Patent Publication Number: US-11040631-B2

Title: Electronic device and method for transmitting and receiving wireless power

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of U.S. application Ser. No. 15/054,824 filed Feb. 26, 2016, which is a continuation of U.S. application Ser. No. 13/469,555 filed on May 11, 2012, now U.S. Pat. No. 9,272,630 issued Mar. 1, 2016, which claims the benefit under 35 U.S.C. § 119(a) of Korean Patent Application No. 10-2011-0050402, filed on May 27, 2011, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes. 
    
    
     BACKGROUND 
     1. Field 
     The following description relates to transmitting and receiving wireless power. 
     2. Description of Related Art 
     Wireless power refers to energy that is transferred from a wireless power transmitter to a wireless power receiver through magnetic coupling. Typically, a wireless power transmission and charging system includes a source device and a target device. The source device may wirelessly transmit a power, and the target device may wirelessly receive a power. The source device may be referred to as a wireless power transmitter, and the target device may be referred to as a wireless power receiver. 
     The source device includes a source resonator, and the target device includes a target resonator. Magnetic coupling or resonance coupling may be formed between the source resonator and the target resonator. 
     SUMMARY 
     According to one general aspect, an electronic device for transmitting and receiving wireless power may include: a resonator configured to operate, based on a plurality of operating modes of the electronic device including a power reception mode, a relay mode, and a power transmission mode, wherein: (i) in the power reception mode, the resonator is configured to receive power from a wireless power transmitter, (ii) in the relay mode, the resonator is configured to relay power received from the wireless power transmitter to a wireless power receiver, and (iii) in the power transmission mode, the resonator is configured to transmit power to the wireless power receiver; and a path controller configured to control at least one electrical pathway of electronic device based on the operating mode. 
     The electronic device may further include: a power converter configured to convert direct current (DC) voltage to alternating current (AC) voltage using a resonance frequency, and to transfer the AC current to the resonator, when the electronic device is operated in the power transmission mode. 
     The electronic device may further include: a power amplifier configured to amplify the DC voltage. 
     The electronic device may further include: a rectification unit configured to generate a DC signal by rectifying an AC signal of a power received via the resonator, when the electronic device is operated in the power reception mode. 
     The electronic device may further include: a DC-to-DC (DC/DC) converter configured to supply voltage of a predetermined level to a load by adjusting a level of the DC signal. 
     The electronic device may further include: a control/communication unit configured to perform a communication with the wireless power transmitter or the wireless power receiver, to determine the operating mode by the communication, to control the path controller based on the determined operating mode, or any combination thereof. 
     The resonator may be configured to receive the power from the wireless power transmitter by passing through one or more electronic devices. 
     The resonator may be configured to transmit the power to the wireless power receiver by passing through one or more electronic devices. 
     The resonator may be configured to simultaneously transmit the power to a plurality of electronic devices. 
     The electronic device may further include: a control/communication unit configured to control a magnetic field to be uniformly distributed, based on a direction of an induced current flowing in the resonator, and on a direction of an input current flowing in a feeding unit, wherein the magnetic field is formed in the resonator. 
     According to another general aspect, a method for transmitting and receiving wireless power in an electronic device may include: determining one of a plurality of operating modes of the electronic device, the plurality of operating modes of the electronic device including a power reception mode, a relay mode, and a power transmission mode; and (i) in the power reception mode, receiving power from a wireless power transmitter, (ii) in the relay mode, relaying power received from the wireless power transmitter to a wireless power receiver, and (iii) in the power transmission mode, transmitting power to the wireless power receiver. 
     The method may further include: performing a communication with another electronic device to determine the operating mode of the electronic device. 
     The method may further include: supplying voltage of a predetermined level to a load by adjusting a level of a DC signal. 
     The method may further include: generating power using a resonance frequency; and transferring the generated power to a resonator. 
     The method may further include: generating a DC signal by rectifying an AC signal of power received via a resonator. 
     The method may further include: receiving the power from the wireless power transmitter by passing through one or more electronic devices. 
     The method may further include: transmitting the power to the wireless power receiver by passing through one or more electronic devices. 
     The method may further include: simultaneously transmitting the power to a plurality of electronic devices. 
     According to yet another aspect, a resonator device may include: a feeder configured to receive an input current and to form a magnetic field; and a resonator configured to form another magnetic field based on an induced current generated by the magnetic field of the feeder, wherein, when the magnetic field formed by the feeder and the another magnetic field formed by the source resonator are combined, the strength of the combined magnetic field changes within the feeder and outside the feeder. 
     The strength of the combined magnetic field may decrease within the feeder and increase outside the feeder; or the strength of the combined magnetic field may increase within the feeder and decease outside the feeder. 
     The resonator and the feeder have a common ground. 
     The resonator may include a capacitor. 
     The feeder may be electrically connected to the capacitor. 
     The feeder may be positioned at least partially within the resonator. 
     The resonator may have a closed loop structure. 
     The resonator may include: a first transmission line comprising a first signal conducting portion, a second signal conducting portion, and a first ground conducting portion, the first ground conducting portion corresponding to the first signal conducting portion and the second signal conducting portion; a first conductor electrically connecting the first signal conducting portion to the first ground conducting portion; a second conductor electrically connecting the second signal conducting portion to the first ground conducting portion; and at least one first capacitor inserted between the first signal conducting portion and the second signal conducting portion, in series with respect to a current flowing through the first signal conducting portion and the second signal conducting portion. 
     The feeder may include: a second transmission line comprising a third signal conducting portion, a fourth signal conducting portion, and a second ground conducting portion, the second ground conducting portion corresponding to the third signal conducting portion and the fourth signal conducting portion; a third conductor electrically connecting the third signal conducting portion to the second ground conducting portion; a fourth conductor electrically connecting the fourth signal conducting portion to the second ground conducting portion; a fifth conductor electrically connecting the first signal conducting portion to the third signal conducting portion; and a sixth conductor electrically connecting the second signal conducting portion to the fourth signal conducting portion. 
     The resonator device may further include: a control/communication unit configured to control the magnetic field to be uniformly distributed, based on a direction of an induced current flowing in the resonator, and on a direction of an input current flowing in the feeder. 
     The controller may be configured to adjust the size of the feeder. 
     The resonator device may further include a matching device configured to match the input impedance to an output impedance. 
     Other features and aspects will be apparent from the following detailed description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a wireless power transmission and charging system. 
         FIG. 2  is a diagram illustrating an electronic device. 
         FIGS. 3A and 3B  are diagrams illustrating a distribution of a magnetic field in a feeder and a source resonator. 
         FIGS. 4A and 4B  are diagrams illustrating a wireless power transmitter. 
         FIG. 5A  is a diagram illustrating a distribution of a magnetic field within a source resonator based on feeding of a feeding unit. 
         FIG. 5B  is a diagram illustrating equivalent circuits of a feeding unit and a source resonator. 
         FIG. 6  is a diagram illustrating another wireless power transmitter. 
         FIG. 7  is a diagram illustrating still another wireless power transmitter. 
         FIGS. 8A through 13B  are diagrams illustrating various resonators. 
         FIG. 14  is a diagram illustrating one equivalent circuit of a resonator of  FIG. 8A . 
         FIG. 15  is a diagram illustrating a method for transmitting and receiving wireless power. 
         FIGS. 16 and 17  are diagrams illustrating a method for transmitting and receiving wireless power between electronic devices. 
         FIG. 18  is a diagram illustrating an electric vehicle charging system. 
         FIG. 19  is a diagram illustrating a wireless power transmission method of an electric vehicle. 
     
    
    
     Throughout the drawings and the detailed description, unless otherwise described, the same drawing reference numerals will be understood to refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience. 
     DETAILED DESCRIPTION 
     The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. Accordingly, various changes, modifications, and equivalents of the methods, apparatuses, and/or systems described herein will be suggested to those of ordinary skill in the art. The progression of processing steps and/or operations described is an example; however, the sequence of and/or operations is not limited to that set forth herein and may be changed as is known in the art, with the exception of steps and/or operations necessarily occurring in a certain order. Also, description of well-known functions and constructions may be omitted for increased clarity and conciseness. 
       FIG. 1  illustrates a wireless power transmission and charging system. 
     As shown, the wireless power transmission and charging system includes a source device  110 , and a target device  120 . 
     The source device  110  may include an alternating current-to-direct current (AC/DC) converter  111 , a power detector  113 , a power converter  114 , a control/communication unit  115 , an impedance adjusting unit  117 , and a source resonator  116 . 
     The target device  120  may include a target resonator  121 , a rectification unit  122 , a DC-to-DC (DC/DC) converter  123 , a switch unit  124 , a charging unit  125 , and a control/communication unit  126 . 
     The AC/DC converter  111  may generate a DC voltage by rectifying an AC voltage (e.g., in a band of tens of hertz (Hz)) output from a power supply  112 . The AC/DC converter  111  may be configured to output a DC voltage of a predetermined level, and/or to adjust an output level of a DC voltage based on the control of the control/communication unit  115 . 
     The power detector  113  may detect an output current and an output voltage of the AC/DC converter  111 , and may transfer, to the control/communication unit  115 , information on the detected current and the detected voltage. Additionally or alternatively, the power detector  113  may detect an input current and an input voltage of the power converter  114 . 
     The power converter  114  may be configured to convert DC voltage of a predetermined level to AC voltage, for instance, using a switching pulse signal (e.g., in a band of a few megahertz (MHz) to tens of MHz). Other frequencies of AC power are also possible. In some implementations, the power converter  114  may convert a DC voltage supplied to a power amplifier to an AC voltage, using a reference resonance frequency F Ref , and may output power. 
     The impedance adjusting unit  117  may include a plurality of, e.g., N, matching switches connected to a plurality of capacitors. The impedance adjusting unit  117  may adjust an impedance of the source resonator  116  by turning ON or OFF the N matching switches. The impedance adjusting unit  117  may include a Pi matching circuit or a T matching circuit, in some instances. 
     The control/communication unit  115  may be configured to detect a reflected wave of a transmission power, and may detect mismatching between the target resonator  121  and the source resonator  116  based on the detected reflected wave. To detect the mismatching, the control/communication unit  115  may detect an envelope of the reflected wave, detect a power amount of the reflected wave, or both. 
     The control/communication unit  115  may calculate and/or compute a voltage standing wave ratio (VSWR), based on a voltage level of the reflected wave, and based on a level of an output voltage of the source resonator  116  or the power converter  114 . For example, if the VSWR is less than a predetermined value, the control/communication unit  115  may determine that the mismatching is detected. For example, the control/communication unit  115  may turn ON or OFF the N matching switches, may determine a tracking impedance Im Best  with an optimal or the best power transmission efficiency, and may adjust the impedance of the source resonator  116  to the tracking impedance Im Best . 
     Additionally or alternatively, the control/communication unit  115  may be configured to adjust a frequency of a switching pulse signal. Under the control of the control/communication unit  115 , the frequency of the switching pulse signal may be determined. And, by controlling the power converter  114 , the control/communication unit  115  may generate a modulation signal to be transmitted to the target device  120 . Also, the control/communication unit  115  may transmit various messages to the target device  120  using in-band communications. Moreover, the control/communication unit  115  may detect a reflected wave, and may demodulate a signal received from the target device  120  through an envelope of the detected reflected wave. 
     The control/communication unit  115  may generate a modulation signal for in-band communication, using various schemes. To generate a modulation signal, the control/communication unit  115  may turn ON or OFF a switching pulse signal, and/or may perform delta-sigma modulation. Additionally or alternatively, the control/communication unit  115  may generate a pulse-width modulation (PWM) signal with a predetermined envelope. 
     The control/communication unit  115  may perform out-band communication using a communication channel. The control/communication unit  115  may include a communication module, for example, configured to handle ZigBee, Bluetooth, Wi-Fi, Wi-max, near field communication (NFC), radio frequency identification (RFID), and/or other communication protocols. The control/communication unit  115  may transmit or receive data to or from the target device  120  using the out-band communication. 
     The source resonator  116  may be configured to transfer electromagnetic energy to the target resonator  121 . For example, the source resonator  116  may transfer, to the target device  120 , communication power used for communication, charging power used for charging or both, using a magnetic coupling with the target resonator  121 . 
     The target resonator  121  may receive electromagnetic energy from the source resonator  116 . For example, the target resonator  121  may receive, from the source device  110 , the communication power and/or the charging power using the magnetic coupling with the source resonator  116 . Additionally or alternatively, the target resonator  121  may receive various messages from the source device  110  using the in-band communication. 
     The rectification unit  122  may generate a DC voltage by rectifying an AC voltage. For instance, the AC voltage may be received from the target resonator  121 . 
     The DC/DC converter  123  may be configured to adjust a level of the DC voltage output from the rectification unit  122  based on a capacity of the charging unit  125 . For example, the DC/DC converter  123  may adjust, from 3 to 10 volt (V), the level of the DC voltage output from the rectification unit  122 . 
     The switch unit  124  may be turned ON or OFF under the control of the control/communication unit  126 . When the switch unit  124  is turned OFF, the control/communication unit  115  of the source device  110  may detect a reflected wave. Moreover, when the switch unit  124  is turned OFF, the magnetic coupling between the source resonator  116  and the target resonator  121  may be eliminated. 
     In some embodiments, the charging unit  125  may include at least one battery. The charging unit  125  may charge the at least one battery using a DC voltage output from the DC/DC converter  123 . 
     The control/communication unit  126  may perform in-band communication for transmitting or receiving data using a resonance frequency, for instance. During the in-band communication, the control/communication unit  126  may demodulate a received signal by detecting a signal between the target resonator  121  and the rectification unit  122 , or detecting an output signal of the rectification unit  122 . The control/communication unit  126  may demodulate a message received using the in-band communication. 
     Additionally or alternatively, the control/communication unit  126  may adjust an impedance of the target resonator  121 , to modulate a signal to be transmitted to the source device  110 . The control/communication unit  126  may modulate the signal to be transmitted to the source device  110 , for instance, by turning ON or OFF the switch unit  124 . For example, the control/communication unit  126  may increase the impedance of the target resonator  121  so that a reflected wave may be detected from the control/communication unit  115  of the source device  110 . For example, depending on whether the reflected wave is detected, the control/communication unit  115  may detect a binary number (e.g., “0” or “1.”) 
     The control/communication unit  126  may be configured to transmit a response message to the wireless power transmitter. The response message may include, for example, a “type of a corresponding target device,” “information on a manufacturer of a corresponding target device,” “a model name of a corresponding target device,” a “battery type of a corresponding target device,” a “scheme of charging a corresponding target device,” an “impedance value of a load of a corresponding target device,” “information on characteristics of a target resonator of a corresponding target device,” “information on a frequency band used by a corresponding target device,” an “amount of a power consumed by a corresponding target device,” an “identifier (ID) of a corresponding target device,” or “information on version or standard of a corresponding target device.” 
     The control/communication unit  126  may also perform out-band communication using a communication channel. The control/communication unit  126  may include a communication module, such as, one configured to process ZigBee, Bluetooth, Wi-Fi, Wi-Max and/or the like communications. The control/communication unit  126  may transmit or receive data to or from the source device  110  using the out-band communication, for instance. 
     The control/communication unit  126  may be configured to receive a wake-up request message from the wireless power transmitter, may detect an amount of a power received to the target resonator  121 , and may transmit, to the wireless power transmitter, information on the detected amount of the power. The information on the detected amount may include, for example, an input voltage value and an input current value of the rectification unit  122 , an output voltage value and an output current value of the rectification unit  122 , an output voltage value and an output current value of the DC/DC converter  123 , and the like. 
     The term “in-band” communication(s), as used herein, means communication(s) in which information (such as, for example, control information, data and/or metadata) is transmitted in the same frequency band, and/or on the same channel, as used for power transmission. According to one or more embodiments, the frequency may be a resonance frequency. And, the term “out-band” communication(s), as used herein, means communication(s) in which information (such as, for example, control information, data and/or metadata) is transmitted in a separate frequency band and/or using a separate or dedicated channel, than used for power transmission. 
       FIG. 2  illustrates an electronic device  220 . 
     As shown, the electronic device  220  includes a resonator  221 , a power converter  228 , a rectification unit  222 , a DC/DC converter  223 , a switch unit  224 , a charging unit  225 , a control/communication unit  226 , and a path controller  227 . The resonator  221  may be operated based on one of a plurality of operating modes of the electronic device  220  including a power reception mode, a relay mode, and a power transmission mode. 
     In the power reception mode, the resonator  221  may be configured as a target resonator so as to receive power from a wireless power transmitter (e.g., using a magnetic coupling). In the relay mode, the resonator  221  may be configured as a relay resonator so as to relay power received from the wireless power transmitter to a wireless power receiver. And, in the power transmission mode, the resonator  221  may be configured as a source resonator so as to transmit power to the wireless power receiver (e.g., using the magnetic coupling). 
     When the electronic device  220  receives a power from another electronic device the resonator  221  may be operated as a target resonator. One the other hand, when the electronic device  220  transmits a power to another electronic device, the resonator  221  may be operated as a source resonator. 
     In some embodiments, the electronic device  220  may be disposed between the wireless power transmitter and the wireless power receiver and the resonator  221  may be operated as a relay resonator. When the resonator  221  is used as a relay resonator, the resonator  221  may not be connected to the power converter  228  and the rectification unit  222 , and may merely increase a range of magnetic coupling, a range of a wireless power transmission, or both. 
     The power converter  228  may perform the same or a similar function to the power converter  114  of  FIG. 1 . For example, when the electronic device  220  is operated in a power transmission mode, the power converter  228  may convert DC voltage to AC voltage using a resonance frequency, and may transfer the generated power to the resonator  221 . And, the DC voltage may be supplied from the charging unit  225  to a power amplifier. 
     The rectification unit  222  may perform the same or a similar function to the rectification unit  122  of  FIG. 1 . For example, when the electronic device  220  is operated in a power reception mode, the rectification unit  222  may generate a DC signal by rectifying an AC signal received via the resonator  221 . 
     The DC/DC converter  223  may perform the same or similar function as the DC/DC converter  123  of  FIG. 1 . Accordingly, the DC/DC converter  223  may supply voltage of a predetermined level to a load by adjusting a level of a DC signal. 
     The path controller  227  may be configured to control a connection of the resonator  221 , the power converter  228  and the rectification unit  222 , based on the operating mode of the electronic device  220 . 
     The switch unit  224  and the charging unit  225  may be configured identical or similar to the switch unit  124  and the charging unit  125  of  FIG. 1 , respectively. 
     The control/communication unit  226  may perform a function of the control/communication unit  115  of  FIG. 1 , a function of the control/communication unit  126  of  FIG. 1 , or both. When the electronic device  220  is operated in the power transmission mode, the control/communication unit  226  may be configured to perform the function of the control/communication unit  115 . On the other hand, when the electronic device  220  is operated in the power reception mode, the control/communication unit  226  may be configured to perform the function of the control/communication unit  126 . 
     The control/communication unit  226  may perform a communication with the wireless power transmitter or the wireless power receiver, may determine the operating mode by the communication, and may control the path controller  227 , based on the determined operating mode. 
       FIGS. 3A and 3B  illustrate a distribution of a magnetic field in a feeder and a source resonator. 
     If a source resonator  320  may receive power through a separate feeder  310 , magnetic fields may be formed in both the feeder and the source resonator. 
     Referring to  FIG. 3A , as an input current flows in the feeder  310 , a magnetic field  330  may be formed. The direction  331  of the magnetic field  330  within the feeder  310  may have a phase opposite to a phase of a direction  333  of the magnetic field  330  outside the feeder  310 . The magnetic field  330  formed by the feeder  310  may cause an induced current to be formed in the source resonator  320 . The direction of the induced current may be opposite to a direction of the input current. 
     Due to the induced current, a magnetic field  340  may be formed in the source resonator  320 . Directions of a magnetic field formed due to an induced current in all positions of the source resonator  320  may be identical in some instances. Accordingly, the direction  341  of the magnetic field  340  formed by the source resonator  320  may have the same phase as a direction  343  of the magnetic field  340  formed by the source resonator  320 . 
     Consequently, when the magnetic field  330  formed by the feeder  310  and the magnetic field  340  formed by the source resonator  320  are combined, the strength of the total magnetic field may decrease within the feeder  310 ; yet may increase outside the feeder  310 . If power is supplied to the source resonator  320  through the feeder  310  configured as illustrated in  FIG. 3 , the strength of the total magnetic field may decrease in the center of the source resonator  320 , but may increase outside the source resonator  320 . And because the magnetic field may be randomly distributed in the source resonator  320 , it may be difficult to perform impedance matching since the input impedance may frequently vary. Additionally, when the strength of the total magnetic field is increased, an efficiency of wireless power transmission may be increased. Conversely, when the strength of the total magnetic field is decreased, the efficiency for wireless power transmission may be reduced. Accordingly, the power transmission efficiency may be reduced on average. 
     In a target resonator, a magnetic field may be distributed as illustrated in  FIG. 3A . Current flowing in the source resonator  320  may be induced by the input current flowing in the feeder  310 . The current flowing in the target resonator may be induced by a magnetic coupling between the source resonator  320  and the target resonator. The current flowing in the target resonator may cause a magnetic field to be formed, so that an induced current may be generated in a feeder located in the target resonator. Within the feeder, a direction of a magnetic field formed by the target resonator may have a phase opposite to a phase of a direction of a magnetic field formed by the feeder and accordingly, strength of the total magnetic field may be reduced. 
       FIG. 3B  illustrates a structure of a wireless power transmitter in which a source resonator  350  and a feeder  360  have a common ground. The source resonator  350  may include a capacitor  351 , in some instances. The feeder  360  may receive an input of a radio frequency (RF) signal via a port  361 . 
     For example, when the RF signal is received to the feeder  360 , an input current may be generated in the feeder  360 . The input current flowing in the feeder  360  may cause a magnetic field to be formed, and a current may be induced in the source resonator  350  by the magnetic field. Additionally, another magnetic field may be formed due to the induced current flowing in the source resonator  350 . As shown, the direction of the input current flowing in the feeder  360  may have a phase opposite to a phase of the direction of the induced current flowing in the source resonator  350 . Accordingly, in a region between the source resonator  350  and the feeder  360 , the direction  371  of the magnetic field formed due to the input current may have the same phase as the direction  373  of the magnetic field formed due to the induced current, and thus the strength of the total magnetic field may increase. Conversely, within the feeder  360 , the direction  381  of the magnetic field formed due to the input current may have a phase opposite to a phase of the direction  383  of the magnetic field formed due to the induced current, and thus the strength of the total magnetic field may decrease. Therefore, the strength of the total magnetic field may decrease in the center of the source resonator  350 , yet may increase outside the source resonator  350 . 
     The feeder  360  may determine the input impedance by adjusting an internal area of the feeder  360 . The input impedance here may refer to impedance viewed in a direction from the feeder  360  to the source resonator  350 . When the internal area of the feeder  360  is increased, the input impedance may be increased. Conversely, when the internal area of the feeder  360  is reduced, the input impedance may be reduced. Since the magnetic field may be randomly distributed in the source resonator  350  despite a reduction in the input impedance, a value of the input impedance may vary depending on a location of a target device. Accordingly, a separate matching network may be provided to match the input impedance to an output impedance of a power amplifier. For example, when the input impedance is increased, the separate matching network may be used to match the increased input impedance to relatively low output impedance. 
     In some implementations, such as, for example, when a target resonator has the same configuration as the source resonator  350 , and when a feeder of the target resonator has the same configuration as the feeder  360 , a separate matching network may be required, because a direction of a current flowing in the target resonator has a phase opposite to a phase of a direction of an induced current flowing in the feeder of the target resonator. 
       FIG. 4A  illustrates a wireless power transmitter. 
     As shown in  FIG. 4A , the wireless power transmitter may include a source resonator  410 , and a feeding unit  420 . The source resonator  410  may include at least one capacitor  411 . The feeding unit  420  may be electrically connected to both ends of the at least one capacitor  411 . 
       FIG. 4B  illustrates, in more detail, the structure of the wireless power transmitter of  FIG. 4A . The source resonator  410  may include a first transmission line, a first conductor  441 , a second conductor  442 , and at least one first capacitor  450 . The first capacitor  450  may be inserted (e.g., in series) between a first signal conducting portion  431  and a second signal conducting portion  432  in the first transmission line, and an electric field may be confined within the first capacitor  450 . For example, the first transmission line may include at least one conductor in an upper portion of the first transmission line, and may also include at least one conductor in a lower portion of the first transmission line. Current may flow through the at least one conductor disposed in the upper portion of the first transmission line, and the at least one conductor disposed in the lower portion of the first transmission line may be electrically grounded. For example, a conductor disposed in an upper portion of the first transmission line may be separated into and thereby be referred to as the first signal conducting portion  431  and the second signal conducting portion  432 . A conductor disposed in a lower portion of the first transmission line may be referred to as a first ground conducting portion  433 . 
     As shown in  FIG. 4B , the source resonator  410  may have a generally two-dimensional (2D) structure. The first transmission line may include the first signal conducting portion  431  and the second signal conducting portion  432  in the upper portion of the first transmission line. In addition, the first transmission line may include the first ground conducting portion  433  in the lower portion of the first transmission line. The first signal conducting portion  431  and the second signal conducting portion  432  may be disposed to face the first ground conducting portion  433  with current flowing through the first signal conducting portion  431  and the second signal conducting portion  432 . 
     Additionally, one end of the first signal conducting portion  431  may be electrically connected (i.e., shorted) to the first conductor  441 , and another end of the first signal conducting portion  431  may be connected to the first capacitor  450 . One end of the second signal conducting portion  432  may be electrically connected (i.e., shorted) to the second conductor  442 , and another end of the second signal conducting portion  432  may be connected to the first capacitor  450 . Accordingly, the first signal conducting portion  431 , the second signal conducting portion  432 , the first ground conducting portion  433 , and the conductors  441  and  442  may be connected to each other, so that the source resonator  410  may have an electrically closed-loop structure. The term “closed-loop structure” as used herein, may include a polygonal structure, for example, a circular structure, a rectangular structure, or the like that is electrically closed. 
     The first capacitor  450  may be inserted into an intermediate portion of the first transmission line. For example, the first capacitor  450  may be inserted into a space between the first signal conducting portion  431  and the second signal conducting portion  432 . The first capacitor  450  may be configured as a lumped element, a distributed element, or the like. For example, a distributed capacitor may include zigzagged conductor lines and a dielectric material that has a high permittivity between the zigzagged conductor lines. 
     When the first capacitor  450  is instead into the first transmission line, the source resonator  410  may have a characteristic of a metamaterial. The metamaterial indicates a material having a predetermined electrical property that has not been discovered in nature, and thus, may have an artificially designed structure. An electromagnetic characteristic of the materials existing in nature may have a unique magnetic permeability or a unique permittivity. Most materials may have a positive magnetic permeability or a positive permittivity. 
     In the case of most materials, a right hand rule may be applied to an electric field, a magnetic field, and a pointing vector, and thus, the corresponding materials may be referred to as right handed materials (RHMs). However, the metamaterial that has a magnetic permeability or a permittivity absent in nature may be classified into an epsilon negative (ENG) material, a mu negative (MNG) material, a double negative (DNG) material, a negative refractive index (NRI) material, a left-handed (LH) material, and the like, based on a sign of the corresponding permittivity or magnetic permeability. 
     When a capacitance of the first capacitor  450  inserted as the lumped element is appropriately determined, the source resonator  410  may have the characteristic of the metamaterial. Because the source resonator  410  may have a negative magnetic permeability by appropriately adjusting the capacitance of the first capacitor  450 , the source resonator  410  may also be referred to as an MNG resonator. Various criteria may be applied to determine the capacitance of the first capacitor  450 . For example, the various criteria may include a criterion for enabling the source resonator  410  to have the characteristic of the metamaterial, a criterion for enabling the source resonator  410  to have a negative magnetic permeability in a target frequency, a criterion for enabling the source resonator  410  to have a zeroth order resonance characteristic in the target frequency, and/or the like. Based on at least one criterion among the aforementioned criteria, the capacitance of the first capacitor  450  may be determined. 
     The source resonator  410 , also referred to as the MNG resonator  410 , may have a zeroth order resonance characteristic of having, as a resonance frequency, a frequency when a propagation constant is “0”. Because the source resonator  410  may have the zeroth order resonance characteristic, the resonance frequency may be independent with respect to a physical size of the MNG resonator  410 . By appropriately designing the first capacitor  450 , the MNG resonator  410  may sufficiently change the resonance frequency. Accordingly, the physical size of the MNG resonator  410  may not be changed. 
     In a near field, the electric field may be concentrated on the first capacitor  450  inserted into the first transmission line. Accordingly, due to the first capacitor  450 , the magnetic field may become dominant in the near field. The MNG resonator  410  may have a relatively high Q-factor using the first capacitor  450  of the lumped element, and thus, it is possible to enhance an efficiency of power transmission. For example, the Q-factor may indicate a level of an ohmic loss or a ratio of a reactance with respect to a resistance in the wireless power transmission. The efficiency of the wireless power transmission may increase according to an increase in the Q-factor. 
     In some embodiments, a magnetic core may be further provided to pass through the MNG resonator  410 . The magnetic core may increase the power transmission distance. 
     Referring to  FIG. 4B , the feeding unit  420  may include a second transmission line, a third conductor  471 , a fourth conductor  472 , a fifth conductor  481 , and a sixth conductor  482 . 
     The second transmission line may include a third signal conducting portion  461  and a fourth signal conducting portion  462  in an upper portion of the second transmission line. In addition, the second transmission line may include a second ground conducting portion  463  in a lower portion of the second transmission line. The third signal conducting portion  461  and the fourth signal conducting portion  462  may be disposed to face the second ground conducting portion  463 . Current may flow through the third signal conducting portion  461  and the fourth signal conducting portion  462 . 
     Additionally, one end of the third signal conducting portion  461  may be shorted to the third conductor  471 , and another end of the third signal conducting portion  461  may be connected to the fifth conductor  481 . One end of the fourth signal conducting portion  462  may be shorted to the fourth conductor  472 , and another end of the fourth signal conducting portion  462  may be connected to the sixth conductor  482 . The fifth conductor  481  may be connected to the first signal conducting portion  431 , and the sixth conductor  482  may be connected to the second signal conducting portion  432 . The fifth conductor  481  and the sixth conductor  482  may be connected in parallel to both ends of the first capacitor  450 . As shown, the fifth conductor  481  and the sixth conductor  482  may be used as input ports to receive an input of an RF signal. 
     Accordingly, the third signal conducting portion  461 , the fourth signal conducting portion  462 , the second ground conducting portion  463 , the third conductor  471 , the fourth conductor  472 , the fifth conductor  481 , the sixth conductor  482 , and the source resonator  410  may be connected to each other so that the source resonator  410  and the feeding unit  420  may have an electrically closed-loop structure. When an RF signal is received via the fifth conductor  481  or the sixth conductor  482 , an input current may flow in the feeding unit  420  and the source resonator  410 , a magnetic field may be formed due to the input current, and a current may be induced to the source resonator  410  by the formed magnetic field. A direction of the input current flowing in the feeding unit  420  may be identical to a direction of the induced current flowing in the source resonator  410  and thus, strength of the total magnetic field may increase in the center of the source resonator  410 , but may decrease outside the source resonator  410 . The direction of the input current and the direction of the induced current will be further described with reference to  FIGS. 5A and 5B . 
     An input impedance may be determined based on an area of a region between the source resonator  410  and the feeding unit  420  and accordingly, a separate matching network used to match the input impedance to an output impedance of a power amplifier may not be required. For example, even when the matching network is used, the input impedance may be determined by adjusting a size of the feeding unit  420  and thus, a structure of the matching network may be simplified. The simplified structure of the matching network may minimize a matching loss of the matching network. 
     The second transmission line, the third conductor  471 , the fourth conductor  472 , the fifth conductor  481 , and the sixth conductor  482  may form the same structure as the source resonator  410 . When the source resonator  410  has a loop structure, the feeding unit  420  may also have a loop structure. For example, if the source resonator  410  has a circular structure, the feeding unit  420  may also have a circular structure. 
     The above-described configuration of the source resonator  410  and configuration of the feeding unit  420  may be similarly applied to the target resonator and the feeding unit of the target resonator, respectively. When the feeding unit of the target resonator is configured as described above, the feeding unit may match an output impedance of the target resonator and an input impedance of the feeding unit, by adjusting a size of the feeding unit. Accordingly, a separate matching network may not be used. 
       FIG. 5A  illustrates a distribution of a magnetic field within a source resonator based on feeding of a feeding unit.  FIG. 5B  illustrates an equivalent circuit of a feeding unit  540 , and an equivalent circuit of a source resonator  550 . 
     As used herein, a feeding operation may refer to supplying a power to a source resonator in a wireless power transmitter, or refer to supplying an AC power to a rectification unit in a wireless power receiver.  FIG. 5A  illustrates a direction of an input current flowing in the feeding unit, and a direction of an induced current induced in the source resonator. Additionally,  FIG. 5A  illustrates a direction of a magnetic field formed due to the input current of the feeding unit, and a direction of a magnetic field formed due to the induced current of the source resonator. 
     Referring to  FIG. 5A , a fifth conductor or a sixth conductor of the feeding unit may be used as an input port  510 . The input port  510  may receive an input of an RF signal. The RF signal may be output from a power amplifier. The power amplifier may increase or decrease the amplitude of the RF signal, on demand by a target device. The RF signal received by the input port  510  may form an input current flowing in the feeding unit, with the input current flowing in a clockwise direction in the feeding unit, along a transmission line of the feeding unit, for instance. The fifth conductor of the feeding unit may be electrically connected to the source resonator. In one embodiment, the fifth conductor may be connected to a first signal conducting portion of the source resonator. Accordingly, the input current may flow in the source resonator, as well as, in the feeding unit. 
     The input current may flow in a counterclockwise direction in the source resonator. The input current flowing in the source resonator may cause a magnetic field to be formed so that an induced current may be generated in the source resonator due to the magnetic field. The induced current may flow in a clockwise direction in the source resonator. Here, the induced current may transfer energy to a capacitor of the source resonator, and a magnetic field may be formed due to the induced current. The input current flowing in the feeding unit and the source resonator may be indicated by a solid line of  FIG. 5A , and the induced current flowing in the source resonator may be indicated by a dotted line of  FIG. 5A . 
     The direction of a magnetic field formed due to a current may be determined based on the right hand rule. As illustrated in  FIG. 5A , within the feeding unit, the direction  521  of a magnetic field formed due to the input current flowing in the feeding unit may be identical to the direction  523  of a magnetic field formed due to the induced current flowing in the source resonator. Accordingly, strength of the total magnetic field may increase within the feeding unit. 
     Additionally, in a region between the feeding unit and the source resonator, the direction  533  of a magnetic field formed due to the input current flowing in the feeding unit has a phase opposite to the phase of a direction  531  of a magnetic field formed due to the induced current flowing in the source resonator, as illustrated in  FIG. 5A . Accordingly, the strength of the total magnetic field may decrease in the region between the feeding unit and the source resonator. 
     Typically, the strength of a magnetic field decreases in the center of a source resonator with the loop structure, and increases outside the source resonator. However, referring to FIG.  5 A, the feeding unit may be electrically connected to both ends of a capacitor of the source resonator, and accordingly the induced current of the source resonator may flow in the same direction as the input current of the feeding unit. Since the induced current of the source resonator flows in the same direction as the input current of the feeding unit, the strength of the total magnetic field may increase within the feeding unit, and may decrease outside the feeding unit. As a result, the strength of the total magnetic field may increase in the center of the source resonator with the loop structure, and may decrease outside the source resonator, due to the feeding unit. Thus, the strength of the total magnetic field may be equalized within the source resonator. Additionally, the power transmission efficiency for transferring a power from the source resonator to a target resonator may be in proportion to the strength of the total magnetic field formed in the source resonator. And when the strength of the total magnetic field increases in the center of the source resonator, the power transmission efficiency may also increase. 
     Referring to  FIG. 5B , the feeding unit  540  and the source resonator  550  may be expressed by the equivalent circuits. Input impedance Z in , viewed in a direction from the feeding unit  540  to the source resonator  550 , may be computed according to Equation 1 as follows: 
     
       
         
           
             
               
                 
                   
                     Z 
                     in 
                   
                   = 
                   
                     
                       
                         ( 
                         
                           ω 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           M 
                         
                         ) 
                       
                       2 
                     
                     Z 
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     In Equation 1, M denotes a mutual inductance between the feeding unit  540  and the source resonator  550 , w denotes a resonance frequency between the feeding unit  540  and the source resonator  550 , and Z denotes the impedance viewed in a direction from the source resonator  550  to a target device. The input impedance Z in  may be in proportion to the mutual inductance M. Accordingly, the input impedance Z in  may be controlled by adjusting the mutual inductance M. The mutual inductance M may be adjusted based on an area of a region between the feeding unit  540  and the source resonator  550 . The area of the region between the feeding unit  540  and the source resonator  550  may be adjusted based on a size of the feeding unit  540 . And, the input impedance Z in  may be determined based on the size of the feeding unit  540 . Thus, a separate matching network may not be required to perform impedance matching with an output impedance of a power amplifier. 
     In a target resonator and a feeding unit included in a wireless power receiver, a magnetic field may be distributed as illustrated in  FIG. 5A . For example, the target resonator may receive a wireless power from a source resonator, using magnetic coupling. Due to the received wireless power, an induced current may be generated in the target resonator. A magnetic field formed due to the induced current in the target resonator may cause another induced current to be generated in the feeding unit. When the target resonator is connected to the feeding unit as illustrated in  FIG. 5A , the induced current generated in the target resonator may flow in the same direction as the induced current generated in the feeding unit. Thus, strength of the total magnetic field may increase within the feeding unit, but may decrease in a region between the feeding unit and the target resonator. 
       FIG. 6  illustrates another wireless power transmitter. 
     A controller  640  may adjust a mutual inductance M between the feeding unit and the source resonator, by adjusting an area of a region  610  between a feeding unit and a source resonator. By adjusting the mutual inductance M, the controller  640  may determine a value of an input impedance Z in . The area of the region  610  may be adjusted by controlling a size of the feeding unit. The size of the feeding unit may be determined based on a distance  620  between a fourth signal conducting portion and a second ground conducting portion, or based on a distance  630  between a third conductor and a fourth conductor. 
     When the area of the region  610  is increased, the mutual inductance M may be increased. Conversely, when area of the region  610  is reduced, the mutual inductance M may be reduced. The controller  640  may be configured to determine the value of the input impedance Z in , by adjusting the size of the feeding unit. For example, in various embodiments, the value of the input impedance Z in  may be adjusted from about 1 ohm (Ω) to 3000Ω, based on the size of the feeding unit. Accordingly, the controller  640  may match the input impedance Z in  to an output impedance of a power amplifier, based on the size of the feeding unit. In some instances, the controller  640  may not need to employ a separate matching network to perform impedance matching between the input impedance Z in  and the output impedance of the power amplifier. For example, when the output impedance of the power amplifier has a value of 50Ω, the controller  640  may adjust the input impedance Z in  to 50Ω, by adjusting the size of the feeding unit. Additionally, even if a matching network is used for an efficiency of matching, the controller  640  may minimize a loss of power transmission efficiency by simplifying a structure of the matching network. 
     The controller  640  may control a magnetic field formed in the source resonator to be uniformly distributed, based on a direction of an induced current flowing in the source resonator, and a direction of an input current flowing in the feeding unit. Since the feeding unit and the source resonator are electrically connected to both ends of a capacitor, the induced current may be flow in the source resonator in the same direction as the input current. The controller  640  may adjust the size of the feeding unit based on distribution of the magnetic field in the source resonator, to strengthen a portion of the magnetic field with a low strength, or to weaken a portion of the magnetic field with a high strength, so that the magnetic field may be uniformly distributed. This is because the controller  640  may enable strength of the total magnetic field to increase within the feeding unit, and enable the strength of the magnetic field to decrease in the region  610  between the feeding unit and the source resonator. 
     When the magnetic field is uniformly distributed in the source resonator, the source resonator may have a constant input impedance value. Due to the constant input impedance value, the wireless power transmitter may prevent the power transmission efficiency from being reduced, and may effectively transmit a power to the target device, regardless of a location of the target device on the source resonator. 
     A wireless power receiver may also include a target resonator, a feeding unit, and a controller. The controller may control an output impedance of the target resonator, by adjusting a size of the feeding unit. The controller  640  may be configured to match the output impedance of the target resonator to an input impedance of the feeding unit, by adjusting an area of a region between the target resonator and the feeding unit. The output impedance of the target resonator may refer to impedance viewed in a direction from the target resonator to the source resonator. The input impedance of the feeding unit may refer to an impedance viewed in a direction from the feeding unit to a load. 
       FIG. 7  illustrates still another wireless power transmitter. 
     Referring to  FIG. 7 , source resonators  720  and  740  may be implemented as spiral resonators. Each of the spiral resonators may be configured by winding a coil a plurality of times (e.g., “n” times) in a generally spiral shape. 
     In  FIG. 7 , a feeding unit  710  may be disposed in the source resonator  720 , in particular, in an innermost turn of the coil wound in the spiral shape. The feeding unit  710  may include an input port  711  that receives an input of an RF signal, and may enable an input current to flow in the feeding unit  710 . The input current may also flow in the source resonator  720 , and may cause a magnetic field to be formed. Additionally, the magnetic field may enable an induced current to be generated in the source resonator  720  in the same direction as the input current. 
     One of both of the source resonators  720  and  740  may include a capacitor. The capacitor may be electrically connected between a winding starting end of the coil and a winding finishing end of the coil. 
     Additionally, a feeding unit  730  may be disposed around the source resonator  740 . As shown, the feeding unit  730  may be positioned outside of the outermost turn of the coil wound in the spiral shape. The feeding unit  730  may include an input port  731 . The input port  731  may receive an input of an RF signal, and may enable an input current to flow in the feeding unit  730 . The input current may also flow in the source resonator  740 , and may cause a magnetic field to be formed. Additionally, the magnetic field may enable an induced current to be generated in the source resonator  740  in the same direction as the input current. 
     A source resonator may be formed in various shapes, for example, a meta-resonator, a coil resonator, a spiral resonator, a helical resonator, or the like. Additionally, a feeding unit enabling an induced current to be generated in the source resonator may be located within or outside the source resonator with the various shapes. For instance, the feeding unit may be electrically connected to both ends of a capacitor included in the source resonator. Portions of the feeding unit that are electrically connected to both ends of the capacitor may not enable an input current to pass directly through the capacitor. The input current may flow through a loop formed by the feeding unit and the source resonator. 
       FIGS. 8A through 13B  illustrate various resonators. A source resonator included in a wireless power transmitter, and a target resonator included in a wireless power receiver may be configured as illustrated in  FIGS. 8A through 13B , for instance. 
       FIGS. 8A and 8B  illustrate examples of a resonator having a three-dimensional (3D) structure. 
     Referring to  FIG. 8A , a resonator  800  having the 3D structure may include a transmission line and a capacitor  820 . The transmission line may include a first signal conducting portion  811 , a second signal conducting portion  812 , and a ground conducting portion  813 . The capacitor  820  may be inserted, for instance, in series between the first signal conducting portion  811  and the second signal conducting portion  812  of the transmission link such that an electric field may be confined within the capacitor  820 . 
     As illustrated in  FIG. 8A , the resonator  800  may have a generally 3D structure. The transmission line may include the first signal conducting portion  811  and the second signal conducting portion  812  in an upper portion of the resonator  800 , and may include the ground conducting portion  813  in a lower portion of the resonator  800 . The first signal conducting portion  811  and the second signal conducting portion  812  may be disposed to face the ground conducting portion  813 . In this arrangement, current may flow in an x direction through the first signal conducting portion  811  and the second signal conducting portion  812 . Due to the current, a magnetic field H(W) may be formed in a −y direction. However, it will be appreciated that the magnetic field H(W) might also be formed in the opposite direction (e.g., a +y direction) in other implementations. 
     In one or more embodiments, one end of the first signal conducting portion  811  may be electrically connected to (i.e., shorted) to a conductor  842 , and another end of the first signal conducting portion  811  may be connected to the capacitor  820 . One end of the second signal conducting portion  812  may be grounded to a conductor  841 , and another end of the second signal conducting portion  812  may be connected to the capacitor  820 . Accordingly, the first signal conducting portion  811 , the second signal conducting portion  812 , the ground conducting portion  813 , and the conductors  841  and  842  may be connected to each other, whereby the resonator  800  may have an electrically closed-loop structure. 
     As illustrated in  FIG. 8A , the capacitor  820  may be inserted or otherwise positioned between the first signal conducting portion  811  and the second signal conducting portion  812 . The capacitor  820  may include, for example, a lumped element, a distributed element, or the like. In one implementation, a distributed capacitor having the shape of the distributed element may include zigzagged conductor lines and a dielectric material having a relatively high permittivity positioned between the zigzagged conductor lines. 
     When the capacitor  820  is inserted into the transmission line, the resonator  800  may have a characteristic of a metamaterial, in some instances. 
     For example, when the capacitance of the capacitor inserted as a lumped element is appropriately determined, the resonator  800  may have the characteristic of the metamaterial. When the resonator  800  has a negative magnetic permeability by appropriately adjusting the capacitance of the capacitor  820 , the resonator  800  may also be referred to as an MNG resonator. Various criteria may be applied to determine the capacitance of the capacitor  820 . For example, the various criteria may include one or more of the following: a criterion to enable the resonator  800  to have the characteristic of the metamaterial, a criterion to enable the resonator  800  to have a negative magnetic permeability in a target frequency, a criterion to enable the resonator  800  to have a zeroth order resonance characteristic in the target frequency, and/or the like. Based on at least one criterion among the aforementioned criteria, the capacitance of the capacitor  820  may be determined. 
     The resonator  800 , also referred to as the MNG resonator  800 , may have a zeroth order resonance characteristic (i.e., having, as a resonance frequency, a frequency when a propagation constant is “0”). If the resonator  800  has a zeroth order resonance characteristic, the resonance frequency may be independent with respect to a physical size of the MNG resonator  800 . Thus, by appropriately designing the capacitor  820 , the MNG resonator  800  may sufficiently change the resonance frequency without substantially changing the physical size of the MNG resonator  800 . 
     Referring to the MNG resonator  800  of  FIG. 8A , in a near field, the electric field may be concentrated on the capacitor  820  inserted into the transmission line. Accordingly, due to the capacitor  820 , the magnetic field may become dominant in the near field. And, since the MNG resonator  800  having the zeroth-order resonance characteristic may have characteristics similar to a magnetic dipole, the magnetic field may become dominant in the near field. A relatively small amount of the electric field formed due to the insertion of the capacitor  820  may be concentrated on the capacitor  820  and thus, the magnetic field may become further dominant. The MNG resonator  800  may have a relatively high Q-factor using the capacitor  820  of the lumped element and thus, it is possible to enhance an efficiency of power transmission. 
     Also, the MNG resonator  800  may include a matcher  830  to be used in impedance matching. The matcher  830  may be configured to appropriately adjust the strength of the magnetic field of the MNG resonator  800 . The impedance of the MNG resonator  800  may be determined by the matcher  830 . In one or more embodiments, current may flow in the MNG resonator  800  via a connector  840 , or may flow out from the MNG resonator  800  via the connector  840 . And the connector  840  may be connected to the ground conducting portion  813  or the matcher  830 . 
     As illustrated in  FIG. 8A , the matcher  830  may be positioned within the loop formed by the loop structure of the resonator  800 . The matcher  830  may be configured to adjust the impedance of the resonator  800  by changing the physical shape of the matcher  830 . For example, the matcher  830  may include a conductor  831  to be used in the impedance matching in a location separate from the ground conducting portion  813  by a distance h. The impedance of the resonator  800  may be changed by adjusting the distance h. 
     In some embodiments, a controller may be provided to control the matcher  830 . In this case, the matcher  830  may change the physical shape of the matcher  830  based on a control signal generated by the controller. For example, the distance h between the conductor  831  of the matcher  830  and the ground conducting portion  813  may be increased or decreased based on the control signal. Accordingly, the physical shape of the matcher  830  may be changed such that the impedance of the resonator  800  may be adjusted. The distance h between the conductor  831  of the matcher  830  and the ground conducting portion  813  may be adjusted using a variety of schemes. Alternatively or additionally, a plurality of conductors may be included in the matcher  830  and the distance h may be adjusted by adaptively activating one of the conductors. For instance, the distance h may be adjusted by adjusting the physical location of the conductor  831  up and down. The distance h may be controlled based on the control signal of the controller. The controller may generate the control signal using various factors. 
     As illustrated in  FIG. 8A , the matcher  830  may be configured as a passive element such as the conductor  831 , for instance. Of course, in other embodiments, the matcher  830  may be configured as an active element such as a diode, a transistor, or the like. When the active element is included in the matcher  830 , the active element may be driven based on the control signal generated by the controller, and the impedance of the resonator  800  may be adjusted based on the control signal. For example, if the active element is a diode included in the matcher  830 , the impedance of the resonator  800  may be adjusted depending on whether the diode is in an ON state or in an OFF state. 
     In some embodiments, a magnetic core may be further provided to pass through the resonator  800  configured as the MNG resonator  800 . The magnetic core may perform a function of increasing a power transmission distance. 
     In addition, the resonator  800  may include a matcher  850  for impedance matching, as illustrate in  FIG. 8B . The matcher  850  may include a transmission line, and conductors  854  and  855 . The transmission line may include a third signal conducting portion  851 , a fourth signal conducting portion  852 , and a ground conducting portion  853 . The conductor  854  may connect the third signal conducting portion  851  and the ground conducting portion  853 , and the conductor  855  may connect the fourth signal conducting portion  852  and the ground conducting portion  853 . The third signal conducting portion  851  and the fourth signal conducting portion  852  may be connected to both ends of the capacitor  820  of the resonator  800 . 
     Additionally, one end of the third signal conducting portion  851  may be shorted to the conductor  854 , and another end of the third signal conducting portion  851  may be connected to one end of the capacitor  820 . One end of the fourth signal conducting portion  852  may be electrically connected (e.g., shorted) to the conductor  855 , and another end of the fourth signal conducting portion  852  may be connected to another end of the capacitor  820 . 
     Accordingly, the matcher  850  and the resonator  800  may be connected to each other, whereby the resonator  800  may have an electrically closed-loop structure. The matcher  850  may appropriately adjust strength of a magnetic field in the resonator  800 . An impedance of the resonator  800  may be determined by the matcher  850 . Additionally, a current may flow into and/or out of the resonator  800  via the connector  840 . The connector  840  may be connected to the matcher  850 . For instance, the connector  840  may be connected to the third signal conducting portion  851  or the fourth signal conducting portion  852 . The current flowing into the resonator  800  via the connector  840  may cause an induced current to be generated in the resonator  800 . Accordingly, the direction of a magnetic field formed by the resonator  800  may be identical to the direction of a magnetic field formed by the matcher  850  and thus, the strength of the total magnetic field may increase within the matcher  850 . Conversely, the direction of a magnetic field formed by the resonator  800  may be opposite to the direction of a magnetic field formed by the matcher  850  and thus, the strength of the total magnetic field may decrease outside the matcher  850 . 
     The matcher  850  may adjust an impedance of the resonator  800  by changing the physical shape of the matcher  850 . For example, the matcher  850  may include the third signal conducting portion  851  and the fourth signal conducting portion  852  for the impedance matching in a location that is separated from the ground conducting portion  853  by a distance h. The impedance of the resonator  800  may be changed by adjusting the distance h. 
     In some embodiments, a controller may be provided to control the matcher  850 . For example, the matcher  850  may be configured to change the physical shape of the matcher  850  based on a control signal generated by the controller. For example, the distance h between the ground conducting portion  853 , and the third signal conducting portion  851  and the fourth signal conducting portion  852  of the matcher  850  may increase or decrease based on the control signal. Accordingly, the physical shape of the matcher  850  may be changed, and the impedance of the resonator  800  may be adjusted. The distance h between the ground conducting portion  853 , and the third signal conducting portion  851  and the fourth signal conducting portion  852  of the matcher  850  may be adjusted using a variety of schemes. As one example, a plurality of conductors may be included in the matcher  850  and the distance h may be adjusted by adaptively activating one of the conductors. As another example, the distance h may be adjusted by adjusting the physical locations of the third signal conducting portion  851  and the fourth signal conducting portion  852  up and down. The distance h may be controlled based on the control signal of the controller. The controller may generate the control signal using various factors. Additionally, a distance w between the conductors  854  and  855  of the matcher  850  may increase or decrease based on the control signal. Accordingly, the physical shape of the matcher  850  may be changed and the impedance of the resonator  800  may be adjusted. 
       FIGS. 9A and 9B  illustrate examples of a bulky-type resonator for wireless power transmission. 
     Referring to  FIG. 9A , a first signal conducting portion  911  and a conductor  942  may be integrally formed, rather than being separately manufactured and being connected to each other. Similarly, a second signal conducting portion  912  and a conductor  941  may also be integrally manufactured. 
     When the second signal conducting portion  912  and the conductor  941  are separately manufactured and then are connected to each other, a loss of conduction may occur due to a seam  950 . Thus, in some implementations, the second signal conducting portion  912  and the conductor  941  may be connected to each other without using a separate seam (i.e., seamlessly connected to each other). Additionally, the conductor  941  and a ground conducting portion  913  may be seamlessly connected to each other. Accordingly, it is possible to decrease a conductor loss caused by the seam  950 . For instance, the second signal conducting portion  912  and the ground conducting portion  913  may be seamlessly and integrally manufactured. Similarly, the first signal conducting portion  911 , the conductor  942  and the ground conducting portion  913  may be seamlessly and integrally manufactured. 
     Referring to  FIG. 9A , a type of a seamless connection connecting at least two partitions into an integrated form is referred to as a bulky type. 
     As used herein, the term “bulky type” may refer to a seamless connection connecting at least two parts in an integrated form. 
     The resonator  900  may include a matcher  930 , as illustrated in  FIG. 9A . For example, the resonator  900  may include a matcher  960 , as illustrated in  FIG. 9B , with, conduction portions  961  and  962  of the matcher  960  may be connected to the capacitor  920 . 
       FIGS. 10A and 10B  illustrate a hollow-type resonator for wireless power transmission. 
     Referring to  FIG. 10A , each of a first signal conducting portion  1011 , a second signal conducting portion  1012 , a ground conducting portion  1013 , and conductors  1041  and  1042  of a resonator  1000  configured as the hollow type structure. As used herein, the term “hollow type” refers to a configuration that may include an empty space inside. 
     For a given resonance frequency, an active current may be modeled to in only a portion of the first signal conducting portion  1011  instead of the entire first signal conducting portion  1011 , may be modeled to flow in only a portion of the second signal conducting portion  1012  instead of the entire second signal conducting portion  1012 , may be modeled to flow in only a portion of the ground conducting portion  1013  instead of the entire ground conducting portion  1013 , and/or may be modeled to flow in only a portion of the conductors  1041  and  1042  instead of the entire conductors  1041  and  1042 . When a depth of the first signal conducting portion  1011 , the second signal conducting portion  1012 , the ground conducting portion  1013 , and the conductors  1041  and  1042  may be significantly deeper than a corresponding skin depth in the given resonance frequency, it may be ineffective. The significantly deeper depth, however, may increase the weight or manufacturing costs of the resonator  1000 , in some instances. 
     Accordingly, for the given resonance frequency, the depth of each of the first signal conducting portion  1011 , the second signal conducting portion  1012 , the ground conducting portion  1013 , and the conductors  1041  and  1042  may be appropriately determined based on the corresponding skin depth of each of the first signal conducting portion  1011 , the second signal conducting portion  1012 , the ground conducting portion  1013 , and the conductors  1041  and  1042 . When the first signal conducting portion  1011 , the second signal conducting portion  1012 , the ground conducting portion  1013 , and the conductors  1041  and  1042  has an appropriate depth deeper than a corresponding skin depth, the resonator  1000  may be manufactured to be lighter in weight, and manufacturing costs of the resonator  1000  may also decrease. 
     For example, as illustrated in  FIG. 10A , the depth of the second signal conducting portion  1012  (as further illustrated in the enlarged view region  1060  indicated by a circle) may be determined as mm, and d may be determined according to 
             d   =       1       2   ⁢   π   ⁢           ⁢   f   ⁢           ⁢   μσ         .           
Here, f denotes a frequency, μ denotes a magnetic permeability, and σ denotes a conductor constant. In one implementation, when the first signal conducting portion  1011 , the second signal conducting portion  1012 , the ground conducting portion  1013 , and the conductors  1041  and  1042  are made of copper and they may have a conductivity of 5.8×10 7  siemens per meter (S·m −1 ), the skin depth may be about 0.6 mm with respect to 10 kHz of the resonance frequency, and the skin depth may be about 0.006 mm with respect to 100 MHz of the resonance frequency.
 
     The resonator  1000  may include a matcher  1030 , as illustrated in  FIG. 10A . 
     For example, the resonator  1000  may include a matcher  1050 , as illustrated in  FIG. 10B  with conduction portions  1051  and  1052  of the matcher  1050  may be connected to the capacitor  1020 . 
       FIGS. 11A and 11B  illustrate a resonator for wireless power transmission using a parallel-sheet configuration. 
     Referring to  FIG. 11A , the parallel-sheet configuration may be applicable to a first signal conducting portion  1111  and a second signal conducting portion  1112  included in a resonator  1100 . 
     Each of the first signal conducting portion  1111  and the second signal conducting portion  1112  may not be a perfect conductor, and thus may have an inherent resistance. Due to this resistance, an ohmic loss may occur. The ohmic loss may decrease a Q-factor and may also decrease a coupling effect. 
     By applying the parallel-sheet configuration to each of the first signal conducting portion  1111  and the second signal conducting portion  1112 , it may be possible to decrease the ohmic loss, and to increase the Q-factor and the coupling effect. Referring to the enlarged view portion  1170  indicated by a circle in  FIG. 11A , when the parallel-sheet configuration is applied, the first signal conducting portion  1111  and the second signal conducting portion  1112  may include a plurality of conductor lines. The plurality of conductor lines may be disposed in parallel, and may be electrically connected (i.e., shorted) at an end portion of each of the first signal conducting portion  1111  and the second signal conducting portion  1112 . 
     When the parallel-sheet configuration is applied to each of the first signal conducting portion  1111  and the second signal conducting portion  1112 , the plurality of conductor lines may be disposed in parallel. Accordingly, the sum of resistances of the conductor lines may decrease. Consequently, the resistance loss may decrease, and the Q-factor and the coupling effect may increase. 
     The resonator  1100  may include a matcher  1130 , as illustrated in  FIG. 11A . 
     For example, the resonator  1100  may include a matcher  1150 , as illustrated in  FIG. 11B , with conduction portions  1151  and  1152  of the matcher  1150  may be connected to the capacitor  1120 . 
       FIGS. 12A and 12B  illustrate a resonator for wireless power transmission including a distributed capacitor. 
     Referring to  FIG. 12A , a capacitor  1220  included in a resonator  1200  is configured for the wireless power transmission. A capacitor may be configured as a lumped element and may have a relatively high equivalent series resistance (ESR). A variety of schemes have been proposed to decrease the ESR contained in the capacitor of the lumped element. According to an example embodiment, by using the capacitor  1220  as a distributed element, it may be possible to decrease the ESR. As will be appreciated, a loss caused by the ESR may decrease a Q-factor and a coupling effect. 
     As illustrated in  FIG. 12A , the capacitor  1220  may be configured with a zigzagged conductive line and a dielectric material. 
     By employing the capacitor  1220  as the distributed element, it may be possible to decrease the loss occurring due to the ESR in some instances. In addition, by disposing, in parallel, a plurality of capacitors as lumped elements, it may be possible to decrease the loss occurring due to the ESR. Since a resistance of each of the capacitors as the lumped elements decreases through a parallel connection, active resistances of parallel-connected capacitors as the lumped elements may also decrease, whereby the loss occurring due to the ESR may decrease. For example, by employing ten capacitors of 1 pF each instead of using a single capacitor of 10 pF, it may be possible to decrease the loss occurring due to the ESR in some instances. 
     As illustrated in  FIG. 12B , the resonator  1200  may include a matcher  1230 . Conduction portions  1231  and  1232  of the matcher  1230  may be connected to the capacitor  1220 . 
       FIG. 13A  illustrates a matcher used in a resonator having the 2D structure, and  FIG. 13B  illustrates an example of a matcher used in a resonator having the 3D structure. 
       FIG. 13A  illustrates a portion of a resonator  1300  including a matcher  1330 , and  FIG. 13B  illustrates a portion of the resonator  800  of  FIG. 8A  including the matcher  830 . 
     Referring to  FIG. 13A , the matcher  1330  includes a conductor  1331 , a conductor  1332 , and a conductor  1333 . The conductors  1332  and  1333  may be connected to the conductor  1331 , and to a first ground conducting portion  1313  of a transmission line. The matcher  1330  may correspond to the feeder  360  of  FIG. 3B . The impedance of the 2D resonator may be determined based on a distance h between the conductor  1331  and the first ground conducting portion  1313 . The distance h between the conductor  1331  and the first ground conducting portion  1313  may be controlled by a controller. The distance h between the conductor  1331  and the first ground conducting portion  1313  may be adjusted using a variety of schemes. For example, the variety of schemes may include one or more of the following: a scheme of adjusting the distance h by adaptively activating one of the conductors  1331 ,  1332 , and  1333 , a scheme of adjusting the physical location of the conductor  1331  up and down, or the like. 
     Referring to  FIG. 13B , the matcher  830  includes the conductor  831 , a conductor  832 , a conductor  833  and conductors  841  and  842 . The conductors  832  and  833  may be connected to the ground conducting portion  813  and the conductor  831 . The impedance of the 3D resonator may be determined based on a distance h between the conductor  831  and the ground conducting portion  813 . The distance h between the conductor  831  and the ground conducting portion  813  may be controlled by the controller, for example. Similar to the matcher  1330  of  FIG. 13A , in the matcher  830 , the distance h between the conductor  831  and the ground conducting portion  813  may be adjusted using a variety of schemes. For example, the variety of schemes may include one or more of the following: a scheme of adjusting the distance h by adaptively activating one of the conductors  831 ,  832 , and  833 , a scheme of adjusting the physical location of the conductor  831  up and down, or the like. 
     In some implementations, the matcher may include an active element. Thus, a scheme of adjusting an impedance of a resonator using the active element may be similar to the examples described above. For example, the impedance of the resonator may be adjusted by changing a path of a current flowing through the matcher using the active element. 
       FIG. 14  illustrates one equivalent circuit of the resonator  800  of  FIG. 8A . 
     The resonator  800  of  FIG. 9  for a wireless power transmission may be modeled to the equivalent circuit of  FIG. 14 . In the equivalent circuit depicted in  FIG. 14 , L R  denotes an inductance of the power transmission line, C L  denotes the capacitor  820  that is inserted in a form of a lumped element in the middle of the power transmission line, and C R  denotes a capacitance between the power transmissions and/or ground of  FIG. 8A . 
     In some instances, the resonator  800  may have a zeroth resonance characteristic. For example, when a propagation constant is “0”, the resonator  800  may be assumed to have ω MZR  as a resonance frequency. The resonance frequency ω MZR  may be expressed by Equation 2 as follows: 
     
       
         
           
             
               
                 
                   
                     ω 
                     MZR 
                   
                   = 
                   
                     1 
                     
                       
                         
                           L 
                           R 
                         
                         ⁢ 
                         
                           C 
                           L 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ] 
                 
               
             
           
         
       
     
     In Equation 2, MZR denotes a Mu zero resonator. 
     Referring to Equation 2, the resonance frequency ω MZR  of the resonator  800  may be determined by L R /C L . A physical size of the resonator  800  and the resonance frequency ω MZR  may be independent with respect to each other. Since the physical sizes are independent with respect to each other, the physical size of the resonator  800  may be sufficiently reduced. 
       FIG. 15  illustrates a method for transmitting and receiving a wireless power. 
     Referring to  FIG. 15 , a first device, a second device, and a third device may be implemented, for example, using the target device  120  of  FIG. 1 , or the electronic device  220  of  FIG. 2 . Additionally, the first device may be implemented, for example, by using the source device  110  of  FIG. 1 . When the second device transmits a power to the third device, the second device may be referred to as a wireless power transmitter, and the third device may be referred to as a wireless power receiver. When the second device and the third device receive a power simultaneously from the first device, the second device and the third device may be referred to as wireless power receivers. 
     In operations  1510  or  1520 , the first device, the second device, and the third device perform communications with different electronic devices, and determine one of a plurality of operating modes by the communications including a power reception mode, a relay mode, and a power transmission mode, for instance. 
     For example, in  1510 , the first device may perform a communication with the second device and the third device, to perform authentication of the second device and the third device, or to check an amount of a power required in each of the second device and the third device. 
     In operation  1531 , the first device selects an operating mode of the first device. In operation  1532 , the second device selects an operating mode of the second device. In operation  1533 , the third device selects an operating mode of the third device. For example, the first device may select the power transmission mode as the operating mode. The second device may select one of the relay mode, the power reception mode, or the power transmission mode, as the operating mode. The third device may select a power reception mode as the operating mode. 
     In operation  1540 , power transmission, power relay, and power reception may be performed. Specifically, in operation  1541 , the first device transmits a power to the second device. In operation  1542 , the second device relays the power received from the first device to the third device. Additionally, in operation  1542 , the second device transmits the power to the third device using a stored power. In some implementations, a plurality of electronic devices may be further located between the second device and the third device. A resonator of the third device may receive a power from the first device, namely a wireless power transmitter, by passing through the plurality of electronic devices. Additionally, a resonator of the second device may transmit a power to the third device, namely a wireless power receiver, by passing through the plurality of electronic devices. In operations  1541  and  1543 , a resonator of the first device may simultaneously transmit a power to the second device and the third device. Thus, the resonator of the first device may simultaneously transmit a power to the plurality of electronic devices. 
     In operation  1550 , the second device and the third device transmit, to the first device, reports for the received powers. For example, the reports may include information on an amount of a power received to a resonator. 
     In operation  1560 , the first device may perform power control. The power control may be performed to adjust a resonance frequency, and to adjust an impedance. 
       FIGS. 16 and 17  illustrate examples of a method for transmitting and receiving wireless power between electronic devices. 
     Referring to  FIG. 16 , an electronic device  1610  may be implemented, for example, using the source device  110  of  FIG. 1 , or the electronic device  220  of  FIG. 2 . An electronic device  1640  may be implemented, for example, using the target device  120  of  FIG. 1 , or the electronic device  220  of  FIG. 2 . For example, the electronic device  1640  may receive a power from the electronic device  1610 , via a plurality of electronic devices, for example electronic devices  1620  and  1630 . Thus, the electronic devices  1620  and  1630  may be operated in the relay mode. A power transfer path from the electronic device  1610  to the electronic device  1640  may be determined by communication, or may be set in advance. 
     Referring to  FIG. 17 , an electronic device  1710  may be implemented, for example, using the source device  110  of  FIG. 1 , or the electronic device  220  of  FIG. 2 . Additionally, each of a plurality of electronic devices, for example electronic devices  1720 ,  1730 , and  1740 , may be implemented, for example, using the target device  120  of  FIG. 1 , or the electronic device  220  of  FIG. 2 . As illustrated in  FIG. 17 , power may be simultaneously transmitted from the electronic device  1710  to the electronic devices  1720 ,  1730 , and  1740 . 
       FIG. 18  illustrates an electric vehicle charging system. 
     Referring to  FIG. 18 , an electric vehicle charging system  1800  includes a source system  1810 , a source resonator  1820 , a target resonator  1830 , a target system  1840 , and an electric vehicle battery  1850 . 
     The electric vehicle charging system  1800  may have a similar structure to the wireless power transmission system of  FIG. 1 . The source system  1810  and the source resonator  1820  in the electric vehicle charging system  1800  may function as a source. Additionally, the target resonator  1830  and the target system  1840  in the electric vehicle charging system  1800  may function as a target. 
     The source system  1810  may include an alternating current-to-direct current (AC/DC) converter, a power detector, a power converter, a control/communication unit, similarly to the source  110  of  FIG. 1 . The target system  1840  may include a rectification unit, a DC-to-DC (DC/DC) converter, a switch unit, a charging unit, and a control/communication unit, similarly to the target  120  of  FIG. 1 . 
     The electric vehicle battery  1850  may be charged by the target system  1840 . 
     The electric vehicle charging system  1800  may use a resonant frequency in a band of a few kilohertz (KHz) to tens of MHz. 
     The source system  1810  may generate power, based on a type of charging vehicle, a capacity of a battery, and a charging state of a battery, and may supply the generated power to the target system  1840 . 
     The source system  1810  may control the source resonator  1820  and the target resonator  1830  to be aligned. For example, when the source resonator  1820  and the target resonator  1830  are not aligned, the controller of the source system  1810  may transmit a message to the target system  1840 , and may control alignment between the source resonator  1820  and the target resonator  1830 . 
     For example, when the target resonator  1830  is not located in a position enabling maximum magnetic resonance, the source resonator  1820  and the target resonator  1830  may not be aligned. When a vehicle does not stop accurately, the source system  1810  may induce a position of the vehicle to be adjusted, and may control the source resonator  1820  and the target resonator  1830  to be aligned. 
     The source system  1810  and the target system  1840  may transmit or receive an ID of a vehicle, or may exchange various messages, through communication. 
     The descriptions of  FIGS. 2 through 15  may be applied to the electric vehicle charging system  1800 . However, the electric vehicle charging system  1800  may use a resonant frequency in a band of a few KHz to tens of MHz, and may transmit power that is equal to or higher than tens of watts to charge the electric vehicle battery  1850 . 
       FIG. 19  illustrates an example of a wireless power transmission method of an electric vehicle. 
     In  FIG. 19 , wireless power transmission may be performed between electric vehicles. 
     A first electric vehicle  1910  may be operated in a power transmission mode, and a second electric vehicle  1920  may be operated in a power reception mode. 
     The first electric vehicle  1910  may have the same configuration as the electronic device  220  of  FIG. 2 . Additionally, the second electric vehicle  1920  may have the same configuration as the electronic device  220  of  FIG. 2 . However, for convenience of description, the electronic device  220  is assumed to include the power converter  228 , the rectification unit  222 , the DC/DC converter  223 , the switch unit  224 , the charging unit  225 , the control/communication unit  226 , and the path controller  227 , excluding the resonator  221 . 
     The first electric vehicle  1910  may further include a source resonator  1930  operated in the power transmission mode, and the second electric vehicle  1920  may further include a target resonator  1940  operated in the power reception mode. 
     The charging unit  225  may be, for example, a battery mounted in an electric vehicle. For example, the charging unit  225  may charge the electric vehicle with power of at least tens of watts. 
     Additionally, the wireless power transmission between the first electric vehicle  1910  and the second electric vehicle  1920  may be performed via repeaters  1950  and  1960 . 
     The first electric vehicle  1910  may perform the wireless power transmission using an external power source, or using power used to charge a battery. 
     According to various embodiments, an electronic device may wirelessly receive a power, while wirelessly transmitting a power. 
     Additionally, an electronic device may wirelessly receive power supply when a power is required, regardless of a location. 
     The units described herein may be implemented using hardware components and software components. For example, a processing device may be implemented using one or more general-purpose or special purpose computers, such as, for example, a processor, a controller and an arithmetic logic unit, a digital signal processor, a microcomputer, a field programmable array, a programmable logic unit, a microprocessor or any other device capable of responding to and executing instructions in a defined manner. The processing device may run an operating system (OS) and one or more software applications that run on the OS. The processing device also may access, store, manipulate, process, and create data in response to execution of the software. For purpose of simplicity, the description of a processing device is used as singular; however, one skilled in the art will appreciated that a processing device may include multiple processing elements and multiple types of processing elements. For example, a processing device may include multiple processors or a processor and a controller. In addition, different processing configurations are possible, such a parallel processor. 
     The software may include a computer program, a piece of code, an instruction, or some combination thereof, for independently or collectively instructing or configuring the processing device to operate as desired. Software and data may be embodied permanently or temporarily in any type of machine, component, physical or virtual equipment, computer storage medium or device, or in a propagated signal wave capable of providing instructions or data to or being interpreted by the processing device. The software also may be distributed over network coupled computer systems so that the software is stored and executed in a distributed fashion. In particular, the software and data may be stored by one or more computer readable recording mediums. The computer readable recording medium may include any data storage device that can store data which can be thereafter read by a computer system or processing device. Examples of the computer readable recording medium include read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storage devices. Also, functional programs, codes, and code segments for accomplishing the example embodiments disclosed herein can be easily construed by programmers skilled in the art to which the embodiments pertain based on and using the flow diagrams and block diagrams of the figures and their corresponding descriptions as provided herein. 
     A number of examples have been described above. Nevertheless, it should be understood that various modifications may be made. For example, suitable results may be achieved if the described techniques are performed in a different order and/or if components in a described system, architecture, device, or circuit are combined in a different manner and/or replaced or supplemented by other components or their equivalents. Accordingly, other implementations are within the scope of the following claims.