Patent Publication Number: US-9853478-B2

Title: Low power detection of wireless power devices

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 61/368,581 entitled “INITIATING COMMUNICATIONS WITH LOW POWER” filed on Jul. 28, 2010, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Field 
     The present invention relates generally to wireless power, and more specifically, to a wireless power transmitter for detecting valid chargeable devices positioned within an associated charging region. 
     Background 
     Approaches are being developed that use over the air power transmission between a transmitter and the device to be charged. These generally fall into two categories. One is based on the coupling of plane wave radiation (also called far-field radiation) between a transmit antenna and receive antenna on the device to be charged which collects the radiated power and rectifies it for charging the battery. Antennas are generally of resonant length in order to improve the coupling efficiency. This approach suffers from the fact that the power coupling falls off quickly with distance between the antennas. So charging over reasonable distances (e.g., &gt;1-2 m) becomes difficult. Additionally, since the system radiates plane waves, unintentional radiation can interfere with other systems if not properly controlled through filtering. 
     Other approaches are based on inductive coupling between a transmit antenna embedded, for example, in a “charging” mat or surface and a receive antenna plus rectifying circuit embedded in the host device to be charged. This approach has the disadvantage that the spacing between transmit and receive antennas must be very close (e.g. mms). Though this approach does have the capability to simultaneously charge multiple devices in the same area, this area is typically small, hence the user must locate the devices to a specific area. 
     In wireless power applications, it may be desirable to conserve energy when devices are not being charged. A need exist for methods, systems, and devices for detecting chargeable devices while conserving energy in wireless power transmitters. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a simplified block diagram of a wireless power transfer system. 
         FIG. 2  shows a simplified schematic diagram of a wireless power transfer system. 
         FIG. 3  illustrates a schematic diagram of a loop antenna for use in exemplary embodiments of the present invention. 
         FIG. 4  is a simplified block diagram of a transmitter, in accordance with an exemplary embodiment of the present invention. 
         FIG. 5  is a simplified block diagram of a receiver, in accordance with an exemplary embodiment of the present invention. 
         FIG. 6  is a flowchart illustrating a method, according to an exemplary embodiment of the present invention. 
         FIG. 7  is a flowchart illustrating another method, in accordance with an exemplary embodiment of the present invention. 
         FIG. 8  is a flowchart illustrating yet another method, in accordance with an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     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 between a transmitter to a receiver without the use of physical electrical conductors. Hereafter, all three of this will be referred to generically as radiated fields, with the understanding that pure magnetic or pure electric fields do not radiate power. These must be coupled to a “receiving antenna” to achieve power transfer. 
       FIG. 1  illustrates a wireless transmission or charging system  100 , in accordance with various exemplary embodiments of the present invention. Input power  102  is provided to a transmitter  104  for generating a field  106  for providing energy transfer. A receiver  108  couples to the 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 very close, transmission losses between the transmitter  104  and the receiver  108  are minimal when the receiver  108  is located in the “near-field” of the 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. 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. When in this near-field a coupling mode may be developed 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 transfer system. The transmitter  104  includes an oscillator  122 , a power amplifier  124  and a filter and matching circuit  126 . The oscillator is configured to generate at a desired frequency, such as 468.75 KHz, 6.78 MHz or 13.56, which may be adjusted in response to adjustment signal  123 . The oscillator signal may be amplified by the power amplifier  124  with an amplification amount 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 . 
     The 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 a device coupled to the receiver (not shown). The matching circuit  132  may be included to match the impedance of the receiver  108  to the receive antenna  118 . The receiver  108  and transmitter  104  may communicate on a separate communication channel  119  (e.g., Bluetooth, zigbee, cellular, etc). 
     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” antenna. Loop antennas may be configured to include an air core or a physical core such as a ferrite core. Air core loop antennas may be more tolerable to extraneous physical devices placed in the vicinity of the 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 powerful. 
     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, although the efficiency may be affected. 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 or magnetic antennas is based on the inductance and capacitance. Inductance in a loop antenna is generally simply 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 resonant 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 or magnetic antenna increases, the efficient energy transfer area of the near-field increases. 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 . 
       FIG. 4  is a simplified block diagram of a transmitter  200 , in accordance with an exemplary embodiment of the present invention. The transmitter  200  includes transmit circuitry  202  and a transmit antenna  204 . Generally, transmit circuitry  202  provides RF power to the transmit antenna  204  by providing an oscillating signal resulting in generation of near-field energy about the transmit antenna  204 . It is noted that transmitter  200  may operate at any suitable frequency. By way of example, transmitter  200  may operate at the 13.56 MHz ISM band. 
     Exemplary transmit circuitry  202  includes a fixed impedance matching circuit  206  for matching the impedance of the transmit circuitry  202  (e.g., 50 ohms) to the transmit antenna  204  and a low pass filter (LPF)  208  configured to reduce harmonic emissions to levels to prevent self-jamming of devices coupled to receivers  108  ( FIG. 1 ). Other exemplary embodiments may include different filter topologies, including but not limited to, notch filters that attenuate specific frequencies while passing others and may include an adaptive impedance match, that can be varied based on measurable transmit metrics, such as output power to the antenna or DC current drawn by the power amplifier. Transmit circuitry  202  further includes a power amplifier  210  configured to drive an RF signal as determined by an oscillator  212 . The transmit circuitry may be comprised of discrete devices or circuits, or alternately, may be comprised of an integrated assembly. An exemplary RF power output from transmit antenna  204  may be on the order of 2.5 Watts. 
     Transmit circuitry  202  further includes a controller  214  for enabling the oscillator  212  during transmit phases (or duty cycles) for specific receivers, for adjusting the frequency or phase of the oscillator, and for adjusting the output power level for implementing a communication protocol for interacting with neighboring devices through their attached receivers. It is noted that the controller  214  may also be referred to herein as processor  214 . As is well known in the art, adjustment of oscillator phase and related circuitry in the transmission path allows for reduction of out of band emissions, especially when transitioning from one frequency to another. 
     The transmit circuitry  202  may further include a load sensing circuit  216  for detecting the presence or absence of active receivers in the vicinity of the near-field generated by transmit antenna  204 . By way of example, a load sensing circuit  216  monitors the current flowing to the power amplifier  210 , which is affected by the presence or absence of active receivers in the vicinity of the near-field generated by transmit antenna  204 . Detection of changes to the loading on the power amplifier  210  are monitored by controller  214  for use in determining whether to enable the oscillator  212  for transmitting energy and to communicate with an active receiver. 
     Transmit antenna  204  may be implemented with a Litz wire or as an antenna strip with the thickness, width and metal type selected to keep resistive losses low. In a conventional implementation, the transmit antenna  204  can generally be configured for association with a larger structure such as a table, mat, lamp or other less portable configuration. Accordingly, the transmit antenna  204  generally will not need “turns” in order to be of a practical dimension. An exemplary implementation of a transmit antenna  204  may be “electrically small” (i.e., fraction of the wavelength) and tuned to resonate at lower usable frequencies by using capacitors to define the resonant frequency. 
     The transmitter  200  may gather and track information about the whereabouts and status of receiver devices that may be associated with the transmitter  200 . Thus, the transmitter circuitry  202  may include a presence detector  280 , an enclosed detector  290 , or a combination thereof, connected to the controller  214  (also referred to as a processor herein). The controller  214  may adjust an amount of power delivered by the amplifier  210  in response to presence signals from the presence detector  280  and the enclosed detector  290 . The transmitter may receive power through a number of power sources, such as, for example, an AC-DC converter (not shown) to convert conventional AC power present in a building, a DC-DC converter (not shown) to convert a conventional DC power source to a voltage suitable for the transmitter  200 , or directly from a conventional DC power source (not shown). 
     As a non-limiting example, the presence detector  280  may be a motion detector utilized to sense the initial presence of a device to be charged that is inserted into the coverage area of the transmitter. After detection, the transmitter may be turned on and the RF power received by the device may be used to toggle a switch on the Rx device in a pre-determined manner, which in turn results in changes to the driving point impedance of the transmitter. 
     As another non-limiting example, the presence detector  280  may be a detector capable of detecting a human, for example, by infrared detection, motion detection, or other suitable means. In some exemplary embodiments, there may be regulations limiting the amount of power that a transmit antenna may transmit at a specific frequency. In some cases, these regulations are meant to protect humans from electromagnetic radiation. However, there may be environments where transmit antennas are placed in areas not occupied by humans, or occupied infrequently by humans, such as, for example, garages, factory floors, shops, and the like. If these environments are free from humans, it may be permissible to increase the power output of the transmit antennas above the normal power restrictions regulations. In other words, the controller  214  may adjust the power output of the transmit antenna  204  to a regulatory level or lower in response to human presence and adjust the power output of the transmit antenna  204  to a level above the regulatory level when a human is outside a regulatory distance from the electromagnetic field of the transmit antenna  204 . 
     As a non-limiting example, the enclosed detector  290  (may also be referred to herein as an enclosed compartment detector or an enclosed space detector) may be a device such as a sense switch for determining when an enclosure is in a closed or open state. When a transmitter is in an enclosure, a power level of the transmitter may be increased. 
     In exemplary embodiments, a method by which the transmitter  200  does not remain on indefinitely may be used. In this case, the transmitter  200  may be programmed to shut off after a user-determined amount of time. This feature prevents the transmitter  200 , notably the power amplifier  210 , from running long after the wireless devices in its perimeter are fully charged. This event may be due to the failure of the circuit to detect the signal sent from either the repeater or the receive coil that a device is fully charged. To prevent the transmitter  200  from automatically shutting down if another device is placed in its perimeter, the transmitter  200  automatic shut off feature may be activated only after a set period of lack of motion detected in its perimeter. The user may be able to determine the inactivity time interval, and change it as desired. As a non-limiting example, the time interval may be longer than that needed to fully charge a specific type of wireless device under the assumption of the device being initially fully discharged. 
       FIG. 5  is a simplified block diagram of a receiver  300 , in accordance with an exemplary embodiment of the present invention. The receiver  300  includes receive circuitry  302  and a receive antenna  304 . Receiver  300  further couples to device  350  for providing received power thereto. It should be noted that receiver  300  is illustrated as being external to device  350  but may be integrated into device  350 . Generally, energy is propagated wirelessly to receive antenna  304  and then coupled through receive circuitry  302  to device  350 . 
     Receive antenna  304  is tuned to resonate at the same frequency, or within a specified range of frequencies, as transmit antenna  204  ( FIG. 4 ). Receive antenna  304  may be similarly dimensioned with transmit antenna  204  or may be differently sized based upon the dimensions of the associated device  350 . By way of example, device  350  may be a portable electronic device having diametric or length dimension smaller that the diameter of length of transmit antenna  204 . In such an example, receive antenna  304  may be implemented as a multi-turn antenna in order to reduce the capacitance value of a tuning capacitor (not shown) and increase the receive antenna&#39;s impedance. By way of example, receive antenna  304  may be placed around the substantial circumference of device  350  in order to maximize the antenna diameter and reduce the number of loop turns (i.e., windings) of the receive antenna and the inter-winding capacitance. 
     Receive circuitry  302  provides an impedance match to the receive antenna  304 . Receive circuitry  302  includes power conversion circuitry  306  for converting a received RF energy source into charging power for use by device  350 . Power conversion circuitry  306  includes an RF-to-DC converter  308  and may also include a DC-to-DC converter  310 . RF-to-DC converter  308  rectifies the RF energy signal received at receive antenna  304  into a non-alternating power while DC-to-DC converter  310  converts the rectified RF energy signal into an energy potential (e.g., voltage) that is compatible with device  350 . Various RF-to-DC converters are contemplated, including partial and full rectifiers, regulators, bridges, doublers, as well as linear and switching converters. 
     Receive circuitry  302  may further include switching circuitry  312  for connecting receive antenna  304  to the power conversion circuitry  306  or alternatively for disconnecting the power conversion circuitry  306 . Disconnecting receive antenna  304  from power conversion circuitry  306  not only suspends charging of device  350 , but also changes the “load” as “seen” by the transmitter  200  ( FIG. 2 ). 
     As disclosed above, transmitter  200  includes load sensing circuit  216  which detects fluctuations in the bias current provided to transmitter power amplifier  210 . Accordingly, transmitter  200  has a mechanism for determining when receivers are present in the transmitter&#39;s near-field. 
     When multiple receivers  300  are present in a transmitter&#39;s near-field, it may be desirable to time-multiplex the loading and unloading of one or more receivers to enable other receivers to more efficiently couple to the transmitter. A receiver may also be cloaked in order to eliminate coupling to other nearby receivers or to reduce loading on nearby transmitters. This “unloading” of a receiver is also known herein as a “cloaking.” Furthermore, this switching between unloading and loading controlled by receiver  300  and detected by transmitter  200  provides a communication mechanism from receiver  300  to transmitter  200  as is explained more fully below. Additionally, a protocol can be associated with the switching which enables the sending of a message from receiver  300  to transmitter  200 . By way of example, a switching speed may be on the order of 100 μsec. 
     In an exemplary embodiment, communication between the transmitter and the receiver refers to a device sensing and charging control mechanism, rather than conventional two-way communication. In other words, the transmitter may use on/off keying of the transmitted signal to adjust whether energy is available in the near-field. The receivers interpret these changes in energy as a message from the transmitter. From the receiver side, the receiver may use tuning and de-tuning of the receive antenna to adjust how much power is being accepted from the near-field. The transmitter can detect this difference in power used from the near-field and interpret these changes as a message from the receiver. It is noted that other forms of modulation of the transmit power and the load behavior may be utilized. 
     Receive circuitry  302  may further include signaling detector and beacon circuitry  314  used to identify received energy fluctuations, which may correspond to informational signaling from the transmitter to the receiver. Furthermore, signaling and beacon circuitry  314  may also be used to detect the transmission of a reduced RF signal energy (i.e., a beacon signal) and to rectify the reduced RF signal energy into a nominal power for awakening either un-powered or power-depleted circuits within receive circuitry  302  in order to configure receive circuitry  302  for wireless charging. 
     Receive circuitry  302  further includes processor  316  for coordinating the processes of receiver  300  described herein including the control of switching circuitry  312  described herein. Cloaking of receiver  300  may also occur upon the occurrence of other events including detection of an external wired charging source (e.g., wall/USB power) providing charging power to device  350 . Processor  316 , in addition to controlling the cloaking of the receiver, may also monitor beacon circuitry  314  to determine a beacon state and extract messages sent from the transmitter. Processor  316  may also adjust DC-to-DC converter  310  for improved performance. 
     It is noted that the exemplary embodiments described herein may be implemented within any suitable wireless power applications, such as wireless charging of mobile devices (e.g., mobile telephones, media players, etc.) or electric vehicles. 
     As will be appreciated by a person having ordinary skill in the art, it may be advantageous to detect when a device is positioned within a charging region of a wireless power transmitter. Further, it may be advantageous to be able to determine whether or not the detected device is a valid chargeable device. 
     Exemplary embodiments, as described herein, relate to detection of valid chargeable devices positioned within a charging region of a wireless power transmitter while conserving energy in the wireless power transmitter. According to one exemplary embodiment, a wireless power transmitter may enter a low-power mode during a period in which the wireless power transmitter is not transmitting power (e.g., a time period in which a charging region of the wireless power transmitter does not include any receivers). While in the low-power mode, the wireless power transmitter may measure a sensed current and compare the measured current to a previously defined baseline current. If the measured current is substantially equal to the baseline current, the wireless power transmitter may enter a sleep mode and, after a delay, may again measure a current and compare the measured current to the baseline current. 
     Further, if the measured current is different than the baseline current, a potential charging device may be present within a charging region of the wireless power transmitter and, therefore, the wireless power transmitter may attempt to establish a communication link with the potential device. If a communication link is established, the presence of a charging device may be verified. If the wireless power transmitter is unable to establish a communication link, the presence of charging device is not verified. 
     With reference again to  FIG. 4 , as previously noted, load sensing circuit  216  may be configured to measure a bias current level provided to transmitter power amplifier  210  to detect the presence or absence devices in the vicinity of the near-field generated by transmit antenna  204 . According to one exemplary embodiment, transmitter  202  may be configured to sense a change in impedance (e.g., reactance) at transmitter  202 . 
     Moreover, controller  214  may be configured for storing a measured bias current level as a baseline current within memory  270 , and, thereafter, comparing a subsequently measured bias current level to the baseline current. Furthermore, it is noted that controller  214  may be configured for adjusting a power mode of transmitter  202 . More specifically, controller  214  may be configured to reduce a power level, or possibly turn off the power, of transmitter  202 . 
     According to one exemplary embodiment, transmitter  202  may be configured to detect a presence of a device within an associated charging region while in a low-power mode. More specifically, transmitter  202 , via controller  214 , may be configured to transition to a low-power mode while an associated charging region lacks any detectable devices and the transmitter is not transmitting power. Furthermore, load sensing circuit  216  may be configured to measure a current level provided to power amplifier  210 . 
     If a baseline current level is not stored within memory  270 , transmitter  202 , and more specifically, controller  214  may be configured to store the sensed current level as a baseline current level within memory  270 . After storing a baseline current level, transmitter  202  (i.e., controller  214 ) may further decrease an associated power level, or the power of transmitter  202  may be turned off entirely. After a short delay (e.g., 1 second), transmitter  202  may again transition to the low-power mode. 
     If, upon measuring a current level, a baseline current is already stored within memory  270 , transmitter  202 , and more specifically, controller  214  may be configured to compare the measured current level to the stored baseline current. If the measured current is substantially equal to the baseline current, transmitter  202  (i.e., controller  214 ) may further decrease an associated power level, or the power of transmitter  202  may be turned off entirely. After a short delay, transmitter  202  may again transition to the low-power mode. If the measured current is not substantially equal to the baseline current (i.e., an amount of current sensed by the transmitter has changed), transmitter  202  may be configured to determine whether an associated charging region includes a valid chargeable device. By way of example, transmitter  202  (i.e., controller  214 ) may attempt to establish a communication link with the detected device to determine whether an associated charging region includes a valid chargeable device. 
     If transmitter  202  determines that a valid chargeable device exists within the charging region (e.g., transmitter  202  successfully establishes a communication link with a chargeable device), transmitter  202  may transmit power thereto. If transmitter  202  determines that a valid chargeable device does not exist within the charging region (e.g., transmitter  202  is unable to establish a communication link with a chargeable device), transmitter  202  may be configured to store the measured current level as the baseline current level. 
     As noted above, the resonant frequency of a loop or magnetic antennas is based on the inductance and capacitance. Inductance in a loop antenna is generally simply 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. According to one exemplary embodiment, a transmitter (e.g., transmitter  202 ) may be configured to detect a change in an associated resonant frequency. It is noted that a change in resonant frequency may be detected by known methods, such as frequency discrimination. Thereafter, transmitter  202  may be configured to determine whether or not an associated charging region includes a valid chargeable device. By way of example, transmitter  202  (i.e., controller  214 ) may attempt to establish a communication link with the detected device to determine whether an associated charging region includes a valid chargeable device. Accordingly, in this embodiment, a self-oscillating circuit of transmitter  202  may remain on to detect a change in an associated resonant frequency, and upon detection of a change, other components of transmitter  202  may be powered to validate a device, transmit power to the device, or both. 
       FIG. 6  illustrates a flowchart illustrating a method  600 , in accordance with an exemplary embodiment of the present invention. Method  600  may include causing a transmitter (e.g., transmitter  202  of  FIG. 4 ) to enter a low-power mode (depicted by numeral  602 ). The transmitter may enter a low-power mode while an associated charging region lacks any potential chargeable devices and the transmitter is not transmitting power. Furthermore, method  600  may include measuring a current sensed by the transmitter (depicted by numeral  604 ). Method  600  may further include determining whether a baseline current has been previously measured be the transmitter (depicted by numeral  606 ). For example only, if a baseline current has been previously measured, the baseline current may be stored within the transmitter. Conversely, if a baseline current has not been previously measured, the transmitter may not include a stored value for the baseline current. 
     If it is determined that the transmitter has not previously measured a baseline current, the measured current may be set as a baseline current (depicted by numeral  608 ). Thereafter, the power of the transmitter may be further decreased, or turned off entirely (depicted by numeral  610 ). After a short delay (depicted by numeral  612 ), method  600  may include causing a transmitter to enter the low-power mode (depicted by numeral  602 ). 
     Reverting back to step  606 , if it is determined that the transmitter has previously measured a baseline current (e.g., the transmitter includes a stored value for a baseline current), the measured current may be compared to the stored baseline current (depicted by numeral  614 ). If the measured current is substantially equal to the baseline current, method  600  may proceed back to step  610 , where the power of the transmitter may be further decreased, or turned off entirely. If the measured current is not substantially equal to the baseline current (i.e., an amount of current sensed by the transmitter has changed), a charging device may potentially be positioned within a charging region of the transmitter and the transmitter may determine whether an associated charging region includes a valid chargeable device (depicted by numeral  616 ). By way of example, the transmitter may determine whether an associated charging region includes a valid chargeable device by attempting to initiate a communication link with a device positioned within a near-field of the transmitter. 
     If the transmitter determines that a valid chargeable device exists (depicted by numeral  618 ) within the charging region (e.g., the transmitter successfully establishes a communication link with a chargeable device) the transmitter may transmit power thereto (depicted by numeral  620 ). If the transmitter determines that a valid chargeable device does not exist within the charging region (e.g., the transmitter is unable to establish a communication link with a chargeable device), method  600  may revert back to step  608 , where the measured current may be set as the baseline current. 
     In comparison to conventional methods and devices, exemplary embodiments of the present invention may require less power to detect and validate chargeable devices positioned within a charging region of a wireless power transmitter. Furthermore, devices may be validated as wireless chargeable devices prior to transmitting power within the charging region. 
       FIG. 7  is a flowchart illustrating a method  700 , in accordance with one or more exemplary embodiments. Method  700  may include comparing a measured current level to a baseline current level to detect a change in a current level measured by the transmitter (depicted by numeral  702 ). Further, method  700  may include attempting to establish a communication link with a detected device if a change in the current level is detected (depicted by numeral  704 ). Moreover, method  700  may include initiating a charging process if the communication link is established (depicted by numeral  706 ). 
       FIG. 8  is a flowchart illustrating another method  800 , in accordance with one or more exemplary embodiments. Method  800  may include detecting a change in at least one parameter at a wireless power transmitter (depicted by numeral  802 ). Method  800  may further include determining whether at least one valid chargeable device is positioned within an associated charging region of the wireless power transmitter when the change in the at least one parameter is detected (depicted by numeral  804 ). 
     Those of skill in the art would understand that 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 exemplary embodiments disclosed herein may be implemented as electronic hardware, 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 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 exemplary embodiments disclosed herein may be implemented or performed 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 steps of a method or algorithm described in connection with the exemplary 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 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 exemplary embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.