Abstract:
A method and apparatus for providing power to e.g., a chargeable device via a radio frequency link. In one aspect, a method of providing power to a chargeable device via radio frequency link comprises generating a substantially un-modulated signal. The method further comprises radiating a substantially un-modulated radio frequency (RF) signal to the chargeable device via a transmit antenna based on the substantially un-modulated signal. The method further comprises powering or charging the chargeable device with power delivered by the substantially un-modulated RF signal.

Description:
PRIORITY AND RELATED APPLICATIONS  
       [0001]     This application claims priority to co-owned U.S. Provisional Patent Application Ser. No. 60/760,064 entitled “Method and System for Charging an Electronic Device via a Wireless Link” filed on Jan. 18, 2006, the disclosure of which is incorporated herein by reference in its entirety. This Application is also related to, and claims priority to, U.S. patent application Ser. No. 11/408,793 entitled “Method and System for Powering an Electronic Device via a Wireless Link” filed on Apr. 21, 2006, assigned to the Assignee hereof, and which is also incorporated herein by reference in its entirety. 
     
    
     COPYRIGHT  
       [0002]     A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.  
       1. FIELD OF THE INVENTION  
       [0003]     This invention relates generally to methods and apparatus for energy or power transfer, and in one aspect to wirelessly charging a portable power source, such as a battery, associated with an electronic device.  
       2. DESCRIPTION OF RELATED TECHNOLOGY  
       [0004]     Methods and systems for the wireless transmission of power are known in the prior art, for example, U.S. Pat. No. 6,633,026 to Tuominen issued Oct. 14, 2003 and entitled “Wireless power transmission” discloses a method for wireless power transmission in a system comprising a power transmitter which in turn comprises a first light source and means for directing the light emitted by the first light source to a desired direction, and at least one power receiver comprising a first photo-detector for receiving the emitted light and for converting it into electric current. A second light source included in the power transmitter is used for transmitting light around the light emitted by the first light source and substantially parallel to it, the intensity of the light being lower than that of the light emitted by the first light source. A second photo-detector included in the power receiver is used for detecting the light emitted by the second light source and for transmitting a control signal to the power transmitter in response to a successful reception of the light emitted by the second light source. The first light source of the power transmitter is switched on in response to the reception of the control signal from the power receiver informing of the reception of the light emitted by the second light source.  
         [0005]     U.S. Pat. No. 6,664,770 to Bartels issued Dec. 16, 2003 and entitled “Wireless power transmission system with increased output voltage” discloses a system for wireless power transmission, which makes it possible to generate an increased voltage on the receiver side using a radio signal that is optimized for this purpose and thereby permits operation particularly of digital semiconductor components in the receiver even if the receiver does not have a power supply of its own.  
         [0006]     U.S. Pat. No. 6,999,857 to Kasper, et al. issued Feb. 14, 2006 and entitled “Data communication and power transmission system for sensing devices” discloses a wireless power transmission and communication network that provides interrogation and powering of sensors for use on undersea vehicles. The invention employs a wave-guide that allows the propagation of electromagnetic waves through a dielectric material that covers the exterior of an undersea vehicle&#39;s hull. Embedded within the dielectric material is an N dimensional array of Micro Electronic Mechanical Systems sensing devices coupled with radio frequency (RF) decoders and transceivers, and strips of conductive metal tape. Electromagnetic waves such as microwaves propagate through the dielectric material both powering the sensor network and addressing and interrogating individual sensing devices. The sensing devices take readings and then format and transmit the data results back across the wave-guide where they are received and processed by a digital processor within the hull of the undersea vehicle.  
         [0007]     U.S. Pat. No. 7,027,311 to Vanderelli, et al. issued Apr. 11, 2006 and entitled “Method and apparatus for a wireless power supply” discloses an apparatus for a wireless power supply including a mechanism for receiving a range of RF radiation across a collection of frequencies. The apparatus includes a mechanism for converting the RF radiation across the collection of frequencies, preferably at a same time into DC. A method for a wireless power supply including the steps of receiving a range of RF radiation across a collection of frequencies. There is the step of converting the RF radiation across the collection of frequencies, preferably at a same time into DC.  
         [0008]     U.S. Pat. No. 7,068,991 to Parise issued Jun. 27, 2006 and entitled “Remote power recharge for electronic equipment” discloses a conductorless charging and power system for electronic appliances and a method for communicating power to a power receiver employing wireless energy transmission. The remote charging system includes a power transmission unit, which transmits energy as a directional power beam, and a power receiver system that receives the transmitted energy. The power receiver system is preferably incorporated in an appliance and includes an energy receptor capable of receiving the wireless power beam and transferring the energy from the beam to an energy storage device included in the appliance: The power transmission unit receives and tracks a power request signal from the power receiver system to track the power receiver system location during energy transmission. Data streams may be incorporated into the wireless signals of the remote charging system, allowing the remote charging system to function as a communications pathway as well as a power delivery system.  
         [0009]     United States Patent Publication No. 20060097667 to Kang, et al. published on May 11, 2006 and entitled “Wireless power supply and method of supplying power” discloses a wireless power supply and method of wirelessly supplying power using light to directly supply power wirelessly to an electrical apparatus without a power cable. The wireless power supply includes: a plurality of pressure switches adapted to switch ON/OFF in response to an applied pressure; and a plurality of light emitting devices respectively connected to the plurality of pressure switches, the plurality of light emitting devices adapted to emit light to supply the power to a load in response to at least one of the pressure switches being switched ON.  
         [0010]     United States Patent Publication No. 20060205381 to Beart, et al. published on Sep. 14, 2006 and entitled “Adapting portable electrical devices to receive power wirelessly” discloses a wireless power receiving apparatus that is retrofitted to a portable electrical device to enable the device to receive power wirelessly. The apparatus comprises a power-receiving element adapted to be attached to the device, e.g. by adhesive, and also being adapted to receive power wirelessly from a transmitter of power when the element and transmitter are in proximity with one another. One or more power connectors are connected electrically to the power-receiving element and are adapted to be connected, when the apparatus is in use, to one or more corresponding power connectors of the portable electrical device to deliver power received by the element to the device. The power-receiving element may be in the form of a sticker or may be carried by or incorporated in a replacement cover portion for the portable electrical device.  
         [0011]     United States Patent Publication No. 20060238365 to Vecchione, et al. published on Oct. 26, 2006 and entitled “Short-range wireless power transmission and reception” discloses a short-range wireless power transmission and reception system and methods. Power is transmitted from the electrical utility mains power supply to electrically powered appliances via electromagnetic radiation. The appliances are capable of receiving the transmitted power, converting it into electricity and storing it for subsequent use, as well as using it directly to power the appliances.  
         [0012]     United States Patent Publication No. 20060266917 to Baldis, et al. published on Nov. 30, 2006 and entitled “Wireless Power Transmission System” discloses a method for wireless power transmission that comprises a transmitter and a receiver. The receiver does not require an independent power source and is comprised of an optical feedback to the transmitter, and therefore does not require a separate communication channel to the transmitter. The transmitter uses the optical feedback to locate and track the receiver. The transmitter can optionally employ a macro adjusters and micro adjusters that direct the beam onto the receiver for optimal power transmission. The system also optionally has a tight loop beam detector to enhance safety of the system. Either the receiver and/or the transmitter may also encode data on the energy transmission, resulting in one-way or two-way data transmission.  
         [0013]     United States Patent Publication No. 20070010295 to Greene, et al. published on Jan. 11, 2007 and entitled “Power transmission system, apparatus and method with communication” discloses a power transmission system with communication having a base station having a wireless power transmitter, a wireless data transmission component and a first wireless data reception component. The system includes a remote station having a power harvester for converting the power from the power transmitter into direct current and a power storage component in communication with the power harvester for storing the direct current. Alternatively, the system includes a base station having a wireless power transmitter which transmits power at a frequency at which any sidebands are at or below a desired level, and a first wireless data communication component.  
         [0014]     Recent developments in technology enable electronic devices, such as without limitation laptop or notebook computers, cell phones and PDAs (personal digital assistant) to run various multimedia or other processing-intensive applications. However, despite the foregoing wireless power transmission systems, these new multimedia applications often require a large amount of power to run, and are unable to be charged via a wireless link. In addition to the convenience associated with a wireless power transmission system, there is also a significant benefit in convenience and safety when any of such devices, for example a cell phone, is kept adequately charged without the need to connect to a powered wire. Therefore it is desired to provide an apparatus and/or system for the powering of certain electronic devices via a wireless link.  
         [0015]     Moreover, delivery of power to electrical and electrical devices (e.g., appliances, lighting, etc.) also would allow a great degree of flexibility in terms of use and placement; e.g., a “wireless” lamp could be placed anywhere in a room without concern for tripping over wires, aesthetics, etc.  
       SUMMARY OF THE INVENTION  
       [0016]     In a first aspect of the invention, apparatus for providing power to a device via a wireless link is disclosed. In one embodiment, the apparatus comprises: a transmitting antenna operative to provide power to the device via the wireless link; a sensing antenna operative to sense signals transmitted by the device; and a control unit assembly operative to control the operation of the transmitting antenna. In one variant, at least a portion of the apparatus is mounted substantially within a ceiling-mounted dome. In another variant, the power transmitted is unmodulated.  
         [0017]     In another variant, the control unit assembly is operative to control the movement of the transmitting antenna in at least two degrees of freedom. The at least two degrees of freedom comprise a substantially azimuthal degree of freedom and a substantially elevational degree of freedom.  
         [0018]     In another variant, the control unit is operative to charge a plurality of devices via a wireless link according to a time-division multiple access (TDMA) scheme.  
         [0019]     In a second aspect of the invention, a method for providing power to a device via a wireless link is disclosed. In one embodiment, the method comprises: detecting a first direction for the device using a sensing antenna; directing a transmission antenna so that it can transmit at least some power in the first direction based at least in part on the act of detecting; and transmitting power from the transmission antenna via the wireless link to the device.  
         [0020]     In a third aspect of the invention, a method for providing power to a plurality of devices via a wireless link is disclosed. In one embodiment, the power is transmitted from a transmitting antenna, and the method comprises: disposing the transmitting antenna so that power can be transmitted to the plurality of devices substantially simultaneously; and transmitting power from the transmission antenna via the wireless link to the plurality of devices according to a multiple access scheme.  
         [0021]     In one variant, the multiple access scheme comprises a substantially time-divided scheme. In another variant, the multiple access scheme comprises a substantially frequency-divided scheme. In yet another variant, the multiple access scheme comprises a substantially frequency-hopped scheme. In still another variant, the multiple access scheme comprises a substantially code-divided scheme. As yet another alternative, the multiple access scheme comprises a sensing scheme wherein a channel is sampled before access is granted.  
         [0022]     In a fourth aspect of the invention, apparatus for providing power to a plurality of devices via a wireless link is disclosed. In one embodiment, the apparatus comprises: a transmitting antenna configured to radiate power, the antenna further comprising apparatus allowing the antenna to selectively transmit power to the plurality of devices; a power source capable of generating the power for transmission; and a controller in signal communication with at least one of the antenna and source, the controller being adapted to cause the antenna to transmit the power to the plurality of devices according to a multiple access scheme.  
         [0023]     In one variant, the antenna is substantially directional, and the multiple access scheme comprises a substantially time-divided scheme.  
         [0024]     In a fifth aspect of the invention, apparatus for receiving power via a wireless link is disclosed. In one embodiment, the power is useful for providing electrical power to one or more components of the apparatus, and the apparatus comprises: a receiving antenna configured to receive power from a transmitting antenna; power source apparatus capable of storing at least a portion of the received power for subsequent use; and a controller in signal communication with at least one of the antenna and source apparatus, the controller being adapted to facilitate selective receipt of the power via the antenna. In one variant, the selective receipt comprises selective receipt according to a multiple access scheme, wherein devices other than the apparatus also receive power substantially simultaneously with the apparatus receiving power. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]     The features, objectives, and advantages of the invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, wherein:  
         [0026]      FIG. 1  illustrates at least one exemplary embodiment of a system for charging an electronic device via a wireless link.  
         [0027]      FIG. 2  is a logical flow diagram that illustrates a first exemplary method of directing power from a transmission antenna.  
         [0028]      FIG. 3  is a logical flow diagram that illustrates a first exemplary method of prioritizing time sharing between a plurality of mobile devices. 
     
    
       [0029]     All Figures disclosed herein are © Copyright 2006-2007 Third Option, L.L.C. All rights reserved.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0030]     Reference is now made to the drawings wherein like numerals refer to like parts throughout.  
         [0031]     As used herein, the terms “mobile device” or “client device” include, but are not limited to, personal digital assistants (PDAs), handheld computers, personal communicators, J2ME equipped devices, cellular telephones, smartphones, “SIP” phones, personal computers (PCs) and minicomputers, whether desktop, laptop, or otherwise, or literally any other device capable of utilizing electrical or electromagnetic power.  
         [0032]     As used herein, the term “application” refers generally to a unit of executable software that implements a certain functionality or theme. The themes of applications vary broadly across any number of disciplines and functions (such as communications, instant messaging, content management, e-commerce transactions, brokerage transactions, home entertainment, calculator etc.), and one application may have more than one theme. The unit of executable software generally runs in a predetermined environment; for example, the unit could comprise a downloadable Java Xlet™ that runs within the Java™ environment;  
         [0033]     As used herein, the terms “microprocessor” and “digital processor” are meant generally to include all types of digital processing devices including, without limitation, digital signal processors (DSPs), reduced instruction set computers (RISC), general-purpose (CISC) processors, microprocessors, gate arrays (e.g., FPGAs), PLDs, reconfigurable compute fabrics (RCFs), array processors, and application-specific integrated circuits (ASICs). Such digital processors may be contained on a single unitary IC die, or distributed across multiple components.  
         [0034]     As used herein, the term “integrated circuit (IC)” refers to any type of device having any level of integration (including without limitation ULSI, VLSI, and LSI) and irrespective of process or base materials (including, without limitation Si, SiGe, CMOS and GaAs). ICs may include, for example, memory devices (e.g., DRAM, SRAM, DDRAM, EEPROM/Flash, ROM), digital processors, SoC devices, FPGAs, ASICs, ADCs, DACs, transceivers, memory controllers, and other devices, as well as any combinations thereof.  
         [0035]     As used herein, the term “memory” includes any type of integrated circuit or other storage device adapted for storing digital data including, without limitation, ROM. PROM, EEPROM, DRAM, SDRAM, DDR/2 SDRAM, EDO/FPMS, RLDRAM, SRAM, “flash” memory (e.g., NAND/NOR), and PSRAM.  
         [0036]     As used herein, the term “cellular” includes any form of cell-based mobile communications system including cellular telephones, “walkie-talkie” devices (such as those marketed by Nextel and Motorola Corporations, and so-called PTx (“push-to-anything”) devices such as the exemplary PTT (push-to-talk over cellular) devices which establish and tear down SIP or other communications sessions as part of their protocol.  
         [0037]     It will be appreciated that while the exemplary embodiments of the invention are described primarily in the context of mobile or client electronic devices, the various aspects of the present invention are in no way so limited, and in fact may be applied to other (e.g., non-mobile and/or non-electronic) devices, whether they include an electrical storage device or otherwise, including without limitation appliances, substantially fixed computer systems, televisions, lighting, and so forth.  
         [0038]     Referring now to  FIG. 1 , one exemplary embodiment of a power transfer system according to the invention is described. In one embodiment, the transmitter  102  of the system may reside within, e.g., a ceiling mounted dome  103  or other such fixture, although mobile applications (e.g., in a car, truck, aircraft, etc.) are also contemplated. The receiver  104  may reside within a device that is capable of using electrical or electromagnetic power and/or wireless charging. The device may comprise, without limitation, at least one of a mobile or cellular telephone, personal data assistant (PDA), portable computer (e.g., a notebook PC), media player, a clock, an electronic display, or any other device that utilizes electric or electromagnetic power; e.g., from a portable source, such as a rechargeable battery.  
         [0039]     Mobile devices that are turned on are considered to be active. In the example of a mobile telephone, the mobile telephone is active because it continuously or periodically communicates with its service-provider&#39;s local cell tower by, for example, exchanging a handshaking signal. It is this handshaking signal that enables the charging system&#39;s transmitter  102  to locate an exact or approximate position of the mobile device and target a concentrated charging beam at its receiver  104  to charge its battery.  
         [0040]     In one embodiment, as shown in Inset  1  ( 106 ) of  FIG. 1 , multiple mobile devices within the coverage of a single transmitter  102  may be charged concurrently. In another embodiment, as shown in Inset 2  ( 108 ) of  FIG. 1 , a single mobile device having a built-in receiver  104  may be located within the coverage of and be charged by multiple transmitters  102 .  
         [0041]     As noted above, the transmitter  102  of the exemplary embodiment is located within, for example, a ceiling dome  103  and powered by, for example, a standard 120 volts AC supply. The transmitter  102  generates signals that carry the charging energy. Signals of various waveforms including, for example, a continuous-wave (CW) single-frequency signal, a sinusoidal wave signal (no harmonics) may be used to carry and deliver the electric power to the receiver  104 . In another embodiment, multiple frequency signals may be used. Also, the signal may be of any frequency and power level suitable for carrying and delivering power sufficient to charge a battery of a mobile device within a range of about 0-40 feet, and preferably within a range of 0-20 feet. One example of the signal may be a single frequency selected in the microwave band. In one embodiment, the signal may be selected with a frequency between 1 GHz-40 GHz, and preferably between 12 GHz-36 GHz. It is desirable to select the transmitter  102  to generate signals of sufficient power to charge the mobile devices wirelessly, while at the same time avoiding undesired results, such as interference with other wireless systems in the vicinity of the transmitter  102 . In one embodiment, the transmitter  102  is selected to generate signals at a power level of about 1 to 50 watts. For example, the power of the transmitter  102  may be selected to communicate to a transmitting antenna  105  a signal at a power level of about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50 Watts. In another embodiment, signals of lower or higher power may also be used to achieve the delivery of power.  
         [0042]     The signal from the transmitter  102  may be fed to the transmitting (TX) antenna  105 , which may be omni-directional or directional. In one embodiment, it is desirable to select the TX antenna  105  as a directional antenna, e.g., with a beam-width angle between 0.1-20 degrees. For example, the beam-width angle may be selected at about 0.1, 0.2, 0.25, 0.5, 0.75, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 degrees. In one embodiment, the TX antenna  105  is configured to emit a signal of about 1 degree in beam width angle, suitable for transmitting signals of frequencies within the 12 GHz to 36 GHz band. The power gain of the TX antenna  105  may be about 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or 16 decibels (dB). When using a 12 decibel power gain, the TX antenna  105  may amplify the transmit signal by about 16 times.  
         [0043]     In one embodiment, the transmitter  102  also comprises a sensing antenna  107 , which is selected to be substantially equally directional as the TX antenna  105 . In one embodiment, the sensing antenna  107  is configured to be suitable for sensing signals already transmitted by a mobile device, e.g., signals of frequencies within the 800 to 1900 MHz band. It is however recognized that the sensing antenna  107  may be sensitive to receive and detect a signal in any desired frequency band. The TX antenna  105  and the sensing antenna  107  will, in one embodiment, advantageously point in substantially the same direction and be mounted on a movable assembly  109  that is configured to be adjustable in azimuth (bearing) and elevation (altitude). By pointing in substantially the same direction, the TX antenna  105  can be directed in a direction of a receiver  104  sensed by the sensing antenna  107  thereby emitting the wireless power signal in a way that optimizes power transfer efficiency between the TX antenna  105  and the RX antenna  113 .  
         [0044]     In another embodiment, the TX antenna  105  and the sensing antenna  107  can be mounted so as to operate in independent directions. The advantage of such an embodiment is that the TX antenna  105  can, for example, operate independently of the sensing antenna  107 . For example, the sensing antenna  107  can advantageously operate in a scanning mode which constantly attempts to reacquire an optimized direction in which the signal emitted by the receiver  104  is maximized thereby providing updated information of e.g. the location of the receiver  104  to a control unit  111 . The control unit includes in one exemplary embodiment integrated circuit components (e.g., digital processor, memory, microcontroller, etc.) used to effect control of the apparatus, e.g., according to the principles and methods described herein, such as via control logic or a computer program of the type well known in the art. The TX antenna  105  can therefore maintain a fixed position on the desired direction, while the sensing antenna  107  scans the field, until the control unit  111  informs the TX antenna  105  that the desired transmission direction has changed (e.g. due to movement of the receiver  104 , etc.). In this way, the transmission direction of the TX antenna  105  can remain static while the sensing antenna  107  continues to optimize transmission direction.  
         [0045]     As previously alluded to, an azimuth/elevation control unit  111  is configured to move the assembly  109  through a search pattern, such as e.g., via the exemplary method  200  illustrated in  FIG. 2 . Upon detecting an active mobile device by the sensing antenna  107  (e.g., by receiving signals in the 800-1900 MHz range), the movable assembly&#39;s  109  position may be fine tuned until the sensing antenna  107  receives signals of maximum or close to a maximum received power from the mobile device in step  202 . One goal that is achieved with this targeting procedure is to accurately align the TX antenna  105  to ensure that it is pointing directly at the mobile device (e.g., its receiving (RX) antenna  113 ), thereby achieving maximum transmit-to-receive power capture in step  204 . In one embodiment, the procedure  200  may then be optionally repeated after a preset timer value has expired. In another embodiment, the procedure  200  may optionally be repeated once the received power from the mobile device detected in step  202  decreases beyond a predetermined threshold value. In yet another embodiment, the procedure  200  may optionally be repeated continuously so as to continuously reassess the proper direction for the TX antenna  105 .  
         [0046]     In one embodiment, the azimuth/elevation control unit  111  may be selected to operate in a manner similar to an infrared tracking security camera, except that the control unit  111  is configured to move the assembly  109  in response to a monitored signal (e.g., handshaking signal) received by the sensing antenna  107  instead of an infrared signal. More particularly, the control unit  111  may be configured to scan for a radio frequency signal within a desired range of frequencies (and power levels) to identify a target device for activating a charging of power via a wireless link  115 . The TX antenna  105  and sensing antenna  107  can then move in tandem or move in an independent manner as described previously.  
         [0047]     In certain embodiments, the transmitter  102  may also comprise a control unit  111  for charging multiple receivers  104  concurrently. In one embodiment, the transmitter  102  comprises a multiple access scheme (e.g., time division multiple access (TDMA)) control unit  111 . The TDMA control unit  111  determines how many active mobile devices lock with the transmitter  102 , and coordinates time sharing the power charging among all of the locked mobile devices. It will be appreciated, however, that other multiple access/power transfer schemes may be used consistent with the invention. For example, in one variant, a frequency-divided (e.g., FDMA) system is used, wherein different devices are provided power using different frequencies (which may be narrowband or broadband in nature). Similarly, a frequency-hopped approach can be used, wherein each device to be powered is assigned a hopping code for access to power transmitted over a plurality of frequencies.  
         [0048]     In another variant, an approach analogous to “carrier” sense (e.g., CSMA) can be used to effectively “grab” the power delivery channel when not in use by other device, recognizing, however, that in the strict sense, there is no “carrier” per se (unless a modulation is optionally applied). In still another variant, a code-divided approach (e.g., CDMA) can be used, so that power is transmitted across a range of frequencies to multiple devices, each of the devices being configured to receive the power transmitted according to their particular spreading code. This selective reception can be accomplished by, e.g., using selective filtering, a receiver which is only sensitive to certain frequencies, or any other techniques well known in the digital communication and multiple access fields. It will be appreciated, however, that unlike the digital communications arts, the apparatus of the present invention can be utilized without modulation if desired; i.e., no data or other modulations need be encoded onto the transferred power unless desired.  
         [0049]     Moreover, combinations of the foregoing can be used. For example, in one such possible combination, the time-divided and frequency-divided approaches are combined, such  
         [0050]     Referring now to  FIG. 3 , information may be detected by the sensing antenna  107  that provides information useful in prioritizing time sharing among all of the locked mobile devices using a predetermined algorithm  300 . In step  302 , the sensing antenna  107  may detect the direction of each of the mobile devices based on e.g. the power level of the respective signals transmitted by the mobile devices. In step  304 , the control unit  111  will parse prioritization information from the signals received from each of the plurality of mobile devices. For example, the sensing antenna  107  may, in one embodiment, receive information indicative a charge level for each of the locked mobile devices. The control unit  111  may then prioritize time sharing amongst the locked mobile devices with the lowest relative charge level in step  306 . In another embodiment, the sensing antenna  107  may receive information which is indicative of rate of current power consumption by each of the locked mobile devices. Hence, the control unit  111  may then prioritize time sharing amongst the locked mobile devices so that those mobile devices currently consuming the largest amount of relative power are prioritized first in the time sharing scheme. Any number of other schemes may be utilized individually or in conjunction with one another, based on available information so as to provide an efficient time sharing scheme.  
         [0051]     The receiver  104  is configured to receive the signal from the transmitter  102  and supply the same to charge the mobile device. In certain-embodiments, the receiver  104  is built into mobile devices. The receiver  104  comprises a wireless charging receiving antenna  113  which may or may not be the same antenna that mobile devices use to communicate with the cell tower. The wireless charging receiving antenna  113  gathers as much of the beamed radio frequency energy from the transmitter  102  and delivers it to a rectifier  117 . The rectifier  117  may be a Germanium-based rectifier characterized by a low barrier or threshold voltage (i.e., low on-power rectifier), to allow activation of the rectifier  117  in the event of receiving a low level signal. The rectifier  117  may also be characterized as a passive RF power sensor to minimize the use of power by the rectifier  117  from the mobile device. In one embodiment, the receiver  104  also comprises a plurality of diodes  119  (e.g., two diodes) which allow the mobile device&#39;s battery to be charged by either the wireless charging link  115  or a wired charging path.  
         [0052]     The rectifier  117  is configured to convert the AC electrical energy from the antenna to a voltage signal, e.g., a DC voltage signal, suitable for charging the mobile device&#39;s battery. In one embodiment, a voltage regulator may be integrated with or in addition to the rectifier to regulate or limit the power supplied to the mobile device at a desired level. The voltage regulator may operate particularly when the physical movement of the mobile device causes the power of the signal received by the RX antenna  113  to vary. This variation may be due to variation in the path of the signal transmitted by the transmitter  102 .  
         [0053]     The exemplary wireless charging system  100  is configured such that sufficient energy is transmitted and delivered at the receiving antenna  113  for charging. As an illustration, a typical cell phone charger may have a maximum rating of about 4.9 volts and 450 milliamperes (mA). The power rating therefore is about 2.2 watts maximum with 1 watts optimum. For this illustration, the transmitter  102  may provide an effective charging area of, for example, 1000 square feet. In one embodiment, the transmitter  102  sends out signals of 25 watts power. The transmitting antenna  105  may be designed to be of a 12 decibel power gain amplifies the signal to be of 400 watts power (i.e., equivalent to 16×25 watts). Considering that a signal may be subject to a maximum of 20 dB loss over a 20 feet transmission path, a mobile device located 20 feet from the transmitting  102  may receive signals of at least 4 watts, sufficient to charge a typical mobile device. Therefore, this embodiment provides a coverage area of more than 1000 square feet.  
         [0054]     It will be recognized that while certain aspects of the invention are described in terms of a specific sequence of steps of a method, these descriptions are only illustrative of the broader methods of the invention, and may be modified as required by the particular application. Certain steps may be rendered unnecessary or optional under certain circumstances. Additionally, certain steps or functionality may be added to the disclosed embodiments, or the order of performance of two or more steps permuted. All such variations are considered to be encompassed within the invention disclosed and claimed herein.  
         [0055]     While the above detailed description has shown, described, and pointed out novel features of the invention as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the art without departing from the invention. The foregoing description is of the best mode presently contemplated of carrying out the invention. This description is in no way meant to be limiting, but rather should be taken as illustrative of the general principles of the invention. The scope of the invention should be determined with reference to the claims.