete recitation of the scope of the disclosure, wherein: 
         FIG. 1  shows an exemplary wireless power system in accordance with an embodiment of the invention. 
         FIG. 2A  illustrates an example hardware controller within a generation unit (GU) in accordance with an embodiment of the invention. 
         FIG. 2B  illustrates a block diagram of an example computing system of the GU in accordance with an embodiment of the invention. 
         FIG. 3  illustrates an example of dynamic volumetric refocusing of RF lensing in accordance with an embodiment of the invention. 
         FIGS. 4A and 4B  illustrate flowcharts of various recovery unit (RU) discovery processes to be performed by the GU in accordance with embodiments of the invention. 
         FIG. 5A  illustrates a schematic of fully passive RU in accordance with an embodiment of the invention. 
         FIG. 5B  illustrates a schematic of a RU with at least some energy storage in accordance with an embodiment of the invention. 
         FIG. 5C  illustrates an exemplary embodiment of an earbud with an integrated passive RU in accordance with an embodiment of the invention. 
         FIG. 6  schematically illustrates an RU discovery process in accordance with an embodiment of the invention. 
         FIG. 7  illustrates a waveform of a sample sequence for sending a data point via the power beam in accordance with an embodiment of the invention. 
         FIG. 8  illustrates a time-division multiplexing (TDM) being used to power multiple RUs in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Turning now to the drawings, wireless power generation units (GU) in accordance with various embodiments of the invention are illustrated. In a number of embodiments, the GUs include multiple synchronized RF sources and antennas, in addition to various other capabilities such as processing capability, hardware interface, and communication capabilities, among other things. In several embodiments, the GU delivers power to one or more recovery unit(s) (RUs). In many embodiments, the phase and amplitude of each source may be adjustable to allow constructive interference in a specific location or multiple locations in space where the RUs may be present. The RUs may have, among other capabilities, additional measurement, processing and communication capabilities with the GU, in addition to power recovery array. For example, the RU(s) can include power recovery devices, such as rectennas to collect the RF energy from the GU and convert the RF energy to power (e.g. DC power). The power may be used to power a device to which the RU is connected. 
       FIG. 1  shows an exemplary wireless power system in accordance with an embodiment of the invention. The wireless power system  100  may include a GU  102  performing wireless power transfer to a RU  104 . The GU may include a hardware controller  106  which may be linked to a central processing unit (CPU)  104 . The CPU  104  may also communicate with a wireless communication unit  108 . The hardware controller  106  is connected to a GU array  110  configured to transfer power  120  to the RU  104 . The RU  104  includes an RU array  112  which is configured to receive the power  120  from the GU array  110 . The GU array  110  may be connected to a power detector  114 . The power detector  114  may send information to the CPU  116  which may be connected to a wireless communication unit  118 . The wireless communication unit  118  of the RU array  112  may send and/or receive wireless communications  122  to/from the wireless communication unit  108  of the GU  102 . While only one RU is illustrated, it is understood that multiple RUs may be present which each may be fed power to the GU  102 . 
     To facilitate efficient power transmission, the GU  102  may transmit and transfer power in different directions and orientations. The GU  102  may be able to change the direction and orientation rapidly and effectively, with as low of power spill over (e.g. power not recovered and thus wasted) as possible. There may exist a combination of phases of the GU array  110  on the GU  102  configured to provide RF power  120  that maximizes the energy concentration transferred to the RU array  112  for a given RU  104  location and orientation. 
     The hardware controller  106  can be utilized within the GU  102  to generate multiple RF outputs with independently controlled phases from a single reference signal in accordance with an embodiment of the invention is illustrated in  FIG. 2A . The hardware controller  106  can independently control the phase setting of each one of the elements using different phase control mechanisms, such as (but not limited to) a phased-locked loop (PLL) with an additional phase controller. Such a PLL could also perform clock multiplication and can be referred to as a clock multiplier unit (CMU)  202 . In the case where a CMU  202  is used for phase shifting, each CMU can control the phase of one transmission element independently via digital steps. Each CMU receives a reference clock signal as an input and applies a phase shift to a multiplied version of the reference clock signal (e.g. a signal having a frequency that is a multiple of the reference signal). In the illustrated embodiment, the CMUs  202  receive a 2.5 GHz CLK_in signal and output a phase shifted 10 GHz signal. Additional phase control can be applied using a rapid phase control circuit  204 . The rapid phase control circuit  204  can be used to modulate a data signal onto the transmitted wireless power signal. In a number of embodiments, a modulation scheme such as (but not limited to) a Phase Shift Keying or Quadrature Phase Shift Keying modulation scheme can be utilized. In several embodiments, a rapid amplitude control circuit can also be provided that can allow the use of more complex modulation schemes including (but not limited to) Quadrature Amplitude Modulation. Separate power amplifiers  206  then output RF signals to each of the elements in the antenna array. 
     In the illustrated embodiment, the hardware controller  106  includes additional hardware enabling measurement of the output power of the power amplifiers. In several embodiments, a multiplexer  208  enables an analog to digital converter  210  to measure a sensor output signal from each of the power amplifiers. The digitized output can be provided to the processing system of the GU to enable monitoring of output power delivered by the individual elements of the antenna array. 
     In addition to changing the phases of the individual elements, the control mechanism may also change the amplitudes of the individual elements, either independently or together with the phase settings. Changing the amplitude of the GU elements may allow further improvement in the overall energy available to the RU for recovery and further minimization of the power spill over. The methods and procedures discussed herein are, in general, applicable to controlling both phase and amplitude even when discussed primarily in one context or the other. 
     The hardware controller  106  may include multiple outputs  212  and can generate independently controlled phases and amplitudes from a single reference signal  214 . The hardware controller  106  may include control elements each connected to one of the multiple outputs  212 . The phase and amplitude of different control elements can be controlled independently. The phase setting of each one of the control elements can be independently controlled by different phase control mechanisms, such as (but not limited to) the phased-locked loop (PLL) with additional phase controller. Such a PLL could also perform clock multiplication and may be a clock multiplier unit (CMU)  202  on the hardware controller  106 . In the case where a CMU  202  is used for phase shifting, each CMU  202  may control the phase of one transmission element independently via digital steps. 
     There may be several methods to find the proper phase/amplitude for each output  212  including a transmit element to achieve maximum power delivery to the RU  104 . Various embodiments utilize control and wireless communication  122  in the RU  104  to provide power delivery feedback information to the GU  102 . Such control and communication circuitry may include some initial power that is assumed to be available to the RU  104  via an energy storage such as battery, super capacitors, etc. to initialize the communication. It may be advantageous to have a focusing mechanism capable of delivering power to a passive RU  104 , an RU  104  in which the energy storage is fully depleted, or in cases where the RU  104  does not contain an energy storage unit. 
       FIG. 2B  illustrates a block diagram of an example computing system  104  of the GU  102  in accordance with an embodiment of the invention. The computing system  104  includes a processor  252  for controlling the operations of an input/output interface  254 , which is capable of receiving and transmitting data, such as information from the wireless communication unit  108  and/or the hardware controller  106 , and memory  256 . The memory  256  includes programming including an RU discovery application  258  and a power delivery application  260  which is executable by the processor  252 . The term “application” herein is utilized to describe machine readable instructions including (but not limited to) software applications, operating system software, firmware, embedded firmware, and/or instructions utilized to configure an FPGA, etc. 
     The processor  252  may execute the RU discovery application  258  to operate the input/output  304  which may send instructions to the hardware controller  106  to operate the GU array  110  to send a wireless scan signal to be captured by the RU antenna array  112  of the RU  104 . The GU array  110  may receive a wireless signal back from the RU antenna array  112  of the RU  104 . The RU discovery application  258  may record the focal coordinates of each RU  104  based upon the signal received by the GU  102  from each RU  104 . In some embodiments, the RU discovery application  258  records the focal coordinates of each RU  104  based upon when the wireless signal is received by the GU  102  and the beam direction of the wireless scan signal at that time. 
     Once the RU discovery application  258  completes the wireless scan to discover the position of all the RUs  104 , the processor  252  may execute the power delivery application  260  to operate the input/output  304  which may send instructions to the hardware controller  106  to operate the GU array  110  to send a wireless power signal to each of the RUs  104 . The power delivery application  260  may operate the GU array  110  to send the wireless power signal to the recorded focal coordinates of each RU  104  to be received by each RU antenna array  112  of the RUs  104 . 
     Various embodiments include dynamic volumetric refocusing of RF arrays which allows for dynamic movement of the focal point of the RF lens to any coordinates by calculating and applying the phase differences to the phase settings of a known reference focal point. This method of refocusing may be fully contained in the GU  102 . In some embodiments, the GU  102  can be used in a wireless power transfer system to avoid new refocusing. In some embodiments, the GU  102  may use this newly evaluated value as the initial condition for the focusing. In some embodiments, the GU  102  can significantly enhance the quality and duration of the optimization process. This approach may provide rapid predictive tracking of the RU units  104 , leading to enhance performance in various applications, such as wireless power transfer, sensing, and communications. 
     Volumetric refocusing may allow sending power to different locations very rapidly.  FIG. 3  illustrates an example of dynamic volumetric refocusing of RF lensing in accordance with an embodiment of the invention. The GU array  110  of the GU  102  may utilize dynamic volumetric refocusing to scan a power delivery to multiple locations. Dynamic volumetric refocusing may only include the coordinates of focal point. This ability can be used to launch a series of  3 D volumetric scans of RF focal point within the field of view of the GU array  110 . This technique can utilize a phase table obtained by focusing into a known location (e.g. a calibration point) and re-calculating the phase settings to refocus the energy to a different point in space. The phase adjustment, Δψ mn , for antenna m, n in the array to refocus the beam to location {right arrow over (R)} 1  from a calibration point {right arrow over (R)} 0  is given by: 
     
       
         
           
             
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     Where ΔL mn ({right arrow over (R)} 0 {right arrow over (R)} 1 ) is the length different of antenna m, n in the array to the points 0 and 1: 
     
       
         
           
             
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     An example of dynamic volumetric refocusing are disclosed in U.S. Pat. Pub. No. 2020/0196097, entitled “Dynamic Focusing and Tracking for Wireless Power Transfer Arrays” and filed Dec. 18, 2019, the disclosure of which including the disclosure related to dynamic volumetric refocusing is hereby incorporated by reference in its entirety for all purposes. 
     In some embodiments, the RU  104  may be a passive RU which can utilize the energy received from such scans to power up its internal circuitry and communicate back with the GU  102 . An example of a passive RU device is described in connection with  FIG. 5A  below. In some embodiments, the RU  104  may at least include some energy storage as described in connection with  FIG. 5B . In these instances, the RU  104  may include a power detector which may wake up a wireless communication unit. 
     In some embodiments, the communication can use any wireless method such as RF, Infrared, light, acoustics, etc. at a frequency substantially different than the power delivery frequency. The use of a different frequency may ensure that the RF wave used for power delivery does not act as a blocker for the communication, hence, a more sensitive receiver can be implemented on the GU  102 , reducing the power requirements of data transmitter circuitry on the RU  104 . 
     In some embodiments, the GU  102  may include an inertial and magnetometer unit (IMU). The IMU may be a sensor that measures acceleration, rotation and earth magnetic field to identify the orientation and movement of a device. The data sent from the RU  104  to the GU  102  may include any combination of (but is not limited to) device ID, received power, orientation, and motion information from the IMU, information from other sensors, power increase/decrease requests, authentication, priority, etc. 
     In some embodiments, the GU  102  may record the received data along with coordinates of focal point from which it receives the communication. Upon completion of scan, the GU may process the recorded data to judge the number of unique RUs in the field of view, the focal coordinates that provides the maximum power to each RU, amount of power to provide to each RU, etc. Then the GU  102  may provide power to the RU(s)  104  by loading the focal coordinate(s) that the RU(s) received power. 
       FIGS. 4A and 4B  illustrate flowcharts of various RU discovery processes to be performed by the GU  102  in accordance with various embodiments of the invention. The RU discovery process may be performed utilizing the RU discovery application  258  described in connection with  FIG. 2B . The term “application” herein is utilized to describe machine readable instructions including (but not limited to) software applications, operating system software, firmware, embedded firmware, and/or instructions utilized to configure an FPGA, etc. In  FIG. 4A , the RU discovery process  400   a  begins by starting ( 402 ) RU discovery by loading  404  a first focal point. The RU discovery process  400   a  then focuses ( 406 ) a wireless scan signal on the first focal point. The RU discovery process  400   a  then waits ( 408 ) for a signal from an RU  104 . If the signal is received ( 410 ) then the RU discovery process  400   a  records ( 412 ) the location of the detected RU. If this focal point was the last point ( 414 ) then the RU discovery process  400   a  ends ( 418 ) discovery and starts ( 420 ) power delivery. 
     Power delivery may be performed using the power delivery application  260  described in connection with  FIG. 2B . The power delivery may include emitting a wireless power signal to the recorded focal coordinates of each RU to be received by each RU antenna array. 
     If the focal point was not the last point ( 414 ) then the RU discovery process  400   a  loads  416  a next scan point and iteratively focuses  406  power on each scan point until the RU discovery process determines ( 414 ) that the last point has been scanned. 
       FIG. 4B  illustrates a RU discovery process  400   b  similar to the RU discovery process  400   a  described in connection with  FIG. 4A  with some additional steps. Many of the steps are identically labeled in  FIG. 4A  and their description will not repeated in detail. In  FIG. 4B , when the GU  102  determines ( 410 ) that a signal has been received, the GU  102  sends ( 452 ) a request for received power from the RU  104 . The received power from the RU  104  may be used to fine tune ( 454 ) the focus by adjusting the array phase of the signal from the GU  102 . After fine tuning the focus, the wireless power signal may be used to power ( 456 ) a device connected to the RU  104 . For example, the RU  104  may include a power management integrated circuit (PMIC) which may be used to power a battery and/or supercapacitor through the wireless power signal. The RU  104  may be added ( 412 ) to the active list of RUs. At the end of the RU discovery process  400   b , the GU  102  may start charging ( 420 ) all active RUs based on the coordinates of all discovered RUs  104 . 
     In some embodiments, multiple RUs can be simultaneously powered by rapidly switching the focal points or splitting the RF beam into multiple simultaneous beams. For time division-based power delivery to multiple RUs, the dwell time on each coordinate may be adjusted based on the power requirement of each RU. The switching time can be fast enough such that the local temporary energy storage device on the RU can maintain continuous operation between the beam switching. 
     The location of RU(s) may also be detected and recorded by GU. This information can be used by the GU to focus power initially to previously known locations of RU to speed up power delivery. In some embodiments, the change in location of RU can be used to trigger an action such as setting off an alert. The alert may notify the GU to rescan the location of the RU to continue power delivery. 
     In some embodiments, the GU may choose the focal point corresponding to an RU that provides the maximum power. In some embodiments, during RU discovery, the GU may choose various patterns and orders for going through various focal points, for instance, interleaving multiple points or rows to form different orders of sweeps. In some embodiments, the GU may perform a fine resolution scan around the coordinate that provided the maximum power to further improve the power delivery to that specific RU. In some embodiments, after powering up the RU controller/communication circuitry, the GU may perform phase optimization to further improve the focus and power delivery to the RU. 
       FIG. 5A  illustrates a schematic of fully passive RU  500   a  in accordance with an embodiment of the invention. The fully passive RU  500   a  includes a power recovery unit  502 , a controller  504 , and a wireless communication circuitry  506 . The fully passive RU  500 A includes a power management integrated circuit (PMIC)  508  which conditions output power from the power recovery unit  502  to a powered device. The PMIC  508  may be an interface between the power recovery unit  502  and the powered device. The voltage/current from the RU  500   a / 500   b  may vary based on the available power. The PMIC  508  may insure that the voltage is regulated at output and the RU  500   a / 500   b  is operating at an optimum recovery point. 
     In some embodiments, the GU  102  may scan the environment with a wireless scan signal which provides enough power to activate a passive RU  500   a . The passive RU  500   a  may receive a wireless power signal through the power recovery unit  502  which may power a wireless communication unit  506  and a controller  504 . When the power recovery unit  502  receives power, the wireless communication unit  506  may send a wireless communication signal back to the GU  102 . When the GU  102  receives the wireless communication signal (e.g. in the manner described above), the GU  102  may record the coordinates of the RU  500   a . As discussed in connection with  FIG. 4B , the wireless communication unit  506  may also transmit the received power from the RU  500   a  which may be used to fine tune the coordinates of the RU  500   a.    
       FIG. 5B  illustrates a schematic of a RU  500   b  with at least some energy storage in accordance with an embodiment of the invention. The RU  500   b  includes all the components of the fully passive RU  500   a  which are identically labeled. The description of these components in  FIG. 5A  are applicable to  FIG. 5B  and will not be repeated in detail. The RU  500   b  also contains an energy storage component  510  for powering up controller  504  and/or the wireless communication unit  506 , but the RU  500   b  stays in a deep sleep mode until the GU volumetric scanning impinges on the RU  500   b  and a power detector  512  detects power from the power recovery unit  502  and wakes up the RU  500   b . In some embodiments the power detector  512  may be part of the power recovery unit  502  itself. The energy storage component  510  allows the GU  102  to use much lower power during the scan and minimize RF exposure. 
     In some embodiments, the PMIC  508  incorporates an energy harvester that harvests ambient energy including the energy from GU volumetric scans to build up or maintain energy inside the energy storage component  510 . 
     In some embodiments, the RU  500   a ,  500   b  may periodically transmit a signal to the GU  102  indicating that it is receiving power. This communication may be used by the GU  102  as a safety interlock to detect the blockage of RF path from GU  102  to RU  500   a ,  500   b . The GU  102  may stop transmitting power or adjust its power level to the RU  500   a ,  500   b  if the power received by RU  500   a ,  500   b  suddenly drops or if reception of such transmissions is stopped. For example, when the controller  504  or wireless communication circuit  506  does not receive enough power to transmit received power to the PMIC, the transmission from the GU  102  may stop. This may be useful in many scenarios, such as those when an object absorbs enough power in the path between the GU  102  and the RU  500   a ,  500   b  so that the PMIC does not receive enough transmitted power to be able to harvest sufficient energy to power the powered device. 
     In some embodiments, the wireless communication circuitry  506  in the RU  500   a ,  500   b  and/or the wireless communication circuitry  108  in the GU  102  may support multiple frequency channels or frequency bands. In some embodiments, the GU  102  may identify the quietest frequency channel/band and transmit information in that frequency channel/band to RU  500   a ,  500   b . The RU  500   a ,  500   b  may use the quietest frequency channel/band with minimal sufficient transmit power to send data back to GU  102  to minimize the communication power consumption and maximize range. 
     In some embodiments, the GU  102  transmits data to RU  500   a ,  500   b  via RF beam used for powering the RU  500   a ,  500   b . Providing a higher power received by the RU  500   a ,  500   b  may eliminate the need for a power-hungry front-end low noise amplifier in the RU  500   a ,  500   b.    
     In some embodiments, the wireless scan signal sent by the GU  102  may include a packet of data that sits on top of the RF beam that encodes information identifying which beam is being sent. The RU  500   a ,  500   b  may sent the information back to the GU  102 . Thus, the GU  102  may be able to identify which scan is being sent back from the RU  500   a ,  500   b.    
     Continuous transmission of status from the RU  500   a ,  500   b  to GU  102  may consume considerable power. Transmitting less status updates may increase the power available to deliver to the output by the PMIC  508 . In some embodiments, the RU  500   a ,  500   b  can utilize a doppler sensing or field perturbance detection system which may detect fluctuations in the received power due to motion of a person or an object outside of the RF beam. In these embodiments, the RU  500   a ,  500   b  may not continuously transmit its status, but only does so when field perturbance is detected. This may lead to increased power delivery to the output while still enabling a robust safety mechanisms. 
     In some embodiments, the RU  500   a ,  500   b  may inform the GU  102  upon detection of such a fluctuation, perform status transmission periodically until the motion is not sensed, and then inform the GU  102  of the end of status transmissions. The GU  102  in this case may only stop the wireless power transmission if the reception of the status is stopped during the motion detection on the RU  500   a ,  500   b.    
     In some embodiments, the RU may be integrated into a wearable device to power the wearable device. The wearable device may include (but are not limited to) earbuds, headphones, active glasses, virtual reality (VR) and augmented reality (AR) devices, watches, health monitors, etc. and can incorporate the passive battery free unit.  FIG. 5C  illustrates an exemplary embodiment of an earbud with an integrated passive RU in accordance with an embodiment of the invention. 
       FIG. 6  schematically illustrates an RU discovery process in accordance with an embodiment of the invention. A GU  102  transits a wireless scan signal. The wireless scan signal may be swept  604  between various signal boundaries  602   a ,  602   b . The wireless scan signal may be swept  604  using dynamic volumetric refocusing as discussed above. When each of the one or more RUs  600  receive the wireless scan signal, each of the RUs  600  can send a wireless signal  606  back to the GU  102 . The GU  102  can be configured to record the focal coordinates of each RU  600  based upon when the wireless signal is received by the GU  102  and the beam direction of the wireless scan signal at that time. The RUs  600  may be fully passive RUs  600   a  described in connection with  FIG. 5A  and/or the RUs  600   b  described in connection with  FIG. 5B . 
     After the GU  102  completes the RU discovery process, the GU  102  can use the recorded focal coordinates of each RU  600  to emit a wireless power signal to each RU  600 . In several embodiments, the amount of wireless power transmitted to each RU  600  can depend upon the characteristics of an RU and/or information maintained concerning or received from the RU. 
     In some embodiments, the GU  102  may encode a beam ID in the RF power beam used to power the RU  500   a ,  500   b . As the GU  102  performs the RF beam scans, it may also transmit the beam ID along with the energy required to power up the RU controller  504  and/or the wireless communication circuitry  506 . The RU  500   a ,  500   b  may record the power levels that it receives with each beam ID associated with it as the GU  102  beam scans over the RU  500   a ,  500   b . The RU  500   a ,  500   b  may then communicate to the GU  102  the beam ID that provided the maximum power, where the GU  102  uses the information to send power directly to the GU  102 . In some embodiments, the GU  102  sets the beam to the associated beam ID to power the RU  500   a ,  500   b . In some embodiments, the GU  102  may run several iterations of finer resolution scans to better target the RU  500   a ,  500   b  and provide more power to the RU  500   a ,  500   b.    
     Encoded data can be transferred from the GU  102  to the RU  500   a ,  500   b  with the RF beam used for powering the RU  500   a ,  500   b . In some embodiments, the encoded data can represent the beam ID. In one example, transmitted data can be framed with a start and stop signal via the power beam.  FIG. 7  illustrates a waveform of a sample sequence for sending a data point via the power beam in accordance with an embodiment of the invention. The signal may include a start signal  702  and a stop signal  704 . The start signal  702  may include changing from a high amplitude (IDLE) signal  702   a  to low amplitude signal  702   b , and the stop signal  704  may include transitioning to a low amplitude signal  704   a . The start signal  702  and stop signal  704  may be uniquely identifiable from any intermediate ongoing switching (e.g., beam switching, TDM, etc.) signals to reduce the chances of invalid data. The start signal  702  to stop signal  704  duration may be significantly less than any TDM switching that is occurring for this reason. 
     To encode the data bits, amplitude modulation can be used to differentiate between 1 and 0 states. Intermediate amplitudes can also be used to allow multiple level signaling. One method of amplitude modulation is obtained by varying the power amplifier output power of each element. Another method of amplitude modulation is obtained by controlling the number of active and off antennas. Another method of amplitude modulation is by defocusing the RF beam. Another method of modulating the amplitude is by shifting the phase of certain antenna elements by 180 degrees. Multiple level signaling can be used to differentiate between start/stop signals and a 0 data bit. 
     The former will result in very low received power level for bit  0 , while the latter provides partial power to the receiver. By making the start/stop signal uniquely identifiable from the data 0, many beams with different power levels can result in data being transmitted and received. From the high amplitude IDLE state, the approximate power the beam delivers can be measured. 
     Encoded data transmitted in this way can be combined with a scanning beam to detect any RU in a designated charging zone. The GU may cycle through a pre-defined set of beams that each have a unique value that is transmitted to any RU near the beam location. The RU can detect which data has the highest transmitted power and report that power to the GU. Based on the power measured and the data received by the RU, the GU can calculate where to apply the beam to power the RU. If the RU reports the highest N (where N&gt;1) beam numbers, the GU can use that information to calculate the size of the focal spot and obtain a more exact location and improve the power delivery. 
     Scan can be ongoing without interrupting the charging of RUs in the charging list. The scan can be interleaved with power beams via time-division multiplexing (TDM) so that multiple RU can be charged while searching for more available RU to power.  FIG. 8  illustrates a TDM being used to power multiple RUs in accordance with an embodiment of the invention. The TDM may be used to power  2  RUs which may be labeled “RU  0 ” and “RU  1 ” while scanning the charge area for other RU to power. There may be some minimum duration the scan time slot may be (t data ) for the GU to transmit the full data frame. Any RU receiving power can take up more time than t data  to minimize the time not powering an RU. Furthermore, a narrow down scan can be performed after initial location estimation to focus the beam more accurately. 
     In the case that the received power in one scan is not large enough to power up the new RU entering the charging area, the RU can utilize a power harvesting approach and gradually store energy from several scans. Once the stored energy level reaches the required limit to transmit data, it will activate the transmitter and send the beam data and power level received back to the GU. 
     DOCTRINE OF EQUIVALENTS 
     While the above description contains many specific embodiments of the invention, these should not be construed as limitations on the scope of the invention, but rather as an example of one embodiment thereof. It is therefore to be understood that the present invention may be practiced in ways other than specifically described, without departing from the scope and spirit of the present invention. Thus, embodiments of the present invention should be considered in all respects as illustrative and not restrictive. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their equivalents.