Abstract:
A power transmission apparatus including a power transmitting unit which includes an induction unit which receives an electrical energy from an external power source by induction and a magnetic resonance unit which transmits the electrical energy to an external receiving unit by magnetic resonance.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a power transmission apparatus, a power reception apparatus and a power transmission system, and particularly to a power transmission apparatus, a power reception apparatus and a power transmission system which can transmit power contactlessly in small equipment. 
     In recent years, research and development of a system for transmitting electric power contactlessly has been conducted. One of such systems is disclosed, for example, in Japanese Patent Laid-Open No. 2008-295191. 
     As a power transmission method for contact less power transmission system such as an electromagnetic induction type power transmission method is available. Further, in recent years, a power transmission method a magnetic field resonance type power transmission method has become available. The magnetic field resonance type power transmission method allows for the transmission of power over a long distance in comparison to an electromagnetic induction type power transmission method. 
       FIG. 1  shows an example of a configuration of an existing power transmission system to which the magnetic field resonance type power transmission method is applied. 
     The existing power transmission system  11  shown in  FIG. 1  consists of a power transmission apparatus  21  and a power reception apparatus  22 . 
     The power transmission apparatus  21  includes an oscillation circuit  31 , a power transmission coil  32  and a resonance circuit  33  which are accommodated in a single housing  21 A. 
     The power reception apparatus  22  includes a resonance circuit  51 , a power reception coil  52 , a bridge rectification circuit  53  and a smoothing capacitor  54  which are accommodated in a single housing  22 A. 
     The existing power transmission system  11  having such a configuration as described above operates in the following manner. 
     In particular, alternating current outputted from the oscillation circuit  31  flows to the power transmission coil  32 , and as result, an oscillating electromagnetic field is generated around the power transmission coil  32 . Alternating current is induced by the oscillating electromagnetic field of the power transmission coil  32  and flows to the resonance circuit  33  on the power transmission side, and as a result, an oscillating electromagnetic field having a predetermined resonance frequency is generated around the resonance circuit  33  on the power transmission side. 
     The resonance circuit  51  on the power reception side of the power reception apparatus  22 , alternating current flows by resonance of the oscillating electromagnetic field of the resonance circuit  33  on the power transmission apparatus  21  side. In particular, wireless non-radiation type energy transfer is carried out using an electromagnetic field mode of oscillation resonance so that alternating current flows to the resonance circuit  51  on the power reception side. As a result, an oscillating electromagnetic field having a predetermined resonance frequency is generated around the resonance circuit  51  on the power reception side. Alternating current is induced by the oscillating electromagnetic field of the resonance circuit  51  on the power reception side and flows to the power reception coil  52 . This alternating current is full-wave rectified by the bridge rectification circuit  53 . The full-wave rectified current in the form of pulsating current is smoothed by the smoothing capacitor  54  and then supplied to a circuit on the following stage not shown. 
     In this manner, in the existing power transmission system  11 , power is supplied contactlessly from the power transmission apparatus  21  to the power reception apparatus  22 . 
     Incidentally, in such a magnetic field resonance type power transmission method applied to the existing power transmission system  11  as described above, if the Q value of the resonance circuit is not raised, then the transmission efficiency cannot be enhanced. In particular, in the example of  FIG. 1 , in order to enhance the transmission efficiency, it is necessary to set the Q value of the resonance circuit  33  on the power transmission side and the resonance circuit  51  on the power reception side to a high value. 
     It is to be noted that, since, with such a frequency as is utilized in the magnetic field resonance type power transmission method, the Q value of the resonance circuit depends upon a characteristic of a coil, the Q value is calculated in accordance with the following expression (1): 
                   Q   =     ω   ⁢     L   R               (   1   )               
where ω is the angular frequency, L the inductance value of the coil of the resonance circuit and R the resistance value of the resonance circuit.
 
       FIG. 2  illustrates an example of variation of the transmission efficiency of power by the magnetic field resonance type power transmission method. 
     In  FIG. 2 , the axis of ordinate indicates an attenuation amount [dB] with respect to a maximum transmission efficiency. The attenuation amount represents a transmission efficiency. The axis of abscissa indicates an oscillation frequency [MHz] of the oscillation circuit (in the example of  FIG. 1 , the oscillation circuit  31 ) on the power transmission side. 
     It is to be noted that, in one embodiment of  FIG. 2 , the resonance frequency is 13.56 MHz of the ISM (Industrial, Scientific, Medical) band. In another embodiment of  FIG. 2 , the resonance frequency is set to 120 kHz. Further, in the example of  FIG. 2 , a very high value of approximately 400 is adopted as both Q values. 
     As shown in  FIG. 2 , where the oscillation frequency is 13.56 MHz which is equal to that of the resonance frequency, the transmission efficiency is highest and the attenuation amount is zero. 
     However, it is difficult to apply the existing power transmission system  11  as a power supply to small equipment such as a portable telephone set, an electronic notebook, a headphone, a music player and the like. 
     In particular, such small equipment frequently is used at a place spaced from a power supply by several meters or more. As a result, efficient power transmission at a transmission distance of several meters or more is required for the existing power transmission system  11 . In order to satisfy the request just described where the existing power transmission system  11  wherein 13.56 MHz described above is used as the resonance frequency is applied, it is necessary to increase the diameter of the coils of the resonance circuit  33  on the power transmission side and the resonance circuit  51  on the power reception side to approximately 0.44 m. It is very difficult to accommodate such a large coil having a diameter of approximately 0.44 m as just described in the inside of a small equipment. 
     Therefore, it is desirable to implement contact less electric power transmission in a small equipment. 
     SUMMARY OF THE INVENTION 
     In an embodiment of the present invention, there is provided a power transmission apparatus comprising a power transmitting unit which includes (1) an induction unit which receives an electrical energy from an external power source by induction and (2) a magnetic resonance unit which transmits the electrical energy to an external receiving unit by magnetic resonance. 
     Another embodiment consistent with the present invention provides the power transmission apparatus further comprising a power supply unit in the power transmission unit which receives the electrical energy from the external power source by induction and provides electrical energy to a plurality of electrical devices in the power transmission unit. 
     Another embodiment consistent with the present invention provides the power transmission system where the external power source is an oscillation unit which generates an electromagnetic field which is induced by the induction unit in the power transmitting unit. 
     Another embodiment consistent with the present invention provides the power transmission system wherein the oscillation unit is separated from the power transmission unit by a distance. 
     Another embodiment consistent with the present invention provides the power transmission system wherein the magnetic resonance unit includes a transmission coil having a diameter of 0.44 m or less. 
     Another embodiment consistent with the present invention provides the power transmission system wherein the magnetic resonance unit generates an electromagnetic wave having a wavelength of 13.56 MHz. 
     Another embodiment consistent with the present invention provides the power transmission system wherein the magnetic resonance unit generates an electromagnetic wave having a wavelength of 120 kHz. 
     Another embodiment consistent with the present invention provides a power receiving apparatus comprising a power receiving unit which includes (1) a magnetic resonance unit that receives an electrical energy from an external source by magnetic resonance and (2) an induction unit which transmits the electrical energy to an external reception unit by induction. 
     Another embodiment consistent with the present invention provides the power receiving apparatus further comprising a power supply unit in the power receiving unit which receives electrical energy from the induction unit and provides electrical energy to a plurality of electrical devices in the power receiving unit. 
     Another embodiment consistent with the present invention provides the power receiving apparatus wherein the power receiving unit is separated from the external reception unit by a distance. 
     Another embodiment consistent with the present invention provides the power receiving apparatus wherein the magnetic resonance unit includes a transmission coil having a diameter of 0.44 m or less. 
     Another embodiment consistent with the present invention provides the power receiving apparatus wherein the magnetic resonance unit generates an electromagnetic wave having a wavelength of 13.56 MHz. 
     Another embodiment consistent with the present invention provides the power receiving apparatus wherein the magnetic resonance unit generates an electromagnetic wave having a wavelength of 120 kHz. 
     Another embodiment consistent with the present invention provides a power transmission system comprising a power transmitting unit which includes (1) an induction unit which receives an electrical energy from an external power source by induction and (2) a magnetic resonance transmitting unit which transmits the electrical energy by magnetic resonance, a power receiving unit which includes (1) a magnetic resonance receiving unit that receives the electrical energy from the power transmission unit by magnetic resonance and (2) an induction unit which transmits the electrical energy to an external reception unit by induction. 
     Another embodiment consistent with the present invention provides the power transmission system wherein the power transmitting unit is separated from the power receiving unit by a distance. 
     Another embodiment consistent with the present invention provides the power transmission system wherein the external power source is separated from power transmitting unit by a distance. 
     Another embodiment consistent with the present invention provides the power transmission system wherein the external reception unit is separated from the power receiving unit by a distance. 
     Another embodiment consistent with the present invention provides the power transmission system wherein the magnetic resonance transmission unit generates an electromagnetic wave having a wavelength of 13.56 MHz. 
     Another embodiment consistent with the present invention provides the power transmission system wherein the magnetic resonance transmission unit generates an electromagnetic wave having a wavelength of 120 kHz. 
     Another embodiment consistent with the present invention provides the power transmission system wherein the distance between the power transmission unit and the power receiving unit is 2.2 m or less. 
     Another embodiment consistent with the present invention provides the power transmission system wherein the magnetic resonance receiving unit includes a coil having a diameter of 0.44 m or less. 
     Another embodiment consistent with the present invention provides the power transmission system wherein the magnetic resonance transmitting unit includes a coil having a diameter of 0.44 m or less. 
     Another embodiment consistent with the present invention provides an electronic apparatus comprising a reception coil in the electronic apparatus in inductive communication with a magnetic resonance receiving unit via an electromagnetic field. Where the magnetic resonance receiving unit receives a magnetic resonance energy and converts the magnetic resonance energy into the electromagnetic field. 
     Another embodiment consistent with the present invention provides the electronic apparatus wherein the magnetic resonance energy is generated from a magnetic resonance unit separated from the magnetic resonance receiving unit by a distance. 
     Another embodiment consistent with the present invention provides the electronic apparatus wherein the distance is 2.2 m or less. 
     Another embodiment consistent with the present invention provides the electronic apparatus wherein the reception unit is separated from the magnetic resonance receiving unit by a distance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block circuit diagram showing an one configuration of an existing power transmission system consistent with the present invention; 
         FIG. 2  is a diagram illustrating on embodiment of variation of the transmission efficiency of power by the magnetic field resonance type power transmission method consistent with the present invention; 
         FIG. 3  depicts a block diagram showing one configuration of a power transmission system consistent with the present invention; 
         FIG. 4  depicts a schematic view showing one configuration of an application of the power transmission system; 
         FIG. 5  depicts a schematic view showing one configuration of a unit used in the power transmission system consistent with the present invention; 
         FIG. 6  depicts a schematic view showing an one configuration of a headphone in which the unit is incorporated consistent with the present invention; 
         FIG. 7  depicts a schematic view showing one configuration an application of the power transmission system consistent with the present invention; 
         FIG. 8  depicts a schematic view showing one configuration of a wireless speaker to which the power transmission system is applied which is consistent with the present invention; 
         FIG. 9  depicts a schematic view showing one configuration of the wireless speaker to which the power transmission system is applied which is consistent with the present invention; 
         FIG. 10  depicts a schematic view showing one configuration of a television image reception apparatus to which the power transmission system is applied which is consistent with the present invention; 
         FIG. 11  depicts a schematic view showing one configuration of a room to which the power transmission system is applied which is consistent with the present invention; 
         FIGS. 12A to 12C  depicts views showing one configuration of a portable type audio player to which the power transmission system is applied which is consistent with the present invention; 
         FIG. 13  depicts a schematic view showing one configuration of a portable telephone set to which the power transmission system is applied which is consistent with the present invention; 
         FIG. 14  depicts a schematic view showing one configuration of a portable type audio player to which the power transmission system is applied which is consistent with the present invention; 
         FIGS. 15A and 15B  depicts schematic views showing one configuration of a housing of the unit consistent with the present invention; 
         FIG. 16  is a block diagram showing one configuration of a power transmission system which is consistent with the present invention; 
         FIG. 17  depicts a flow chart illustrating one configuration of a resonance frequency controlling process of the power transmission system which is consistent with the present invention; 
         FIG. 18  depicts a diagram illustrating a relationship between an application voltage of a varicap element on the power reception side and an output voltage value which is consistent with the present invention; and 
         FIG. 19  depicts a block diagram showing one configuration of hardware of an information processing apparatus which is consistent with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments of the present invention are described below with reference to the drawings. 
     Referring first to  FIG. 3 , there is shown a configuration of the power transmission system according to the first embodiment of the present invention. 
     The power transmission system  81  shown is configured from a power transmission apparatus  91  and a power reception apparatus  92 . The power transmission apparatus  91  and the power reception apparatus  92  are disposed physically separately from each other in a spaced relationship by a distance L. 
     The power transmission apparatus  91  is configured from a unit  101  having a single housing and another unit  102  having a single housing. The unit  101  and the unit  102  can be physically separated from each other, and are disposed, where power is to be transmitted to the power reception apparatus  92 , in a contacting relationship with each other or in a spaced relationship from each other by a distance of approximately several cm. 
     The unit  101  is configured from an oscillation circuit  121  as an oscillation section and a power transmission coil  122  connected to the oscillation circuit  121 . 
     Meanwhile, the unit  102  is configured from a power transmission side resonance circuit  131  as a resonance section and a unit power supply circuit  132  as a power supplying section. The power transmission side resonance circuit  131  is configured from a coil having an inductance Ls and a capacitor having a capacitance Cs. While a capacitor having a predetermined value may be connected as the capacitor of the capacitance Cs, the capacitance Cs may be provided as stray capacitance formed by disposing end portions of the coil in a spaced relationship by a predetermined distance from each other and in an opposing relationship to each other. The unit power supply circuit  132  is configured from a coil  141 , a bridge rectification circuit  142  and a smoothing capacitor  143 . The bridge rectification circuit  142  is connected to the coil  141 . The smoothing capacitor  143  is connected to both of output terminals of the bridge rectification circuit  142 . A member for which power is required such as an LED (Light Emitting Diode) or a lamp not shown is connected across the smoothing capacitor  143 . 
     The power reception apparatus  92  is configured from a unit  103  having a single housing and another unit  104  having a single housing. The unit  103  and the unit  104  can be physically separated from each other, and are disposed, where power is to be received from the power transmission apparatus  91 , in a contacting relationship with each other or in a spaced relationship from each other by a distance of approximately several cm. 
     The unit  103  is configured from a power reception side resonance circuit  151  as a resonance section and a unit power supply circuit  152  as a power supplying section. The power reception side resonance circuit  151  is configured from a coil having an inductance Lr and a capacitor having a capacitance Cr. While a capacitor having a predetermined value may be connected as the capacitor of the capacitance Cr, the capacitance Cr may be provided as stray capacitance formed by disposing end portions of the coil in a spaced relationship by a predetermined distance from each other and in an opposing relationship to each other. The unit power supply circuit  152  is configured from a coil  161 , a bridge rectification circuit  162  and a smoothing capacitor  163 . The bridge rectification circuit  162  is connected to the coil  161 . The smoothing capacitor  163  is connected to both terminals of outputs of the bridge rectification circuit  162 . A member for which power is required such as an LED or a lamp not shown is connected across the smoothing capacitor  163 . 
     The unit  104  is configured from a power reception coil  171 , a bridge rectification circuit  172  and a smoothing capacitor  173 . The bridge rectification circuit  172  is connected to the power reception coil  171 . The smoothing capacitor  173  which configures a power supplying section together with the bridge rectification circuit  172  is connected to both of output terminals of the bridge rectification circuit  172 . A member for which power is required such as a charging circuit for a small equipment is connected across the smoothing capacitor  173 . 
     It is to be noted that, taking a comparatively high frequency of alternating current to be applied to the bridge rectification circuits into consideration, the bridge rectification circuits  142 ,  162  and  172  in the present embodiment are configured individually from a fast recovery diode. Further, the smoothing capacitors  143 ,  163  and  173  in the present embodiment are configured individually from an electrolytic capacitor. 
     The power transmission system  81  having such a configuration as described above operates in the following manner. 
     In particular, in the power transmission apparatus  91 , if the oscillation circuit  121  of the unit  101  starts oscillation operation, then the oscillation circuit  121  outputs alternating current having a predetermined frequency f 121  (hereinafter referred to as oscillation frequency f 121 ). The alternating current outputted from the oscillation circuit  121  flows to the power transmission coil  122 , and as a result, an oscillating electromagnetic field of the oscillation frequency f 121  is generated around the power transmission coil  122 . In other words, the oscillating electromagnetic field of the oscillation frequency  121  is generated around the unit  101 . 
     Alternating current flows to the power transmission side resonance circuit  131  of the unit  102  disposed in the proximity of the unit  101  by induction by the oscillating electromagnetic field around the unit  101 . As a result, an oscillating electromagnetic field of a resonance frequency f 121  represented by the an expression (2) given below is generated around the power transmission side resonance circuit  131 . In particular, an equivalent circuit of the power transmission side resonance circuit  131  is an LC circuit configured from an inductance LS of a coil and a stray capacitance Cs as illustrated in  FIG. 3 . In this instance, the resonance frequency f 131  of the power transmission side resonance circuit  131  is given to the following expression (2): 
     
       
         
           
             
               
                 
                   
                     f 
                     131 
                   
                   = 
                   
                     1 
                     
                       2 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       π 
                       ⁢ 
                       
                         LsCs 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     In the power reception apparatus  92 , alternating current flows to the power reception side resonance circuit  151  of the unit  103  by resonance of the oscillating electromagnetic field of the power transmission side resonance circuit  131  of the unit  102  on the power transmission apparatus  91  side. In particular, radio non-radiation type energy transfer is carried out using an electromagnetic field mode of oscillation resonance so that the alternating current flows to the power reception side resonance circuit  151 . As a result, an oscillating electromagnetic field having a resonance frequency f 151  represented by an expression (3) given below is generated around the power reception side resonance circuit  151 . In particular, an equivalent circuit of the power reception side resonance circuit  151  is an LC circuit configured from an inductance Lr of a coil and a stray capacitance Cr as seen in  FIG. 3 . In this instance, the resonance frequency f 151  of the power reception side resonance circuit  151  is represented by the following expression (3): 
     
       
         
           
             
               
                 
                   
                     f 
                     151 
                   
                   = 
                   
                     1 
                     
                       2 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       π 
                       ⁢ 
                       
                         LrCr 
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     It is to be noted that ideally the resonance frequency f 131  on the power transmission side and the resonance frequency f 151  on the power reception side are both equal to the oscillation frequency f 121  of the oscillation circuit  121 . Here, the reason why the term [ideally] is used is that there is the possibility that the resonance frequencies f 131  and f 151  may be displaced from the oscillation frequency f 121  caused by variation of the use environment during actual use. 
     The oscillating electromagnetic field is generated around the power reception side resonance circuit  151 , that is, around the unit  103  of the power reception apparatus  92  in such a manner as described above. Then, in the unit  104 , alternating current flows to the power reception coil  171  by induction by the oscillating electromagnetic field. The alternating current is subjected to full-wave rectification carried out by the bridge rectification circuit  172 . The full-wave rectified current in the form of pulsating current is smoothed by the smoothing capacitor  173 , and the resulting current is supplied to a part for which power is required such as a charging circuit for a small apparatus not shown or the like. 
     In the power transmission system  81 , power is supplied contactlessly to the power reception apparatus  92  by resonance of the magnetic field from the power transmission apparatus  91  in this manner. 
     Further, power is supplied from the unit power supply circuit  132  to parts in the unit  102  of the power transmission apparatus  91 . In particular, alternating current flows to the coil  141  by induction by the oscillating electromagnetic field generated around the power transmission coil  122  of the unit  101  and the power transmission side resonance circuit  131  of the unit  102 . The alternating current is subjected to full-wave rectification carried out by the bridge rectification circuit  142 . The full-wave rectified current in the form of pulsating current is smoothed by the smoothing capacitor  143  into direct current and then supplied to the parts not shown in the unit  102 . The parts in the unit  102  may be, for example, an LED and a lamp. In this instance, the LED or the lamp can be turned on with the power supplied from the unit power supply circuit  132  to indicate that, for example, the unit  102  or the power transmission system  81  is operating. 
     Similarly, power is supplied from the unit power supply circuit  152  to parts in the unit  103  of the power reception apparatus  92 . In particular, alternating current flows to the coil  161  by induction by the oscillating electromagnetic field generated around the power reception side resonance circuit  151 . The alternating current is subjected to full-wave rectification carried out by bridge rectification circuit  162 . The full-wave rectified current in the form of pulsating current is smoothed by the smoothing capacitor  163  into direct current and then is supplied to the parts not shown in the unit  103 . The parts in the unit  103  may be, for example, an LED and a lamp. In this instance, the LED or the lamp can be turned on with the power supplied from the unit power supply circuit  152  to indicate that, for example, the unit  103  or the power transmission system  81  is operating. 
     Since the unit power supply circuit  132  of the unit  102  and the unit power supply circuit  152  of the unit  103  are used as power supplies for internal parts of the unit  102  and the unit  103  in this manner, they can be omitted where such parts do not exist. 
     Incidentally, in the magnetic resonance type power transmission technique applied to the power transmission system  81 , from a point of view of the transmission efficiency, the ratio of the wavelength λ of an electromagnetic wave to be transmitted, the distance between the power transmission side and the power reception side, and the diameter of the coils of the transmission side and the reception side preferably has a value approximately 50: a value lower than 5:1. Such a ratio as just given is hereinafter referred to as ideal ratio. 
     In particular, for example, if the transmission frequency is 13.56 MHz of the ISM band, then since the wavelength λ is determined as λ=300/13.56=22 m, preferably the distance between the transmission side and the reception side is set to 2.2 or less and the diameter of the coils is set to 0.44 m. It is to be noted that the numerical values determined from the ideal ratio are ideal values, and the transmission efficiency sometimes drops by some fluctuation of the values. 
     In this manner, for example, where the magnetic resonance type power transmission technique is applied to power transmission for a small apparatus, if a distance of a value around 2.2 m is assured as the distance between the transmission side and the reception side and a coil having a diameter of approximately 0.44 m is adopted, then wireless power transmission can be implemented. 
     The assurance itself of the distance of approximately 2.2 m is possible not only with the power transmission system  81  of the present embodiment but also with the existing power transmission system  11 . However, the power reception apparatus  22  of the existing power transmission system  11  of  FIG. 1  is accommodated in a single housing and cannot be separated. Accordingly, to adopt a coil having a diameter of approximately 0.44 m signifies to set the diameter of the coil of the reception side resonance circuit  51  or the power reception coil  52  to approximately 0.44 m, that is, to make the size of the power reception apparatus  22  greater than that of a circle of the diameter of 0.44 m. It is very difficult to build the power reception apparatus  22  having such a great size as just described in a small-sized apparatus. This applies not only to power transmission to a small-sized apparatus but also to contactless charging of an electronic automobile or the like. In other words, it is difficult to adopt the existing power transmission system  11  for an application to power transmission to a small-sized apparatus or contactless charging of an electric automobile or the like. 
     In contrast, in the power transmission system  81  of the present embodiment, the unit  103  and the unit  104  which compose the power reception apparatus  92  are physically separable from each other as described above. Accordingly, if the diameter of the coil of the power reception side resonance circuit  151  in the unit  103 , that is, of the coil which forms the reactance Lr, is set to 0.44 m, then it is possible to make the diameter of the power reception coil  171  in the unit  104  much smaller than 0.44 m. In other words, it is possible to form the unit  104  in a small size. Accordingly, it can be achieved readily to incorporate the unit  104  of the small size in a small-sized apparatus or in an apparatus for contactless charging such as an electric automobile. Furthermore, also it is possible, for example, to incorporate the bridge rectification circuit  172  and the smoothing capacitor  173  in a housing of a small-sized apparatus and dispose the power reception coil  171  outside the housing of the small-sized apparatus without the provision of a housing for exclusive use for the unit  104 . 
     In the following, various apparatus to which the power transmission system  81  of the present invention is applied are described with reference to  FIGS. 4 to 15B . 
     [Example of the Configuration of Apparatus to which the Power Transmission System of an Embodiment of the Invention is Applied] 
       FIG. 4  shows an example of a configuration where the power transmission system  81  of the present invention is applied to a headphone. 
     It is to be noted that the headphone  182  must only have a function of being mounted on the head of a user and outputting sound to an ear of the user and is not particularly restricted in terms of the type, shape and so forth. For example, the headphone may be a wireless headphone, a noise cancellation headphone or the like. 
     In the example shown in  FIG. 4 , of the units  101  to  104  which configure the power transmission system  81 , the units  101  to  103  are accommodated in respective housings for exclusive use while the unit  104  is accommodated in the headphone  182 . The housings of the units  101  to  103  should be formed from a material having a low dielectric constant such as a plastics material. Though not shown, a charging circuit for the headphone  182  is connected across the smoothing capacitor  173  of the unit  104 . In other words, the power transmission system  81  is adopted as a charging power supply for the headphone  182 . 
     The unit  101  and the unit  102  are laminated in order from below and disposed on the ground below a table  181 . The unit  103  is disposed on an upper face of the table  181  spaced by approximately 1 m upwardly from the upper face of the housing of the unit  102 . In other words, the distance L between the unit  102  and the unit  103  is approximately 1 m, and a distance equal to or smaller than 2.2 m of the preferred distance between the transmission side and the reception side calculated using the ideal ratio is assured. The headphone  182  in which the unit  104  is built can be carried freely by the user, and if there is the necessity for charging, then the user would place the headphone  182  on the unit  103 . 
     An external power supply  191  is used as the power supply for the unit  101 . In particular, the oscillation circuit  121  in the unit  101  is driven by the power supply from the external power supply  191 . Though not shown, for example, in the present embodiment, a one-turn coil having a diameter of 0.44 m is adopted as the power transmission coil  122 . 
       FIG. 5  shows an appearance configuration of the unit  102  shown in  FIG. 4 . For the convenience of illustration, the unit  102  is shown such that the coil  131 L therein can be observed. The coil  131 L which configures the power transmission side resonance circuit  131  of the unit  102  is formed, for example, in the present embodiment, as a five-turn coil having an air-core coil structure and having the preferred diameter of 0.44 m determined from the ideal ratio. Further, a terminal end of the coil  131 L is opened to form a stray capacitance Cs. As a result, the resonance frequency f 131  becomes 13.56 MHz. In this manner, the preferred diameter of 0.44 m determined from the ideal ratio is assured by the diameter of the coil  131 L on the transmission side. 
     Though not shown, the unit  103  has a structure similar to that of the unit  102  shown in  FIG. 4 . The coil which is a component of the power reception side resonance circuit  151  of the unit  103  is, for example, in the present embodiment, a 5-turn coil having an air-core structure and having the preferred diameter of 0.44 m determined from the ideal ratio. Further, the coil is open at a terminal end thereof to produce stray capacitance Cr, and as a result, the resonance frequency f 151  is 13.56 MHz. In this manner, the preferred diameter of 0.44 m determined from the ideal ratio is assured also by the diameter of the coil on the reception side. 
       FIG. 6  shows an example of a configuration of the headphone  182  which incorporates the unit  104 . Though not shown, the bridge rectification circuit  172  and the smoothing capacitor  173  are built in the headphone  182  while the power reception coil  171  is built in one of enclosures. For the convenience of illustration, the power reception coil  171  is shown projecting to the outside of the enclosure. The power reception coil  171  is, for example, in the present embodiment, a 20-turn coil of a diameter of 4 cm. The reason why the diameter of the power reception coil  171  on the unit  104  side can be made small in this manner is that the unit  103  can assure the preferred coil diameter of 0.44 m calculated using the ideal ratio. In other words, the power reception coil  171  is not limited to that described above only if it can be built in the headphone  182  and has a size with which it can be charged from the power reception side resonance circuit  151  of the unit  103 . 
       FIG. 7  shows another example of an application of the power transmission system  81  of the present invention. 
     It is to be noted that, in order to clearly indicate a difference, the unit  104  incorporated in the headphone  182  is hereinafter referred to particularly as unit  104 - 1  and the unit  104  incorporated in a portable telephone set  183  is hereinafter referred to particularly as unit  104 - 2 . 
     The unit  104 - 1  has a configuration similar to that of the unit  104  described hereinabove with reference to  FIGS. 4 to 6  and is incorporated in the headphone  182 . Accordingly, overlapping description of the unit  104 - 1  is omitted herein to avoid redundancy. 
     The unit  104 - 2  is incorporated in the portable telephone set  183 . Though not shown, a charging circuit of the portable telephone set  183  is connected across the smoothing capacitor  173  of the unit  104 - 2 . In other words, the power transmission system  81  is adopted as a charging power supply for the headphone  182  and the portable telephone set  183 . 
     The portable telephone set  183  in which the unit  104 - 2  is built can be carried freely by the user. When it is necessary to charge the portable telephone set  183 , the user would place the portable telephone set  183  on the unit  103 . 
     In the example of  FIG. 7 , the headphone  182  which has the unit  104 - 1  built therein and the portable telephone set  183  which has the unit  104 - 2  built therein are placed simultaneously on the upper face of the unit  103 . In such an instance as just described, the headphone  182  and the portable telephone set  183  can receive power transmitted from the power transmission apparatus  91  through the units  103  and  104 , respectively. Consequently, the headphone  182  and the portable telephone set  183  placed on the upper face of the housing of the unit  103  are charged by the power transmission system  81 . 
     In this manner, the unit  103  can relay power transmitted from the power transmission apparatus  91  to a plurality of units  104  disposed around the housing thereof. 
       FIG. 8  shows an example of a configuration of a wireless speaker to which the power transmission system  81  according to an embodiment of the present invention is applied. 
     Referring to  FIG. 8 , in the example shown, the units  101  to  104  which configure the power transmission system  81  are accommodated in respective housings for exclusive use. The housings for the units  101  to  104  are preferably made of a material having a low dielectric constant such as a plastics material. Though not shown, the opposite terminals of the smoothing capacitor  173  of the unit  104  are used as output terminals of the units  101  to  104 , and power supply terminals such as a power supply plug socket of a wireless speaker  211  are connected to the output terminals. In other words, the power transmission system  81  is adopted as a power supply for the wireless speaker. 
     In the example shown in  FIG. 8 , the unit  103  and the unit  104  as well as the wireless speaker  211  are laminated in order from the location nearest to a wall face of a wall  201  of a room, that is, in the rightward direction in  FIG. 4 . The unit  103 , unit  104  and wireless speaker  211  are removably fastened to each other by fixing members  221  serving as fastening means such as hooks mounted for pivotal motion for locking by grooves or projections. 
     In the example shown in  FIG. 8 , though not shown, the unit  102  and the unit  101  are secured to a face of the wall  201  opposite to the face of the wall  201  on which the unit  103  and the unit  104  are secured, for example, to a wall face of a neighboring room. The unit  102  and the unit  101  are laminated in order from the location nearest to the opposite face of the wall  201 , that is, in the leftward direction in  FIG. 8 . 
     The distance L between the unit  102  and the unit  103  substantially coincides with the thickness of the wall  201 . Accordingly, where the wall  201  has a general thickness, a distance equal to or smaller than 2.2 m suitable as a distance between the transmission side and the reception side calculated using the ideal ratio can be assured as the distance L. 
     The unit  103  and the unit  104  which configure the power reception apparatus  92  can be physically separated from each other, and the unit  104  is provided independently of the wireless speaker  211 . Accordingly, the user can remove the fixing members  221  as occasion demands to individually separate the unit  103 , unit  104  and wireless speaker  211  from each other. Further, while, in the present embodiment, transmission of power from the unit  104  to the wireless speaker  211  is carried out by direct connection between the output terminals of the unit  104  and the power supply terminals of the wireless speaker  211 , it is not particularly limited to the connection of the present embodiment. For example, contacts of the conductive fixing members  221  may be used to transmit power from the unit  104  to the wireless speaker  211 . 
       FIG. 9  shows another example of a configuration of a wireless speaker to which the power transmission system  81  according to an embodiment of the present invention is applied. 
     Referring to  FIG. 9 , also in the example shown, power is supplied to a wireless speaker  211  securely mounted on a wall face of a wall  201  by the power transmission system  81 . However, in the example shown in  FIG. 9 , the unit  103  is built in the wall  201  which has a thickness of approximately 10 cm constructed by a two-by-four construction method. Accordingly, the unit  104  and the wireless speaker  211  are laminated in order from the location nearest to the wall face of the wall  201  of the room, that is, in the rightward direction in  FIG. 9  and removably secured to each other by fixing members  221  such as hooks mounted for pivotal motion for being locked by grooves or projections. 
     Here, if the preferred diameter of 0.44 mm of a coil calculated using the ideal ratio can be assured by the unit  103  built in the wall  201 , then the diameter of the power reception coil  171  on the unit  104  side can be reduced. Accordingly, the size of the unit  104  to be suspended on the wall face of the wall  201  can be reduced in comparison with that of the example of  FIG. 8 . In other words, the power transmission system  81  can be adopted as a power supply for the wireless speaker  211  of a small size without degrading the external appearance. 
     Further, that the size of the set of the unit  104  and the wireless speaker  211  is small signifies that it is easy to carry the same. Accordingly, if a plurality of rooms individually have a wall in which the unit  103  is built, then the user can remove the set of the unit  104  and the wireless speaker  211  having the small size and dispose the same on a wall of another room. In other words, it is easy to use the wireless speaker  211  in a plurality of rooms. 
     It is to be noted that the target of transmission of power by the power transmission system  81  is not limited to the wireless speaker  211  but may be, for example, a wireless television receiver. Meanwhile, the fixing members  221  are not limited to the hooks but may be a hook and loop fastener or the like. 
       FIG. 10  shows an example of a configuration of a television receiver to which the power transmission system  81  according to an embodiment of the present invention is applied. 
     Referring to  FIG. 10 , in the example shown, the unit  103  is built in a rack  241  while the unit  104  not shown in  FIG. 10  is built in a television receiver  242 . Further, though not shown, the unit  101  and the unit  102  are laminated in order in a downward direction of the unit  103  and disposed, for example, on a face  243   a  of an accommodating shelf  243  of the rack  241 . 
     Since the unit  103  and the unit  104  can be physically separated from each other in this manner, only it is necessary to build the unit  104  in the television receiver  242  but it is not necessary to build the unit  103  in the television receiver  242 . If the diameter of 0.44 m is assured for the coil of the power reception side resonance circuit  151  in the unit  103  built in the rack  241 , then the size of the unit  104  built in the television receiver  242  can be reduced. Accordingly, the unit  104  can be built readily in the television receiver  242  of a small size. In other words, the power transmission system  81  of the present invention can be applied also to the television receiver  242  of a small size. 
     It is to be noted that, in the power transmission system  81  of the present invention, from a point of view of the efficiency in power transmission, a normal to a loop plane formed from the power transmission coil of the power transmission side resonance circuit  131  included in the unit  102  and a normal to a loop plane formed from the power reception coil of the power reception side resonance circuit  151  included in the unit  103  should coincide with each other. Accordingly, where the direction of the normal to the loop plane of the power reception coil of the unit  103  is the vertical direction, it is preferable to dispose the unit  102  such that also the direction of the normal to the loop plane of the power transmission coil of the unit  102  may be the vertical direction. In other words, it is preferable to select a face of the housing of the unit  102  which opposes to the loop plane of the power transmission coil as an installation face and dispose the unit  102  such that the installation face of the housing of the unit  102  is opposed to the face  243   a  of the accommodating shelf  243  of the rack  241 . In other words, it is not preferable from the point of view of the efficiency in power transmission to dispose the unit  102  in such a manner as to rest on the rear of the television receiver  242  or the rack  241  such that the installation face of the unit  102  and the face  243   a  of the accommodating shelf  243  of the rack  241  extend substantially perpendicularly to each other. 
       FIG. 11  shows an example of a configuration of a room to which the power transmission system  81  of the present invention is applied. 
     If the room has a size of six mats, then the distance between walls of the room is approximately 2 m. Accordingly, even if the unit  102  and the unit  103  are built in two arbitrary walls as shown in  FIG. 11 , the distance L between the unit  102  and the unit  103  can be set to a preferable distance of approximately 2.2 m between the power transmission side and the power reception side calculated using then ideal ratio. In other words, power transmission between six walls having a size of six mats or the like on which the unit  102  and the unit  103  are disposed as shown in  FIG. 11  can be achieved by the power transmission system  81 . 
     In particular, for example, it is possible to build the unit  102  in the floor face  261 - 1  of the room  260  and build the unit  103  in the ceiling face  261 - 2  opposing to the floor face  261 - 1 . 
     In this instance, though not shown, the unit  101  is disposed below the unit  102  in a spaced relationship by a distance of approximately several cm from the unit  102 . 
     Further, though not shown, the unit  104  is disposed above the unit  103  in a spaced relationship by a distance of several cm from the unit  103 . At this time, if the diameter of the coil of the power reception side resonance circuit  151  in the unit  103  is set to 0.44 m, then the power reception coil  171  in the unit  104  can be formed in a small size. In such an instance, it is possible, for example, to build the unit  104  of a small size in a male fitting which can be carried and form the unit  103  so as to include a plug receiver or female fitting therein. With the configuration, the user can dispose the unit  103  and the unit  104  simply by only inserting the male fitting into the female fitting. 
     It is to be noted that the unit  102  can be built not only in the floor face  261 - 1  of the room  260  but also in any arbitrary face of the room  260 , for example, into the side face  261 - 3 . 
     Meanwhile, although the power from the unit  102  is transmitted most effectively to a perpendicular direction to the plane in which the unit  102  is built, that is, in a direction toward the opposing face, it is not transmitted only to the direction but is transmitted also to the other faces of the room  260 . For example, where the unit  102  is built in the floor face  261 - 1 , power is transmitted not only to the opposing ceiling face  261 - 2  but also to the other wall faces such as the perpendicular floor face  261 - 4 . Accordingly, even where the unit  102  is built in the floor face  261 - 1 , there is no necessity to particularly build the unit  103  in the ceiling face  261 - 2  but the unit  103  can be built in the other wall faces such as the wall face  261 - 4 . In short, the unit  103  can be built in an arbitrary wall face of the room  260  without depending upon the arrangement position of the unit  102 . 
     The power transmission system  81  of the present invention can be applied to various fields because the units  101  to  104  of the components thereof can be physically separated from each other as described above. Particularly, there is no necessity to provide a housing for exclusive use for the unit  104 . Accordingly, for example, it is possible to accommodate the bridge rectification circuit  172  and the smoothing capacitor  173  from among the components of the unit  104  in a housing of a small-sized apparatus and dispose the power reception coil  171  outside the small-sized apparatus. In this manner, the power transmission system  81  of the present invention can be applied readily as a power supply for a small-sized apparatus. 
     In the following, particular examples of a small-sized apparatus to which the power transmission system  81  of the present invention is applied are described with reference to  FIGS. 12A to 14 . In particular, in the examples described below, the power transmission system  81  of the present invention is adopted as a charging power supply for a small-sized apparatus by disposing the power reception coil  171  of one turn in a part of the small-sized apparatus or in an accessory of the small-sized apparatus. 
     Referring first to  FIGS. 12A to 12C , there is shown an example of a configuration of a portable audio player to which the power transmission system  81  of the present invention is applied. 
     In the example shown in  FIGS. 12A to 12C , the units  101  to  103  not shown from among the units  101  to  104  which compose the power transmission system  81  are accommodated in respective housings for exclusive use, and the unit  104  is incorporated in a portable audio player. 
       FIG. 12A  shows a basic configuration of a portable audio player  280  represented by the Walkman (registered trademark of Sony Corporation). An earphone  282 - 1  and another earphone  282 - 2  are connected to each other by a head band  283 . When the left and right earphones  282 - 1  and  282 - 2  are disposed in the proximity of each other, they are coupled to and integrated with each other by magnetic force of magnets  281  installed in the earphones  282 - 1  and  282 - 2 . 
       FIG. 12B  shows arrangement of coils of the portable audio player  280  shown in  FIG. 12A . Referring to  FIG. 12B , a bridge rectification circuit  172  and a smoothing capacitor  173  are built in the earphone  282 - 1 , and also parts to which power is supplied such as a charging circuit not shown are built in the earphone  282 - 1 . A conductor which forms the power reception coil  171  is built in the head band  283 , and if the left and right earphones  282 - 1  and  282 - 2  are brought into contact with each other by the magnets  281 , then the conductor built in the head band  283  is connected at contacts P 1  and P 2  thereof to configure the power reception coil  171  of one loop. 
       FIG. 12C  shows an electric configuration of the unit  104  built in the portable audio player  280  shown in  FIG. 12B . When the contact P 1  and the contact P 2  are connected to each other, the power reception coil  171  of one loop is configured as described above, and as a result, the power reception coil  171 , bridge rectification circuit  172  and smoothing capacitor  173  are electrically connected to each other. Accordingly, power transmitted from the unit  103  is provided to those parts of the portable audio player  280  such as the charging circuit which require power through the unit  104 . 
     It is to be noted that, although it is possible to fold back the conductor in the head band  283  to configure a coil, the directions flowing in the two folded back conductor portions are opposite to each other. As a result, no current flows after all and no power is obtained. In other words, the power reception coil  171  does not operate. Accordingly, it is preferable to use the contact P 1  and the contact P 2  to connect the conductor in the head band  283  to configure the power reception coil  171  as shown in  FIGS. 12A to 12C . 
     If the portable audio player  280  having such a configuration as described above is placed on an upper face of the unit  103  in a state wherein the left and right earphones  282 - 1  and  282 - 2  are coupled to each other by the magnets  281 , then power from the unit  103  is supplied to the portable audio player  280 . In other words, where the portable audio player  280  requires charging or power, only it is necessary for the user to couple the left and right earphones  282 - 1  and  282 - 2  to each other by means of the magnets  281  and place the portable audio player  280  on the upper face of the unit  103 . 
       FIG. 13  shows an example of a configuration of a portable telephone set to which the power transmission system  81  of the present invention is applied. 
     Referring to  FIG. 13 , in the example shown, the units  101  to  103  not shown from among the units  101  to  104  which configure the power transmission system  81  are accommodated in respective housings for exclusive use. The unit  104  is incorporated in the portable telephone set  291 . The bridge rectification circuit  172  and the smoothing capacitor  173  of the unit  104  are accommodated in a housing of the portable telephone set  291  while the power reception coil  171  of one turn of the unit  104  is accommodated in a strap  291 A of the portable telephone set  291 . 
     If such a portable telephone set  291  as described above is placed on the upper face of the unit  103 , then power from the unit  103  is supplied to the portable telephone set  291 . In other words, it is only necessary for the user to place, when the portable telephone set  291  requires charging or power, the portable telephone set  291  on the upper face of the unit  103 . 
       FIG. 14  shows an example of a configuration of a portable audio player to which the power transmission system  81  of the present invention is applied. 
     Referring to  FIG. 14 , in the example shown, the units  101  to  103  not shown from among the units  101  to  104  which configure the power transmission system  81  are accommodated in respective housings for exclusive use. The unit  104  is incorporated in the portable audio player  295 . The bridge rectification circuit  172  and the smoothing capacitor  173  of the unit  104  are accommodated in a housing of the portable audio player  295  while the power reception coil  171  of one turn of the unit  104  is accommodated in a strap  295 A of the portable audio player  295 . 
     If such a portable audio player  295  as described above is placed on the upper face of the unit  104 , then power from the unit  103  is supplied to the portable audio player  295 . In other words, when the portable audio player  295  requires charting or power, it is necessary for the user only to place the portable audio player  295  on the upper face of the unit  103 . 
     It is to be noted that the small-sized apparatus to which the power transmission system  81  of the present invention can be applied is any small-sized apparatus which requires power and is not particularly limited to the small-sized apparatus of the examples described above. For example, though not shown, it is possible to incorporate the unit  104  in a wristwatch of the electronic type and dispose the power reception coil  171  on the band of the wristwatch such that the power transmission system of the present invention is adopted as a power supply for the wristwatch. 
     In the foregoing, several particular examples of the power transmission system  81  of the present invention are described paying attention to the unit  104 . Now, particular examples of the power transmission system  81  of the present invention are described paying attention to the unit  103 . 
     As described hereinabove, even if the arrangement relationship of the power reception side resonance circuit  151  of the unit  103  and the power reception coil  171  of the unit  104  varies by approximately several cm, the power transmission system  81  of the present invention can transmit power. However, the transmission efficiency varies in response to the relative arrangement relationship of the power reception side resonance circuit  151  and the power reception coil  171 . Accordingly, the housing of the unit  103  preferably has a shape with which the arrangement relationship of the power reception side resonance circuit  151  and the power reception coil  171  is minimized when the unit  104  is placed on the housing of the unit  103 . 
       FIGS. 15A and 15B  show an example of a configuration of the housing of the unit  103 . In particular,  FIG. 15A  shows a perspective view of the housing and  FIG. 15B  shows a side elevational sectional view of the housing. 
     Referring to  FIGS. 15A and 15B , the upper face of the housing of the unit  103 , that is, the face of the housing on which the unit  104  is to be placed, has unevenness formed thereon by providing a gradient around the coil  151 L of the reception side resonance circuit  151  built in the unit  103 . 
     In particular, a recess  103 B is formed at a portion of the upper face of the housing around the coil  151 L which configures the built-in power reception side resonance circuit  151 . Accordingly, when the user places the headphone  182  in which the unit  104  is built on the upper face of the unit  103 , even if the headphone  182  is placed at a central portion of the upper face, the headphone  182  drops along the gradient  103 C formed on the upper face of the unit  103  until it is disposed in the recess  103 B. In particular, when the headphone  182  is disposed in the recess  103 B, the power reception side resonance circuit  151  and the power reception coil  171  are positioned in the proximity of each other, and an optimum relative arrangement relationship is established between them. As a result, the transmission efficiency of the power transmission system  81  is improved. 
     It is to be noted that, while, in the example of  FIGS. 15A and 15B , the recess  103 B is formed on the inner side of the loop of the coil  151 L which configures the power reception side resonance circuit  151  from within the upper face of the unit  103 , the formation of the recess  103 B is not limited to this. For example, the recess  103 B may be formed on the outer side of the loop of the coil  151 L which configures the power reception side resonance circuit  151 . 
     The power transmission system  81  of the first embodiment of the present invention has been described as above. 
     Incidentally, the power transmission system  81  of the present invention applies a magnetic field resonance type power transmission technique. In the power transmission system  81  according to the first embodiment described above, the resonance frequencies f 131  and f 151  are ideally 13.56 MHz of the ISM band. In this instance, the attenuation amount is 0 and the transmission efficiency is highest where the resonance frequency f 121  of the oscillation circuit  121  of the power transmission apparatus  91  is 13.56 MHz equal to the resonance frequencies f 131  and f 151  as seen from  FIG. 2 . In another embodiment, the resonance frequencies f 131  and f 151  are 120 kHz of the ISM band. 
     However, even if the resonance frequency f 121  is displaced only by such a small amount as approximately 0.5 MHz from 13.56 MHz of the resonance frequencies f 131  and f 151  as seen in  FIG. 2 , the transmission efficiency drops by a great amount of approximately 20 dB. This signifies that, where the resonance frequency f 121  is fixed to 13.56 MHz, if a metal article or a man approaches the resonance circuit to vary the stray capacitance, resulting in variation of the resonance frequencies f 131  and f 151 , then the transmission efficiency drops significantly. The resonance frequencies f 131  and f 151  of the power transmission side resonance circuit  131  and the power reception side resonance circuit  151  having high Q values are generally likely to be influenced by a neighboring metal article or man, the temperature, the humidity and so forth. 
     Further, the power transmission side resonance circuit  131  and the power reception side resonance circuit  151  are designed such that the resonance frequencies f 131  and f 151  thereof ideally coincide with the resonance frequency f 121  as described hereinabove. However, it is difficult to produce, by mass production, the power transmission side resonance circuit  131  and the power reception side resonance circuit  151  whose resonance frequencies f 131  and f 151  coincide with a high degree of accuracy with the resonance frequency f 121 . 
     From the foregoing, the resonance frequencies f 131  and f 151  during use of the power transmission side resonance circuit  131  and the power reception side resonance circuit  151  are sometimes different from the resonance frequency f 121 . In such an instance, the transmission efficiency deteriorates. 
     Therefore, in the power transmission system  81  according to the second embodiment of the present invention, a technique of varying the resonance frequencies so as to coincide with the oscillation frequency in response to an environment therearound is applied. It is to be noted that such a technique as just described is hereinafter referred to as resonance frequency variation technique. 
       FIG. 16  shows a configuration of the power transmission system of the second embodiment of the present invention. 
     Referring to  FIG. 16 , the power transmission system  301  includes several common components to those of the power transmission system described hereinabove with reference to  FIG. 3 . Overlapping description of such common components is omitted herein to avoid redundancy. 
     The power transmission system  301  shown includes a power transmission apparatus  491  and a power reception apparatus  492 . The power transmission apparatus  491  and the power reception apparatus  492  are disposed physically separately from each other in a spaced distance from each other by a distance L. 
     The power transmission apparatus  491  is configured from a unit  501  having a single housing and another unit  502  having a single housing. The unit  501  and the unit  502  can be physically separated from each other, and where power is to be transmitted to the power reception apparatus  492 , the unit  501  and the unit  502  are disposed in contact with each other or in a spaced relationship from each other by a distance of, for example, approximately several cm. 
     The unit  501  has a configuration similar to that of the unit  101  described hereinabove with reference to  FIG. 3 . In particular, the unit  501  is configured from an oscillation circuit  121  and a power transmission coil  122  connected to the oscillation circuit  121 . 
     A power transmission side resonance circuit  621  is provided in the unit  502 . The power transmission side resonance circuit  621  includes the power transmission side resonance circuit  131  described hereinabove with reference to  FIG. 3  and a series circuit of a varicap element  641  and a capacitor  642  connected in parallel to the power transmission side resonance circuit  131 . 
     If the capacitance value of the varicap element  641  is represented by Cvs and the capacitance value of the capacitor  642  is represented by Ccs, then the resonance frequency f 621  of the power transmission side resonance circuit  621  is represented by the following expression (4): 
     
       
         
           
             
               
                 
                   
                     f 
                     621 
                   
                   = 
                   
                     1 
                     
                       2 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       π 
                       ⁢ 
                       
                         
                           Ls 
                           ⁡ 
                           
                             ( 
                             
                               Cs 
                               + 
                               
                                 CvsCcs 
                                 
                                   Cvs 
                                   + 
                                   Ccs 
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     In the expression (4), the capacitance value Ccs of the capacitor  642  is a predetermined value while the capacitance value Cvs of the varicap element  641  is a variable value. The varicap element  641  is a device also called varactor diode or variable capacitance diode and has a characteristic that, as the application voltage increases, the capacitance value Cvs thereof decreases. 
     In particular, the application voltage to the varicap element  641  is varied to vary the capacitance value Cvs of the varicap element  641 , and as a result, the resonance frequency f 621  of the power transmission side resonance circuit  621  can be varied thereby. Accordingly, it is possible to suppress a drop of the transmission efficiency, that is, to transmit power stably in a contactless condition, by varying the resonance frequency f 621  of the power transmission side resonance circuit  621  so as to coincide with the resonance frequency f 121 . 
     In order to vary the resonance frequency f 621  of the power transmission side resonance circuit  621  so as to coincide with the resonance frequency f 121 , it is preferable to carry out appropriate control of the capacitance value Cvs of the varicap element  641 , that is, to carry out appropriate control of the application voltage to the varicap element  641 . Therefore, in order to implement such control (hereinafter referred to as transmission side resonance frequency variation control), the power transmission apparatus  491  further includes an antenna  622 , a reception circuit  623  and a D/A conversion circuit  624 . 
     The reception circuit  623  as control means receives control data transmitted thereto by wireless from the power reception apparatus  492  through the antenna  622 . Although details are hereinafter described, the control data includes a changing instruction of the application voltage to the varicap element  641  and so forth. 
     Thus, the reception circuit  623  generates an instruction in the form of digital data of an application voltage to the varicap element  641  and supplies the instruction to the D/A conversion circuit  624 . The D/A conversion circuit  624  varies the application voltage to the varicap element  641  in accordance with the instruction from the reception circuit  623 . In particular, the D/A conversion circuit  624  applies an analog voltage corresponding to the digital data or instruction from the reception circuit  623  to the varicap element  641 . 
     Consequently, the capacitance value Cvs of the varicap element  641  varies, and as a result, the resonance frequency f 621  of the power transmission side resonance circuit  621  varies. 
     In this manner, the transmission side resonance frequency variation control is executed based on the control data transmitted from the power reception apparatus  492 . It is to be noted that details of the transmission side resonance frequency variation control are hereinafter described with reference to  FIG. 17 . 
     The circuits for implementing such transmission side resonance frequency variation control as just described, that is, the reception circuit  623  and the D/A conversion circuit  624 , are an example of parts which require power. Accordingly, in order to supply power to the reception circuit  623  and the D/A conversion circuit  624 , a unit power supply circuit  132  having a configuration similar to that of the unit  102  described hereinabove with reference to  FIG. 3  is provided in the unit  502 . 
     The power reception apparatus  492  is configured from a unit  503  having a single housing and another unit  504  having a single housing. The unit  503  and the unit  504  can be physically separated from each other, and when power from the power transmission apparatus  491  is to be received, the unit  503  and the unit  504  are disposed in a contacting relationship with each other or in a spaced relationship from each other by a distance of, for example, approximately several cm. 
     The unit  503  includes a power reception side resonance circuit  661  and further includes a unit power supply circuit  152  having a configuration similar to that of the unit  103  described hereinabove with reference to  FIG. 3 . The power reception side resonance circuit  661  includes the power reception side resonance circuit  151  described hereinabove with reference to  FIG. 3  and a series circuit of a varicap  681  and a capacitor  682  connected in parallel. 
     If the capacitance value of the varicap  681  is represented by Cvr and the capacitance value of the capacitor  682  is represented by Ccr, then the resonance frequency f 661  of the power reception side resonance circuit  661  is represented by the following expression (5): 
     
       
         
           
             
               
                 
                   
                     f 
                     661 
                   
                   = 
                   
                     1 
                     
                       2 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       π 
                       ⁢ 
                       
                         
                           Lr 
                           ⁡ 
                           
                             ( 
                             
                               Cr 
                               + 
                               
                                 CvrCcr 
                                 
                                   Cvr 
                                   + 
                                   Ccr 
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     In the expression (5), the capacitance value Ccr of the capacitor  682  is a predetermined value while the capacitance value Cvr of the varicap  681  is a variable value from a similar reason to that described hereinabove with regard to the expression (4) given hereinabove. 
     The capacitance value Cvr of the varicap  681  varies by varying the application voltage to the varicap  681 , and as a result, the resonance frequency f 661  of the power reception side resonance circuit  661  can be varied thereby. Consequently, it is possible to suppress deterioration of the transmission efficiency, that is, to transmit the power stably in a contactless condition, by varying the resonance frequency f 661  of the power reception side resonance circuit  661  so as to coincide with the resonance frequency f 121 . 
     In other words, in order to vary the resonance frequency f 661  of the power reception side resonance circuit  661  so as to coincide with the resonance frequency f 121 , it is preferable to carry out appropriate control of the capacitance value Cvr of the varicap  681 , that is, to carry out appropriate control of the application voltage to the varicap  681 . Therefore, in order to implement such control (hereinafter referred to as reception side resonance frequency variation control), the power reception apparatus  492  further includes an A/D conversion circuit  662 , a microcomputer  663  and a D/A conversion circuit  664 . 
     The A/D conversion circuit  662  converts an analog voltage across the smoothing capacitor  163  into an output voltage value V in the form of digital data and supplies the output voltage value V to the microcomputer  663 . 
     The microcomputer  663  controls operation of the entire unit  503 . 
     For example, the microcomputer  663  generates an instruction or digital data of an application voltage to the varicap  681  on the reception side based on the output voltage value V of the A/D conversion circuit  662  and supplies the instruction to the D/A conversion circuit  664 . 
     The D/A conversion circuit  664  varies the application voltage to the varicap  681  in accordance with the instruction from the microcomputer  663 . The D/A conversion circuit  664  applies an analog voltage corresponding to the digital data or instruction from the microcomputer  663  to the varicap  681 . 
     Consequently, the capacitance value Cvr of the varicap  681  is changed, and as a result, the resonance frequency f 661  of the power reception side resonance circuit  661  varies. 
     In this manner, the reception side resonance frequency variation control is executed based on the output voltage value V of the A/D conversion circuit  662 . It is to be noted that the reception side resonance frequency variation control is hereinafter described in detail with reference to  FIG. 17 . 
     Further, for example, the microcomputer  663  generates control data including a changing instruction of the application voltage to the varicap element  641  on the transmission side based on the output voltage value of the A/D conversion circuit  662 . 
     The control data is used for the transmission side resonance frequency variation control as described hereinabove. The control data need be transferred to the power transmission apparatus  491 . To this end, the power reception apparatus  492  further includes a transmission circuit  665  and an antenna  666 . 
     In particular, the control data generated by the microcomputer  663  is supplied to the transmission circuit  665  serving as control means. The transmission circuit  665  transmits the control data from the microcomputer  663  by wireless to the power transmission apparatus  491  through the antenna  666 . Consequently, as described hereinabove, the power transmission apparatus  491  uses the control data to vary the application voltage to the varicap element  641  on the transmission side. Thus, the capacitance value Cs is changed, and as a result, the resonance frequency f 621  of the power transmission side resonance circuit  621  varies. The transmission side resonance frequency variation control is executed in this manner. It is to be noted that further details of the transmission side resonance frequency variation control are hereinafter described with reference to  FIG. 17 . 
     The circuitry for implementing such transmission side resonance frequency variation control and reception side resonance frequency variation control as described above, that is, the A/D conversion circuit  662 , microcomputer  663 , D/A conversion circuit  664  and transmission circuit  665 , are an example of parts which require power. Accordingly, the unit power supply circuit  152  supplies power to the parts mentioned. 
     The unit  504  has a configuration similar to that of the unit  104  described hereinabove with reference to  FIG. 3 . In particular, the unit  504  includes a power reception coil  171 , a bridge rectification circuit  172  and a smoothing capacitor  173 . 
     [Example of Operation of the Power Transmission System of the Second Embodiment] 
     Now, an example of operation of the power transmission system  301  having the configuration described above with reference to  FIG. 16  is described. 
     It is to be noted, however, that, from within operation of the power transmission system  301 , operation itself of power transmission from the power transmission apparatus  491  to the power reception apparatus  492  is basically similar to that of the power transmission system  81  described hereinabove with reference to  FIG. 3 . Therefore, overlapping description the power transmission operation is omitted herein to avoid redundancy. 
     Therefore, of the operation of the power transmission system  301 , a process of implementing the reception side resonance frequency variation control and the transmission side resonance frequency variation control is described below. It is to be noted that the process is hereinafter referred to as resonance frequency controlling process. 
     The power supplied from the power transmission apparatus  491  to the power reception apparatus  492  is hereinafter referred to as reception power. Where the reception power is represented by P, the reception power P is represented by the following expression (6): 
                   P   =       V   2     R             (   6   )               
where R is the resistance value of a load to the power reception apparatus  492 .
 
     Here, the transmission side resonance frequency variation control and the reception side resonance frequency variation control are controls for varying the resonance frequencies f 621  and f 661  so as to coincide with the resonance frequency f 121 . Since the transmission efficiency is highest when the resonance frequencies f 621  and f 661  coincide with the resonance frequency f 121  as described hereinabove with reference to  FIG. 2 , the reception power P is in the maximum. In particular, control for varying the resonance frequencies f 621  and f 661  so that the reception power P may be maximized should be adopted as the transmission side resonance frequency variation control and the reception side resonance frequency variation control. More particularly, if the load is a fixed load, then the resistance value R of the load is fixed, and the reception power P increases in proportion to the square of the output voltage value V as given by the expression (6) given hereinabove. Accordingly, the control for varying the resonance frequencies f 621  and f 661  so as to maximize the output voltage value V should be adopted as the reception side resonance frequency variation control. An example of a resonance frequency controlling process for implementing such reception side resonance frequency variation control and transmission side resonance frequency variation control is illustrated in  FIG. 17 . 
     Referring to  FIG. 17 , first at step S 11 , the microcomputer  663  increments the instruction of the application voltage to the varicap  681  on the reception side one by one step and measures the output voltage value V for each voltage step. 
     At step S 12 , the microcomputer  663  sets an instruction when the output voltage value V becomes highest as an optimum instruction for the varicap  681  on the reception side. 
     Thereafter, the microcomputer  663  continues to output the optimum instruction in the form of digital data to the D/A conversion circuit  664 . Consequently, the resonance frequency f 661  of the power reception side resonance circuit  661  soon becomes equal to the frequency with which the output voltage value V becomes highest, that is, to a frequency substantially coincident with the resonance frequency f 121 . 
     More particularly, for example, if the application voltage to the varicap  681  rises, then the capacitance value Cvr of the varicap  681  decreases as described hereinabove, and the resonance frequency f 661  of the power reception side resonance circuit  661  increases as indicated by the expression (5) given hereinabove. On the contrary, if the application voltage to the varicap  681  drops, then the capacitance value Cvr of the varicap  681  increases as described hereinabove, and the resonance frequency f 661  of the power reception side resonance circuit  661  decreases as indicated by the expression (5) given hereinabove. 
     Accordingly, in order to make the resonance frequency f 661  of the power reception side resonance circuit  661  substantially coincide with the resonance frequency f 121 , it is necessary to make it possible to adjust the resonance frequency f 661  in both of the increasing direction and the decreasing direction. In other words, it is necessary to make it possible to adjust the capacitance value Cvr of the varicap  681  not only in the increasing direction but also in the decreasing direction such that the capacitance value Cvr of the varicap  681  with which the reception power P is maximized falls in the variation range even when a metal article or a man approaches. Further, since the varicap  681  has some dispersion in characteristic, it is necessary to make such adjustment possible taking the dispersion into consideration. 
     In order to make such adjustment possible, preferably the resonance frequency f 681  in an ideal state in which any of a metal article and a man is not positioned in the neighborhood is equal to an object frequency, that is, an object resonance frequency f 121  when the capacitance value Cvr of the varicap  681  is equal to a middle capacitance value within the variation range. Therefore, for example, in the present embodiment, the inductance Lr of the coil of the power reception side resonance circuit  661  and the capacitance value Ccr of the capacitor  682  are adjusted so as to establish the state just described. 
     Accordingly, for example, in the present embodiment, when the instruction of an application voltage to the varicap  681  on the reception side is increased one by one step by the processing at step S 11 , the output voltage value V should naturally become the maximum value at a particular voltage step before the instruction of the highest voltage step is reached. For example, in an ideal state wherein any of a metal item and a man is not positioned in the neighborhood, the output voltage value V should naturally become the maximum value at a substantially middle voltage step within the variation range of the instruction of an application voltage to the varicap  681 . On the other hand, for example, in a state wherein a metal article or a man is positioned in the neighborhood, the output voltage value V should naturally become the maximum value at a voltage step displaced a little forwardly or backwardly of the middle step. 
     For example,  FIG. 18  illustrates a relationship between the application voltage to the varicap  681  on the reception side and the output voltage value V. 
     Referring to  FIG. 18 , the axis of ordinate indicates the output voltage value V, and the axis of abscissa indicates the application voltage to the varicap  681  on the reception side. 
     From the example of  FIG. 18 , it can be seen that the output voltage value V exhibits a mountain-shaped variation such that, when the application voltage to the varicap  681  on the reception side is approximately 10 V, the top of the mountain is exhibited, that is, the output voltage value V exhibits the maximum value. 
     Therefore, in the processing at step S 12 , the instruction or digital data when the output voltage value V exhibits a maximum value, in the example of  FIG. 18 , the instruction at a voltage step around approximately 10 V, is set as the optimum instruction for the varicap  681  on the reception side. 
     In this manner, the reception side resonance frequency variation control is implemented by the processing at steps S 11  and S 12 . 
     Then, the transmission side resonance frequency variation control is implemented by processing at steps beginning with step S 13 . 
     In particular, at step S 13 , the microcomputer  663  increments the instruction of the application voltage to the varicap element  641  on the transmission side one by one voltage step and outputs the output voltage value V for each voltage step. 
     In particular, for example, the microcomputer  663  generates control data including a changing instruction for incrementing the instruction of the application voltage to the varicap element  641  on the transmission side by one voltage step and so forth and transmits the control data by wireless to the power transmission apparatus  491  through the transmission circuit  665  and the antenna  666 . Then, the power transmission apparatus  491  increases the application voltage to the varicap  641  on the transmission side one by one step based on the control data as described above. Consequently, the capacitance value Cvs varies to vary the resonance frequency f 621  of the power transmission side resonance circuit  621 . As a result, the output voltage value V of the power reception apparatus  492  varies. Therefore, the microcomputer  663  measures the varied output voltage value V. As the processing at step S 13 , such a sequence of processes as just described are executed for each voltage step. 
     It is to be noted that, from a reason similar to that described hereinabove with regard to the varicap  681  on the reception side, preferably the resonance frequency f 621  in an ideal state in which any of a metal item and a man is not positioned closely is equal to an object frequency, that is, an object resonance frequency f 121  when the capacitance value Cvs of the varicap element  641  is equal to a middle capacitance value within the variation range. Therefore, for example, in the present embodiment, the inductance Ls of the coil of the power transmission side resonance circuit  621  and the capacitance value Ccs of the capacitor  642  are adjusted so as to establish the state just described. 
     At step S 14 , the microcomputer  663  sets the instruction when the output voltage value V becomes a maximum value as an optimum instruction for the varicap element  641  on the power transmission side. 
     In particular, for example, the microcomputer  663  generates control data including a setting command for an optimum instruction of the application voltage to the varicap element  641  on the transmission side and so forth and transmits the control data to the power transmission apparatus  491  through the transmission circuit  665  and the antenna  666 . 
     Consequently, the power transmission apparatus  491  continues to apply an application voltage in accordance with the optimum instruction to the varicap element  641  on the transmission side. As a result, the resonance frequency f 621  of the power transmission side resonance circuit  621  soon becomes equal to a frequency with which the output voltage value V is maximized, that is, which substantially coincides with the resonance frequency f 121 . 
     In the power transmission system  301  of the second embodiment, the resonance frequency controlling process is executed in this manner. Consequently, the resonance frequencies are automatically controlled so that the reception power P exhibits a maximum value. As a result, power can be supplied stably from the power transmission apparatus  491  to the power reception apparatus  492 . 
     This does not vary even if the resonance frequency f 621  or f 661  disperses. In other words, in the power transmission system  301  of the second embodiment, since the resonance frequency controlling process is executed, a dispersion of the resonance frequencies f 621  and f 661  is permitted. As a result, where the power transmission system  301  of the second embodiment is compared with the power transmission system  81  of the first embodiment, it is facilitated to produce the power transmission system  301  of the second embodiment by mass production. In particular, since the power transmission system  81  of the first embodiment cannot execute the resonance frequency controlling process, a dispersion of the resonance frequency is not permitted. However, it is difficult to suppress a dispersion of the resonance frequency in production, and as a result, it is estimated that it may possibly be difficult to produce the power transmission system  81  of the first embodiment by mass production. This difficulty is eliminated by the power transmission system  301  of the second embodiment because a dispersion of the resonance frequencies f 621  and f 661  is permitted. 
     It is to be noted that the starting timing of the resonance frequency controlling process of  FIG. 17  is not restricted particularly. For example, as the starting timing, a timing at which the power reception apparatus  492  is energized can be adopted. Or, for example, a timing at which the output voltage value V drops, another timing at which a predetermined interval of time elapses, a further timing designated by the user or some other timing can be adopted as the starting timing. 
     Further, in the resonance frequency controlling process, two controls including the reception side resonance frequency variation control and the transmission side resonance frequency variation control are implemented. However, it is possible to carry out only one of the two controls. For example, where one of the power transmission side resonance circuit  621  and the power reception side resonance circuit  661  is disposed at a remote place which is not approached by a metal article or a man and is not influenced by them, only the other one of them may be controlled. 
     Further, from a point of view that the reception side resonance frequency variation control and the transmission side resonance frequency variation control are implemented, the controlling techniques may be any technique only if it can control the resonance frequency so that the reception power P may be maximized and are not restricted particularly to the technique described hereinabove. 
     For example, as a technique for varying the resonance frequency, that is, as the resonance frequency variation technique described hereinabove, a method of varying the application voltage to the varicap elements  641  and  681  is adopted. However, the resonance frequency variation technique is not restricted particularly to the example described hereinabove, but, for example, a technique of using a motor-driven variable capacitor or variable resistor other than a varicap element to vary the inductance L or the capacitance C of a resonance circuit can be adopted. Also, for example, a technique of displacing the core of a coil which configures a resonance circuit or changing the distance of a coil or electrically switching a tap of a coil to vary the inductance L can be adopted. 
     Also it is possible to change the oscillation frequency of the oscillation circuit  121  of the unit  501  in accordance with a signal from the transmission circuit  665 . In this instance, the antenna  622  and the reception circuit  623  are provided in the unit  501 . 
     Also the power transmission system  301  according to the embodiment of  FIG. 16  can naturally be applied to the configuration shown in  FIGS. 4 to 15B . 
     [Application of the Invention to a Program] 
     While the series of processes described above can be executed by hardware, it may otherwise be executed by software. 
     In this instance, for example, a personal computer shown in  FIG. 19  may be used at least as part of the image processing apparatus described hereinabove. 
     Referring to  FIG. 19 , a central processing unit (CPU)  801  executes various processes in accordance with a program stored in a ROM (Read Only Memory)  802 . Further, the CPU  801  executes various processes in accordance with a program loaded from a storage section  808  into a RAM (Random Access Memory)  803 . Also data necessary for the CPU  801  to execute the processes are suitably stored into the RAM  803 . 
     The CPU  801 , ROM  802  and RAM  803  are connected to one another by a bus  804 . Also an input/output interface  805  is connected to the bus  804 . 
     An inputting section  806  including a keyboard, a mouse and so forth and an outputting section  807  including a display unit are connected to the input/output interface  805 . Further, a storage section  808  formed from a hard disk or the like and a communication section  809  including a modem, a terminal adapter and so forth are connected to the input/output interface  805 . The communication section  809  controls communication carried out with another apparatus not shown through a network including the Internet. 
     Further, as occasion demands, a drive  810  is connected to the input/output interface  805 . A removable medium  811  formed from a magnetic disk, an optical disk, a magneto-optical disk, a semiconductor memory or the like is suitably loaded into the drive  810 . Thus, a computer program read from the loaded medium is installed into the storage section  808  as occasion demands. 
     Where the series of processes is executed by software, a program which constructs the software is installed from a network or a recording medium into a computer incorporated in hardware for exclusive use or, for example, a personal computer for universal use which can execute various functions by installing various programs. 
     The recording medium which includes such a program as described above may be formed as the removable medium  811  which is a package medium and includes a magnetic disk including a floppy disk, an optical disc including a CD-ROM (Compact Disc-Read Only Memory) and a DVD (Digital Versatile Disc), or a magneto-optical disc including an MD (MiniDisc), or a semiconductor memory, which has the program recorded thereon or therein and is distributed to provide the program to a user separately from an apparatus main frame. Else, the recording medium is formed as the ROM  802  or a hard disk or the like included in the storage section  808 , in which the program is recorded and which is provided to a user in a state wherein the ROM  802  or the hard disk is incorporated in advance in the apparatus main frame. 
     It is to be noted that, in the present specification, the steps which describe the program recorded in a recording medium may be but need not necessarily be processed in a time series in the order as described, and include processes which are executed in parallel or individually without being processed in a time series. 
     The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2009-231673 filed in the Japan Patent Office on Oct. 5, 2009, the entire content of which is hereby incorporated by reference. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factor in so far as they are within the scope of the appended claims or the equivalents thereof.