Abstract:
A method for managing a data transfer system includes recovering energy at peripheral devices, and wireless transfer recovered energy to a base by synchronizing RF signals transmitted by double-loop antennas. Synchronizing includes implementing a listening phase to detect a radio-frequency signal transmitted by said central base, and either sending an RF signal that is synchronous with the detected signal or transmitting a signal at a predetermined frequency depending on whether an RF signal is detected at the base. The method includes, in response to receiving a signal from the peripheral device at that frequency, causing the base to recover the received signal and to re-transmit at the predetermined frequency to the peripheral devices. This signal synchronization enables simultaneous energy transfer from peripheral devices to the central base while avoiding mutually destructive effects between said signals.

Description:
RELATED APPLICATIONS 
       [0001]    Under 35 USC 119, this application claims the benefit of the priority date of French Patent Application 1152124, filed Mar. 15, 2011, the contents of which are herein incorporated by reference. 
       FIELD OF DISCLOSURE 
       [0002]    The present invention relates to the field of data transfer systems and, more particularly, the distributed data transfer systems which comprise a plurality of peripheral devices intended to communicate with a central base via a radiofrequency communication. 
       BACKGROUND 
       [0003]    In order to perform this data transfer, an energy source is necessary. In the prior art, the radiofrequency identification (RFID) technique is known and is represented in  FIG. 1  in which the central base, also called reader  1 , comprises an energy source, for example a battery  3 , which enables the central base  1  to power a radiofrequency transmitter  5 . The radiofrequency signals are sent to peripheral devices called tags  7  comprising an antenna  9 . The radiofrequency signals are used to power the tags  7  and to recover,data associated with the peripheral devices  7 . However, the battery  3  of the central base  1  has to be regularly changed or recharged by an external energy source which can be a drawback in certain environments or for certain applications. 
       SUMMARY 
       [0004]    The aim of the present invention is therefore to overcome the abovementioned drawbacks of the prior art and to propose a method and a system with which to optimize the management of the energy. 
         [0005]    Thus, the present invention relates to a method for managing a data transfer system comprising
   a plurality of peripheral devices,   a central base,   the data transfer system also comprising radiofrequency communication means enabling data to be transferred between the peripheral devices and the central base
 
in which
   energy is recovered on the peripheral devices, and   at least a portion of the recovered energy is transferred to the central base via the radiofrequency communication means.   
 
         [0011]    According to another aspect of the present invention, the peripheral devices comprise identification means and the data transferred between a peripheral device and the central base comprise an identifier of said peripheral device. 
         [0012]    According to a supplementary aspect of the present invention, the peripheral devices comprise means for measuring at least one physical quantity, the data transferred between a peripheral device and the central base comprise at least one value of the at least one measured physical quantity and the central base comprises means for processing the transferred data corresponding to the at least one value of the at least one measured physical quantity. 
         [0013]    According to another embodiment, the transfer of energy from the peripheral devices to the central base is performed by inductive coupling of the radiofrequency communication means. 
         [0014]    According to an additional embodiment, the energy recovery comprises the conversion of energy available on the peripheral devices into electrical energy. 
         [0015]    According to a supplementary aspect, the acquisition system comprises a central base comprising an antenna tuned to a predetermined frequency and the peripheral devices comprise a double-loop antenna having a zero mutual impedance, a first loop handling the transmission of a radiofrequency signal and a second loop handling the reception of a radiofrequency signal, the synchronization of the signals transmitted by the plurality of antennas comprising the following steps:
       when the process of communication from the peripheral device to the central base is triggered, a listening phase is implemented by the loop of the antenna configured to receive a radiofrequency signal in order to detect any radiofrequency signal transmitted by the central base,
           if a radiofrequency signal transmitted by the central base is detected, the peripheral device then uses the detected radiofrequency signal to transmit, to the central base, a signal that is synchronous and in phase with the detected radiofrequency signal,   if no radiofrequency signal transmitted by the central base is detected, the peripheral device then transmits a radiofrequency signal at the predetermined frequency,   
           when the central base receives a radiofrequency signal transmitted by a peripheral device at the predetermined frequency, it recovers the received radiofrequency signal and retransmits a radiofrequency signal at the predetermined frequency to the peripheral devices,
 
the synchronization of the radiofrequency signals enabling a simultaneous energy transfer from the peripheral devices to the central base without having any mutually destructive effect between the radiofrequency signals.
       
 
         [0020]    According to another embodiment, the generation by a peripheral device of a signal synchronous with a detected signal is performed by a shaping electronic circuit. 
         [0021]    According to an additional embodiment, the generation by a peripheral device of a signal synchronous with a detected signal is performed by successive approximations by shifting the phase to find the resonance of the detected signal. 
         [0022]    According to a supplementary embodiment, the transmission by a peripheral device of a signal at a predetermined frequency is performed by a local oscillator of the peripheral device. 
         [0023]    According to another embodiment, the transmission by a peripheral device of a signal at a predetermined frequency is performed on the basis of a filtered electronic noise at the predetermined frequency. 
         [0024]    According to an additional embodiment, the predetermined frequency is 13.56 MHz. 
         [0025]    According to a supplementary embodiment, at a given instant, a single peripheral device transmits data to the central base. 
         [0026]    According to another embodiment, the transmission of the data to the central base is done sequentially between the peripheral devices according to an anti-collision protocol. 
         [0027]    According to an additional embodiment, the transfer of at least a portion of the recovered energy to the central base is performed when the quantity of energy recovered reaches a predetermined threshold. 
         [0028]    According to a supplementary embodiment, the energy is stored on the peripheral devices. 
         [0029]    According to another embodiment, the energy is stored on the central base. 
         [0030]    According to an additional embodiment, the central base transmits a predetermined triggering signal to a peripheral device in order to trigger the acquisition of the data then transmits a signal to the peripheral device so as to recover the data acquired by radiofrequency identification. 
         [0031]    The embodiments of the present invention also relate to a data transfer system comprising
   a plurality of peripheral devices,   a central base,   the data transfer system comprising radiofrequency communication means enabling the transfer of data between the peripheral devices and the central base,   in which the plurality of peripheral devices comprises energy recovery means intended to supply, on the one hand, the plurality of peripheral devices and, on the other hand, the central base via the radiofrequency communication means.   
 
         [0036]    According to another aspect of the present invention, the peripheral devices comprise identification means enabling an identifier of the corresponding peripheral device to be supplied, the communication means enabling said identifier to be transferred from the corresponding peripheral device to the central base. 
         [0037]    According to an additional aspect of the present invention, the peripheral devices comprises means for measuring at least one physical quantity,
   the communication means allowing for the transfer of at least one value of the at least one measured physical quantity from the peripheral devices to the central base,   and the central base comprises means for processing the transferred data corresponding to the at least one value of the at least one measured physical quantity.   
 
         [0040]    According to another embodiment, the plurality of peripheral devices comprises a double-loop antenna in which a first loop is configured to transmit a radiofrequency signal, the second loop being configured to receive a radiofrequency signal, the first and second loops being configured to obtain a zero mutual impedance. 
         [0041]    According to an additional embodiment, the double-loop antennas of the peripheral devices are configured so as to transmit a radiofrequency signal at a predetermined common frequency and in phase with one another. 
         [0042]    According to a supplementary embodiment, the plurality of peripheral devices comprises means for storing the recovered energy. 
         [0043]    According to another embodiment, the central base comprises means for storing the recovered energy. 
         [0044]    According to an additional embodiment, the acquisition system corresponds to scales comprising peripheral devices arranged at the level of the position of the feet of the user on the scales, said peripheral devices comprising means for recovering the energy supplied by the presence of the user on the scales and means for measuring the force associated with the presence of the user, the central base comprising means for determining the weight of the user from the measurements supplied by the peripheral devices and means for displaying the determined weight. 
         [0045]    According to a supplementary embodiment, the means for recovering the energy supplied by the presence of the user on the scales comprise a magnetic generator and the means for measuring the force associated with the presence of the user comprise strain gauges. 
         [0046]    According to another embodiment, the acquisition system corresponds to a defibrillator comprising peripheral devices arranged in proximity to the heart of the user, said peripheral devices comprising means for recovering the energy supplied by the beats of the heart of the user, means for measuring the heart rate and means for applying an electrical discharge, the central base comprising means for determining, on the basis of the measurements of the heart rate supplied by the peripheral devices, the need to apply an electrical discharge. 
         [0047]    According to an additional embodiment, the acquisition system is intended to monitor physiological constants of a person, the peripheral devices comprising means for measuring these physiological constants and means for recovering the energy supplied by the body of the person, the central base comprising means for saving and/or displaying the physiological parameters of the person. 
         [0048]    According to a supplementary embodiment, the means for measuring the physiological constants of a person and the means for recovering the energy supplied by the body of a person comprise thermocouples. 
         [0049]    Other features and advantages of the invention will emerge from the description thereof that will now be given, with reference to the appended drawings which represent, as a nonlimiting indication, a possible embodiment of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0050]    In these drawings: 
           [0051]      FIG. 1  represents a diagram of a data transfer system based on radiofrequency identification according to the prior art; 
           [0052]      FIG. 2  represents a general diagram of a data transfer system according to the embodiments of the present invention; 
           [0053]      FIG. 3  represents a diagram of a data transfer system according to the embodiments of the present invention; 
           [0054]      FIG. 4  represents a diagram of a data transfer system according to an embodiment of the present invention; 
           [0055]      FIG. 5  represents an exemplary embodiment of the communication means between the peripheral devices and the central base; 
           [0056]      FIG. 6  represents an overall diagram of the transmission and reception modules of a peripheral device according to a first embodiment, 
           [0057]      FIG. 7  represents a detailed diagram of an exemplary embodiment of a reception and amplification circuit of a peripheral device, 
           [0058]      FIG. 8  represents a detailed diagram of an exemplary embodiment of a shaping circuit of a peripheral device, 
           [0059]      FIG. 9  represents a detailed diagram of an exemplary embodiment of a circuit for controlling a switch of a peripheral device, 
           [0060]      FIG. 10  represents a detailed diagram of an exemplary embodiment of a local oscillator of a peripheral device, 
           [0061]      FIG. 11  represents a detailed diagram of an exemplary embodiment of a power amplifier of a peripheral device, 
           [0062]      FIG. 12  represents a detailed diagram of an exemplary embodiment of a bandpass transmission filter of a peripheral device, 
           [0063]      FIG. 13  represents an overall diagram of the transmission and reception modules of a peripheral device according to a second embodiment, 
           [0064]      FIG. 14  represents a diagram of the activity of the peripheral devices and of the central base during a data transfer from the peripheral devices to the central base according to a first process, 
           [0065]      FIG. 15  represents a diagram of the activity of the peripheral devices and of the central base during a data transfer from the peripheral devices to the central base according to a second process, 
           [0066]      FIG. 16  represents a diagram of scales comprising a data transfer system according to the embodiments of the present invention. 
       
    
    
       [0067]    In all these figures, the same elements are given the same reference numbers. 
       DETAILED DESCRIPTION 
       [0068]    Hereinafter in the description, the term “RFID” is used as the acronym for radiofrequency identification. 
         [0069]    The embodiments of the present invention relate to a data transfer system  13 , represented generally in  FIG. 2 , comprising a plurality of peripheral devices  15  comprising energy recovery means  19  intended to supply, in particular, a central base  21  programmed to receive data transmitted by the peripheral devices  15  and perform a data processing. The data transfer system  13  also comprises radiofrequency communication means  24 , the radiofrequency communication means  24  being intended to transmit the data  26  between the peripheral devices  15  and the central base  21  and allowing at least a portion of the energy recovered  28  on the peripheral devices  15  to be transmitted to the central base  21 . The transfer of energy is performed by an inductive coupling of the radiofrequency signals  27  transmitted by the peripheral devices  15 . 
         [0070]    According to one aspect of the present invention, the peripheral devices  15  comprise identification means, for example a memory comprising an identifier, so that the data transfer comprises the transfer of the identifier associated with the peripheral device  15  to the central base  21 . 
         [0071]    According to another aspect of the present invention represented in  FIG. 3 , the peripheral devices  15  comprise means  17  for measuring a physical quantity and transmit the data corresponding to the measured values to the central base  21  via the communication means  24 , the central base comprising means  18  for processing the measured values transmitted by the peripheral devices  15 . 
         [0072]    The measurement means  17  and energy recovery means  19  may be combined or may be separate, like the energy source and the physical quantity to be measured. Furthermore, the energy recovery means  19  recover the energy available in their environment, for example a motion, heat or radiation, etc., and convert that energy into electrical energy in order to transfer this energy to the central base  21  via the radiofrequency communication means  24 . 
         [0073]    According to a first embodiment represented in  FIG. 4 , the central base  21  is passive and comprises an antenna  25 . The peripheral devices  15 , of which there are three, comprise means for storing the recovered energy such as, for example, a rechargeable battery  29 . This energy is used on the one hand to power the measuring means  17  and on the other hand to power the communication means  24  and the passive central base  21 . 
         [0074]    The radiofrequency communication means  24  are represented in detail in  FIG. 5  in the case of two peripheral devices  15 . The communication means  24  comprise, on each peripheral device  15 , a double-loop antenna  23 . A first loop  31  connected to a transmission module  33  is configured to transmit radiofrequency signals  27  and a second loop  35  connected to a reception module  37  is configured to receive radiofrequency signals  27 . In order to avoid disturbances between the signals transmitted and received, the double-loop antenna  23  is configured so as to obtain a zero mutual impedance between the two loops  31  and  35 . 
         [0075]    Furthermore, the central base  21  comprises an antenna  25  intended to receive the radiofrequency signals  27  transmitted by the peripheral devices  15  and to retransmit radiofrequency signals  27  to the peripheral devices  15 , the retransmitted signals being the signals received and modified to insert data to be transmitted to the peripheral devices  15 . 
         [0076]    In order to transmit data, these radiofrequency signals  27  are modulated, for example by an amplitude or frequency modulation on the peripheral devices  15  and by a charge modulation on the central base  21 . The carrier used for the modulation has a predetermined frequency, for example 13.56 MHz, to which the antennas  23  and  25  of the peripheral devices  15  and of the central base  21  are tuned. 
         [0077]    Furthermore, in the present embodiment, the energy recovery means  19  are the same for all the peripheral devices  15  and are powered by a common energy source. The communication protocol with the central base  21  for transmitting the data corresponding to the measurements is initialized when the level of energy stored in the storage means  29  corresponds to a predetermined threshold or at a predefined instant by using internal clocks situated in the peripheral devices. Thus, the communication protocols of the peripheral devices  15  are established almost simultaneously. 
         [0078]    In order to avoid a destructive effect from the different radiofrequency signals  27  originating from the different peripheral devices  15 , synchronization of the transmission of these radiofrequency signals  27  is necessary. 
         [0079]    Two distinct protocols can be used for such synchronization: 
         [0080]    According to a first synchronization protocol, the initialization of the radiofrequency communication comprises the following steps:
   when the process of communication between the peripheral device  15  and the central base  21  is triggered, the peripheral device  15  proceeds with a listening phase during which the loop  35  of the antenna  23  is configured to detect any radiofrequency signal  27  transmitted by the central base  21  at a predetermined frequency, 13.56 MHz for example, to which the antenna  25  of the central base is tuned,
       if a radiofrequency signal transmitted (in fact retransmitted) by the central base  21  is detected, the peripheral device  15  then uses this detected radiofrequency signal to generate and transmit, to the central base  21 , a radiofrequency signal that is synchronous and in phase with the detected signal. The generation of the synchronous radiofrequency signal is performed, for example, by a shaping electronic circuit which is used to create a signal that is synchronous with the received signal.   if no radiofrequency signal transmitted by the central base  21  is detected, the peripheral device then transmits a radiofrequency signal at the predetermined frequency, 13.56 MHz for example,   
       when the central base  21  receives a radiofrequency signal transmitted by a peripheral device  15  at the predetermined frequency, the central base  21  recovers the received radio frequency signal and retransmits a signal at the predetermined frequency to the peripheral devices  15 .   
 
         [0085]    Thus, all the radiofrequency signals  27  transmitted by the peripheral devices  15  are synchronized which allows for a simultaneous transfer of energy from the peripheral devices  15  to the central base  21  without having any mutually destructive effect between the radiofrequency signals  27 . 
         [0086]    The transmission by a peripheral device  15  of a radiofrequency signal  27  at a predetermined frequency can be performed by a local oscillator tuned to this frequency but may also be performed on the basis of noise by filtering this noise at the predetermined frequency. 
         [0087]    An exemplary embodiment of the communication means  24  and, more particularly, of the transmission  33  and reception  37  modules that can be used to generate a signal synchronous with a received signal or with a predetermined wavelength is presented in  FIG. 6 . 
         [0088]    The reception loop  35  of the antenna  23  is linked to a reception and amplification circuit  39 , the circuit diagram of which is represented in  FIG. 7 . 
         [0089]    The input  41  is linked to a zero-crossing detection circuit  43  comprising a capacitor C 1  linked to the mid-point of a branch comprising two resistors R 1  and R 2  mounted in series. The resistor R 1  is linked to a voltage potential V 1  and the resistor R 2  is linked to the ground. This zero-crossing detection circuit  43  makes it possible to “position” the signal at the centre of the amplification band in order to be amplified by the amplifier circuit  45 . 
         [0090]    The amplifier circuit  45  comprises a first and a second operational amplifiers AO 1  and AO 2  cascade-mounted by the positive input terminal of the second amplifier AO 2 , the positive input terminal of the first amplifier AO 1  being linked to the mid-point of the zero-crossing detection circuit  43 . A resistor R 3  is connected between the negative input terminal of the amplifier AO 1  and a voltage potential V 2  linked to the ground via a capacitor C 3 . A resistor R 4  in parallel with a capacitor C 2  links the negative input terminal to the output terminal of the amplifier AO 1 , the output terminal of the amplifier AO 1  being linked to the ground via a capacitor C 4 . A resistor R 5  is mounted between the negative input terminal of the amplifier AO 2  and the voltage potential V 2 . A resistor R 6  is connected between the negative input terminal and the output terminal of the amplifier AO 2 . The signal amplified by the amplifier circuit  45  is then transmitted at the output  47  of the reception and amplification circuit  39  to the shaping circuit  49  on the one hand and to the control circuit of the switch  51  on the other hand. 
         [0091]    The shaping circuit  49  is represented in  FIG. 8  and comprises a capacitor C 5  linked on the one hand to the input  47  of the shaping circuit and on the other hand to the mid-point of a branch comprising two resistors R 7  and R 8  mounted in series. The resistor R 7  is linked to a voltage potential V 3  and the resistor R 8  is linked to the ground. The mid-point is linked to the positive input terminal of an operational amplifier AO 3 . The negative input terminal of the amplifier AO 3  is linked to a voltage potential V 4 . At the output  53  of the shaping circuit  49 , a square wave signal is obtained which is transmitted to the switch  55 . 
         [0092]    The control circuit  51  of the switch  55  is used to control the position of the switch  55  which can be linked to the output  53  of the shaping circuit  49  or to a local oscillator  57  depending on the reception or non-reception of a signal on the reception loop  35  of the antenna  23 . 
         [0093]    The details of the control circuit  51  are represented in  FIG. 9 . The control circuit  51  comprises a capacitor C 6  linked to the mid-point of a branch comprising two resistors R 9  and R 10  mounted in series, the resistor R 9  being linked to a voltage potential V 5  and the resistor R 10  being linked to the ground. The mid-point is connected to a Zener diode DZ 1  linked to the positive input terminal of an amplifier AO 4  and to the ground via a capacitor C 7 . The negative input terminal of the amplifier AO 4  is linked to a voltage potential V 6  and the output terminal of the amplifier AO 4  is linked to the ground via two resistors R 11  and R 12  mounted in series, the mid-point of which is the output terminal  59  of the control circuit  51 . The voltage potential V 6  corresponds to the detection threshold. The average voltage of the signal is thus compared to the threshold voltage V 6  to determine the presence of a signal received on the reception loop  35 . If a signal is received, the voltage at the output  59  of the control circuit  51  controls the connection of the switch to the output  53  of the shaping circuit  49 , otherwise the switch is connected to the local oscillator  57 . 
         [0094]    The local oscillator  57  can be modelled as represented in  FIG. 10 . The local oscillator comprises a quartz Q 1  linked on one side to the ground via a capacitor C 9  and to a resistor R 14  linked to the output of an “AND” logic connector AND 1  and on the other side to the ground via a capacitor C 8  and to a first input terminal of the connector AND 1 . A resistor R 13  links the first input terminal and the output terminal of the connector AND 1 . The second input terminal of the connector AND 1  is linked to a voltage source V 7  and to a first input terminal of an “AND” logic connector AND 2 . The output terminal of the connector AND 1  is linked to the second input terminal of the connector AND 2 . The output terminal of the connector AND 2  corresponds to the output  61  of the local oscillator  57 , the signal created at the output  61  of the local oscillator  57  being sent to the switch  55 . 
         [0095]    The output signal of the switch  55  (originating either from the shaping circuit  51  or from the local oscillator  57 ) is sent to the input  62  of a power amplifier  63 , the details of which are represented in  FIG. 11 . 
         [0096]    The power amplifier  63  comprises a first amplification stage  65  comprising a capacitor C 10  mounted in series with a resistor R 15  linked to the mid-point of a branch comprising a first and a second resistor R 16  and R 17  mounted in series, the first resistor R 16  being linked to the ground and the second resistor R 17  being linked to a voltage potential V 8 . The mid-point is also linked to a Schmitt trigger A 1 , the output of the Schmitt trigger A 1  being linked to the input  68  of the second amplification stage  67 . The input  68  is linked to a first branch comprising three Schmitt triggers A 2 , A 3 , A 4  mounted in parallel, in series with a capacitor C 11 , said first branch being connected to a link point  70  and to a second branch comprising two Schmitt triggers mounted in parallel, in series with a capacitor C 12 , said second branch being connected to a link point  72 . The link points  70  and  72  correspond to the intermediate points of a branch comprising three resistors R 18 , R 19  and R 20  in series, the link point  70  being situated between the resistors R 18  and R 19  and the link point  72  being situated between the resistors R 19  and R 20 . The resistor R 18  is connected to a voltage potential V 9  and the resistor R 20  is connected to the ground. Two p-type MOSFET transistors T 1  and T 2  have their gate linked to the link point  70 , their source linked to the voltage potential V 9  and their drain linked to a first terminal of a resistor R 21 . An n-type MOSFET transistor T 3  has its gate linked to the link point  72 , its source linked to the ground and its drain linked to the first terminal of the resistor R 21 , the second terminal of the resistor R 21  being linked to the output  69  of the power amplifier  63 . 
         [0097]    At the output  69  of the power amplifier  63 , the amplified signal is transmitted to a bandpass transmission filter  71  so as to select the desired frequency, for example 13.56 MHz. 
         [0098]    An example of a bandpass transmission filter  71  is described in  FIG. 12 . The input of the filter  71  corresponds to the output  69  of the amplifier  63  and is connected to a branch comprising an inductor L 1  and two capacitors C 13  and C 15  mounted in series and linking the output  73  of the filter  71 . A capacitor C 14  in series with an inductor L 2  are mounted in parallel with the capacitor C 15 . Furthermore, the connection between the capacitor C 14  and the inductor L 2  is linked to the ground. 
         [0099]    The values of the inductors and of the capacitors make it possible to determine the cut-off frequencies of the filter and thus adjust the frequency that is to be transmitted. 
         [0100]    Thus, the devices described can be used to transmit a signal that is synchronous and in phase with a received signal or to transmit a signal at a given frequency. Furthermore, the signal transmitted at a given frequency can be generated from noise, for example the electronic noise of the power amplifier, this noise being filtered to obtain the desired frequency for the transmitted signal, which makes it possible to dispense with the local oscillator  57 . 
         [0101]    According to a second synchronization protocol, the synchronization of the radiofrequency signals transmitted by the communication means of the peripheral devices  15  is obtained by searching for the resonance of the signal received by the antenna by successive approximations of a phase offset. 
         [0102]      FIG. 13  represents an exemplary embodiment of the reception  37  and transmission  33  modules that can be used to obtain a synchronization by searching for the resonance. 
         [0103]    The radiofrequency signal received on the reception loop  35  of the antenna  23  is transmitted to a reception circuit  75  so as to be demodulated and then is sent to a resonance analysis module  77  in which an analysis of the signal is used to determine its amplitude. Depending on the amplitude determined in the resonance analysis module  77 , a signal is sent to a phase offset module  79  which will order an offset of the phase shift of the signal transmitted by the local oscillator  81 . Thus, the phase of the signal is controlled as a function of the amplitude measured in the resonance analysis module  77 . The adjustment of the phase is done, for example, by successive approximations (small phase offset), and makes it possible to tend towards the maximum resonance. The signal generated by the local oscillator is transmitted to a signal shaping circuit  83  and then to a transmission circuit  85  powering the transmission loop  31  of the antenna  23 . 
         [0104]    The search for the maximum resonance is continuous and the direction of the phase offset is determined on the basis of the measurement history: in case of a decrease in amplitude after a phase offset, the direction of the phase offset is reversed. 
         [0105]    Thus, all the peripheral devices are synchronized with the resonance of a received signal, which makes it possible to obtain a mutual synchronization of the peripheral devices  15 . 
         [0106]    Once the signals from the different peripheral devices  15  have been synchronized, the peripheral devices  15  can transmit energy to the central base  21  without there being any destructive effect between the signals received at the central base  21 . When the quantity of energy received is sufficient to activate the central base  21 , the latter retransmits an activation signal (corresponding, for example, to a simple beep) by a charge modulation of the received signals to indicate to the peripheral devices  15  that they can now transfer data to it. 
         [0107]    In order to avoid a loss of data, an anti-collision protocol is necessary. This anti-collision protocol makes it possible to prevent the peripheral devices  15  from transmitting data simultaneously. For this, time slots are allocated to the different peripheral devices  15 , according, for example, to an identification number assigned at the time of manufacture or on initialization of the data transfer system  13 . During a time slot, the peripheral device  15  whose identification number is associated with this slot can transmit a data frame to the central base  21 . 
         [0108]    Two alternatives are then possible depending on the operating mode of the central base:
   If the energy supplied by a single peripheral device  15  is sufficient to enable the central base  21  to receive the data, then the different peripheral devices  15  each transmit a signal in turn during the time slot that is allocated to them, this signal making it possible both to supply energy to the central base  21  and to transmit the data corresponding to the measurements performed by the measurement means  17  of the peripheral device  15 . Moreover, the duration of these time slots can vary according to the protocol chosen and may, for example, correspond to 10 or 20 ms.   
 
         [0110]    A diagram representing the various data transmission steps in the case of three peripheral devices  15   a,    15   b  and  15   c  and a central base  21  as a function of the time t is represented in  FIG. 14 . 
         [0111]    The phase T 1  common to all the peripheral devices  15  corresponds to the synchronization phase according to one of the synchronization protocols described previously. At the end of the synchronization phase, the central base  21  receives energy and when this energy reaches a predetermined threshold, the phase T 2  corresponding to the return by the central base  21  of an activation signal to the peripheral devices  15  is initiated. On reception of the activation signal, the first peripheral device, here the peripheral device  15   a,  sends the data corresponding to its measurements during the phase T 3 , the phase T 3  corresponding to a predetermined time slot enabling a peripheral device  15  to transfer the data corresponding to the measurements. Then, at the end of the phase T 3 , the second peripheral device  15   b  sends the data corresponding to its measurements during the phase T 4 . Then, at the end of the phase T 4 , the third peripheral device  15   c  sends the data corresponding to its measurements during the phase T 5 . After the phase T 5 , the phase T 6  corresponds to the processing of the data by the central base  21 ; this processing may require more energy than the reception of the data so that all the peripheral devices  15  transmit a signal intended to transfer energy to the central base  21  during the phase T 6 . In the case where the energy from a single peripheral device  15  is sufficient to power the central base  21  during the processing of the data, only the third peripheral device  15   c,  for example, continues to transmit, in order to transmit energy during the phase T 6 . Once the phase T 6  has ended, the central base  21  can, for example, send a deactivation signal to the peripheral devices  15  (still by charge modulation) to inform them of the end of the data processing in order for them to stop transmitting.
   If the central base  21  requires the energy supplied by all the peripheral devices  15  to receive the data, all the peripheral devices  15  transmit signals enabling energy to be transmitted throughout the duration of the transmission of the data and the peripheral devices  15  each in turn send the data corresponding to the measurements performed by their measurement means  17 .   
 
         [0113]    A diagram representing the different data transmission steps in the case of three peripheral devices  15   a,    15   b  and  15   c  and a central base  21  as a function of time t is represented in  FIG. 15 . 
         [0114]    The phase T 1  is common to the preceding embodiment and corresponds to the synchronization of the peripheral devices by one of the methods described previously. At the end of the phase T 1 , the peripheral devices  15   a,    15   b  and  15   c  transmit a signal to transfer energy to the central base  21 . When the energy level of the central base  21  is sufficient to receive data, the central base  21  retransmits an activation signal (phase T 2 ). The first peripheral device  15   a  then transmits the data corresponding to its measurements (phase T 3 ). At the end of the phase T 3 , the second peripheral device  15 b transmits the data corresponding to its measurements (phase T 4 ) then, at the end of the phase T 4 , the third peripheral device  15   c  transmits the data corresponding to its measurements. Furthermore, during the phases T 3 , T 4  and T 5 , all the peripheral devices  15  ( 15   a,    15   b  and  15   c ) continue to transmit in order to transfer energy to the central base  21 . For the phase T 6 , the peripheral devices  15  continue to transmit in order to transfer energy to the central base  21  and enable the data to be processed. Once the data has been processed, the central base  21  may, for example, retransmit a deactivation signal to the peripheral devices  15  to inform them of the end of the processing of the data so that they stop transmitting. 
         [0115]    Furthermore, the processing of the data may comprise, for example, a calculation to obtain the value of a predefined parameter, a back-up of the data and/or of a calculated parameter, display of the data and/or of a calculated parameter, etc. 
         [0116]    Moreover, in order for the transmission of the data not to disturb the synchronization of the signals and therefore the transfer of energy to the central base  21 , the signal modulation rate is limited (&lt;100%). 
         [0117]    According to a second embodiment, the central base  21  comprises means for storing the energy transmitted by the peripheral devices  15 , such as for example a rechargeable battery. Thus, when the peripheral devices  15  recover energy, they then transmit at least a portion of this energy to the central base  21 , which then stores this energy. This energy is used to power a standby mode of the central base  21  which triggers, in a programmable manner, a measurement acquisition cycle. The measurement acquisition cycle proceeds according to a radiofrequency identification (RFID) protocol in which the peripheral devices  15  act passively as transponders, the energy required by the peripheral devices  15  being supplied by the central base  21 . Thus, in this embodiment, the signals are transmitted by the central base  21  and a charge modulation is performed on the peripheral devices  15  in order to retransmit the data corresponding to the measurements performed to the central base  21 . This embodiment therefore makes it possible to use the standardized RFID communication protocols. However, this embodiment relies on a dual transfer of energy by inductive coupling which results in heavy losses. 
         [0118]    In order to better understand the embodiments of the present invention, different applications of these embodiments will now be described in detail. 
         [0119]    A first application relates to scales  89  represented in  FIG. 16 , of which the peripheral devices  15  comprise means  17  for measuring the force created by the presence of a user on the scales  89 . These measurement means are, for example, strain gauges situated on a proof body at the level of the feet of the user. The peripheral devices also comprise energy recovery means  19 , for example a magnetic microgenerator in which the energy imparted by the presence of the user on the scales is transposed into a rotational motion then converted into electricity via an alternator, which make it possible to recover the energy supplied by the presence of the user. In the example of  FIG. 16 , the data transfer system, that is to say, the scales  89 , comprises four peripheral devices  15  that are situated in front of and behind the position of the feet of the user on the scales  89  in order to recover a maximum of energy. The peripheral devices also comprise radiofrequency communication means  24 , for example a transmission-reception electrical circuit as shown in  FIG. 5  coupled to a double-loop antenna configured with zero mutual impedance enabling energy to be transferred to the central base  21 . 
         [0120]    The central base  21  comprises communication means  24  enabling the radiofrequency signals  27  transmitted by the peripheral devices  15  to be received and processing means  18  enabling the weight of the user to be determined on the basis of the data corresponding to the measurements from the strain gauges transmitted by the peripheral devices  15  and means for displaying this weight. Thus, when the user stands on the scales  89 , his or her weight drives the microgenerator which creates an electrical voltage which is used to power on the one hand the strain gauges and on the other hand the radiofrequency communication means  24  and transfer energy to the central base  21 . Furthermore, the weight of the user causes the strain gauges to be deformed, which makes it possible to determine the weight of the user. The radiofrequency signals  27  transmitted to the central base  21  then enable it to determine the weight of the user and to display this weight. Thus, such a scales  89  operates without the provision of external energy (battery or connection to the mains) and does not require any connecting cables between the strain gauges and the central base  21 . 
         [0121]    A second application relates to a defibrillator. Some people with cardiac problems require the use of an implanted defibrillator, in other words, an appliance which continuously monitors the beats of the heart and, when necessary, sends an electrical discharge to stimulate or regulate the heart, the measurement and stimulation electrodes being implanted directly on the heart. The present application consists in recovering a portion of the energy supplied by the beats of the heart, for example by piezoelectric or electromagnetic elements, in order to power on the one hand the electrodes for performing the heart rate measurements and on the other hand power radiofrequency communication means so that the result of the measurements can be transferred to a central base situated, for example, on the bed or the seat of the user. Furthermore, the recovered energy can also be used to recharge a battery intended to ensure the electrical discharge. However, in this application, a monitoring of the level of the battery intended to ensure the electrical discharge may be provided, as well as other means for recharging this battery in the case where the recharging by the peripheral devices is insufficient to generate an adequate electrical discharge. 
         [0122]    The measurements of the heart rate may thus be transferred continuously to the central base which may, for example, display these data in the form of a plot and determine whether or not an electrical discharge needs to be sent, for example if the heart rate exceeds a predetermined threshold. 
         [0123]    Thus, by recovering the energy supplied by the beats of the heart, the present application makes it possible to do away with the presence of cables between the implanted electrodes and the central base and thus improve the comfort of the user. 
         [0124]    Furthermore, the implanted electrodes can be used during hospital examinations by using an external radiofrequency antenna. 
         [0125]    A third application relates to a device for monitoring physiological constants of a person situated, for example, in a hospital bed, the peripheral devices comprising means for measuring the physiological constants such as, for example, the voltage, the heart rate, the temperature, etc., and means for recovering the energy associated with the environment of these measurements such as, for example, the recovery of the heat energy by thermocouples, of the mechanical energy associated with the internal and external movements of the body of the person by piezoelectric elements. The recovered energy thus makes it possible to power the sensors and communicate with the central base. The central base may be composed, for example, of a device consisting of a relay antenna capable of receiving the data from the peripheral devices and of saving these data, this device being situated in proximity to the patient, for example on his or her clothing, the data stored by the central base being recovered by a reader of RFID type external to the data transfer system. Moreover, the data can also be saved in the measurement means. 
         [0126]    The embodiments of the present invention therefore make it possible to use the peripheral devices of a network of sensors such as microgenerators capable of being self-powered and of powering a central base handling the processing of the data measured by the sensors while doing away with cables between the peripheral devices and the central base. Such embodiments make it possible to optimize the use of the energy supplied by the environment of the data transfer system and to envisage locating data transfer systems in environments that are difficult to access.