Abstract:
When a portable electronic appliance is provided with two systems, a wireless power-feeding system and a wireless communication system, each system requires two power-receiving devices, a coil and an antenna, leading to a problem of increased electronic appliance size and cost. Wireless power feeding employs the resonance method and uses a resonance coil using the resonance method and a power-receiving coil that receives power from the resonance coil. At least one of the resonance coil and the power-receiving coil can also be used as an antenna for wireless communication. Thus, a power-receiving device that can be used for two systems, wireless power feeding and wireless communication, can be provided.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a power-receiving device, a wireless power-feeding system including the power-receiving device, and a wireless communication system including the power-receiving device. 
     2. Description of the Related Art 
     Various electronic appliances have spread and a variety of products is shipped to the market. In recent years, the spread of portable electronic appliances such as cellular phones and digital video cameras is apparent. 
     A cellular phone or a digital video camera has a built-in battery serving as a power storage means. Currently, such a battery is charged, in most cases, by bringing it in direct contact with a household AC power source serving as a power-feeding means. In view of this, research and development of methods of wirelessly charging batteries or feeding electricity to loads for improved convenience have advanced. Typical examples of methods for wireless power-feeding systems include the electromagnetic coupling method (also called electromagnetic induction method), the radio wave method (also called micro wave method), and the resonance method (also called magnetic resonance method). 
     A wireless power-feeding system using the electromagnetic coupling method cannot yield high transmission efficiency when a power-feeding coil in a power-feeding device and a power-receiving coil in an electronic appliance are displaced. Accordingly, a power-feeding device equipped with a plurality of power-feeding coils, and a technique to move the power-feeding coil so that it can be aligned with the power-receiving coil have been developed (see Patent Document 1, for example). 
     Wireless power-feeding systems using the resonance method have attracted attention and their research and development have been promoted because they yield high transmission efficiency, for middle and long distance use (see Patent Document 2, for example). 
     On the other hand, more and more portable electronic appliances such as recent cellular phones and smartphones function as wireless IC cards having applications such as electronic money. Since wireless IC cards need a wireless communication function, these portable electronic appliances have a built-in antenna for communication (see Patent Document 3, for example). 
     REFERENCE 
     
         
         [Patent Document 1] Japanese Published Patent Application No. 2010-273473 
         [Patent Document 2] Japanese Published Patent Application No. 2010-252468 
         [Patent Document 3] Japanese Published Patent Application No. 2008-210301 
       
    
     SUMMARY OF THE INVENTION 
     Conventionally, when a portable electronic appliance is provided with two systems, a wireless power-feeding system (hereinafter also called wireless power feeding) and a wireless communication system (hereinafter also called wireless communication), each system requires two power-receiving, devices such as a coil and an antenna, leading to a problem of increased electronic appliance size and cost. 
     In view of this, it is an object of one embodiment of the present invention to provide a power-receiving device that yields high transmission efficiency and can be used for two systems, wireless power feeding and wireless communication. 
     One embodiment of the present invention employs the resonance method for wireless power feeding and uses a resonance coil using the resonance method and a power-receiving coil that receives power from the resonance coil. At least one of the resonance coil and the power-receiving coil can also be used as an antenna for wireless communication. Thus, a power-receiving device that can be used for two systems, wireless power feeding and wireless communication, can be provided. The details will be given below. 
     One embodiment of the present invention is a power-receiving device including: a power-receiving resonance coil generating a first high-frequency voltage by a resonance method; and a power-receiving coil generating a second high-frequency voltage by using electromagnetic induction between the power-receiving coil and the power-receiving resonance coil. At least one of the power-receiving resonance coil and the power-receiving coil receives a signal on a carrier wave or an amplitude modulation wave by using electromagnetic induction. The power-receiving coil is electrically connected to a wireless power-feeding unit and a wireless communication unit. The wireless power-feeding unit includes a rectifier circuit rectifying the second high-frequency voltage generated by the power-receiving coil, a converter electrically connected to the rectifier circuit, and a load receiving power converted by the converter. The wireless communication unit includes a reception circuit receiving the signal, a power-receiving controller controlling the signal received by the reception circuit, a modulation transistor electrically connected to the power-receiving controller, and a load modulation element electrically connected to the modulation transistor. The wireless power-feeding unit and the wireless communication unit are integrated. 
     One embodiment of the present invention is a power-receiving device including: a power-receiving resonance coil generating a first high-frequency voltage by a resonance method; and a power-receiving coil generating a second high-frequency voltage by using electromagnetic induction between the power-receiving coil and the power-receiving resonance coil. At least one of the power-receiving resonance coil and the power-receiving coil receives a signal on a carrier wave or an amplitude modulation wave by using electromagnetic induction. The power-receiving coil is electrically connected to a wireless power-feeding unit and a wireless communication unit. The wireless power-feeding unit includes a rectifier circuit rectifying the second high-frequency voltage generated by the power-receiving coil, a converter electrically connected to the rectifier circuit, and a load receiving power converted by the converter. The wireless communication unit includes a reception circuit receiving the signal, a power-receiving controller controlling the signal received by the reception circuit, a modulation transistor electrically connected to the power-receiving controller, and a load modulation element electrically connected to the modulation transistor. The power-receiving resonance coil and the power-receiving coil are placed to at least partly overlap with each other. The wireless power-feeding unit and the wireless communication unit are integrated. 
     One embodiment of the present invention is a wireless power-feeding system including the above-described power-receiving device and a power-transmitting device. The power-transmitting device includes a high-frequency power source generating a third high-frequency voltage, a power-transmitting coil receiving the third high-frequency voltage, and a power-transmitting resonance coil generating a fourth high-frequency voltage by using electromagnetic induction between the power-transmitting resonance coil and the power-transmitting coil. The first high-frequency voltage is generated by magnetic resonance between the power-transmitting resonance coil and the power-receiving device. 
     One embodiment of the present invention is a wireless communication system including the above-described power-receiving device and a communication device. The communication device includes an oscillator generating a carrier wave, a modulation circuit converting the carrier wave into an amplitude modulation wave, a matching circuit for subjecting the amplitude modulation wave to matching, and an antenna electrically connected to the matching circuit. A signal on a carrier wave or an amplitude modulation wave is transmitted and received with electromagnetic induction between the antenna and the power-receiving device. 
     One embodiment of the present invention can provide a power-receiving device that yields high transmission efficiency and can be used for two systems, wireless power feeding and wireless communication. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A to 1C  are diagrams for describing a structure according to Embodiment 1. 
         FIG. 2  is a diagram for describing a structure according to Embodiment 1. 
         FIG. 3  is a diagram for describing a structure according to Embodiment 1. 
         FIGS. 4A to 4C  are diagrams for describing a structure according to Embodiment 2. 
         FIGS. 5A to 5E  are diagrams for describing a structure according to Example 1. 
         FIG. 6  is a diagram for describing the results obtained in Example 1. 
         FIGS. 7A to 7D  are diagrams for describing a structure according to Example 2. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention will be described below with reference to the drawings. Note that the embodiments can be implemented in various different ways. It will be readily appreciated by those skilled in the art that modes and details of the embodiments can be modified in various ways without departing from the spirit and scope of the present invention. The present invention therefore should not be construed as being limited to the description of the embodiments. Note that in structures of the present invention described below, reference numerals denoting the same portions are used in common in different drawings. 
     Note that the size and the like of each object shown in the drawings in the embodiments are exaggerated for simplicity in some cases. Each object therefore is not necessarily in such scale. 
     Note that, in this specification, the terms “first” to “n-th (n is a natural number)” are used only to prevent confusion between components, and thus do not limit numbers. 
     Embodiment 1 
     This embodiment describes a power-receiving device according to one embodiment of the present invention with reference to  FIGS. 1A to 1C ,  FIG. 2 , and  FIG. 3 . 
       FIG. 1A  is a plan view showing a power-receiving device viewed from a first surface side.  FIG. 1B  is a plan view showing the power-receiving device viewed from a second surface side.  FIG. 1C  is a cross-sectional view taken along dashed line X 1 -Y 1  in  FIGS. 1A and 1B . 
     The power-receiving device shown in  FIGS. 1A to 1C  includes a substrate  102 , a power-receiving resonance coil  104  formed over the first surface of the substrate  102 , a capacitor  106  connected to the power-receiving resonance coil  104 , and a power-receiving coil  108  formed over the second surface of the substrate  102 . 
     A glass epoxy substrate, a glass composite substrate, a paper-phenolic substrate, or a flexible substrate such as a film can be used as the substrate  102 . 
     The power-receiving resonance coil  104  formed over the first surface of the substrate  102  is brought into resonance (the resonance method) with a power-transmitting resonance coil (not shown in  FIGS. 1A and 1B ) in a power-transmitting device to generate a first high-frequency voltage; thus, power transmission is achieved. The power-receiving resonance coil  104  is a coil of wires made of a low-resistance material such as copper, silver, or aluminum. The use of a low-resistance material for the power-receiving resonance coil  104  is preferable because it enables power to be transmitted with high efficiency. Note that the number of turns of the coil can be adjusted as appropriate. 
     The capacitor  106  is an element provided to adjust the self-resonant frequency of the power-receiving resonance coil  104 . Note that the capacitor  106  is not necessarily provided in the case where floating capacitance between the coil wires of the power-receiving resonance coil  104  eliminates the need for adjustment of the self-resonant frequency of the power-receiving resonance coil  104 . When the capacitor  106  is not provided, both ends of the coil wires of the power-receiving resonance coil  104  are open. 
     Power transmission to the power-receiving coil  108  formed over the second surface of the substrate  102  is achieved by generating a second high-frequency voltage with electromagnetic induction between the power-receiving coil  108  and the power-receiving resonance coil  104  formed over the first surface of the substrate  102 . It is preferable that the power-receiving resonance coil  104  and the power-receiving coil  108  be placed to at least partly overlap with each other with the substrate  102  therebetween, and the number of turns of the power-receiving coil  108  be, smaller than that of the power-receiving resonance coil  104 . Such placement and structure enhance magnetic coupling between the power-receiving coil  108  and the power-receiving resonance coil  104  and increase particularly short-distance power-transmission efficiency in the case of power feeding using the resonance method. Thus, the power-receiving device can receive power transmitted to the power-receiving resonance coil  104  with high efficiency. 
     The following describes the specific structure of the power-receiving device shown in  FIGS. 1A to 1C  and a wireless power-feeding system using the power-receiving device with reference to  FIG. 2 . 
     Note that a portion having the same function as that of any component in  FIGS. 1A to 1C  is denoted by the reference numeral of that component and its detailed description is omitted. 
       FIG. 2  is a block diagram showing a wireless power-feeding system using resonance between the power-receiving device shown in  FIGS. 1A to 1C  and a separately provided power-transmitting device  250  (the resonance method).  FIG. 2  shows electromagnetic power transmission achieved by resonance, between a power-transmitting resonance coil  254  in the power-transmitting device  250  and the power-receiving resonance coil  104  in a power-receiving device  200 . In the block diagram of  FIG. 2 , the circuits in the power-receiving device  200  and the power-transmitting device  250  are classified according to their functions and shown as independent units. Note that it is actually difficult to completely separate the circuits in the power-receiving device  200  and the power-transmitting device  250  functionally; therefore, one circuit can have a plurality of functions. In other words, a plurality of circuits can achieve a function corresponding to that of one unit. 
     The power-receiving device  200  shown in  FIG. 2  includes the power-receiving resonance coil  104  generating the first high-frequency voltage by the resonance method, and the power-receiving coil  108  the second generating high-frequency voltage with electromagnetic induction between the power-receiving coil  108  and the power-receiving resonance coil  104 . At least one of the power-receiving resonance coil  104  and the power-receiving coil  108  receives a signal on a carrier wave or an amplitude modulation wave by using electromagnetic induction. 
     The power-receiving coil  108  is electrically connected to a wireless power-feeding unit  230  and a wireless communication unit  240 . The wireless power-feeding unit  230  includes a rectifier circuit  208  rectifying the second high-frequency voltage generated by the power-receiving coil  108 , a DCDC converter  210  electrically connected to the rectifier circuit  208 , and a load  212  receiving power converted by the DCDC converter  210 . The wireless communication unit  240  includes a reception circuit  214  receiving a signal that has been received by at least one of the power-receiving resonance coil  104  and the power-receiving coil  108 , a reception controller  220  controlling a signal that has been received by the reception circuit  214 , a modulation transistor  206  electrically connected to the reception controller  220 , and a load modulation element  204  electrically connected to the modulation transistor  206 . The wireless power-feeding unit  230  and the wireless communication unit  240  are integrated. 
     The power-receiving device  200  may include a directional coupler  202 . The directional coupler  202  separates a modulation signal on a power-transmission carrier from the carrier and transmits the modulation signal to the reception circuit  214 . Note that the directional coupler  202  is not necessarily provided. For example, when high power is transmitted, it is preferable to provide the directional coupler  202  as shown in this embodiment. 
     As described above, in the power-receiving device  200 , the wireless power-feeding unit  230  and the wireless communication unit  240  are integrated, and the power-receiving coil  108 , which is included in the power-receiving device shown in  FIG. 1 , is connected to a plurality of circuits and devices. 
     The power-transmitting device  250  includes a capacitor  252 , the power-transmitting resonance coil  254 , a power-transmitting coil  256 , and a high-frequency power source  258 . 
     The following describes the operation of the power-receiving device  200  and power-transmitting device  250 . 
     Power transmission to the power-receiving device  200  is achieved by resonance between the power-receiving resonance coil  104  and the power-transmitting resonance coil  254  in the power-transmitting device  250 . Power transmitted to the power-receiving resonance coil  104  is transmitted to the power-receiving coil  108  by the electromagnetic coupling method. 
     Power transmitted to the power-receiving coil  108  is transmitted to the load  212  via the directional coupler  202 , the rectifier circuit  208 , and the DCDC converter  210 . In other words, power transmitted to the power-receiving coil  108  is transmitted to the wireless power-feeding unit  230 . 
     Note that the DCDC converter  210  converts a current that has been rectified by the rectifier circuit  208  into a desired current (power) needed for the load  212  located at the subsequent stage. 
     The load  212  can be any device that can operate when receiving power wirelessly. Examples of such a device include a battery, an electric motor, a bulb, and an electronic device operating with a battery, such as a cellular phone. 
     The directional coupler  202  is electrically connected to the reception circuit  214  in the wireless communication unit  240 . However, in the wireless power-feeding system, the wireless communication unit  240  in the power-receiving device  200  does not function. 
     In the power-transmitting device  250 , the frequency (oscillation frequency) of an alternating-current (AC) signal output from the high-frequency power source  258  is applied to the power-transmitting coil  256 . Power transmitted to the power-transmitting coil  256  is transmitted to the power-transmitting resonance coil  254  by the electromagnetic coupling method. The power-transmitting resonance coil  254  is provided with the capacitor  252 . The self-resonant frequency of the power-transmitting resonance coil  254  can be adjusted using the capacitor  252 . 
     Note that the frequency of an AC signal output from the high-frequency power source  258  is not limited to a particular frequency and can be any oscillation frequency with which the power-transmitting device  250  can transmit power to the power-receiving device  200  by the resonance method. The oscillation frequency in the resonance method can be used, for example, in a frequency band of several kilohertz to several gigahertz. 
     As described above, power generated with the high-frequency power source  258  in the power-transmitting device  250  can be transmitted with resonance between the power-transmitting resonance coil  254  and the power-receiving resonance coil  104  in the power-receiving device  200  (the resonance method). Thus, unlike wireless power-feeding using the electromagnetic coupling method, wireless power-feeding using the resonance method can widen an area where power can be fed and achieve high transmission efficiency. 
     Next, a wireless communication system using the power-receiving device  200  in  FIG. 2  will be described with reference to  FIG. 3 . 
     Note that a portion having the same function as that of any component in  FIGS. 1A to 1C  and  FIG. 2  is denoted by the same reference numeral as that of the component and its detailed description is omitted. 
       FIG. 3  is a block diagram showing a system of wireless communication between the power-receiving device  200  shown in  FIG. 2  and a separately provided communication device  270 . In the block diagram of  FIG. 3 , the circuits in the power-receiving device  200  and the power communication device  270  are classified according to their functions and shown as independent units. Note that it is actually difficult to completely separate the circuits in the power-receiving device  200  and the power communication device  270  functionally; therefore, one circuit can have a plurality of functions. In other words, a plurality of circuits can achieve a function corresponding to that of one unit. 
     The power-receiving device  200  shown in  FIG. 3  includes the power-receiving resonance coil  104  generating the first high-frequency voltage with the resonance method, and the power-receiving coil  108  generating the second high-frequency voltage with electromagnetic induction between the power-receiving coil  108  and the power-receiving resonance coil  104 . At least one of the power-receiving resonance coil  104  and the power-receiving coil  108  receives a signal on a carrier wave or an amplitude modulation wave by using electromagnetic induction. 
     The power-receiving coil  108  is electrically connected to a wireless power-feeding unit  230  and a wireless communication unit  240 . The wireless power-feeding unit  230  includes a rectifier circuit  208  rectifying the second high-frequency voltage generated with the power-receiving coil  108 , a DCDC converter  210  electrically connected to the rectifier circuit  208 , and a load  212  receiving power that has been converted by the DCDC converter  210 . The wireless communication unit  240  includes a reception circuit  214  receiving a signal that has been received by at least one of the power-receiving resonance coil  104  and the power-receiving coil  108 , a reception controller  220  controlling a signal that has been received by the reception circuit  214 , a modulation transistor  206  electrically connected to the reception controller  220 , and a load modulation element  204  electrically connected to the modulation transistor  206 . The wireless power-feeding unit  230  and the wireless communication unit  240  are integrated. 
     The power-receiving device  200  can include a directional coupler  202 . The directional coupler  202  separates a modulation signal on a power-transmission carrier from the carrier and transmits the modulation signal to the reception circuit  214 . The directional coupler  202  is electrically connected to the reception circuit  214  and the reception controller  220 . The reception circuit  214  can be composed of a plurality of circuits such as a low pass filter (a type of filter circuit), an amplification circuit, and a demodulation circuit. 
     Note that while wireless communication is carried out, the wireless power-feeding unit  230  does not function. Note that the wireless power-feeding unit  230  may have a function of, for example, referring the amount of remaining battery or the like according to an instruction of a received signal and sending it back. 
     A communication device  270  includes an antenna  272 , a directional coupler  274 , a modulation circuit  276 , an oscillator  278 , a power-receiving circuit  280 , a communication controller  282 , and a matching circuit  284 . 
     Note that a frequency band produced by the oscillator  278  is not limited to a particular band and can be any frequency band as appropriate. Examples of applicable frequency bands include an HF band of 3 MHz to 30 MHz (13.56 MHz for example), a UHF band of 300 MHz to 3 GHz (433 MHz, 953 MHz, or 2.45 GHz for example), and 135 kHz. 
     The communication device  270  serves as a so-called reader/writer. Like the reception circuit  214  in the power-receiving device  200 , the power-receiving circuit  280  can be composed of a plurality of circuits such as a low pass filter, an amplification circuit, and a demodulation circuit. 
     Wireless communication is carried out in the following manner. Reception of a signal on a carrier wave or amplitude modulation wave is achieved by using electromagnetic induction between the antenna  272  provided in the communication device  270  and at least one of the power-receiving resonance coil  104  and the power-receiving coil  108  provided in the power-receiving device  200 , allowing wireless communication. 
     Specifically, in order to send data from the communication device  270  to the power-receiving device  200 , a carrier wave is first generated with the oscillator  278  in the communication device  270 . A modulation wave is then superimposed on the carrier wave with the modulation circuit  276  to generate an amplitude modulation wave. Subsequently, the amplitude modulation wave is output to the antenna  272  via the matching circuit  284  and the directional coupler  274 . The amplitude modulation wave output to the antenna  272  is received by the power-receiving resonance coil  104  or power-receiving coil  108  in the power-receiving device  200 . The amplitude modulation wave applied to the power-receiving coil  108  is applied to the reception controller  220  via the directional coupler  202  and the reception circuit  214 . In this way, the signal on the carrier wave generated in the communication device  270  is sent to the power-receiving device  200 . 
     In order to send back data from the power-receiving, device  200  to the communication device  270 , a signal (power) is sent from the reception controller  220  in the power-receiving device  200  to the power-receiving coil  108  via the modulation transistor  206  and the load modulation element  204 . The signal applied to the power-receiving coil  108  is also applied to the power-receiving resonance coil  104  with the electromagnetic coupling method. The communication device  270  receives the signal applied to the power-receiving coil  108  or the power-receiving resonance coil  104 , at the antenna  272 . The received signal is applied to the communication controller  282  via the directional coupler  274  and the power-receiving circuit  280 . In this way, the signal from the power-receiving device  200  is sent back to the communication device  270 . 
     In this way, the power-receiving device  200  described in this embodiment can transmit and receive a signal on a carrier wave or an amplitude modulation wave to/from the antenna  272  via at least one of the power-receiving resonance coil  104  and the power-receiving coil  108 . In other words, wireless communication can be achieved by using the power-receiving resonance coil  104  or the power-receiving coil  108 . 
     Although this embodiment describes a structure in which the power-receiving device  200  and one of the power-transmitting device  250  and the communication device  270  are used, as an example, the power-transmitting device  250  and the communication device  270  may be combined into one device. 
     As described above, the power-receiving device described in this embodiment can be used for two systems, a wireless power feeding system and a wireless communication system, and yields high transmission efficiency. 
     This embodiment can be implemented in appropriate combination with any structure described in the other embodiments. 
     Embodiment 2 
     In this embodiment, applications of a wireless power-feeding system using the power-receiving device described in the above embodiment are described. Examples of the applications of the wireless power feeding system using the power-receiving device according to one embodiment of the present invention include portable electronic devices such as a digital video camera and a personal digital assistant (e.g., a mobile computer, a cellular phone, a portable game machine, and an e-book reader). Examples will be described bellow refereeing to drawings. 
       FIG. 4A  shows an example in which a wireless power-feeding system is used for a cellular phone and a personal digital assistant and which is composed of a power-transmitting device  700 , a power plug  702 , and a cellular phone  704  including a power-receiving device  706 , and a cellular phone  708  including a power-receiving device  710 . A wireless power-feeding system using the power-receiving device described in the above embodiment is applicable between the power-transmitting device  700  and the power-receiving device  706 , and between the power-transmitting device  700  and the power-receiving device  710 . 
     For example, the power-transmitting device  700  can use the structure of the power-transmitting device  250  in  FIG. 2  described in Embodiment 1, while the power-receiving device  706  and the power-receiving device  710  can use the structure of the power-receiving device  200  in  FIG. 2  and  FIG. 3  described in Embodiment 1. The power plug  702  is connected to an external power source (not shown). 
     As described above, in this embodiment, a plurality of power-receiving devices (power-receiving device  706  and power-receiving device  710 ) can be used for one power-transmitting device. The wireless power-feeding system enables power feeding using the resonance method, and thus can widen an area where power can be fed and achieve high transmission efficiency. 
     The following describes the cellular phone  708  including the power-receiving device  710  in  FIG. 4A  in detail with reference to  FIGS. 4B and 4C .  FIGS. 4B and 4C  are perspective views of the cellular phone. 
       FIG. 4B  shows the front (display surface) of the cellular phone  708  and illustrates a front housing  711 , a speaker part  712 , a display part  713 , a microphone part  714 , a terminal part  716 , and a terminal part  722 . 
       FIG. 4C  shows the back of the cellular phone  708  and illustrates a back housing  718 , a terminal part  716 , a terminal part  722 , a camera module  723 , a lens part  724 , and a light  726 . The power-receiving device  710  and a battery  728  are stored in the back housing  718 . 
     For example, the power-receiving device  710  can use the structure of the power-receiving device  200  in  FIG. 2  and  FIG. 3  described in Embodiment 1. By using the load  212  in  FIG. 2  and  FIG. 3  described in Embodiment 1 as the battery  728 , power received by the power-receiving device  710  can be stored in the battery  728 . 
     Moreover, the power-receiving device  710  stored in the cellular phone  708  is capable of wireless communication as well. 
     As described above, the power-receiving device described in this embodiment can be used for two systems, wireless power-feeding and wireless communication, and yields high transmission efficiency. 
     This embodiment can be implemented in appropriate combination with any structure described in the other embodiments. 
     Example 1 
     In Example 1, a wireless power-feeding system with a simple structure was evaluated by using the power-receiving device in  FIG. 1  described in Embodiment 1. Description will be given with reference to  FIGS. 5A to 5E  and  FIG. 6 . 
       FIG. 5A  is a plan view of a power-receiving device  500 , which shows a substrate  502  viewed from a first surface side.  FIG. 5B  is a plan view of the power-receiving device  500 , which shows the substrate  502  viewed from a second surface side.  FIG. 5C  is a cross-sectional view taken along dashed line X 2 -Y 2  in  FIGS. 5A and 5B .  FIG. 5D  is a plan view of a power-transmitting device  550 .  FIG. 5E  is a cross-sectional view taken along dashed line V-W in  FIG. 5D . 
     The power-receiving device  500  includes the substrate  502 , a power-receiving resonance coil  504 , a capacitor  506 , a power-receiving coil  508 , wiring  510 , a socket  512 , and a bulb  514 . 
     The substrate  502  is a glass epoxy substrate that measures 4.2 cm wide by 7.2 cm long by 0.7 mm thick. The power-receiving resonance coil  504  is made of copper wire and has the following specs: the coil width is 1 mm, the coil separation is 1 mm, the number of coil turns is 4, and the coil thickness is 35 μm. The power-receiving coil  508  is made of copper wire and has the following specs: the coil width is 1 mm, the number of turns is 1, and the coil thickness is 35 μm. The capacitor  506  is a RF chip capacitor having a capacitance of 59 pF. The wiring  510  is connected to the power-receiving coil  508  and is electrically connected to the bulb  514  via the socket  512 . Thus, applying power to the power-receiving coil  508  lights the bulb  514 . 
     The power-transmitting device  550  includes a power-transmitting board  520  and a power-transmitting resonance coil  522 . 
     The power-transmitting board  520  is a Styrofoam plate that measures 20 cm wide by 20 cm long by 1 cm thick. The power-transmitting resonance coil  522  is made of copper wire and has the following specs: the coil outer diameter is 15 cm, the coil separation is 1 cm, the number of coil turns is 3, and the coil diameter is 3 mm. Note that coordinates P 1  to P 9  representing measurement points spaced every 5 cm are written on the power-transmitting board  520 . 
     The conditions for the power-transmitting device  550  are as follows: the grid power is 1 W, the oscillation frequency is 15.30 MHz, and the self-resonant frequency of the power-transmitting resonance coil  522  is 14.95 MHz. 
     With the above-described structure, in Example 1, wireless power-feeding was carried out by the resonance method using the power-receiving resonance coil  504  provided in the power-receiving device  500  and the power-transmitting resonance coil  522  provided in the power-transmitting device  550 . 
     Power from the power-transmitting device  550  is applied to the bulb  514  via the power-receiving resonance coil  504 , the power-receiving coil  508 , the wiring  510 , and the socket  512  provided in the power-receiving device  500 . Note that the coordinates P 1  to P 9  shown in  FIG. 5D  were used as evaluation coordinates. 
       FIG. 6  shows the results of lighting tests on the bulb  514  at P 1  to P 9 . 
     From  FIG. 6 , it was confirmed that the bulb  514  could be lit at all the coordinates P 1  to P 9 . It was also confirmed that the brightness was approximately the same at all the coordinates and that, from the results of another measurement using the network analyzer N5230A by Agilent Technologies Inc., the transmission efficiency was as high as 80% to 95% 
     As described above, it was confirmed that the power-receiving device evaluated in Example 1 yielded high transmission efficiency in a wide area. 
     This embodiment can be implemented in appropriate combination with any structure described in Example 2 or the embodiments. 
     Example 2 
     In Example 2, a wireless communication system with a simple structure was evaluated by using the power-receiving device in  FIG. 1  described in Embodiment 1. Description will be given with reference to  FIGS. 7A to 7D . 
       FIG. 7A  is a plan view of a power-receiving device  600 , which shows a substrate  602  viewed from a first surface side.  FIG. 7B  is a plan view of the power-receiving device  600 , which shows the substrate  602  viewed from a second surface side.  FIG. 7C  is a cross-sectional view taken along dashed line X 3 -Y 3  in  FIGS. 7A and 7B . 
     The power-receiving device  600  includes the substrate  602 , a power-receiving resonance coil  604 , a capacitor  606 , a power-receiving coil  608 , a wiring  610 , and a chip  612 . 
     The substrate  602  is a glass epoxy substrate that measures 4.2 cm wide by 7.2 cm long by 0.7 mm thick. The power-receiving resonance coil  604  is made of copper wire and has the following specs: the coil width is 1 mm, the coil separation is 1 mm, the number of coil turns is 4, and the coil thickness is 35 μm. The power-receiving coil  608  is made of copper wire and has the following specs: the coil width is 1 mm, the number of turns is 1, and the coil thickness is 35 μm. The wiring  610  is connected to the power-receiving coil  608  and is electrically connected to the chip  612 . Thus, applying power to the power-receiving coil  608  operates the chip  612 . 
       FIG. 7D  is a block diagram showing wireless communication using the electromagnetic coupling method between the power-receiving device according to Example 2 and a separately provided communication device, and illustrates the power-receiving device  600 , a signal analyzer  620 , and a communication device  630  including an antenna  632 , a communication controller  634 , and a load  636 . In the block diagram of  FIG. 7D , the circuits in the power-receiving device and the communication device are classified according to their functions and shown as independent units. 
     Note that the communication controller  634  is composed of various circuits, such as a low pass filter, a transformer, and a rectifier circuit, and devices. 
     The power-receiving device  600  is electrically connected to the signal analyzer  620  which is capable of conducting signal analysis when the power-receiving device  600  wirelessly receives data. 
     In Example 2, an evaluation was conducted of whether the power-receiving device  600  received data, with the distance between the power-receiving device  600  and the antenna  632  provided in the communication device  630  varied between 35 mm to 300 mm and with three values of the output power of the communication device  630 : 0 dBm, 10 dBm, and 20 dBm. Table 1 shows the evaluation results. 
     
       
         
               
               
             
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Output power [dBm] 
               
             
          
           
               
                   
                 0 
                 10 
                 20 
               
               
                   
                   
               
             
          
           
               
                   
                 Distance between power- 
                 35 
                 X 
                 ◯ 
                 ◯ 
               
               
                   
                 receiving device and 
                 50 
                 X 
                 ◯ 
                 ◯ 
               
               
                   
                 antenna [mm] 
                 70 
                 X 
                 ◯ 
                 ◯ 
               
               
                   
                   
                 90 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                   
                   
                 130 
                 ◯ 
                 ◯ 
                 ◯ 
               
               
                   
                   
                 170 
                 Δ 
                 ◯ 
                 ◯ 
               
               
                   
                   
                 210 
                 Δ 
                 Δ 
                 ◯ 
               
               
                   
                   
                 250 
                 X 
                 Δ 
                 ◯ 
               
               
                   
                   
                 300 
                 X 
                 Δ 
                 Δ 
               
               
                   
                   
               
             
          
         
       
     
     In Table 1, a circle represents the case where the power-receiving device  600  receives correct data from the communication device  630 , a triangle represents the case where the power-receiving device  600  receives any incorrect data from the communication device  630 , and a cross represents the case where the power-receiving device  600  fails to receive data from the communication device  630 . 
     As shown in Table 1, with an output power of 0 dBm, correct data is received with a distance ranging from 90 mm to 130 mm, white partly incorrect data is received with a distance ranging from 170 mm to 210 mm. With an output power of 10 dBm, correct data is received with a distance ranging from 35 mm to 170 mm, while partly incorrect data is received with a distance ranging from 210 mm to 300 mm. With an output power of 20 dBm, correct data is received with a distance ranging from 35 mm to 250 mm, while partly incorrect data is received with a distance of 300 mm. 
     Thus, it was confirmed that the power-receiving device shown in Example 2 is capable of wireless communication. 
     This embodiment can be implemented in appropriate combination with any structure described in Example 1 or the embodiments. 
     This application is based on Japanese Patent Application serial No. 2011-053317 filed with Japan Patent Office on Mar. 10, 2011, the entire contents of which are hereby incorporated by reference.