Patent Publication Number: US-2022231541-A1

Title: Loop antennas with selectively-activated feeds to control propagation patterns of wireless power signals

Description:
RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 16/296,145, filed on Mar. 7, 2019, entitled “Loop Antennas With Selectively-Activated Feeds To Control Propagation Patterns Of Wireless Power Signals,” which claims the benefit of U.S. Provisional Patent Application Ser. No. 62/643,118, filed Mar. 14, 2018, entitled “Loop Antennas With Selectively-Activated Feeds To Control Propagation Patterns Of Wireless Power Signals,” each of which is herein fully incorporated by reference in its respective entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to loop antennas for wireless power transmission, and more particularly to loop antennas with selectively-activated feeds to control propagation patterns of wireless power signals. 
     BACKGROUND 
     Portable electronic devices such as smartphones, tablets, notebooks and other electronic devices have become a necessity for communicating and interacting with others. The frequent use of portable electronic devices, however, uses a significant amount of power, which quickly depletes the batteries attached to these devices. Inductive charging pads and corresponding inductive coils in portable devices allow users to wirelessly charge a device by placing the device at a particular position on an inductive pad to allow for a contact-based charging of the device due to magnetic coupling between respective coils in the inductive pad and in the device. 
     Conventional inductive charging pads, however, suffer from many drawbacks. For one, users typically must place their devices at a specific position and in a certain orientation on the charging pad because gaps (“dead zones” or “cold zones”) exist on the surface of the charging pad. In other words, for optimal charging, the coil in the charging pad needs to be aligned with the coil in the device in order for the required magnetic coupling to occur. Additionally, placement of other metallic objects near an inductive charging pad may interfere with operation of the inductive charging pad, so even if the user places their device at the exact right position, if another metal object is also on the pad, then magnetic coupling still may not occur and the device will not be charged by the inductive charging pad. This results in a frustrating experience for many users as they may be unable to properly charge their devices. 
     Charging using electromagnetic radiation (e.g., microwave radiation waves) offers promise, but RF charging is typically focused on far-field charging and not near-field or mid-field charging where the device to be charged is placed on or near the RF energy transmitter. 
     SUMMARY 
     Accordingly, there is a need for a wireless charging solution that (i) radiates energy at a mid-field distance (and various other distances) to wirelessly deliver power to a receiver, and (ii) allows users to place their devices at any position on or near the pad and still receive wirelessly delivered energy. A method of operating one such example wireless power transmitter is described below. 
     In the following description, references to “mid-field” transmission refer to radiation of electromagnetic waves by an antenna (e.g., the loop antenna described herein) for distances up to approximately a wavelength of an operating frequency of the antenna (e.g., a wavelength of an operating frequency of 5.8 GHz is approximately 5.17 centimeters, so the mid-field transmission distance of the antenna in this example would be approximately 5.17 centimeters). In some embodiments, the operating frequency ranges from 400 MHz to 60 GHz. For the purposes of the following description, a mid-field charging pad (or mid-field radio-frequency charging pad) is a wireless-power-transmitting device that includes one or more wireless power transmitters, each of which is configured to radiate electromagnetic waves to receiver devices that are located within a mid-field distance of the charging pad (e.g., within 0-5.17 centimeters of the charging pad, if the one or more wireless power transmitters of the charging pad are using an operating frequency of 5.8 GHz). 
     (A1) In some embodiments, a method of wirelessly charging a receiver device includes, providing a wireless power transmitter including (i) a ground plate, (ii) a conductive wire offset from the ground plate, the conductive wire forming a loop antenna, (iii) a plurality of feed elements extending from the ground plate to the conductive wire, each feed element being connected to the conductive wire at a different position on the conductive wire, and (iv) a power amplifier connected to one or more feed elements of the plurality of feed elements. The method further includes selectively feeding, by the power amplifier, an RF signal to a respective feed element of the one or more feed elements based on a location of a receiver device relative to the plurality of feed elements. The method further includes (i) exciting, by the respective feed element fed by the power amplifier, the conductive wire, and (ii) radiating, by the conductive wire, the RF signal for wirelessly powering the receiver device. 
     (A2) In some embodiments of the method of A1, the method further includes: (i) selecting, by a controller of the wireless power transmitter, the respective feed element of the one or more feed elements based on the location of the receiver device relative to the plurality of feed elements, and (ii) sending, by the controller, an instruction to the power amplifier that causes the power amplifier to feed the RF signal to the respective feed element. 
     (A3) In some embodiments of the method of A2, the method further includes receiving, by a communications radio of the wireless power transmitter, a communications signal from a corresponding communications radio of the receiver device. Moreover, the method further includes determining, by the controller, the location of the receiver device relative to the plurality of feed elements based, at least in part, on the communications signal. In some embodiments, the operations of A3 are performed prior to the operations of A2. 
     (A4) In some embodiments of the method of any of A2-A3, the method further includes detecting, by one or more sensors of the wireless power transmitter, a presence of the receiver device. Moreover, the method further includes determining, by the controller, the location of the receiver device relative to the plurality of feed elements based on information generated by the one or more sensors. In some embodiments, determining the location of the receiver device relative to the plurality of feed elements is based on a combination of the communications signal and the information generated by the one or more sensors. In some embodiments, the operations of A4 are performed prior to the operations of A2. 
     (A5) In some embodiments of the method of any of A1-A4, radiating the RF signal includes radiating the RF signal from the conductive wire with different propagation patterns (e.g., radiation patterns) depending on which of the plurality of feed elements is fed by the power amplifier. 
     (A6) In some embodiments of the method of A5, the RF signal is radiated from the conductive wire with the different propagation patterns, wherein the different propagation patterns are based, at least in part, on a plurality of physical dimensions of the wireless power transmitter, including: a width of the conductive wire; a length of the conductive wire; a thickness of the conductive wire; a diameter of the conductive wire; a shape of the loop; and a magnitude of the offset between the ground plate and the conductive wire. 
     (A7) In some embodiments of the method of any of A5-A6, when the respective feed element is a first feed element of the one or more feed elements that is connected to the conductive wire at a first position, the method further includes feeding, via the power amplifier, the RF signal to the first feed element when the location of the receiver device is within a first threshold distance from the first position. 
     (A8) In some embodiments of the method of A7, radiating the RF signal includes radiating the RF signal from the conductive wire in a first propagation pattern of the different propagation patterns when the first feed element of the one or more feed elements is fed by the power amplifier, where a high concentration of RF energy in the first propagation pattern is steered to travel towards the location of the receiver device. 
     (A9) In some embodiments of the method of any of A5-A8, when the respective feed element is a second feed element, distinct from the first feed element, of the one or more feed elements that is connected to the conductive wire at a second position, distinct from the first position, the method further includes feeding, via the power amplifier, the RF signal to the second feed element when the receiver device is located at a second location, distinct from the location, the second location being within a second threshold distance from the second position. 
     (A10) In some embodiments of the method of A9, radiating the RF signal includes radiating the RF signal in a second propagation pattern of the different propagation patterns when the second feed element of the one or more feed elements is fed by the power amplifier, where a high concentration of RF energy in the second propagation pattern is steered to travel towards the second location of the receiver device. 
     (A11) In some embodiments of the method of A10, the RF signal radiated in the first propagation pattern propagates away from the first position in a first direction towards the location of the receiver device, and the RF signal radiated in the second propagation pattern propagates away from the second position in a second direction towards the second location of the receiver device. In some embodiments, the second direction is different from the first direction. In some embodiments, the second direction is the same as the first direction. 
     (A12) In some embodiments of the method of any of A8-A11, the first propagation pattern has a first polarization and the second propagation pattern has a second polarization. In some embodiments, the second polarization differs from the first polarization. In some embodiments, the second polarization is the same as the first polarization. 
     (A13) In some embodiments of the method of any of A1-A12, the ground plate is disposed in a first plane, the conductive wire is disposed in a second plane, and the second plane is substantially parallel to the first plane. 
     (A14) In some embodiments of the method of A13, the second plane is offset from the first plane by a distance. 
     (A15) In some embodiments of the method of any of A13-A14, each of the plurality of feed elements is substantially perpendicular to the first and second planes. 
     (A16) In some embodiments of the method of any of A1-A15, the one or more feed elements are one or more first feed elements, and the wireless power transmitter further includes a second power amplifier connected to one or more second feed elements of the plurality of feed elements. 
     (A17) In some embodiments of the method of any of A1-A16, the one or more feed elements includes at least two feed elements, and feeding the RF signal includes feeding the RF signal to the at least two feed elements upon determining that the location of the receiver device is between the two feed elements. 
     (A18) In some embodiments of the method of any of A1-A17, the conductive wire includes a plurality of contiguous segments and each of the plurality of feed elements is positioned between a respective pair of segments of the plurality of contiguous segments. 
     (A19) In some embodiments of the method of claim A18, one or more first segments of the plurality of contiguous segments have a first shape and one or more second segments of the plurality of contiguous segments have a second shape different from the first shape. 
     (A20) In some embodiments of the method of any of A17-A19, further including radiating, via one or more (or each) of the plurality of contiguous segments, the RF signal when one of the plurality of feed elements is fed by the power amplifier. 
     (A21) In some embodiments of the method of any of A1-A20, the plurality of feed elements is configured to provide the RF signal to the conductive wire at the different positions. 
     (A22) In some embodiments of the method of any of A1-A21, the RF signal is transmitted at a frequency of 5.8 GHz, 2.4 GHz, or 900 MHz. 
     (A23) In some embodiments of the method of any of A7 and A9, the RF signal has a wavelength, the first and second threshold distances are within a mid-field transmission distance of the wireless power transmitter, and the mid-field transmission distance is within the wavelength of the RF signal from the wireless power transmitter. 
     (A24) In one other aspect, a wireless power transmitter is provided, and the wireless power transmitter includes the structural characteristics for a wireless power transmitter described above in any of A1-A22, and the wireless power transmitter is also configured to perform the method steps described above in any of A1-A23. 
     (A25) In another aspect, a transmitter pad that includes one or more of the wireless power transmitters described in any of A1-A23 is provided. In some embodiments, the transmitter pad is in communication with one or more processors and memory storing one or more programs which, when executed by the one or more processors, cause the transmitter pad to perform the method described in any one of A1-A23. 
     (A26) In yet another aspect, a transmitter pad (that includes one or more of the wireless power transmitters described in any of A1-A23) is provided and the transmitter pad includes means for performing the method described in any of A1-A23. 
     (A27) In still another aspect, a non-transitory computer-readable storage medium is provided (e.g., as a memory device, such as external or internal storage, that is in communication with a transmitter pad). The non-transitory computer-readable storage medium stores executable instructions that, when executed by a transmitter pad (that includes a plurality of wireless power transmitters) with one or more processors/cores, cause the transmitter pad to perform the method described in any one of A1-A23. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. 
       So that the present disclosure can be understood in greater detail, a more particular description may be had by reference to the features of various embodiments, some of which are illustrated in the appended drawings. The appended drawings, however, merely illustrate pertinent features of the present disclosure and are therefore not to be considered limiting, for the description may admit to other effective features. 
         FIGS. 1A-1B  show diagrams illustrating a representative transmitter pad in accordance with some embodiments. 
         FIG. 2  is a schematic of a representative transmitter in accordance with some embodiments. 
         FIG. 3A  is a top view of a representative wireless power transmitter in accordance with some embodiments. 
         FIG. 3B  is a cross-sectional view (taken along line A-A 1 ) of the representative wireless power transmitter of  FIG. 3A  in accordance with some embodiments. 
         FIG. 4  is a flow diagram showing a method of wirelessly charging a receiver device in accordance with some embodiments. 
         FIGS. 5A-5B  show various power distributions from a wireless power transmitter in accordance with some embodiments. 
         FIGS. 6A-6B  show various propagation patterns radiating from a wireless power transmitter in accordance with some embodiments. 
     
    
    
     In accordance with common practice, the various features illustrated in the drawings may not be drawn to scale. Accordingly, the dimensions of the various features may be arbitrarily expanded or reduced for clarity. In addition, some of the drawings may not depict all of the components of a given system, method or device. Finally, like reference numerals may be used to denote like features throughout the specification and figures. 
     DETAILED DESCRIPTION 
     Numerous details are described herein in order to provide a thorough understanding of the example embodiments illustrated in the accompanying drawings. However, some embodiments may be practiced without many of the specific details, and the scope of the claims is only limited by those features and aspects specifically recited in the claims. Furthermore, well-known processes, components, and materials have not been described in exhaustive detail so as not to unnecessarily obscure pertinent aspects of the embodiments described herein. 
       FIG. 1A  is a high-level block diagram of a transmitter pad  100 , in accordance with some embodiments. The transmitter pad  100  (also referred to interchangeably herein as a mid-field radio-frequency (RF) charging pad, mid-field charging pad, or radio-frequency charging pad) includes components  102 . The transmitter pad  100  is configured to generate electromagnetic energy (e.g., RF power transmission waves/RF signals) that is received by a receiver that is placed in proximity (e.g., within a mid-field distance, such as approximately 12.5 centimeters from the transmitter pad  100  if the wireless power transmitters of the pad are currently using an operation frequency of 2.4 GHz) or on top of the transmitter pad  100 . the descriptions herein, RF power transmission waves are used as a primary illustrative example, but one or ordinary skill in the art will appreciate in view of these descriptions that any type of electromagnetic radiation waves may be used instead in certain embodiments or implementations. 
     The components  102  of the transmitter pad  100  include, for example, one or more processors/cores  104 , a memory  106 , one or more transmitter zones  110  (each including respective one or more wireless power transmitters  300 , and an example transmitter  300  is illustrated in  FIGS. 3A-3B ), one or more communications components  112 , and/or one or more transmitter sensors  114 . In some embodiments, these components  102  are interconnected by way of a communications bus  108 . In some embodiments, the components  102  are housed within the transmitter pad  100 . Alternatively, in some embodiments, one or more of the components  102  are disposed outside (e.g., external) the transmitter pad  100 . For example, the one or more processors  104 , the memory  106 , the one or more communications components  112 , may be external while the respective one or more transmitters  300  of each respective transmitter zone  100  and the one or more transmitter sensors  114  may be internal (or some other combination/arrangement of components). 
     In some embodiments, the communication component(s)  112  include, e.g., hardware capable of data communications using any of a variety of wireless protocols (e.g., IEEE 802.15.4, Wi-Fi, ZigBee, 6LoWPAN, Thread, Z-Wave, Bluetooth Smart, ISA100.11a, WirelessHART, MiWi, etc.) wired protocols (e.g., Ethernet, HomePlug, etc.), and/or any other suitable communication protocol, including communication protocols not yet developed as of the filing date of this document. 
     In some embodiments, the communications component  112  transmits communication signals to the receiver  120  by way of the electronic device. For example, the communications component  112  may convey information to a communications component of the electronic device, which the electronic device may in turn convey to the receiver  120  (e.g., via a bus). 
     In some embodiments, the receiver  120  includes a communications component configured to communicate various types of data with the transmitter pad  100 , through a respective communication signal generated by a receiver-side communications component. The data may include location indicators for the receiver  120 , a power status of the electronic device, status information for the receiver  120  (e.g., a frequency at which a wireless-power-receiving antenna of the receiver  120  is tuned, a polarization of the wireless-power-receiving antenna, etc.), status information for the electronic device (e.g., a current battery-charge level for the electronic device), status information about power waves being transmitted to the receiver  120  by the pad  100  (e.g., an amount of energy the receiver  120  is able to extract from the power waves). 
     In some embodiments, the data contained within communication signals is used by the electronic device, receiver  120 , and/or transmitter pad  100  for determining adjustments of one or more characteristics used by any of the transmitters  300  to transmit power waves. Using a communication signal, the transmitter pad  100  receives data that is used, e.g., to identify receivers  120  on the transmitter pad  100 , identify electronic devices, determine safe and effective waveform characteristics for power waves, and/or determine which feed to activate for one or more of the transmitters  300 . 
     In some embodiments, the transmitter pad  100  is designed to lay flat on a surface (e.g., horizontally) while in some embodiments the transmitter pad  100  is designed to be positioned at an angle relative to the surface (e.g., substantially vertical). In some embodiments, a housing for the transmitter pad  100  is shaped such that the transmitter pad  100  is stable when positioned in a substantially vertical manner. Moreover, the transmitter pad  100  may include a stand (e.g., kick stand) that extends away from the transmitter pad  100  to provide additional support. 
     In some embodiments, the one or more transmitter sensors  114  are positioned at one or more locations on the transmitter pad  100  (e.g., not specific to any transmitter zone  110 ). Alternatively, in some embodiments, a first set sensors of the one or more sensors  114  is part of a first transmitter zone  110 -A, a second set sensors of the one or more sensors  114  is part of a second transmitter zone  110 -B, and so on. In such an arrangement, the various sets of sensors provide respective sensor information to the one or more processors  104 , and the one or more processors  104  use the sensor information to determine a location of the receiver  120  relative to the one or more transmitter zones  110 . 
     Non-limiting examples of transmitter sensors  114  include, e.g., infrared, pyroelectric, ultrasonic, laser, optical, Doppler, gyro, accelerometer, microwave, millimeter, RF standing-wave sensors, resonant LC sensors, capacitive sensors, light sensor, and/or inductive sensors, and a hall sensor. In some embodiments, technologies for transmitter sensor(s)  114  include binary sensors that acquire stereoscopic sensor data, such as the location of a human or other sensitive object. 
     In some embodiments, memory  106  of the transmitter pad  100  stores one or more programs (e.g., sets of instructions) and/or data structures, collectively referred to herein as “modules.” In some embodiments, memory  106 , or the non-transitory computer readable storage medium of memory  106  stores the following modules  107  (e.g., programs and/or data structures), or a subset or superset thereof:
         information received from receiver  120  (e.g., generated by a sensor of the receiver  120  and then transmitted to the transmitter pad  100 , or generated by a communications component of the receiver  120  (or the electronic device coupled thereto) and then transmitted to the transmitter pad  100 );   information received from transmitter sensor(s)  114 ;   RF power transmission signals generation module for generating and transmitting (e.g., in conjunction with respective transmitter(s)  300 ) RF power transmission signals; and/or   a characteristic selection module for selecting waveform characteristics of the RF power transmission signals.       

     The above-identified modules (e.g., data structures and/or programs including sets of instructions) need not be implemented as separate software programs, procedures, or modules, and thus various subsets of these modules may be combined or otherwise re-arranged in various embodiments. In some embodiments, memory  106  stores a subset of the modules identified above. Furthermore, the memory  106  may store additional modules not described above. In some embodiments, the modules stored in memory  106 , or a non-transitory computer readable storage medium of memory  106 , provide instructions for implementing respective operations in the methods described below. In some embodiments, some or all of these modules may be implemented with specialized hardware circuits that subsume part or all of the module functionality. One or more of the above-identified elements may be executed by one or more of the processor(s)  104 . In some embodiments, one or more of the modules described with regard to memory  106  is implemented on memory of a server (not shown) that is communicatively coupled to the transmitter pad  100  and/or by a memory of electronic device and/or receiver  120 . In addition, memory  106  may store other information such as certain thresholds and criteria, as well as identifiers of certain receivers. 
     Turning to  FIG. 1B , a simplified top view of the transmitter pad  100  is illustrated.  FIG. 1B  shows a receiver  120  (e.g., a receiver that is internally or externally coupled to an electronic device) that is placed on top of the transmitter pad  100  and then receives energy from one or more of the transmitters  300 . In some embodiments, the receiver  120  includes one or more antennas for receiving energy (e.g., RF signals) from the transmitter pad  100  and a communications component for receiving communications (or sending communications) sent by the transmitter pad  100 . The communications component of the receiver  120  may also include hardware capable of data communications using the variety of wireless protocols listed above with reference to the communication component(s)  112 . 
     The receiver  120  converts energy from received signals (also referred to herein as RF power transmission signals, or simply, RF signals, power waves, or power transmission signals) into electrical energy to power and/or charge an electronic device coupled to the receiver  120 . For example, the receiver  120  uses power-conversion circuitry to convert captured energy from power waves (received via a wireless-power-receiver antenna) to alternating current (AC) electricity or direct current (DC) electricity usable to power and/or charge an electronic device. Non-limiting examples of power-conversion circuitry can include rectifiers, rectifying circuits, voltage conditioners, among suitable circuitry and devices. 
     In some embodiments, the receiver  120  is a standalone device that is detachably coupled to one or more electronic devices. For example, the electronic device has processor(s) for controlling one or more functions of the electronic device and the receiver  120  has processor(s) for controlling one or more functions of the receiver  120 . In some embodiments, the receiver  120  is a component of the electronic device. For example, processor(s) of the electronic device control functions of the electronic device and the receiver  120 . In addition, in some embodiments, the receiver  120  includes processor(s) which communicate with processor(s) of the electronic device. It is noted that the combination of the receiver  120  and the electronic device is sometimes referred to herein simply as a “receiver device.” 
     In some embodiments, the receiver  120  receives one or more power waves directly from the transmitter pad  100  (and in particular, from one or more of the transmitter(s)  300 ). In some embodiments, the receiver  120  harvests power from one or more power waves transmitted by transmitter pad  100 . As will be discussed in greater detail below, the one or more power waves are generated at one or more different positions along a respective conductive wire  202 -A of a respective transmitter  300  that is positioned within a respective transmitter zone  110 , and the generated one or more power waves propagate away from the respective transmitter  300  in a particular pattern. In some embodiments, the transmitter pad  100  is a mid-field transmitter that transmits the one or more power waves within a mid-field distance of its charging surface. 
     In some embodiments, after energy is harvested from the one or more power waves (as discussed in greater detail below), circuitry (e.g., integrated circuits, amplifiers, rectifiers, and/or voltage conditioner) of the receiver  120  converts the energy to usable power (i.e., electricity), which powers the electronic device associated with the receiver  120  (and/or the usable power is stored in a battery of electronic device). In some embodiments, a rectifying circuit of the receiver  120  converts the electrical energy from AC to DC for use by the electronic device. In some embodiments, a voltage conditioning circuit increases or decreases the voltage of the electrical energy as required by the electronic device, and may produce a constant voltage for providing electricity in a form required by the electronic device. 
     In some embodiments, a plurality of electronic devices may be positioned on a surface of the transmitter pad  100 , each having at least one respective receiver  120  that is used to receive power waves from the transmitter pad  100 . In some embodiments, the transmitter pad  100  adjusts one or more characteristics (e.g., waveform characteristics, such as phase, gain, amplitude, frequency, etc.) of the power waves and controls which feeds of respective transmitters  110  are activated to controllably form propagation patterns of radio-frequency energy transmitter to each of the respective receivers  120 . 
     In some embodiments, the one or more transmitter zones  110  cover all or a portion of a surface area of the transmitter pad  100 . The transmitter zones  110  may also form a top surface (i.e., a charging surface) of the transmitter pad  100 . Further, in some embodiments, the one or more transmitter zones  110  and other components  102  of the transmitter pad  100  may be encapsulated within a plastic or other type of covering (e.g., a housing). 
     In some embodiments, circuits (not shown) of the transmitter pad  100 , such as a controller circuit and/or waveform generator, may at least partially control the behavior of the transmitters  110 . For example, based on the information received from the receiver  120  by way of a communication signal (or data gathered by transmitter sensor(s)  114 ), a controller circuit (e.g., controller  209 ,  FIG. 2 ) may determine a set of one or more waveform characteristics (e.g., amplitude, frequency, direction, phase, among other characteristics) used for transmitting the power waves that would effectively provide power to the receiver  120 . The controller circuit may also identify one or more transmitter zones  110  (and transmitters  300  included therein) that would be effective in transmitting the power waves (e.g., receiver  120  may be positioned between two transmitter zones  110 , and in such a case, respective transmitters  300  positioned within two transmitter zones  110  may be activated). Upon identifying the one or more transmitter zones  110  and/or particular transmitters  300  positioned therein, the controller circuit may also select a respective feed element of one or more feed elements (e.g., one of the plurality of feed elements  204 -A- 204 -D,  FIG. 2 ) from each of the transmitters  300  based on a location of the receiver device relative to the plurality of feed elements. In doing so, the controller circuit may send an instruction to a power amplifier of the one or more transmitters  110  that causes the power amplifier to feed an RF signal to the selected respective feed elements of the one or more transmitters  110 . 
       FIG. 2  is a schematic of a representative transmitter zone  110  in accordance with some embodiments. The representative transmitter zone  110  is an example of one of the transmitter zones  110 -A- 110 -N ( FIG. 1B ). The components in  FIG. 2  are illustrated in a particular arrangement for ease of illustration and one skilled in the art will appreciate that other arrangements are possible. Moreover, while some example features are illustrated, various other features have not been illustrated for the sake of brevity and so as not to obscure pertinent aspects of the example implementations disclosed herein. 
     As a non-limiting example, the representative transmitter zone  110  includes a transmitter  300  (which includes an antenna element  202 , a plurality of feeds  204 -A,  204 -B, . . .  204 -N, and a power amplifier  206  (or multiple power amplifiers)). The components of the representative transmitter zone  110  are coupled via busing  108  or the components are directly coupled to one another. Additionally, the representative transmitter zone  110  includes switches  208 -A,  208 -B, . . .  208 -N positioned between the power amplifier  206  and each respective feed  204 . In some embodiments, instead of using switches to couple a single power amplifier  206  with multiple feeds  204 , multiple power amplifiers may each be coupled directly with a single feed  204  (or two power amplifiers may each be coupled with one or more of the feeds via the switching arrangement illustrated in  FIG. 2 ). Other configurations of power amplifiers and feeds are also within the scope of this disclosure, as one of skill will readily appreciate upon reading the descriptions herein. 
     In some embodiments, the power amplifier(s)  206  and any switches  208  can be configured as part of the transmitter  300  (not illustrated) while, in other embodiments, the power amplifier(s)  206  and any switches  208  can be configured as external to the transmitter  300  and coupled to feeds of an antenna element  202  (as illustrated in  FIG. 2 ). In some embodiments, power amplifiers  206  may be shared across multiple transmitter zones  110 . 
     The antenna element  202  is coupled with the plurality of feeds  204 -A,  204 -B, . . .  204 -N. In some embodiments (as shown in  FIG. 3B ), the antenna element  202  is directly coupled with each of the feeds  204 -A,  204 -B, . . .  204 -N. The antenna element  202  is used to radiate one or more RF signals that provide wirelessly delivered power to a receiver  120 . In some embodiments, the radiated one or more RF signals are received by the receiver  120  when the receiver is located anywhere between a top surface of the transmitter zone  110  and up to a wavelength of an operating frequency of the transmitter  300  away from the transmitter zone  110  (e.g., the receiver  120  is within a mid-field transmission distance of the transmitter  300 ). In some embodiments, the antenna element  202  is a conductive wire forming a loop antenna (e.g., a substantially contiguous loop antenna). The antenna element  202  may be made from a suitable material that is capable of conducting the RF signals. 
     Each feed  204  is coupled with the antenna element  202  at a different position (e.g., positions A-D,  FIG. 3A ) on the antenna element  202 . For example, the feed  204 -A is coupled with the antenna element  202  at a first position, the feed  204 -B is coupled with the antenna  202  at a second position, and so on. Each of the plurality of feeds  204 -A,  204 -B, . . .  204 -N provides the one or more RF signals to be radiated by the antenna element  202  at a particular position along the antenna element  202  (as explained in more detail below). Each feed  204  may be made from any suitable conductive material (e.g., aluminum, copper, etc.). 
     The power amplifier is used to selectively provide power to one or more of the feeds  204 -A,  204 -B, . . .  204 -N by closing one or more of the switches  208 -A,  208 -B, . . .  208 -N. The power amplifier  206  may be instructed (e.g., by the controller  209 ) to close a respective switch of the one or more of the switches  208 -A,  208 -B, . . .  208 -N depending on a location of the receiver  120  relative to the plurality of feeds  204 -A- 204 -D. Although not shown, the one or more of the switches  208 -A,  208 -B, . . .  208 -N may be part of (e.g., internal to) the power amplifier. Operation of the power amplifier is discussed in further detail below with reference to the method  400 . 
     In some embodiments, the power amplifier  206  is coupled with a power supply (not shown), and the power amplifier  206  draws energy from the power supply to provide RF signals to one or more of the feeds  204 -A,  204 -B, . . .  204 -N. Moreover, in some embodiments (not shown), the power amplifier  206  is coupled with an RF power transmitter integrated circuit (e.g., the RF integrated circuit may be part of the transmitter zone  110  or more generally part of the transmitter pad  100 ). The RF integrated circuit is configured to generate a suitable RF signal and provide that RF signal to the power amplifier  206 , and the power amplifier  206  in turn provides the RF signal to one or more of the feeds  204 -A,  204 -B, . . .  204 -N. In some embodiments, the RF integrated circuit includes an RF oscillator and/or a frequency modulator that is used to generate the RF signal so that is appropriate for transmission to an RF receiver  120  (e.g., the RF signal has an appropriate power level, frequency, etc. to ensure that a maximum amount of energy is transferred from the transmitter  300  to the RF receiver  120 ). 
     In some embodiments, the power amplifier  206  is coupled to an internal or external (with respect to the transmitter pad  100 ) controller  209 , and in turn is coupled to the one or more processors  104  ( FIG. 1A ). In some embodiments, the controller  209  and the one or more processors  104  are not part of a particular transmitter zone  110  (e.g., the controller  209  is an internal component of the transmitter pad  100  overall and is in communication with each of the transmitter zones  110 ). Alternatively, in some embodiments, respective controllers  209  and respective one or more processors  104  are each internally associated with each of the respective transmitter zones  110 . The controller  209  and the one or more processors  104  are configured to control operation of the power amplifier  206 . For example, the controller  209  or the one or more processors  104  may select a respective feed of the feed  204 -A,  204 -B, . . .  204 -N based on the location of the receiver  120  relative to the feeds  204 -A,  204 -B, . . .  204 -N. Further, the controller  209  may send an instruction to the power amplifier  206  that causes the power amplifier  206  to feed one or more RF signals to the respective feed that was selected based on the location of the receiver. 
     In some embodiments, the controller  209  (or a component thereof, e.g., the one or more processors  104 ) uses information received by the one or more communication components  112  and/or detected by the one or more transmitter sensors  114  to determine the location of the receiver  120  relative to the feeds  204 -A,  204 -B, . . .  204 -N. Determining the location of the receiver  120  is discussed in further detail below with reference to the method  400 . 
       FIGS. 3A-3B  illustrate various views of a representative transmitter  300  in accordance with some embodiments. The transmitter  300  is an example wireless power transmitter included in one of the transmitter zones  110  ( FIG. 1A  and  FIG. 2 ). As shown, the transmitter  300  includes a ground plate  210 , an antenna element  202 , and a plurality of feeds  204 -A- 204 -D. It is noted that the representative transmitter  300 , and its various components, may not be drawn to scale. Moreover, while some example features are illustrated, various other features have not been illustrated for the sake of brevity and so as not to obscure pertinent aspects of the example implementations disclosed herein. 
     The ground plate defines a plurality of openings  212 -A- 212 -D, where each of the plurality of openings  212 -A- 212 -D is sized to receive and accommodate one of the plurality of feeds  204 . The number of openings corresponds to the number of feeds. In some embodiments, the ground plate  210  forms a bottom surface of the transmitter pad  100 . The ground plate  210  can be made from various materials as known by those skilled in the art. As explained below, the transmitter  300  can include any number of feeds, depending on the circumstances. 
     The antenna element  202  is offset from the ground plate (e.g., distance (D),  FIG. 3B ). In such an arrangement, the ground plate  210  defines a first plane (e.g., a first horizontal plane: the bottom surface) and the antenna element  202  defines a second plane (e.g., a second horizontal plane: the top surface) that is offset from the first plane. A gap is formed between the ground plate  210  and the antenna element  202 . 
     Each of the plurality of feeds  204 -A- 204 -D is disposed in a respective opening of the plurality of openings  212 -A- 212 -D, and each of the feeds  204 -A- 204 -D connects to the antenna element  202  at a different position along the conductive wire  202 -A. In such an arrangement, the feeds  204 -A- 204 -D support the antenna element  204  along a length of the antenna element  202 . For example, with reference to  FIG. 3B , feeds  204 -A and  204 -B extend through their respective openings  212 -A and  212 -B to the antenna element  202 , and in doing so, structurally support the antenna element  202 . Each of the plurality of feeds  204 -A- 204 -D is substantially perpendicular to the ground plate  210  and the antenna element  202  (e.g., each of the plurality of feeds  204 -A- 204 -D is disposed along a respective vertical axis while the conductive plate and antenna element are disposed along respective horizontal axes/planes). Although four feeds are shown in  FIG. 3A , the transmitter  300  can include any number of feeds, depending on circumstances (e.g., could be less than or greater than four feeds). 
     In some embodiments, the antenna element  202  includes a plurality of contiguous segments  202 -A- 202 -D, and each of the plurality of feeds  204 -A- 204 -D is positioned between a respective pair of adjacent segments (e.g., positioned between abutting ends of adjacent segments). For example, a first feed  204 -A of the plurality of feeds  204  is positioned between a third segment  202 -C and a fourth segment  202 -D of the plurality of contiguous segments (i.e., a first respective pair of adjacent segments), a second feed  204 -B of the plurality of feeds  204  is positioned between the fourth segment  202 -D and a first segment  202 -A of the plurality of contiguous segments (i.e., a second respective pair of adjacent segments), and so on. In such an arrangement, each of the plurality of feeds  204 -A- 204 -D is mechanically (and electrically) coupled with two segments. 
     In some embodiments (not illustrated), a shape of each segment in the plurality of contiguous segments  202 -A- 202 -D is substantially the same (e.g., each is rectangular or some other shape). In some embodiments, a shape of at least one segment in the plurality of contiguous segments  202 -A- 202 -D differs from shapes of other segments in the plurality of contiguous segments  202 -A- 202 -D. For example, segments  202 -B and  202 -D have a first shape (e.g., a rectangle) and segments  202 -A and  202 -C have a second shape that differs from the first shape. It is noted that various combinations of shapes can be used to form the contiguous segments of antenna element  202 , and the shapes shown in  FIG. 3A  are merely examples. 
       FIG. 3B  is a cross-sectional view (taken along line A-A′) of the representative transmitter  300  of  FIG. 3A  in accordance with some embodiments. Feeds  204 -A and  202 -B are directly coupled with two segments of the antenna element  202  (although not shown, feeds  204 -C and  204 -D have the same arrangement). As shown in the magnified view  311 , the fourth segment  202 -D is directly coupled with the feed  204 -B at a first connection point  312  and the first segment  202 -A is directly coupled with the feed  204 -B at a second connection point  314  (the other feeds are connected to respective segments in an analogous fashion). In such an arrangement, when the power amplifier  206  feeds an RF signal to the feed  204 -B, the RF signal travels along the feed  204 -B and then travels through the segments  202 -A to  202 -D of the antenna element  202 . 
     Depending on which one of the feeds  204  is selected to be fed by the power amplifier  206 , the antenna element  202  is configured to radiate RF energy with different propagation patterns and concentrations. In some circumstances, a high concentration of the radiated RF energy is created at a mid-field distance from the selected feed(s). In some instances, the “high concentration” of RF energy includes approximately 50 percent of the radiated energy, although greater and lesser percentages can be achieved. For example, with reference to  FIG. 5A , when the power amplifier  206  feeds an RF signal to feed  204 -C (shown schematically in  FIG. 5A ), a high concentration of energy radiated by the transmitter  300  is created at a mid-field distance D 1  from the antenna  202 . A similar result is shown in  FIG. 5B  for activation of the feed  204 -D. 
     In some embodiments, by activating one of the feeds (e.g., the feed  204 -D in the above example), impedance changes may be introduced at each of the feeds that are not activated (e.g., the feeds  204 -A,  204 -B, and  204 -C are not activated in the above example, thereby introducing impedance along the antenna element at respective points where these feeds contact the antenna element  202 ). The selective activation of different feeds may also help to steer a direction along which the RF energy radiates away from the transmitter  300 . For example, as shown in  FIG. 6A , when only feed  204 -C is activated, then the RF energy radiates away from the transmitter  300  in a substantially right-moving direction (from a viewpoint facing the top surface of the transmitter  300  or a top surface of a transmitter zone  110  in which the transmitter  300  is positioned). As another example, as shown in  FIG. 6B , when only feed  204 -D is activated, then the RF energy radiates away from the transmitter  300  in a substantially left-moving direction (from a viewpoint facing the top surface of the transmitter  300  or a top surface of a transmitter zone  110  in which the transmitter  300  is positioned). In this way, the transmitter  300  is configured in such a way that radiation of the RF energy may be controlled to ensure that a higher concentration of RF energy reaches a targeted receiver  120  (which may be positioned up to a wavelength away from the transmitter  300  or the transmitter zone  110  in which the transmitter  300  is positioned). 
     The connection point arrangement illustrated in  FIG. 3B  is merely one possible arrangement of the antenna element  202  and the feeds  204 . In an alternative embodiment, each feed  204 -A- 204 -D may be directly coupled with the antenna element  202  at a single connection point. In this alternative embodiment, the antenna element  202  is not divided into a plurality of contiguous segments but is instead a continuous antenna element  202 . Each feed  204 -A- 204 -D, in this alternative embodiment, is only connected to the continuous antenna element  202  at a respective second connection point, and each respective second connection point is at a different position along the conductive wire of the antenna element  202 . 
     As explained in greater detail below with reference to  FIG. 4 , the antenna element  202  is configured to radiate an RF signal (or multiple RF signals) with different propagation patterns depending on which of the plurality of feed elements  204  is fed by the power amplifier  206  ( FIG. 2 ). In some instances, physical dimensions of the antenna element  202  (and other physical dimensions of the transmitter  300 ) dictate (or at least partially dictate) the resulting propagation patterns. The physical dimensions include but are not limited to a width (W) of the antenna element  202 , a length (L 3 ) of the antenna element  202 , a height (L 1 ) of the antenna element  202 , a length (L 2 ) of one or more segments of the antenna element  202 , a thickness (T) of the antenna element  202 , a shape of the antenna element  202 , and a magnitude (D) of the offset between the ground plate  210  and the antenna element  202 . 
     In some embodiments, a value for each of the physical dimensions is defined according to a wavelength (λ) and a frequency of the one or more RF signals to be radiated by the antenna element  202 . The transmitter pad  100  can include transmitters  300  that are dimensioned to cause transmission of RF signals at frequencies ranging from one or more of 400 MHz (λ=0.75 meters) to 60 GHz (λ=0.005 meters), depending on the application. Accordingly, when operating at a frequency of 900 MHz (λ=0.333 meters), the width (W) of an example antenna element  202  of a transmitter  300  is approximately 0.005994 meters (i.e., approximately 6 mm), the height (L 1 ) of the example antenna element  202  is approximately 0.0333 meters (i.e., approximately 33 mm), the length (L 3 ) of the example antenna element  202  is approximately 0.11655 meters (i.e., approximately 116.5 mm), a length (L 2 ) of segment  202 -B and segment  202 -D of the example antenna element  202  is approximately 0.04995 meters (i.e., approximately 50 mm), a magnitude (D) of the offset between the ground plate  210  and the example antenna element  202  is approximately 0.02331 meters (i.e., approximately 23.3 mm), a length (L F ) of each feed  204  of the example antenna element  202  is approximately 0.02731 meters (i.e., approximately 27.3 mm). Moreover, a height and a length of the ground plate  210  of the example antenna element  202  can be 0.04995 meters (i.e., approximately 50 mm) and 0.14985 meters (i.e., approximately 150 mm), respectively. In some embodiments, the thickness (T) is either equal to or less than the width (W) of the example antenna element  202 . One skilled in the art will appreciate that the dimensions above are merely one example. Various other dimensions are possible, depending on the circumstances. 
     Method of Operation 
       FIG. 4  is a flow diagram showing a method of wireless power transmission in accordance with some embodiments. Operations (e.g., steps) of the method  400  may be performed by a controller of a transmitter pad (e.g., controller  209  of transmitter pad  100 ,  FIG. 2 ), the transmitter pad including one or more transmitter zones (e.g., transmitter zones  110 ,  FIGS. 1A-1B ; which each include respective one or more transmitters  300 ,  FIG. 3A ). At least some of the operations shown in  FIG. 4  correspond to instructions stored in a computer memory or computer-readable storage medium (e.g., memory  106  of the transmitter pad  100 ,  FIG. 1A ). 
     The method  400  includes providing ( 402 ) a wireless power transmitter (e.g., transmitter  300 ,  FIG. 3A ) including (i) a ground plate (e.g., ground plate  210 ,  FIG. 3A ), (ii) a conductive wire (e.g., antenna element  202 ,  FIG. 3A ) offset from the ground plate, the conductive wire forming a loop antenna, (iii) a plurality of feed elements (e.g., feeds  204 -A- 204 -D,  FIG. 3A ) extending from the ground plate to the conductive wire, each feed element being connected to the conductive wire at a different position on the conductive wire (e.g., positions A-D,  FIG. 3A ), and (iv) a power amplifier (e.g., power amplifier  206 ,  FIG. 2 ) connected to one or more feed elements of the plurality of feed elements. In some embodiments, the ground plate includes a plurality of openings (e.g., openings  212 -A- 212 -D,  FIG. 3A ), and each of the plurality of feeds is disposed in a respective opening of the plurality of openings (e.g., as shown in  FIGS. 3A and 3B ). Structural aspects of the wireless power transmitter are discussed in further detail above with reference to  FIGS. 3A and 3B . 
     In some embodiments, the method  400  further includes selecting ( 404 ), by a controller (e.g., controller  209  or a component thereof, such as one or more processors  104 ,  FIG. 2 ) of the wireless power transmitter, a respective feed element of the one or more feed elements based on a location of a receiver device relative to the plurality of feed elements. For example, with reference to  FIG. 3A , if the receiver device is located nearest feed element  204 -A relative to the other feed elements  204 -B- 204 -D, then the controller selects the feed element  204 -A. In some circumstances, the receiver device is located between two or more of the plurality of feed elements. In such circumstances, the method  400  may include selecting, by the controller, at least two feed elements based on a location of the receiver device relative to the plurality of feed elements. Further, the controller may select all of the plurality of feed elements in some instances. 
     In some embodiments, the method  400  further includes sending ( 406 ), by the controller, an instruction to the power amplifier that causes the power amplifier to feed the RF signal to the respective feed element. For example, with reference to  FIG. 2 , if the respective feed element is feed  204 -A, then the controller  209  sends an instruction (e.g., via busing  108 ) that causes the power amplifier to close the switch  208 -A, and in turn feed the RF signal to the feed  204 -A. 
     In some embodiments, the wireless power transmitter includes a communications radio (e.g., communications component  112 ,  FIG. 1A ), and the method  400  further includes receiving a communications signal from a corresponding communications radio of the receiver device. Further, the controller (or a component thereof) may determine the location of the receiver device relative to the plurality of feed elements based on the communications signal (e.g., using information included with or indicated by the communications signal). In some embodiments, the receiving and the determining are performed prior to the selecting ( 404 ) and the sending ( 406 ). In some embodiments, the controller determines the location of the receiver device relative to the plurality of feed elements based on signal strength of the communication signal, triangulation, and/or response time (e.g., the receiver device timestamps the communication signal when sent which is then compared against a timestamp of the communication signal when it is received at the wireless power transmitter). Additional location determining techniques can also be used. 
     In some embodiments, the wireless power transmitter includes one or more sensors (e.g., transmitter sensors  114 ,  FIG. 1A ), and the method  400  further includes detecting, via the one or more sensors, a presence of the receiver device. Further, the controller (or a component thereof) may determine the location of the receiver device relative to the plurality of feed elements based on information generated by the one or more sensors. In some embodiments, the detecting and the determining are performed prior to the selecting ( 404 ) and the sending ( 406 ). In some embodiments, the one or more sensors include one or more of a pressure sensor, an infrared sensor, an electromagnetic sensor, an acoustic sensor, a capacitive sensor, a light sensor, an inductive sensor, and a hall sensor. As an example, a light sensor may detect a change in light near the wireless power transmitter when the receiver device is positioned on or proximate to the wireless power transmitter. In another example (in addition to or separated from the previous example), an infrared sensor may detect a change in temperature near the wireless power transmitter when the receiver device is positioned on or proximate to the wireless power transmitter. In some embodiments, information collected from multiple sensors can be used to determine the location of the receiver device. 
     In some embodiments, each of the plurality of feeds is associated with a respective sensor (e.g., the respective sensor is positioned near (or perhaps on) the feed and the respective sensor takes readings near the feed). In this way, readings from each of the sensors can be compared (e.g., by the one or more processors  104 ), and the controller may determine the location of the receiver device relative to the plurality of feed elements based on the comparing. For example, if a largest change in light occurs at feed  204 -A relative to changes in light occurring at the other feeds, then the controller can determine that the receiver device is located closest to the feed  204 -A. 
     In some embodiments, the controller determines the location of the receiver device relative to the plurality of feed elements using two or more forms of information (e.g., signal strength in combination with a thermal imaging data, or some other combination communications-based and sensor-based information). 
     The method  400  further includes selectively feeding ( 408 ), by the power amplifier, an RF signal to the respective feed element of the one or more feed elements based on the location of a receiver device relative to the plurality of feed elements. For example, with reference to  FIG. 3A , a first feed element  204 -A of the one or more feed elements  202 -A- 202 -D is connected to the conductive wire  202  at a first position (e.g., position A) and a second feed element  202 -B, distinct from the first feed element  202 -A, of the one or more feed elements  202 -A- 202 -D is connected to the conductive wire  202  at a second position (e.g., position B). In such a configuration, the power amplifier: (i) may feed the RF signal to the first feed element when the location of the receiver device is within a threshold distance from the first position, and (ii) may feed the RF signal to the second feed element when the location of the receiver device is within the threshold distance from the second position. In some embodiments, feeding the RF signal to the one or more feed elements includes feeding the RF signal to two of the plurality of feed elements upon determining that the location of the receiver device is between the two feed elements. 
     In some embodiments, the selective-feeding operation ( 408 ) is performed in response to the power amplifier receiving the instruction from the controller. 
     The method  400  further includes (i) exciting ( 410 ), by the respective feed element fed by the power amplifier, the conductive wire and then (ii) radiating ( 412 ), by the conductive wire, the RF signal for wirelessly powering the receiver device. The conductive wire may radiate the RF signal from the conductive wire with different propagation patterns depending on which of the plurality of feed elements is fed by the power amplifier. For example, the conductive wire radiates the RF signal from the conductive wire in a first propagation pattern of the different propagation patterns when a first feed element of the one or more feed elements is fed by the power amplifier. In this example, a high concentration of radiated RF energy in the first propagation pattern is created at a mid-field distance away from the feed  204 -C. In some instances, the “high concentration” of RF energy includes approximately 50 percent of the radiated energy, although greater and lesser percentages can be achieved. Also, a concentration of RF energy in the first propagation pattern forms around the first feed element and the first propagation pattern propagates away from the first feed element in a first direction (or a set of first directions) towards the location of the receiver device. To illustrate, with reference to  FIG. 5A , a high concentration of radiated RF energy  504  is created at a mid-field distance (e.g., distance D 1 ) away from the feed  204 -C. Moreover, with reference to  FIG. 6A , the resulting propagation pattern  600  of RF energy from feeding the RF signal to the feed  204 -C moves substantially rightward to cause the RF energy to travel towards the location of a receiver device, which in this example would be positioned at the mid-field distance. In this way, the method  400  allows for selectively activating individual feed elements of a loop antenna to ensure that RF energy is propagated in such a way that a sufficiently high concentration of the RF energy is optimally propagated towards a location of a receiver device. 
     In another example, the conductive wire may radiate the RF signal in a second propagation pattern of the different propagation patterns when a second feed element of the one or more feed elements is fed by the power amplifier. In this example, a high concentration of RF energy in the second propagation pattern is created at a mid-field distance away from the feed  204 -D. Also, a concentration of RF energy in the second propagation pattern forms around the second feed element and the second propagation pattern propagates away from the second feed element in a second direction (or a set of second directions) towards a location of the receiver device. To illustrate, with reference to  FIG. 5B , a high concentration of RF energy  514  is created at a mid-field distance away from the feed  204 -D (e.g., distance D 2 ). Moreover, with reference to  FIG. 6B , the resulting propagation pattern  610  from feeding the RF signal to the feed  204 -D causes movement of the RF energy in a substantially leftward direction to cause the RF energy to travel towards a second location of the receiver device, which in this example would be positioned at the mid-field distance. 
     In some embodiments, the wireless power transmitter is configured such that in use the first propagation pattern has a first polarization and the second propagation pattern has a second polarization. In some embodiments, the second polarization differs from the first polarization. 
     In some embodiments, the different propagation patterns are based, at least in part, on a plurality of physical dimensions of the wireless power transmitter. The plurality of physical dimensions may include but is not limited to: (i) a width of the conductive wire (e.g., width (W),  FIG. 3A ), (ii) a length of the conductive wire (e.g., length (L 3 ),  FIG. 3A ), (iii) a height of the conductive wire (e.g., height (L 1 ),  FIG. 3A ), (iv) a thickness of the conductive wire (e.g., thickness (T),  FIG. 3B ), (v) a shape of the loop, and (vi) a magnitude of the offset between the ground plate and the conductive wire (e.g., offset (D),  FIG. 3B ). Physical characteristics of the conductive wire (e.g., the antenna element  202 ) are discussed in further detail above with reference to  FIGS. 3A and 3B . 
     In some embodiments, the conductive wire includes a plurality of contiguous segments (e.g., segments  202 -A- 202 -D,  FIG. 3A ), and each of the plurality of feed elements is positioned between a respective pair of adjacent segments of the plurality of contiguous segments (e.g., feed  204 -A is positioned between segments  202 -C and  202 -D). Further, in some embodiments, one or more first segments of the plurality of contiguous segments have a first shape and one or more second segments of the plurality of contiguous segments have a second shape different from the first shape. In some embodiments, each of the plurality of contiguous segments radiates the RF signal when one of the plurality of feed elements is fed by the power amplifier. The plurality of contiguous segments is discussed in greater detail above with reference to  FIGS. 3A-3B . 
       FIGS. 5A-5B  show various power distributions from a transmitter (e.g., transmitter  300 ,  FIG. 3A ) in accordance with some embodiments. In  FIG. 5A , when a feed  204 -C is activated (e.g., fed by the power amplifier  206 ), the feed  204 -C excites the antenna element  202  and the antenna element  202  radiates an RF signal having the illustrated power distribution  503 . The power distribution  503  illustrates concentrations of the RF signal at a mid-field distance (D 1 ) from the antenna element  202 . As shown, the RF signal has a high concentration  504  at the mid-field distance (D 1 ) from the antenna element  202  (and more particularly, the feed  204 -C). In  FIG. 5B , when a feed  204 -D is activated (e.g., fed by the power amplifier  206 ), the feed  204 -D excites the antenna element  202  and the antenna element  202  radiates an RF signal having the illustrated power distribution  513 . As illustrated in the power distribution  513 , the RF signal has a high concentration  514  at a mid-field distance (D 2 ) from the antenna element  202  (and more particularly, the feed  204 -D). In some instances, a “high concentration” includes approximately 50 percent of the radiated RF energy. 
       FIGS. 6A-6B  show various propagation patterns  600  and  610  radiating from a transmitter in accordance with some embodiments. The propagation patterns  600  and  610  shown in  FIGS. 6A-6B  correspond to the power distributions shown and described in  FIGS. 5A-5B . For example, the propagation pattern  600  results from the feed  204 -C being activated and the propagation pattern  610  results from the feed  204 -D being activated. As described above with reference to the method  400 , the transmitter is configured such that a concentration of RF energy in a first propagation pattern may propagate in a first direction (or a first set of directions) and a concentration of RF energy in a second propagation pattern may propagate in a second direction (or a second set of directions). For example, the propagation pattern  600  points substantially to the right, at least for portions of the propagation pattern  600  having a high concentration of RF energy, whereas the propagation pattern  610  points substantially to the left, at least for portions of the propagation pattern  610  having a high concentration of RF energy. Accordingly, when a receiver  120  is positioned, e.g., to the right of the transmitter, and is within a predefined distance from the transmitter (e.g., within a mid-field distance from the transmitter), the transmitter can selectively activate one of its feeds to direct RF energy to the right of the transmitter. 
     In some embodiments, the transmitter dynamically adjusts a shape and/or direction of the propagation patterns  600  and  610  by changing one or more characteristics of the RF signal. For example, the one or more characteristics may include but are not limited to frequency, gain, amplitude, and phase. In doing so, with reference to the propagation pattern  600 , the transmitter may adjust one or more of the one or more characteristics so that the propagation pattern  600  points more right or less right (or perhaps more up or down, or a combination thereof). The transmitter may adjust the shape and/or direction of a propagation pattern depending on a location of the receiver  120  relative to the one or more feeds of the transmitter. Additionally, the physical dimensions of the transmitter impact the resulting propagation patterns  600  and  610  (e.g., an antenna element having a first width (W) may tend to create a first propagation pattern and an antenna element having a second width (W) may tend to create a second propagation pattern different from the first propagation pattern). The various other dimensions discussed above with reference to  FIGS. 3A-3B  may also impact the resulting propagation patterns  600  and  610 . 
     Method of Fabrication 
     A method of fabricating a wireless power transmitter (e.g., transmitter  300 ,  FIG. 3A ) includes providing a ground plate (e.g., ground plate  210 ,  FIG. 3A ) and removing material from the ground plate to define one or more openings (e.g., holes) in the ground plate (e.g., openings  212 -A- 212 -D). The one or more openings being sized to receive feed elements (e.g., feeds  204 -A- 204 -D). In some embodiments, the removing is performed using a drilling operation. The method further includes disposing/attaching a feed in each of the one or more openings such that the wireless power transmitter includes one or more feeds. In some embodiments, each of the feeds is mechanically and/or chemically (e.g., using an adhesive) attached to its respective opening. The one or more feeds are substantially perpendicular to the ground plate and extend away from the ground plate, as shown in  FIG. 3B . The method further includes attaching an antenna element (e.g., antenna element  202 ) to the one or more feeds. In some embodiments, the antenna element is mechanically and/or chemically attached to the feeds. Connection points between the antenna element and feed elements are discussed in further detail above with reference to  FIG. 3B . The antenna element may be offset from the ground plate by a distance (e.g., magnitude (D) of the offset,  FIG. 3B ). In some embodiments, the antenna element is substantially parallel to the ground plate. 
     In some embodiments, one or more wireless power transmitters are fabricated using the method above, and grouped together to form a transmission pad  100  (i.e., an array of wireless power transmitters). In some embodiments, the ground plate may be a single ground plate used by the one or more wireless power transmitters. Alternatively, in some embodiments, each of the one or more wireless power transmitters has a distinct ground plate. An array of wireless power transmitters may be formed by positioning each of the wireless power transmitters within respective transmitter zones, and then interconnecting components of each of the transmitter zones with a common controller for the transmitter pad. 
     The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the description of the invention and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term “and/or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof. 
     The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.