Abstract:
A power receiving apparatus includes: a resonance element having a specific resonance frequency and adapted to couple in a non-contacting relationship to a different resonance element through a resonance relationship; a rectification section configured to rectify ac current of the resonance frequency in response to energy received by the resonance element; and a switching section configured to cut off a supplying path of the ac current from the resonance element to the rectification section; the resonance element maintaining the coupling state through the resonance relationship to the different resonance element also when the supplying path of the ac current to the rectification section is blocked by the switching section.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to an apparatus and a method for transmitting power by radio utilizing resonance of an electromagnetic field. 
         [0003]    2. Description of the Related Art 
         [0004]    As a technique for transmitting power by radio, a technique is well known which utilizes electromagnetic induction. In the power transmission which utilizes electromagnetic induction, current is supplied to one of two coils positioned closely to each other such that electromagnetic force is generated in the other coil by intermediation of magnetic fluxes generated from the one coil. 
         [0005]    However, according to the power transmission which utilizes the electromagnetic induction, the two coils must be positioned closely to each other. Therefore, the power transmission has a problem that the distance over which the power can be transmitted is restricted. Further, if the axes of the coils upon electromagnetic induction coupling are brought out of alignment with each other, then the transmission efficiency is degraded. Therefore, the alignment upon coupling is significant. 
         [0006]    In the meantime, a method wherein resonance of an electromagnetic field is utilized to transmit power has been proposed recently. According to the resonance type radio power transmission, power can be transmitted over such a distance as three to four meters and besides high power can be transmitted. Therefore, resonance type radio power transmission has an advantage that also a system which does not have a secondary cell, that is, a rechargeable battery, on the reception side can be constructed readily. 
         [0007]    Further, the resonance type radio power transmission has little influence on any other electronic apparatus because energy is not transmitted if it has no resonating mechanism. Further, there is an advantage also in that, even if the alignment upon coupling is not very good, the transmission efficiency does not drop very much. 
         [0008]    A power transmission system which uses a resonance phenomenon in a magnetic field is disclosed, for example, in U.S. Published Patent Application No. 2007/0222542 (hereinafter referred to as Patent Document 1). 
         [0009]    An example of a configuration of the power transmission system which uses a magnetic field resonance phenomenon is shown in  FIG. 9 .  FIG. 9  particularly shows an example of a system configuration where a power transmitting apparatus  10  of a supplying source of power and a power receiving apparatus  20  of a supplying destination or receiving side of power are provided in a one-by-one corresponding relationship to each other. 
         [0010]    Referring to  FIG. 9 , the power transmitting apparatus  10  includes a resonance element  11 , an excitation element  12  and a frequency signal generation section  13 . 
         [0011]    The resonance element  11  is formed, for example, from an air-core coil in the form of a loop coil. The excitation element  12  is formed, for example, from an air-core coil, which is connected at the opposite ends thereof to two output terminals of the frequency signal generation section  13 . The resonance element  11  and the excitation element  12  are placed in a relationship wherein they are coupled strongly with each other by electromagnetic induction. 
         [0012]    The air-core coil which forms the resonance element  11  has not only inductance but also coil internal capacitance and has a self resonance frequency which depends upon the inductance and the capacitance. 
         [0013]    The frequency signal generation section  13  generates a frequency signal of a frequency equal to the self resonance frequency of the resonance element  11 . The frequency signal generation section  13  may be formed from a Colpitts type oscillation circuit, a Hartley type oscillation circuit or the like. 
         [0014]    Though not shown, the power transmitting apparatus  10  receives supply of power from an ac power supply so that a frequency signal is generated from the frequency signal generation section  13 . 
         [0015]    Meanwhile, the power receiving apparatus  20  include a resonance element  21 , an excitation element  22 , a rectification circuit  23  and a load  24 . 
         [0016]    The resonance element  21  is formed, for example, from an air-core coil in the form of a loop coil similarly to the resonance element  11 . The excitation element  22  is formed, for example, from an air-core coil, which is connected at the opposite ends thereof to two input terminals of the rectification circuit  23 . The resonance element  21  and the excitation element  22  are configured so as to have a relationship wherein they are coupled strongly to each other by electromagnetic induction. 
         [0017]    The air-core coil which forms the resonance element  21  has not only inductance but also coil internal capacitance and has a self resonance frequency which depends upon the inductance and the capacitance similarly as in the resonance element  11 . 
         [0018]    The self resonance frequencies of the resonance element  11  and the resonance element  21  are equal to each other and a frequency fo. 
         [0019]    In such a system configuration as described above, the frequency signal generation section  13  in the power transmitting apparatus  10  supplies a frequency signal equal to the self resonance frequency fo of the resonance elements  11  and  21  to the excitation element  12 . 
         [0020]    Accordingly, ac current of the frequency fo flows to the air-core coil of the excitation element  12 , and induction current of the same frequency fo is induced in the resonance element  11  formed similarly from an air-core coil by electromagnetic induction. 
         [0021]    In the circuit configuration of  FIG. 9 , the self resonance frequency of the air-core coil which forms the resonance element  21  of the power receiving apparatus  20  is the frequency fo and coincides with the self resonance frequency of the resonance element  11  of the power transmitting apparatus  10 . Accordingly, the resonance element  11  of the power transmitting apparatus  10  and the resonance element  21  of the power receiving apparatus  20  have a magnetic field resonance relationship and exhibit a maximum coupling amount and minimum loss at the frequency fo. 
         [0022]    Since the resonance element  11  of the power transmitting apparatus  10  and the resonance element  21  of the power receiving apparatus  20  in the present circuit configuration have a magnetic field resonance relationship as described above, ac current is supplied in a contactless fashion from the resonance element  11  to the resonance element  21  at the resonance frequency fo. 
         [0023]    In the power receiving apparatus  20 , induction current is induced in the excitation element  22  by electromagnetic induction by ac current appearing in the resonance element  21 . The induction current induced in the excitation element  22  is rectified into dc current by the rectification circuit  23  and supplied as power supply current to the load  24 . 
         [0024]    In this manner, a magnetic field resonance phenomenon is utilized to transmit power by radio from the power transmitting apparatus  10  to the power receiving apparatus  20 . 
         [0025]    A relationship between the frequency of the frequency signal from the frequency signal generation section  13  in the power transmission system of the configuration shown in  FIG. 9  and the coupling amount in magnetic field resonance is illustrated in  FIG. 10 . As can be seen apparently from  FIG. 10 , the power transmission system of the configuration of  FIG. 9  indicates frequency selectivity wherein a maximum coupling amount is obtained at the resonance frequency fo. 
         [0026]      FIG. 11  illustrates a relationship between the distance D between the resonance element  11  of the power transmitting apparatus  10  and the resonance element  21  of the power receiving apparatus  20  and the coupling amount in magnetic field resonance. From  FIG. 11 , it can be recognized that, although the coupling amount increases as the distance decreases, where the distance is very short, the coupling amount is rather low. Thus, it can be recognized that a certain distance exists at which the coupling amount is maximum at a certain resonance frequency. 
         [0027]      FIG. 12  illustrates a relationship between the resonance frequency and the distance between resonance elements at which a maximum coupling amount is obtained. From  FIG. 12 , it can be seen that a maximum coupling amount is obtained if, where the resonance frequency is low, the distance between the resonance elements is increased, but where the resonance frequency is high, the distance between the resonance elements is decreased. 
       SUMMARY OF THE INVENTION 
       [0028]    As described above, in the power transmission system of the resonance type, even if the distance between the power transmitting apparatus and the power receiving apparatus is comparatively great or even if the coupling axes are somewhat out of alignment with each other, power transmission can be carried out. 
         [0029]    Therefore, it is possible to transmit power from a single power transmitting apparatus  10  of a power supplying source to a plurality of power supplying destinations as seen in  FIG. 13 , which illustrates that power is transmitted to two power receiving apparatus  20 A and  20 B as power supplying designations. It is to be noted that the power receiving apparatus  20 A and  20 B have a configuration quite same as that of the power receiving apparatus  20  described hereinabove and include like components which are indicated by like reference symbols with suffixes A and B added thereto, respectively. 
         [0030]    It is assumed here that the self resonance frequency of the resonance element  11  of the power transmitting apparatus  10  and the self resonance frequency of resonance elements  21 A and  21 B of the two power receiving apparatus  20 A and  20 B are equal to each other. 
         [0031]    Since the coupling amount between a power supplying source and a power supplying destination increases as the distance between the resonance elements decreases, in the example shown in  FIG. 13 , the power receiving apparatus  20 B has a coupling amount greater than that of the power receiving apparatus  20 A to the power transmitting apparatus  10 . 
         [0032]    Since power to be supplied from the power supplying source to the power supplying destination increases as the distance between the resonance elements increases, the power supplied from the power transmitting apparatus  10  is relatively higher to the power receiving apparatus  20 B than to the power receiving apparatus  20 A. 
         [0033]    Incidentally, apart from a case wherein it is necessary to render operative both of the power receiving apparatus  20 A and the power receiving apparatus  20 B and supply of dc current to loads is demanded, a case wherein there is no necessity to render one of the two apparatus operative matters. 
         [0034]    In particular, each of the power receiving apparatus described above is configured such that it normally receives power transmitted thereto by radio. Therefore, even where any of the power receiving apparatus does not demand reception of power, if the power receiving apparatus is positioned such that it can receive supply of power from the power transmitting apparatus  10 , then power is supplied to the power receiving apparatus uselessly and rectified by the rectification circuit  23  and then consumed. 
         [0035]    Thus, if a plurality of power receiving apparatus have a magnetic field resonance relationship with the power transmitting apparatus  10  as seen in  FIG. 13 , then electric energy from the power transmitting apparatus  10  is distributed and transmitted to the plural power receiving apparatus. Therefore, the power received by each of the power receiving apparatus decreases in response to the number of such power receiving apparatus, resulting in a problem that the power receiving apparatus which demands reception of power cannot receive sufficient power from the power transmitting apparatus. 
         [0036]    Particularly if the power receiving apparatus  20 B positioned nearer to the power transmitting apparatus  10  in  FIG. 13  need not operate and does not demand reception of power, the power to be supplied to the power receiving apparatus  20 A which demands reception of power decreases in a distribution relationship, which is not efficient. 
         [0037]    Therefore, it is desirable to provide an apparatus and a method which can eliminate such a problem as described above. 
         [0038]    According to the present embodiment, there is provided a power receiving apparatus including a resonance element having a specific resonance frequency and adapted to couple in a non-contacting relationship to a different resonance element through a resonance relationship, rectification means for rectifying ac current of the resonance frequency in response to energy received by the resonance element, and switching means for cutting off a supplying path of the ac current from the resonance element to the rectification means, the resonance element maintaining the coupling state through the resonance relationship to the different resonance element also when the supplying path of the ac current to the rectification means is blocked by the switching means. 
         [0039]    It is assumed that the power receiving apparatus is positioned such that it couples to the power transmitting apparatus through a resonance relationship and couples also to a different power receiving apparatus through a resonance relationship. In this instance, the resonance element of the power receiving apparatus couples to both of the resonance element provided in the power transmitting apparatus and the resonance element of the different power receiving apparatus through a resonance relationship. 
         [0040]    When the power receiving apparatus having the configuration described above need not receive supply of power, the supplying path of ac current from the resonance element to the rectification means is cut off by the switching means. 
         [0041]    However, at this time, the resonance element of the power receiving apparatus is kept in the state wherein it couples to the different resonance element through a resonance relationship. Accordingly, in the power receiving apparatus, the power which the resonance element receives from the power transmitting apparatus is transferred to the resonance element of the difference power receiving apparatus which is kept coupled to the resonance element through a resonance relationship while supply of current to the rectification means is cut off by the switching means. 
         [0042]    Thus, the resonance element of the power receiving apparatus in which the supplying path of ac current from the resonance element to the rectification means is cut off plays a role of repeating means for repeating power from the power transmitting apparatus to the different power receiving apparatus. 
         [0043]    In this instance, the different power receiving apparatus receives supply of power transmitted through the coupling through a direct resonance relationship with the power transmitting apparatus and besides receives reception of power through the coupling through a resonance relationship with the power receiving apparatus. Consequently, the power supply amount to the different power receiving apparatus increases. 
         [0044]    Consequently, with the power receiving apparatus, power transmitted thereto through the coupling through a resonance relationship from the power transmitting apparatus can be repeated so as to be transmitted to the different power receiving apparatus without consuming the power wastefully. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0045]      FIG. 1  is a diagrammatic view showing an example of a configuration of a power receiving apparatus according to an embodiment of the present invention; 
           [0046]      FIG. 2  is a diagrammatic view showing an example of a power transmission system which includes the power receiving apparatus of  FIG. 1 ; 
           [0047]      FIG. 3  is a diagrammatic view showing an example of a configuration of a power receiving apparatus according to another embodiment of the present invention; 
           [0048]      FIG. 4  is a flow chart illustrating processing operation of the power receiving apparatus of  FIG. 3 ; 
           [0049]      FIGS. 5A and 5B  are a diagrammatic view and a cross sectional view, respectively, showing an example of a charging system as a power transmission system according to a further embodiment of the present invention; 
           [0050]      FIG. 6  is a diagrammatic view showing an example of a configuration of a charging system as a power transmission system according to a still further embodiment of the present invention; 
           [0051]      FIG. 7  is a flow chart illustrating an example of processing operation of a power transmitting apparatus in the charging system of  FIG. 6 ; 
           [0052]      FIG. 8  is a flow chart illustrating an example of processing operation of a power receiving apparatus in the charging system of  FIG. 6 ; 
           [0053]      FIG. 9  is a diagrammatic view showing an example of a configuration of a power transmission system of the magnetic field resonance type; 
           [0054]      FIGS. 10 ,  11  and  12  are diagrams illustrating characteristics of the power transmission system of the magnetic field resonance type shown in  FIG. 9 ; and 
           [0055]      FIG. 13  is a diagrammatic view illustrating a problem of an existing power transmission system of the magnetic field resonance type shown in  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0056]    In the following, power receiving apparatus and power transmission systems including the power receiving apparatus according to preferred embodiments of the present invention are described with reference to the accompanying drawings. 
       Power Receiving Apparatus According to the First Embodiment 
       [0057]      FIG. 1  shows an example of a configuration of a power receiving apparatus according to a first embodiment of the present invention. Those parts shown in  FIG. 1  which are identical to those parts of the power receiving apparatus in the power transmission system shown in  FIG. 9  are denoted by identical reference symbols. 
         [0058]    Referring to  FIG. 1 , the power receiving apparatus  200  according to the first embodiment includes a resonance element  21 , an excitation element  22 , a rectification circuit  23 , a load  24 , and a power supply controlling switch  25  provided on a current path between the excitation element  22  and the rectification circuit  23 . 
         [0059]    The resonance element  21  is formed, for example, from an air-core coil in the form of a loop coil similarly to the resonance element  11 . 
         [0060]    The excitation element  22  is formed, for example, from an air-core coil, which is connected at a terminal thereof to one of input terminals of the rectification circuit  23 . The excitation element  22  is connected at the other terminal of the air-core coil thereof to the other one of the input terminals of the rectification circuit  23  through the power supply controlling switch  25 . 
         [0061]    The resonance element  21  and the excitation element  22  are configured so as to have a relationship in which they are coupled strongly to each other by electromagnetic induction. 
         [0062]    The air-core coil of the resonance element  21  has not only inductance but also coil internal capacitance and has a frequency fo which depends upon the inductance and the capacitance. As described hereinabove, the frequency fo of the resonance element  11  is equal to the self resonance frequency of the resonance element  11  of the power transmitting apparatus  10 . 
         [0063]    The power supply controlling switch  25  may be formed from a mechanical switch which is manually operated by a user or a relay switch or a semiconductor switch which switches on and off in response to a predetermined operation by a user. 
         [0064]    When the power supply controlling switch  25  is in an on or closed state, the resonance element  21  in the power receiving apparatus  200  is coupled to the resonance element  11  of the power transmitting apparatus  10  through a magnetic field resonance relationship therebetween, and similar operation to that described above is carried out. In particular, induction current is induced in the excitation element  22  by electromagnetic induction by ac current appearing in the resonance element  21 . The induction current induced in the excitation element  22  is rectified into dc current by the rectification circuit  23  and then supplied as power supply current to the load  24 . 
         [0065]    On the other hand, when the power supply controlling switch  25  is in an off or open state, no current flows through the excitation element  22 . Accordingly, even if the resonance element  11  of the power transmitting apparatus  10  and the resonance element  21  of the power receiving apparatus  200  are coupled to each other through the magnetic field resonance relationship therebetween and ac current flows through the resonance element  21 , no induction current flows through the excitation element  22 . 
         [0066]    In other words, when the power supply controlling switch  25  is off, supply of ac current from the resonance element  21  to the rectification circuit  23  is blocked. 
         [0067]    Accordingly, when the power supply controlling switch  25  is off, no dc current is supplied to the load  24  in the power receiving apparatus  200 , and no power is consumed in the power receiving apparatus  200 . 
         [0068]    However, the resonance element  21  of the power receiving apparatus  200  in which the power supply controlling switch  25  is off in this manner can be coupled to the resonance element of a different power receiving apparatus through a magnetic field resonance relationship. Then, if such a different power receiving apparatus as just mentioned exists, then ac magnetic field energy transmitted to the resonance element  21  of the power receiving apparatus  200  in which the power supply controlling switch  25  is off is sent to the resonance element of the different power receiving apparatus. 
         [0069]    In other words, the resonance element  21  of the power receiving apparatus  200  in which the power supply controlling switch  25  is off acts as a repeater which transmits ac magnetic field energy supplied thereto from the power transmitting apparatus  10  to the resonance element of the different power receiving apparatus. 
         [0070]    The state wherein the resonance element  21  acts as a repeater is described more particularly with reference to  FIG. 2  which shows a power transmission system according to an embodiment of the present invention. 
         [0071]    Referring to  FIG. 2 , in the power transmission system shown, while power is supplied from the power transmitting apparatus  10  of a power supplying source to a certain power receiving apparatus  200 A, there exists a different power receiving apparatus  200 B which can be coupled to the power transmitting apparatus  10  through a magnetic field resonance relationship. 
         [0072]    In the power transmission system of  FIG. 2 , the power receiving apparatus  200 A and  200 B have a configuration quite similar to that of the power receiving apparatus  200  described hereinabove and includes like components to those of the power receiving apparatus  200 . Such like components are denoted by like reference symbols with the suffixes A and B added thereto, respectively. 
         [0073]    In the power transmission system of  FIG. 2 , it is shown that the power receiving apparatus  200 B which need not receive supply of power is positioned nearer to the power transmitting apparatus  10  which serves as a power supplying source than the power receiving apparatus  200 A to which power is to be supplied and therefore has a coupling amount to the power transmitting apparatus  10  greater than that of the power receiving apparatus  200 A. 
         [0074]    Further, in the power transmission system of  FIG. 2 , the power receiving apparatus  200 A and the power receiving apparatus  200 B have such a positional relationship to each other that they are coupled to each other through a magnetic field resonance relationship. 
         [0075]    Further, in the power transmission system shown in  FIG. 2 , the power supply controlling switch  25 A of the power receiving apparatus  200 A is in an on or closed state in order that the power receiving apparatus  200 A may receive supply of power from the power transmitting apparatus  10  of a power supply source. Meanwhile, since the power receiving apparatus  200 B need not receive supply of power from the power transmitting apparatus  10 , the power supply controlling switch  25  is in an off or open state. 
         [0076]    Accordingly, between the power transmitting apparatus  10  and the power receiving apparatus  200 A, the resonance elements  11  and  21 A are coupled to each other through a magnetic field resonance relationship, and since the power supply controlling switch  25 A is on, induction current flows through the excitation element  22 A. The induction current induced in the excitation element  22 A is rectified into dc current by the rectification circuit  23 A and supplied as power supply current to the load  24  not shown in  FIG. 2 . 
         [0077]    In the meantime, between the power transmitting apparatus  10  and the power receiving apparatus  200 B, the resonance elements  11  and  21 B are coupled to each other through a magnetic field resonance relationship. Consequently, ac magnetic field energy from the power transmitting apparatus  10  is transmitted to the resonance element  21 B of the power receiving apparatus  200 B. However, in the power receiving apparatus  200 B, since the power supply controlling switch is in an off or open state, no induction current flows to the excitation element  22 B, and no current is supplied to the rectification circuit  23 B and no power is consumed. 
         [0078]    Here, the power receiving apparatus  200 A and the power receiving apparatus  200 B have such a positional relationship that they are coupled to each other through a magnetic field resonance relationship. Accordingly, ac magnetic field energy transmitted from the power transmitting apparatus  10  to the resonance element  21 B of the power receiving apparatus  200 B is sent to the resonance element  21 A of the power receiving apparatus  200 A. 
         [0079]    In other words, in the power transmission system of  FIG. 2 , part of the ac magnetic field energy sent out from the power transmitting apparatus  10  is sent to the resonance element  21 A of the power receiving apparatus  200 A through the resonance element  21 B of the power receiving apparatus  200 B. 
         [0080]    In the power transmission system of  FIG. 13 , ac magnetic field energy sent from the power transmitting apparatus  10  to the power receiving apparatus  20 B is consumed in the power receiving apparatus  20 B. However, in the power transmission system of  FIG. 2 , such ac magnetic field energy is not consumed but is sent to the power receiving apparatus  200 A through the power receiving apparatus  200 B. 
         [0081]    In this manner, the power receiving apparatus  200 A receives supply of power from the power transmitting apparatus  10  through coupling by a direct magnetic field resonance relationship and further receives supply of power through the power receiving apparatus  200 B. Accordingly, in the power transmission system of  FIG. 2 , the power receiving apparatus  200 A can receive all of the ac magnetic field energy sent out from the power transmitting apparatus  10 . Consequently, the power receiving apparatus  200 A can receive supply of power efficiently. 
         [0082]    It is to be noted that, since the power supply controlling switch  25 A in the power receiving apparatus  200 A which is to receive supply of power from the power transmitting apparatus  10  is in an on state as can be seen from  FIG. 2 , the power receiving apparatus  200 A may have the configuration of the power receiving apparatus  20  shown in  FIG. 9  which does not include the power supply controlling switch  25 . In particular, in the power transmission system of  FIG. 2 , all of the power receiving apparatus may not include the configuration of the power receiving apparatus  200  of the present embodiment. 
         [0083]    It is to be noted that, while, in the first embodiment described above, the power supply controlling switch  25  is a mechanical switch or a relay switch, the power supply controlling switch  25  may otherwise have a configuration of a semiconductor switch. In this instance, a controlling section formed, for example, from a microcomputer for receiving an operation input of a user is provided such that it controls the power supply controlling switch  25  to switch in response to an operation input of the user indicative of whether or not the power receiving apparatus should be rendered operative. In particular, if the user inputs an instruction operation for rendering the power receiving apparatus operative, then the control section controls the power supply controlling switch to an on state, but if the user inputs another instruction operation for rendering the power receiving apparatus inoperative, then the control section controls power supply controlling switch to an off state. 
       Power Receiving Apparatus of the Second Embodiment 
       [0084]    In the power receiving apparatus  200  of the first embodiment, the power supply controlling switch is controlled to switch only in response to an operation of the user. In contrast, in the power receiving apparatus of the second embodiment, the power supply controlling switch is automatically controlled to switch. 
         [0085]      FIG. 3  shows an example of a configuration of the power receiving apparatus  300  of the second embodiment. The power receiving apparatus  300  includes several common components to those of the power receiving apparatus  200  of the first embodiment, and overlapping description of the common components of the power receiving apparatus  200  is omitted herein to avoid redundancy. 
         [0086]    Referring to  FIG. 3 , the power receiving apparatus  300  shown includes a battery  301 B of the rechargeable type and further includes a charging circuit  301  for charging the rechargeable battery  301 B, a power supply switch  302 , a control section  303  and an operation section  304 . 
         [0087]    The power receiving apparatus  300  further includes a power supply controlling switch circuit  250  in place of the power supply controlling switch  25 . The power supply controlling switch circuit  250  is formed, for example, from a semiconductor switching element. 
         [0088]    In the present second embodiment, the power receiving apparatus  300  receives radio power transmitted from the power transmitting apparatus  10  and uses the radio power to charge the battery  301 B and then supplies power supply current to a load. 
         [0089]    The charging circuit  301  charges the battery  301 B with dc current from the rectification circuit  23  when the power supply controlling switch circuit  250  is on. In the power receiving apparatus  300 , the charging circuit  301  has a function of detecting that the battery  301 B is charged up and notifying the control section  303  of such charge up. 
         [0090]    The power supply switch  302  is interposed between an output terminal of the rectification circuit  23  and the load  24  and controlled between on and off in accordance with a switching signal from the control section  303 . Also this power supply switch  302  is formed, for example, from a semiconductor switching element. 
         [0091]    When the power supply controlling switch circuit  250  is on and the power supply switch  302  is on, the power receiving apparatus  300  receives radio power transmitted from the power transmitting apparatus  10 , and while the battery  301 B is charged by the charging circuit  301 , the power receiving apparatus  300  supplies power also to the load  24 . 
         [0092]    The control section  303  includes, for example, a microcomputer, and power is normally supplied from the battery  301 B to the control section  303 . 
         [0093]    The operation section  304  includes a power supply key and is connected to the control section  303 . If the operation section  304  receives an operation input information of the power supply key, then it decides whether the operation input information represents an operation to switch on the power supply or another operation to switch off the power supply. Then, the control section  303  controls the power supply switch  302  to an on state or an off state in response to a result of the decision. 
         [0094]    On the other hand, if the control section  303  receives a notification from the charging circuit  301  that the charging circuit  301 B is charged up, then it switches off the power supply controlling switch circuit  250 . Accordingly, at this time, the power receiving apparatus  300  does not consume ac magnetic field energy sent thereto from the power transmitting apparatus  10 , and the resonance element  21  acts as a repeater of the ac magnetic field energy as described hereinabove. 
         [0095]    If the battery  301 B is not charged up, then the control section  303  controls the power supply controlling switch circuit  250  to an on state, and the power receiving apparatus  300  converts ac magnetic field energy sent thereto from the power transmitting apparatus  10  into dc current by means of the rectification circuit thereof and then consumes the dc current. 
         [0096]      FIG. 4  illustrates processing operation by the control section  303  for controlling the power supply controlling switch circuit  250  between on and off. 
         [0097]    The control section  303  first checks a notification of charge up from the charging circuit  301  at step S 101 . Then at step S 102 , the control section  303  decides whether or not the battery  301 B is in a charged up state at step S 102 . If it is decided that the battery  301 B is not in a charged up state, then the control section  303  controls the power supply controlling switch circuit  250  to be kept on at step S 103 . Thereafter, the processing returns to step S 101 . 
         [0098]    On the other hand, if it is decided at step S 102  that the battery  301 B is in a charged up state, then the control section  303  controls the power supply controlling switch circuit  250  to change over to an off state at step S 104 . Thereafter, the processing returns to step S 101 . 
         [0099]    In the power receiving apparatus  300  of the present second embodiment, when the battery  301 B is in a charged up state, it need not receive supply of power from the power transmitting apparatus  10 , and consequently, the power supply controlling switch circuit  250  is switched off automatically. 
         [0100]    Accordingly, with the power receiving apparatus  300  of the present second embodiment, different from the power receiving apparatus  200  of the first embodiment, even if the user does not manually carry out a switching operation of the power supply controlling switch, it is possible to prevent unnecessary consumption of ac magnetic field energy and achieve efficient radio power transmission. 
         [0101]    Further, where all of a plurality of power receiving apparatus which receive ac magnetic field energy from the power transmitting apparatus  10  have the configuration of the power receiving apparatus  300  of the second embodiment, the time before all of the plural power receiving apparatus are placed into a fully charged stage can be reduced. 
         [0102]    In particular, where all of the batteries of the plural power receiving apparatus  300  are not in a charged up state, ac magnetic field energy from the power transmitting apparatus  10  is distributed to the plural power receiving apparatus  300  to carry out charging. However, in a power reception state wherein the batteries are in a charged up state, the power supply controlling switch circuit  250  is off and acts as a repeater for the ac magnetic field energy. Therefore, the ac magnetic field energy to be transmitted to a power receiving apparatus which has a battery which is not in a charged up state as yet increases. 
         [0103]    Consequently, since ac magnetic field energy from the power transmitting apparatus  10  can be transmitted efficiently until all of a plurality of power receiving apparatus are placed into a charged up state, the time before all of the plural power receiving apparatus are placed into a charged up state can be reduced. 
       Third Embodiment 
     Power Transmission System (Charging System) 
       [0104]    In the present third embodiment, the present invention is embodied as a charging system or charging apparatus for charging the power receiving apparatus  300  of the second embodiment.  FIGS. 5A and 5B  show appearance of the charging system as a power transmission system of the present third embodiment. 
         [0105]    In the charging system of the present embodiment, a power transmitting apparatus  10  is provided in the inside of a box-shaped charging cradle, and a plurality of power receiving apparatus  300  are placed on the charging cradle. 
         [0106]      FIG. 5A  shows a top plan of a charging cradle  400  which forms the charging system of the present embodiment, and  FIG. 5B  shows a cross section taken along line X-X. 
         [0107]    The charging cradle  400  is formed in a flattened box shape made of a non-magnetic material. In the inside of the charging cradle  400 , the power transmitting apparatus  10  serving as a power supplying source is disposed at a central position of the charging cradle  400 . A broken line shown in  FIG. 5A  indicates an air-core coil which forms the resonance element  11  of the power transmitting apparatus  10 . 
         [0108]    On a receiving face  400 A of the charging cradle  400  which receives a plurality of power receiving apparatus  300 , a plurality of marks MK each indicative of a position at which a power receiving apparatus  300  is to be placed, in the example of  FIG. 5A , a plurality of circular marks, are provided, for example, by printing. 
         [0109]    As seen in  FIGS. 5A and 5B , the marks MK are provided such that the centers thereof are positioned on a circle at an equal distance from the position of the center of the charging cradle  400  at which the power transmitting apparatus  10  is disposed. This is because it is intended to make all of the coupling amounts through a magnetic field resonance relationship between the plural power receiving apparatus  300  placed on the charging cradle  400  and the power transmitting apparatus  10  equal to each other. 
         [0110]    In particular, in the present charging cradle  400 , if a power receiving apparatus  300  is placed at one of the plural marks MK, then on whichever one of the plural marks MK the power receiving apparatus  300  is placed, the power receiving apparatus  300  can receive ac magnetic field energy of an equal magnitude from the power transmitting apparatus  10 . 
         [0111]    Further, if a plurality of power receiving apparatus  300  are placed on the charging cradle  400 , then ac magnetic field energy is first distributed and supplied equally to all of the power receiving apparatus  300  from the power transmitting apparatus  10 . 
         [0112]    Then, if the battery  301 B of any of the power receiving apparatus  300  is placed into a charged up state, then the resonance element of the power receiving apparatus  300  now acts as a repeater of the ac magnetic field energy as described hereinabove. Accordingly, to any other power receiving apparatus  300  whose battery  301 B is not in a charged up state, ac magnetic field energy is additionally transmitted through the repeater in addition to the ac magnetic field energy originally supplied thereto from the power transmitting apparatus  10 . 
         [0113]    In particular, the power receiving apparatus  300  whose battery  301 B is fully charged does not consume the ac magnetic field energy being received till then but repeats the ac magnetic field energy to the other power receiving apparatus  300  whose battery  301 B is not in a charged up state. Accordingly, the ac magnetic field energy to be applied to the other power receiving apparatus  300  whose battery  301 B is not in a fully charged state increases from that till then. 
         [0114]    Therefore, with the charging system of the present embodiment, it can charge a plurality of power receiving apparatus efficiently. 
       Fourth Embodiment 
     Power Transmission System or Charging System 
       [0115]    Also in the present fourth embodiment, the present invention is applied to a charging system as an example of a power transmission system similarly to the third embodiment. 
         [0116]    Although the charging system of the present fourth embodiment has a basic configuration which includes a charging cradle similar to that in the third embodiment, it is different from the third configuration in that each of a power transmitting apparatus of a supplying source of charging power and a power receiving apparatus for receiving the charging power include a communication section. 
         [0117]    In the present fourth embodiment, each power receiving apparatus sends a residual charging amount of a battery to the power transmitting apparatus. 
         [0118]    The power transmitting apparatus produces a charging schedule plan in response to the received residual charging amounts of the plural power receiving apparatus and sends a controlling instruction for placing the power supply controlling switch circuit into an on state or an off state to each of the plural power receiving apparatus in accordance with the charging schedule plan. 
         [0119]    Each of the power receiving apparatus executes an operation to place the power supply controlling switch circuit thereof into an on or off state in response to the controlling instruction from the power transmitting apparatus. 
         [0120]    Consequently, in the charging system of the present fourth embodiment, the plural power receiving apparatus can be charged up rapidly in appropriate charging time. 
         [0121]      FIG. 6  shows an example of a configuration of the power transmitting apparatus  100  and the power receiving apparatus  500  which form the charging system of the present fourth embodiment. Those parts shown in  FIG. 6  which are identical to those shown in abovementioned embodiments are denoted by identical reference symbols. 
         [0122]    Referring to  FIG. 6 , the power transmitting apparatus  100  includes a control section  111  and a communication section  112  in addition to a resonance element  11 , an excitation element  12  and a frequency signal generation section  13 . 
         [0123]    The control section  111  is configured including, for example, a microcomputer and analyzes information received from the power receiving apparatus  500  through the communication section  112  or produces and transmits transmission information to the power receiving apparatus  500  through the communication section  112 . 
         [0124]    The communication section  112  is formed, for example, from a Bluetooth unit or a ZigBee unit. 
         [0125]    Further, similarly to the power receiving apparatus  300  of the second embodiment, the power receiving apparatus  500  includes a power supply controlling switch circuit  250 , a charging circuit  301  for charging a battery  301 B, a power supply switch  302 , a control section  303  and an operation section  304  and additionally includes a communication section  501 . 
         [0126]    The charging circuit  301  notifies the control section  303  of a residual charging amount or battery remaining amount of the battery  301 B and of a charged up state, a little different from that in the second embodiment. 
         [0127]    In the present fourth embodiment, the control section  303  transmits the residual charging amount or battery remaining amount of the battery  301 B received from the charging circuit  301  to the power transmitting apparatus  100  through the communication section  501  together with identification information of the power receiving apparatus  500  itself. 
         [0128]    In the present fourth embodiment, it is possible for a user to input additional information such as whether or not charging is demanded urgently or charging may be carried out slowly through the operation section  304 . 
         [0129]    Upon such notification of the residual charging amount, the control section  303  additionally transmits the additional information to the power transmitting apparatus  100 . 
         [0130]    Further, when the control section  303  receives a notification representing that the battery  301 B is charged up from the charging circuit  301 , it switches off the power supply controlling switch circuit  250  and transmits a notification that the battery  301 B is charged up to the power transmitting apparatus  100  through the communication section  501  together with the identification information of the power receiving apparatus  500  itself. 
         [0131]    When the control section  111  of the power transmitting apparatus  100  receives a notification of a residual charging amount or a notification of full charge from the power receiving apparatus  500 , then it produces or modifies a charging schedule plan. Then, the control section  111  produces on/off controlling instructions for the power supply controlling switch circuit to each of the plural power receiving apparatus in accordance with the charging schedule plan and then transmits the controlling instructions through the communication section  112 . 
       Processing Operation of the Control Section  111  of the Power Transmission Apparatus  100   
       [0132]      FIG. 7  is a flow chart illustrating processing operation executed by the control section  111  of the power transmitting apparatus  100 . 
         [0133]    The processing operation in  FIG. 7  is carried out when plural power receiving apparatus  500  as power supplying destinations are placed on the charging cradle and the power supply for the charging system is switched on to supply power to the power transmitting apparatus  100 . 
         [0134]    The control section  111  receives a residual charging amount and additional information to the residual charging amount from the plural power receiving apparatus  500  which are power supplying destinations at step S 111  at the communication section  112 . 
         [0135]    Then, the control section  111  produces a charging schedule plan for the plural power receiving apparatus  500  from the received residual charging amounts and additional information at step S 112 . 
         [0136]    In particular, the control section  111  recognizes identification information of each power receiving apparatus from the received information and then checks the residual charging amount, emergency for charging and so forth of each power receiving apparatus. Then, the control section  111  produces an optimum charging schedule plan based on the received information and determines, in accordance with the charging schedule plan, which power supply controlling switching circuit  250  is to be switched on or off in the power receiving apparatus. 
         [0137]    Then, the control section  111  transmits the determined on/off controlling information for the power supply controlling switching circuits  250  of the power receiving apparatus  500  to the respective power receiving apparatus  500  in a matched relationship with the identification information through the communication section  212  at step S 113 . 
         [0138]    Then, the control section  111  monitors reception of charge up information from any power receiving apparatus  500  at step S 114  and decides, if it is decided that such charge up information is received, whether or not all of the power receiving apparatus  500  are charged up at step S 115 . 
         [0139]    If it is decided at step S 115  that not all of the power receiving apparatus  500  are charged up, then the control section  111  decides whether or not the charging schedule plan need be revised for those power receiving apparatus  500  which are not charged up at step S 116 . In particular, since there possibly is a case wherein, for example, while the battery is not charged up, the power supply controlling switching circuit  250  in an off state need be changed to an on state, the necessity for the change and so forth is decided. 
         [0140]    If it is decided at step S 116  that the charging schedule plan need not be revised, then the processing of the control section  111  returns to step S 114 . 
         [0141]    On the other hand, if it is decided at step S 116  that the charging schedule need be revised, then the control section  111  re-produces a charging schedule plan for the power receiving apparatus other than the power receiving apparatus which is or are charged up. Then, the control section  111  produces, in accordance with the re-produced charging schedule plan, an on/off controlling instruction for each of the power supply controlling switching circuit  250  of the power receiving apparatus  500  other than those power receiving apparatus  500  which is or are charged up and transmits the on/off controlling instruction to the pertaining power receiving apparatus  500  at step S 117 . Then, the processing returns to step S 114  to repetitively carry out the processes at the steps beginning with step S 114 . 
         [0142]    If it is decided at step S 115  that all of the power receiving apparatus  500  are charged up, then the control section  111  switches off the main power supply to the power transmitting apparatus  100  and then ends the processing routine. 
       Processing Operation of the Control Section  303  of the Power Receiving Apparatus  500   
       [0143]      FIG. 8  illustrates processing operation to be executed by the control section  303  of the power receiving apparatus  500 . 
         [0144]    The control section  303  transmits identification information (ID) of the power transmitting apparatus  100  itself, a residual charging amount and additional information to the power transmitting apparatus  100  which is a power supplying source through the communication section  501  at step S 201 . 
         [0145]    Then, the control section  303  decides whether or not a switching on or off instruction for the power supply controlling switching circuit  250  from the power transmitting apparatus  100  is received through the communication section  501  at step S 202 . 
         [0146]    If it is decided at step S 202  that such a switching on or off instruction for the power supply controlling switching circuit  250  is not received, then the control section  303  repetitively carries out the process at step S 202 . 
         [0147]    On the other hand, if it is decided at step S 202  that a switching on or off instruction for the power supply controlling switching circuit  250  is received, then the control section  303  controls switching on or off of the power supply controlling switching circuit  250  in accordance with the received instruction at step S 203 . 
         [0148]    Then, the control section  303  decides at step S 204  whether or not the power supply controlling switching circuit  250  is off. If it is decided that the power supply controlling switching circuit  250  is off, then the processing returns to step S 202  to repetitively carry out the processes at the steps beginning with step S 202 . 
         [0149]    On the other hand, if it is decided at step S 204  that the power supply controlling switching circuit  250  is not off, then the control section  303  decides whether or not the battery  301 B is charged up at step S 205 . 
         [0150]    If it is decided at step S 205  that the battery  301 B is not charged up, then the processing of the control section  303  returns to step S 202  to repetitively carry out the processes at the steps beginning with step S 202 . 
         [0151]    On the other hand, if it is decided at step S 205  that the battery  301 B is charged up, then the control section  303  transmits charge up information together with the ID of the power receiving apparatus  500  itself to the power transmitting apparatus  100  which is a power supplying source through the communication section  501  at step S 206 . 
         [0152]    Further, the control section  303  changes over the power supply controlling switching circuit  250  to an off state at step S 207  and then ends the processing routine. 
       Other Embodiments and Modifications 
       [0153]    It is to be noted that, in the description of the embodiments given above, only a case is described wherein the power receiving apparatus  200  in which the power supply controlling switch is in an off state repeats ac magnetic field energy from the power transmitting apparatus  10  to a different power receiving apparatus. However, in a situation wherein the power supply controlling switch is in an off state in a plurality of power receiving apparatus  200 , it sometimes occurs that a power receiving apparatus transmits alternating current magnetic field energy transmitted thereto from a different power receiving apparatus which operates as a repeating apparatus to a further different power receiving apparatus. 
         [0154]    Further, although a case is described wherein the power transmission system of the fourth embodiment described above is a charging system, the present embodiment is not limited to this. For example, each of the plural power receiving apparatus may not include a rechargeable battery but may include a function for issuing a notification regarding whether or not the power receiving apparatus itself need operate to the power transmitting apparatus. On the other hand, the power transmitting apparatus may include a function for issuing an instruction for on/off control of the power supply controlling switching circuit of the power receiving apparatus based on the notification. 
         [0155]    With such a power transmission system as just described, the power transmitting apparatus monitors the information regarding whether or not the power transmitting apparatus need operate from the power receiving apparatus and issues an instruction for on/off control of the power supply controlling switching circuit so that suitable power supply can be usually carried out for any power receiving apparatus for which power supply is demanded. 
         [0156]    Further, while, in the embodiments described above, the excitation element  22  is provided between the resonance element  21  and the rectification circuit  23  so that impedance conversion is carried out to carry out effective ac power transmission, the excitation element may be omitted. 
         [0157]    In particular, while, in this instance, both terminals of the resonance element  21  are connected to one and the other one of the input terminal of the rectification circuit  23 , in the present embodiment, the power supply controlling switch is provided between one of both terminals of the resonance element  21  and one of the input terminals of the rectification circuit  23 . 
         [0158]    Further, the power supply controlling switch in this instance is changed over to a state wherein ac current from the resonance element  21  is supplied to the rectification circuit  23  when supply of the power from the power transmitting apparatus is received by the power receiving apparatus. Further, when supply of the ac current from the resonance element  21  to the rectification circuit  23  is to be blocked, the power supply controlling switch cuts off the connection between one of the terminals of the resonance element  21  and one of the input terminals of the rectification circuit  23  and changes over so that both terminals of the resonance element  21  are connected to each other to form a loop coil. Consequently, the resonance element  21  is placed into a state wherein it can carry out magnetic field resonance coupling with a different resonance element. 
         [0159]    It is to be noted that, while a case wherein a resonance relationship between resonance elements is magnetic field resonance is described in the description of the embodiments, the present invention can be applied also to electric field resonance. 
         [0160]    The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2009-170805 filed in the Japan Patent Office on Jul. 22, 2009, the entire content of which is hereby incorporated by reference. 
         [0161]    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 factors insofar as they are within the scope of the appended claims or the equivalents thereof.