Abstract:
A relaying device for providing optimum communication between a non-contact information medium and an information read/write device, and a communication system employing the relaying device, in which the adverse effect on communication, brought about by limitations on the mounting site of the information read/write device may be eliminated. The relaying device is formed by a resonance circuit  34  including a first antenna coil  31 , electromagnetically coupled to an antenna coil  11  of the information read/write device  10 , a second antenna coil  32 , connected in series with the first antenna coil  31  and electro-magnetically coupled to an antenna coil  21  of the non-contact information medium  20 , and a tuning capacitor  33  connected in series with the first antenna coil  31  and the second antenna coil  32 . The first antenna coil  31 , second antenna coil  32  and the tuning capacitor  33  making up the resonance circuit  34  is resonated with the same resonance frequency as that of the resonance circuit  13  of the information read/write device  10  and that of the resonance circuit  23  of the non-contact information medium  20.

Description:
BACKGROUND OF THE INVENTION  
     FIELD OF THE INVENTION  
       [0001]     This invention relates to an RFID (Radio Frequency IDentification) employing a non-contact information medium, such as a non-contact IC (Integrated Circuit) tag or a non-contact IC card. More particularly, it relates to a relaying device for providing optimum communication between a non-contact information medium and an information read/write device, and to a communication system employing the relaying device.  
         [0002]     The RFID system, as the communication system employing a non-contact information medium, such as a non-contact IC card or a non-contact IC tag, has been devised and put to practical use. The RFID system allows information communication to be performed between an IC chip enclosed in the non-contact information medium, and a reader/writer, and is utilized in an automatic ticket checker in a railroad station or for book lending in a lending library. It is estimated that, in near future, the system will be used for exchanging the private information in a wide variety of fields.  
         [0003]     The non-contact IC card is a generic term for a card-shaped non-contact information medium, such as a so-called credit card. On the other hand, the non-contact IC tag is a generic term for a non-contact information medium of a shape other than the card shape, a non-contact information medium of a label size smaller than the credit card size, such as a stamp size or a size smaller than the stamp size, or a non-contact information medium of a round or a star shape.  
         [0004]     In the RFID system by the electromagnetic coupling system, the non-contact information medium receives electrical waves, transmitted from the reader/writer, to obtain the operating power from the received electrical waves by electromagnetic induction, and effects data communication with the reader/writer by exploiting the received electrical waves. The non-contact information medium and the reader/writer each include an antenna coil for transmitting/receiving the electrical waves. The optimum communication distance between the reader/writer of the electromagnetic coupling system and the non-contact information medium is usually several cm to tens of cm.  
         [0000]     [Patent Publication 1] Japanese Laid-Open Patent Publication 2000-315908  
         [0005]     For example, if the non-contact information medium is a non-contact IC card, the card size of the same size as the credit card size (54 mm in length, 85.6 mm in width and 0.76 mm in thickness), as provided for by the ISO (International Organization for Standardization), is generally used.  
         [0006]     In such case, the antenna coil  100 , enclosed in the non-contact IC card, is sized to approximately the size of the non-contact IC card, in order to permit the largest amount possible of the flux from the reader/writer as possible to traverse the inside of the coil, as shown in  FIG. 17A . If the non-contact information medium is a non-contact IC tag, the antenna coil is of such a shape as to permit the largest amount possible of the flux to traverse the inside of the coil, depending on the standard or the size of the non-contact IC tag.  
         [0007]     In this manner, the shape of the antenna coil of the non-contact information medium is determined to a more or less extent by e.g. the relevant standard.  
         [0008]     On the other hand, the shape of the antenna coil of the reader/writer is appreciably influenced by the structure of the equipment carrying the reader/writer thereon.  
         [0009]     In case the inside space of a casing of the device carrying the reader/writer thereon is occupied by densely arranged component parts, there is not sufficient space available for properly mounting the reader/writer. In such case, the antenna coil area is decreased compared to the available space in the casing, or the reader/writer is mounted on the back side of the casing of the carrying device, in order to exploit the small space left in the casing.  
         [0010]     In particular, if the reader/writer is mounted on the back side of the casing of the carrying device, an aperture must be formed in a portion of the casing in order to pass the magnetic flux emanating from the magnetic field generated by the antenna coil of the reader/writer to the antenna coil of the non-contact information medium.  
         [0011]     In general, the casing is provided for protecting the circuitry in the casing against impacts from outside, or for shielding the electromagnetic noise, emanating from the electronic circuit in the casing and hence the processing such as perforating the casing is to be avoided as far as is possible. If the casing is to be perforated, out of necessity, the-area of an aperture produced needs to be as small as possible.  
         [0012]     Consequently, the antenna coil of the reader/writer is of an extremely small size as compared the size of the antenna coil enclosed in the non-contact information medium. For example, an antenna coil  200  of the reader/writer, shown in  FIG. 17B , is of a size appreciably smaller than the size of the antenna coil  100  enclosed in the inside of the non-contact IC card shown in  FIG. 17A .  
         [0013]     If the size of the antenna coil on the reader/writer side is this small, the amount of the magnetic flux generated by the current flowing in the antenna coil is also extremely small, so that, if the non-contact information medium is moved to the vicinity of the antenna coil of the reader/writer, the amount of the magnetic flux necessary to operate the non-contact information medium cannot be generated.  
         [0014]      FIG. 18  shows the manner in which the magnetic flux by the magnetic field generated by the antenna coil  200  provided to the reader/writer traverses the inside of the antenna coil  100  enclosed within the non-contact IC card. As may be seen from  FIG. 18 , since it is the magnetic flux by the magnetic field at the center of the antenna coil  200  that traverses the inside of the antenna coil  100 , the antenna coil  100  must be moved to a position closer to the antenna coil  200  in order to procure an appropriate amount of the magnetic flux.  
         [0015]      FIG. 19  shows a communication system  150 , made up by a reader/writer  201  having an antenna coil  200 , mounted to the back side of the metal casing  205 , and by a non-contact IC card  101 , having an antenna coil  100 .  
         [0016]     The reader/writer  201  includes an antenna coil  200 , as an inductor arranged on a substrate  204 , a tuning capacitor  203 , connected in series with the antenna coil  200 , to form a parallel resonance circuit, and an IC for a reader/writer  202  for controlling the data transmission/receipt with the non-contact IC card  101 . A casing  205 , having the reader/writer  201  mounted thereon, is perforated at  205 A in register with the antenna coil  200 .  
         [0017]     In a majority of cases, the casing  205  of the equipment, adapted for loading the reader/writer  201  thereon, is formed of metal for procuring the strength or for preventing leakage to outside of the electromagnetic noise caused by the internal electronic circuitry. However, if a substrate  204  is mounted to the metal casing  205 , the magnetic flux of the magnetic filed, generated by the antenna coil  200 , is lost in the casing  205 , such that it is only the small amount of the magnetic flux generated at the center of the antenna coil  200  that is allowed to pass through the inside of the antenna coil of the non-contact IC card  101 .  
         [0018]     Thus, with the communication system  150 , shown in  FIG. 19 , the non-contact IC card  101  and the reader/writer  201  cannot communicate with each other.  
         [0019]     That is, a wide variety of constraints are imposed on the antenna coil of the reader/writer, by the structure of the equipment adapted for loading the reader/writer thereon, such that it is difficult to set the antenna coil shape or area in such a manner as to permit optimum communication with the non-contact information medium. There is also a problem that, given the limited space within the equipment adapted for loading the reader/writer thereon, it is also extremely difficult to eliminate the adverse effect of the metal components interfering with the wireless communication.  
         [0020]     For overcoming this deficiency, the antenna coil of the reader/writer  201  is designed as an antenna coil  210  substantially coextensive as the antenna coil of the non-contact IC card, and is mounted on the back side of a resin cover  220 , fitted to the casing  205 , so as to operate as a relaying antenna, as shown in  FIG. 21 . In this manner, it is possible to cope with the constraint of the antenna area or to eliminate the adverse effect from the metal casing  205 .  
         [0021]     The antenna coil  210  is connected to the substrate  204  by fitting a jack  212 , mounted to the distal end of a lead wire  211 , extending from the antenna coil  210 , into a plug  213  provided to the substrate  202  exposed through the aperture  205 A formed in the casing  205 .  
         [0022]     Consequently, the antenna coil  210  is inconvenient to mount or dismantle, especially for maintenance, such that, in the worst of cases, the lead wire  211  may be ruptured, or the reader/writer  201  may be destroyed.  
       SUMMARY OF THE INVENTION  
       [0023]     In view of the above-depicted status of the art, it is an object of the present invention to provide a relaying device and a communication system in which, in wireless communication by the electro-magnetic coupling system between an information read/write device and a non-contact information medium, mediated by a carrier wave of a preset frequency, the adverse effect on the communication, brought about by the limitation as to the mounting site of the information read/write device, may be eliminated, and the use configuration of the information read/write device and a non-contact information medium may be flexibly coped with to achieve optimum communication.  
         [0024]     In one aspect, the present invention provides a relaying apparatus for relaying wireless communication of the electromagnetic coupling system, mediated by a carrier wave of a preset frequency, between an information read/write device and a non-contact information medium. The relaying apparatus comprises a first antenna coil electro-magnetically coupled to an antenna coil of the information read/write device, a second antenna coil, connected in series with the first antenna coil and electro-magnetically coupled with an antenna coil of the non-contact information medium, and a tuning capacitor connected in series with the first antenna coil and with the second antenna coil. The first antenna coil, second antenna coil and the tuning capacitor form a resonance circuit resonated at the resonance frequency which is the same as the resonance frequency of a resonance circuit of the read/write device and the resonance frequency of a resonance circuit of the non-contact information medium.  
         [0025]     In another aspect, the present invention provides a relaying device for providing optimum communication between a non-contact information medium and an information read/write device, and a communication system employing the relaying device, in which the adverse effect on communication, brought about by limitations on the mounting site of the information read/write device may be eliminated. The relaying device is formed by a resonance circuit including a first antenna coil, electro-magnetically coupled to an antenna coil of the information read/write device, a second antenna coil, connected in series with the first antenna coil and electro-magnetically coupled to an antenna coil of the non-contact information medium, and a tuning capacitor connected in series with the first antenna coil and the second antenna coil. The first antenna coil, second antenna coil and the tuning capacitor making up the resonance circuit is resonated with the same resonance frequency as that of the resonance circuit of the information read/write device and that of the resonance circuit of the non-contact information medium.  
         [0026]     In a further aspect, the present invention provides a communication system for wireless communication of the electromagnetic coupling system, mediated by a carrier wave of a preset frequency, in which the communication system comprises an information read/write device including a first resonance circuit made up by a first antenna coil and by a first tuning capacitor connected in series with the first antenna coil, with the information read/write device having wireless communication with a circuit electromagnetically coupled to the first antenna coil, with the resonance frequency of the first resonance circuit as the frequency of the carrier wave. The communication system also comprises a non-contact information medium including a second resonance circuit made up by a second antenna coil and by a second tuning capacitor connected in series with the second antenna coil, with the second resonance circuit resonating with a resonance frequency which is the same as the resonance frequency of the first resonance circuit and having wireless communication with a circuit electro-magnetically coupled to the second antenna coil, and a relaying device including a third resonance circuit, made up by a third antenna coil, electro-magnetically coupled to the first antenna coil of the information write device, a fourth antenna coil connected in series with the third coil and electro-magnetically coupled with the antenna coil of the non-contact information medium, and a third tuning capacitor connected in series with the third and fourth antenna coils. The third relaying circuit resonates with the same resonance frequency as the resonance frequency of the first resonance circuit and the second resonance circuit. The relaying device relays the wireless communication between the information read/write device and the non-contact information medium.  
         [0027]     In yet another aspect, the present invention provides a communication system for wireless communication of the electromagnetic coupling system, mediated by a carrier wave of a preset frequency, in which the communication system comprises an information read/write device including a first resonance circuit made up by a first antenna coil and by a first tuning capacitor connected in series with the first antenna coil, with the information read/write device having wireless communication with a circuit electromagnetically coupled to the first antenna coil, with the resonance frequency of the first resonance circuit as the frequency of the carrier wave. The communication system also comprises a non-contact information medium including a second resonance circuit made up by a second antenna coil and by a second tuning capacitor connected in series with the second antenna coil, with the second resonance circuit resonating with a resonance frequency which is the same as the resonance frequency of the first resonance circuit and having wireless communication with a circuit electroinagnetically coupled to the second antenna coil, and a relaying device including a third resonance circuit, made up by a third antenna coil, electromagnetically coupled to the first antenna coil of the information write device, a fourth antenna coil connected in series with the third coil and electromagnetically coupled with the antenna coil of the non-contact information medium, and a third tuning capacitor connected in series with each of the third and fourth antenna coils. The third relaying circuit resonates with the same resonance frequency as the resonance frequency of the first resonance circuit and the second resonance circuit. The relaying device relays the wireless communication between the information read/write device and the non-contact information medium.  
         [0028]     The relaying device of the present invention includes, for wireless communication by the electromagnetic coupling system between the information read/write device and the non-contact information medium, a first antenna coil, electro-magnetically coupled to an antenna coil of the information read/write device, and a second antenna coil, electromnagnetically coupled to an antenna coil of the non-contact information medium, and assures optimum wireless communication even in cases wherein the antenna coil of the information read/write device has a shape and a size differing appreciably from those of the antenna coil of the non-contact information medium.  
         [0029]     The wireless communication between the non-contact information medium and a wide variety of use configurations of the read/write device may be optimized by a simple technique of changing the size/shape of the first and second antenna coils of the relaying device so that the first and second antenna coils may be electro-magnetically coupled to the antenna coils of the information read/write device and the non-contact information medium, respectively.  
         [0030]     The communication system of the present invention includes, for wireless communication by the electromagnetic coupling system between the information read/write device and the non-contact information medium, a third antenna coil, electromagnetically coupled to the first antenna coil of the information read/write device, and a fourth antenna coil, electromagnetically coupled to the second antenna coil of the non-contact information medium, and assures optimum wireless communication even in cases wherein the antenna coil of the information read/write device has a shape and a size differing appreciably from those of the antenna coil of the non-ontact information medium.  
         [0031]     Moreover, the wireless communication between the non-contact information medium and a wide variety of use configurations of the read/write device may be optimized by a simple technique of changing the size/shape of the third and fourth antenna coils of the relaying device of the communication system so that the third and fourth antenna coils will be electromagnetically coupled to the first antenna coils of the information read/write device and the second antenna coil of the non-contact information medium, respectively.  
         [0032]     In case limitations are imposed on the space in which to mount the first antenna coil, it is sufficient that the third antenna coil is changed in shape/size so as to be electrically coupled to the first antenna coil. In case limitations are imposed that the first antenna coil has to be mounted on a metal component, such as a casing, the size of the first antenna coil or the aperture formed in the casing may be of the smallest size possible to assure the strength of the casing as well as to avoid adverse effects by the metal components.  
         [0033]     The relaying device of the communication system of the present invention performs wireless communication of the electromagnetic coupling system with the information read/write device, no laborious processing, such as wiring, is needed, and is able to relay the wireless communication with the non-contact information medium by fitting the relaying device on a removable cover or to a door that may be opened/closed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]      FIG. 1  illustrates the configuration of a communication system sowing the best embodiment of the present invention.  
         [0035]      FIG. 2  illustrates the configuration of a matching tuning circuit of the communication system.  
         [0036]      FIG. 3  shows an example of concrete setup of the communication system.  
         [0037]      FIG. 4  illustrates the configuration of a matching tuning circuit of the communication system.  
         [0038]      FIG. 5  shows an induction current I flowing in a matching tuning circuit of the communication system.  
         [0039]      FIG. 6  shows another example of concrete setup of the communication system.  
         [0040]      FIG. 7  shows a matching tuning circuit provided with a parallel-connected antenna coil.  
         [0041]      FIG. 8  illustrates an experiment 1 carried out for verifying the effect of the matching tuning circuit.  
         [0042]      FIG. 9  illustrates a communication range XY in the experiment 1.  
         [0043]      FIG. 10  shows the results of an experiment on a communication range Z in the experiment 1.  
         [0044]      FIG. 11  shows the results of an experiment on the communication range XY in the experiment 1.  
         [0045]      FIG. 12  illustrates an experiment 2 carried out for verifying the effect of the matching tuning circuit.  
         [0046]      FIG. 13  illustrates an iron plate used in the experiment 2.  
         [0047]      FIG. 14  shows the communication range XY in the experiment 2.  
         [0048]      FIG. 15  shows the results of an experiment on the communication range Z in the experiment 2.  
         [0049]      FIG. 16  shows the results of an experiment on the communication range Z in the experiment 2.  
         [0050]      FIG. 17A  shows an example of an antenna coil of a non-contact IC card and  FIG. 17B  shows an example of an antenna coil for a reader/writer.  
         [0051]      FIG. 18  shows the magnetic flux passed through the antenna coil of the non-contact IC card.  
         [0052]      FIG. 19  shows an example of concrete setup of a reader/writer of a communication system shown as a prior art.  
         [0053]      FIG. 20  shows the magnetic flux passed through an antenna coil of a non-contact IC card when an antenna coil of the reader/writer is mounted on a metal chassis.  
         [0054]      FIG. 21  shows an example of mounting the antenna coil of the reader/writer of the communication system of the prior art as a relay antenna. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0055]     Referring now to the drawings, the best embodiments of a relay apparatus and a communication system of the present invention are explained in detail.  
         [0056]     Referring first to  FIG. 1 , a communication system  1  as the best embodiment for carrying out the present invention is explained.  
         [0057]     The communication system  1 , shown in  FIG. 1 , is an RFID (Radio Frequency Identification), by the electromagnetic coupling system, provided with a reader/writer  10 , a non-contact IC card  20 , and a matching tuning circuit  30 .  
         [0058]     In this communication system  1 , the non-contact IC card  20 , as a non-contact information medium, receives electrical waves, transmitted from the reader/writer  10  through the matching tuning circuit  30 , to obtain the power by electromagnetic induction, and has data communication with the reader/writer  10 , with use of the electrical waves, through the matching tuning circuit  30 .  
         [0059]     The reader/writer  10  includes a parallel resonance circuit  13 , comprised of a serial connection of an antenna coil  11 , as an inductor, and a tuning capacitor  12 . A reader/writer for IC  14  is connected in parallel with this parallel resonance circuit  13 . The reader/writer  10  is tuned to a frequency fc in the vicinity of, for example, 13.56 MHz, as the a.c. voltage is applied to the parallel resonance circuit  13 , under control by the reader/writer for IC  14 .  
         [0060]     The reader/writer  10  has wireless communication with the non-contact IC card  20 , using the electrical waves, which have modulated a carrier having this frequency fc as the carrier frequency. Although the carrier frequency is the frequency fc, in the following explanation, the carrier frequency fc is not limited to 13.56 MHz.  
         [0061]     The reader/writer for IC  14  is provided with an interfacing circuit, not shown, and is connected to and controlled by a CPU (central processing unit) of a counterpart device, having loaded thereon the reader/writer  10 .  
         [0062]     The reader/writer for IC  14  controls the operation in sending data from the reader/writer  10  to the non-contact IC card  20  and in receiving data sent from the non-contact IC card  20 .  
         [0063]     In data transmission, the reader/writer for IC  14  modulates the carrier wave of the carrier frequency fc with data being transmitted to generate transmission signals. As the data modulating system, ASK (amplitude shift keying), PWM (pulse width modulation) or the PSK (phase shift keying), for example, may be used.  
         [0064]     The transmission signals, generated on modulation, are sent to the antenna coil  11  to generate a magnetic field. The magnetic field, generated in the antenna coil  11 , is changed in keeping with the transmission signals, such that data carried by the carrier wave with the carrier frequency fc is transmitted, as changes in the magnetic flux, to an antenna coil  31  of the matching tuning circuit  30 , electromagnetically coupled to the antenna coil  11 .  
         [0065]     In data receipt, the reader/writer for IC  14  demodulates the data, transmitted from the non-contact IC card  20  through the matching tuning circuit  30  and received as changes in the magnetic flux by the antenna coil  11 . On receipt of the data by the antenna coil  11  from the non-contact IC card  20 , the induced current is generated in the antenna coil  11  as a result of changes in the magnetic flux in the antenna coil  31  of the matching tuning circuit  30  electromagnetically coupled with the antenna coil  11 .  
         [0066]     As the induced current, generated in the antenna coil  11 , is changed with the magnetic flux, the data carried by the carrier wave with the carrier frequency fc is transmitted to the antenna coil  11  as changes in the induced current.  
         [0067]     The reader/writer for IC  14  demodulates this induced current to acquire data transmitted from the non-contact IC card  20 .  
         [0068]     The non-contact IC card  20  includes a parallel resonance circuit  23 , which is a serial connection of an antenna coil  21 , as an inductor, and a tuning capacitor  22 . An IC for a card  24  is connected in parallel with this parallel resonance circuit  23 .  
         [0069]     The antenna coil  21  receives the electrical waves, transmitted from the reader/writer  10  through the matching tuning circuit  30 , as changes in the magnetic flux. In the parallel resonance circuit  23 , there is generated the induced electromotive force operating in a direction of obstructing changes in the magnetic flux of the electrical waves received by the antenna coil  11 . By this induced electromotive force, the parallel resonance circuit  23  is tuned in the vicinity of the frequency fc=13.56 MHz.  
         [0070]     The IC for a card  24 , connected in parallel with the parallel resonance circuit  23 , is operated with this induced electromotive force as the operating power. The IC for a card  24 , supplied with the operating power, controls the operation in receiving data sent from the reader/writer  10  and in transmitting data to the reader/writer  10 .  
         [0071]     In data receipt, the IC for a card  24  demodulates the electrical waves, transmitted from the reader/writer  10  through the matching tuning circuit  30  and received as changed in the magnetic flux in the antenna coil  21 .  
         [0072]     In data transmission, the IC for a card  24  modulates the carrier wave, with the carrier frequency fc, with data to be transmitted, to generate transmission signals. The IC for a card  24  changes the load of the antenna coil  21 , responsive to data to be transmitted, to modulate the carrier wave, by way of load modulation.  
         [0073]     The transmission signals, generated on modulation, are sent to the antenna coil  21  to generate a magnetic field. As the magnetic field, generated in the antenna coil  21 , is changed with the transmission signals, the data carried by the carrier wave, with the carrier frequency fc, is transmitted, as changes in the magnetic flux, to an antenna coil  32  of the matching tuning circuit  30 , electromagnetically coupled with the antenna coil  21 .  
         [0074]     The matching tuning circuit  30  includes a parallel resonance circuit  34 , comprised of a series connection of an antenna coil  31 , as a first inductor, an antenna coil  32 , as a second inductor, and a tuning capacitor  33 .  
         [0075]     Specifically, the matching tuning circuit  30  is comprised of the antenna coils  31 ,  32 , arranged on a substrate  35 , so as to be connected in series with the tuning capacitor  33 .  
         [0076]     The antenna coil  31  is electro-magnetically coupled, in a non-contact fashion, with the antenna coil  11 , forming the parallel resonance circuit  13  in the reader/writer  10 , and is shaped for communicating with the reader/writer  10 .  
         [0077]     The antenna coil  31  may be of any suitable shape, on the condition that it may communicate with the reader/writer  10 . For example, the antenna coil  31  may be of an elliptical or a square shape, to say nothing of the circular shape shown in  FIG. 1 .  
         [0078]     The antenna coil  31  does not have to be of the same shape as the antenna coil  11 , on the condition that the antenna coil  31  is able to communicate with the reader/writer  10 . However, in case the antenna coil  31  is approximately of the same shape and of the same size as the antenna coil  11 , the electromagnetic coupling may be stronger to achieve stable and highly efficient data communication.  
         [0079]     On the other hand, the antenna coil  32  is electromnagnetically coupled, in a non-contact fashion, with the antenna coil  21  on the non-contact IC card  20 , forming the parallel resonance circuit  23 , such as to communicate with the non-contact IC card  20 .  
         [0080]     The antenna coil  32  may be of any suitable shape, on the condition that it may communicate with the reader/writer  10 . For example, the antenna coil  31  may be of an elliptical or a circular shape, to say nothing of the square shape shown in  FIG. 1 .  
         [0081]     The antenna coil  32  is desirably larger in size than the antenna coil  21 , provided to the non-contact IC card  20 , since then a sufficient amount of the magnetic flux can be passed through the antenna coil  21  even in case the center of the antenna coil  21  is offset from the center of the antenna coil  32 .  
         [0082]     For example, in case the non-contact information medium is a non-contact IC card, and is used as a commutation ticket for railway or bus, the non-contact IC card cannot be placed at a constant fixed position at all times with respect to the antenna coil  32  of the matching tuning circuit  30  for data communication. Thus, in such case, the antenna coil  32  is larger in size than the antenna coil of the non-contact IC card to assure more reliable data communication.  
         [0083]     For example, if the non-contact information medium is a non-contact IC tag affixed to a toner cartridge of a printer, as a consumable commodity, and is to have data communication with the reader/writer  10  mounted to a preset inner chassis in a printer casing, in order to manage the residual toner quantity, the non-contact IC tag may be placed in a fixed position relative to the antenna coil  32  of the matching tnning circuit  30  for data communication. Thus, in such a case, more efficient data communication may be had with the antenna coil  32  sized to be approximately equal to the size of the antenna coil of the non-contact IC tag.  
         [0084]     If the antenna coil  32  is slightly smaller in size than the antenna coil  21 , communication may be had by adjusting the output of the reader/writer  10 .  
         [0085]     The antenna coil  32  does not have to be of the same size and shape as the antenna coil  21 , on the condition that the antenna coil  32  is able to communicate with the non-contact IC card  20 , as discussed above. However, if the antenna coil  32  is of the same size and shape as the antenna coil  21 , the electromagnetic coupling becomes stronger to realize more efficient stable data communication.  
         [0086]     That is, the size as well as the shape of the antenna coils  31 ,  32  of the matching tuning circuit  30  is limited to a more or less extent by the shape of the antenna coil  11  of the reader/writer  10  and by the shape of the antenna coil  21  of the non-contact IC card  20 , respectively, for the realization of the efficient stable wireless communication.  
         [0087]     With the communication system  1 , shown as the best embodiment for carrying out the present invention, the non-contact IC card  20  is used as the non-contact information medium. Hence, in the following explanation, it is assumed that the shape and the size of the antenna coil  32  are approximately the same as those of the antenna coil  21  of the noncontact IC card  20 , and also that the shape and the size of the antenna coil  31  are approximately the same as those of the antenna coil  11  of the reader/writer  10 .  
         [0088]     Since the antenna coils  31 ,  32  are connected in series with each other so that these coils are wound in the same direction, the antenna coils  31 ,  32  may be deemed to be an inductor having a combined inductance L=L 1 +L 2 , where L 1  is the inductance of the antenna coil  31  and L 2  is the inductance of the antenna coil  32 . Consequently, the parallel resonance circuit  34  may be deemed to be a resonance circuit comprised of a series connection of an inductor having a combined inductance L and the tuning capacitor  33 .  
         [0089]     Referring to  FIG. 3 , a concrete setup example of the reader/writer  10  and the matching tuning circuit  30  is shown and, based on this setup example, the operating principle of the matching tuning circuit  30  is explained.  
         [0090]     It is assumed that the reader/writer  10 , provided on a substrate  15 , is mounted on the back side of a metal chassis  50 , as a casing of an apparatus on which to mount the reader/writer  10 . The metal chassis  50 , on which the reader/writer  10  is mounted in this manner, has an aperture  50 A in a location which is to be register with the mounting position of the antenna coil  11  of the reader/writer  10 .  
         [0091]     The opening area of the aperture  50 A is selected to be such that the strength of the metal chassis  50  is not impaired and such that there is no risk of leakage of the electromagnetic noise produced by e.g. an electronic circuit within the metal chassis  50 . The shape and the size of the antenna coil  11  of the reader/writer  10  are selected so that the antenna coil will be housed within this aperture  50 A.  
         [0092]     Since the antenna coil  31  of the matching tuning circuit  30  is shaped so that the antenna coil  31  is electro-magnetically coupled with the antenna coil  11  in a non-contact fashion and so that the antenna coil  31  may communicate with the reader/writer  10 , the shape of the antenna coil  31  is determined to a more or less extent if once the shape of the antenna coil  11  is determined.  
         [0093]     On the other hand, the matching tuning circuit  30  is mounted for facing the reader/writer  10 , mounted on the metal chassis  50 , with the metal chassis  50  in-between. The matching tuning circuit  30  is mounted at this time so that the antenna coil  31  overlies the aperture  50 A formed in the metal chassis  50 . By so doing, the antenna coil  11  of the reader/writer  10  and the antenna coil  31  of the matching tuning circuit  30  may be electromagnetically coupled to each other in a non-contact fashion.  
         [0094]     Since the reader/writer  10  mounted to the metal chassis  50  and the matching tuning circuit  30  may have wireless communication by the antenna coils  11 ,  31  being electromagnetically coupled to each other in a non-contact fashion, no physical connection between the reader/writer  10  and the matching tuning circuit  30  is needed and hence the matching tuning circuit  30  may be mounted in position by a simplified technique of directly bonding the substrate  30  to the metal chassis  50  with e.g. a double-sided adhesive tape.  
         [0095]     The matching tuning circuit  30 , mounted to the metal chassis  50  operates as follows, by the electrical waves, transmitted from the reader/writer  10 .  
         [0096]     The antenna coil  31  of the parallel resonance circuit  34  of the matching tuning circuit  30  is traversed by a magnetic flux A, generated by a magnetic field, generated in turn by the antenna coil  11  of the reader/writer  10 , for electromagnetically coupling the antenna coils  11 ,  31  to each other.  
         [0097]     The induced electromotive force is generated in the parallel resonance circuit  34  by the magnetic flux A traversing the antenna coil  31 , so that the induced current I by the induced electromotive force flows through the entire circuit. The parallel resonance circuit  34  is tuned by the induced electromotive force in the vicinity of the frequency fc=13.56 MHz.  
         [0098]     When the induced current I flows through the antenna coil  32 , a magnetic field is generated in the coil  32 .  
         [0099]     At this time, the non-contact IC card  20  may be moved to the vicinity of the matching tuning circuit  30 . Thus, the magnetic flux B, generated by the magnetic field, generated in turn in the antenna coil  32 , is passed through the inside of the antenna coil  21 , as shown in  FIG. 4 . This electromagnetically couples the antenna coils  32 ,  21  to each other.  
         [0100]     When the magnetic flux B traverses the antenna coil  21  of the non-ontact IC card  20  in this manner, the non-contact IC card  20  is activated so that the reader/writer  10  and the non-contact IC card  20  are now able to have wireless communication with each other through the matching tuning circuit  30 .  
         [0101]     Referring to the cross-sectional view of  FIG. 6 , another setup example of the reader/writer  10  and the matching tuning circuit  30  is hereinafter explained.  
         [0102]     Referring to  FIG. 6 , the reader/writer  10  is mounted on the back-side surface of a metal chassis  51 , as a casing of a device, adapted for being loaded with the reader/writer  10 , so that the antenna coil  11  will be in register with an aperture  51 A of the metal chassis  51 .  
         [0103]     On the front side surface of the metal chassis  51 , having the reader/writer  10  mounted thereon, there is provided a metal component  52 , such as a screw, such that the matching tuning circuit  30  cannot directly be mounted thereon, as shown in  FIG. 6 .  
         [0104]     Thus, the matching tuning circuit  30  is mounted in position by bonding the substrate  35  of the matching tuning circuit  30  on the back side surface of a resin cover  53  overlying the aperture S 5 A of the metal chassis  51 .  
         [0105]     The matching tuning circuit  30  is bonded to the back-side surface of the resin cover  53 , so that, when the resin cover  53  is mounted to the metal chassis  51 , the antenna coil  31  of the matching tuning circuit  30  is in register with the antenna coil  11  of the reader/writer  10 .  
         [0106]     The cover  53 , to which is bonded the matching tuning circuit  30 , is formed of nonmagnetic resin, in order to cause no loss of the magnetic flux by the magnetic field generated in the antenna coil  32  of the matching tuning circuit  30 . The substrate  35  of the matching tuning circuit  30  is of an extremely thin thickness, and is e.g. a flexible substrate, so as not to affect the magnetic field generated in the antenna coil  32 .  
         [0107]     A shield plate  54  may also be provided in order to prevent the effect of the electromagnetic noise generated in the device designed for carrying the reader/writer  10 . The shield plate  54  needs only to be mounted to overlie the antenna coil  11 . At this time, caution should be exercised so that the shield plate  54  is kept aloof from the reader/writer  10  in order to prevent the function of the antenna coil  11  from being impaired.  
         [0108]     The matching tuning circuit  30 , mounted to the resin cover  53 , may also be mounted to the inner side of a rotatable door, provided to e.g. a casing of the device loaded with the reader/writer  10 , in a manner not shown, for saving the spacing.  
         [0109]     Thus, there is no necessity for providing the wiring for the matching tuning circuit  30 , in order for the matching tuning circuit  30  to communicate with the reader/writer  10 , and the matching tuning circuit  30  may be separated from the reader/writer  10  and mounted freely to any place within the sphere of electromagnetic coupling. The result is the communication system  1  with an extremely high degree of mounting freedom.  
         [0110]     In the matching tuning circuit  30  of the above-described communication system  1 , the antenna coils  31 ,  32  are connected in series with each other. In the communication system  1 , a matching tuning circuit  40 , in which a parallel resonance circuit  41  is made up by a parallel connection of the antenna coils  31 ,  32  and the tuning capacitor  33 , as shown in  FIG. 7 , may be used in place of the matching tuning circuit  30 . The case of using the matching tuning circuit  40  is not explained in detail because the operation of the communication system  1  gives the identical effect in case the matching tuning circuit  40  is used in place of the matching tuning circuit  30 .  
         [0111]     Meanwhile, the tuning capacitor  33  is connected in series with both the antenna coils  31 ,  32 , as shown in  FIG. 7 .  
       Embodiment  
       [0112]     By way of an embodiment, the results of an experiment, conducted for measuring the effect by the matching tuning circuit  30 , are shown.  
         [0113]     In the experiment, the area which allows for communication for the case of using the matching tuning circuit  30  and that for the case of not using the matching tuning circuit  30 , in the wireless communication between the reader/writer  10  and the non-contact IC card  20 , were measured and compared to each other.  
         [0114]     The same experiment was conducted as an iron plate having an aperture of the same shape as the antenna coil  11  of the reader/writer  10  was interposed between the reader/writer  10  and the non-contact IC card  20 , in order to verify the effect by the matching tuning circuit  30  under the actual assumed use condition of the matching tuning circuit  30 , as shown in  FIGS. 3 and 6 .  
         [0000]     (Experiment 1)  
         [0115]     In an experiment 1, measurement was made of the area which allows for communication, in case the reader/writer  10  and the non-contact IC card  20  were arranged in a free space devoid of an obstacle, and the reader/writer  10  was activated in this state, and of the area which allows for communication, in case the matching tuning circuit  30  was interposed between the reader/writer  10  and the non-contact IC card  20 , and the reader/writer  10  was activated in this state, as shown in  FIG. 8 .  
         [0116]     The antenna coil  11  of the reader/writer  10  was circular in shape, with a diameter on the order of 25 mm. The antenna coil  31  of the matching tuning circuit  30  was of approximately the same shape. The non-contact IC card  20  used was of the size of 54 mm in length, 85.6 mm in width and 0.76 mm in thickness, as provided for in the ISO (International Organization for Standardization). The antenna coil  21 , enclosed in the non-contact IC card  20 , was wound to approximate the size of the non-contact IC card  20 . The antenna coil  32  of the matching tnning circuit  30  was approximately of the same shape as the antenna coil  21 .  
         [0117]     The area which allows for communication, and which is to be measured, is now explained. The area which allows for communication, and which is now to be measured, is defined by a distance for communication Z, representing the distance which allows for communication, in case the non-contact IC card  20  is moved vertically relative to the reader/writer  10 , and by a distance for communication XY, representing the distance which allows for communication, in case the non-contact IC card  20  is moved horizontally relative to the reader/writer  10 .  
         [0118]     Specifically, the distance for communication Z is a distance up to which the communication is possible when the center of the antenna coil  11  of the reader/writer  10 , placed horizontally, is confounded with the center of the major plane surface of the non-contact IC card  20 , and when the non-contact IC card  20  is moved in the vertical direction, as it is kept parallel to the antenna coil  11 .  
         [0119]     The distance for communication XY is a distance up to which the communication is possible when the non-contact IC card  20 , placed horizontally at a preset distance with respect to the antenna coil  11  of the reader/writer  10 , is optionally moved along the X-axis direction and along the Yogis direction within the X-Y coordinate plane shown in  FIG. 9 . This distance for communication may be found by measuring the trajectory of the center point of the non-contact IC card  20 .  
         [0120]     This distance for communication Z and the distance for communication XY, thus measured, may be used as indexes for the effect of the matching tuning circuit  30 .  
         [0121]     First,  FIG. 10  shows the results of measurement of the distance for communication Z without the matching tuning circuit  30  and the results of measurement of the distance for communication Z with the matching tuning circuit  30  placed in position. Meanwhile, since the matching tuning circuit  30  is mounted at a distance of 10 mm from the antenna coil  11  of the non-contact IC card  10 , the distance for communication for the case the matching tuning circuit  30  is placed in position was measured from the position of the intervening matching tuning circuit  30 .  
         [0122]     The distance for communication Z without the matching tuning circuit  30  was 10 to 25 mm, as shown in  FIG. 10 . The same distance Z with the matching tuning circuit  30  interposed in position was 20 to 75 mm. Thus, it may be seen that, by placing the matching tuning circuit  30  between the reader/writer  10  and the non-contact IC card  20 , the distance for communication Z is approximately tripled.  
         [0123]     If, in case the matching tuning circuit  30  is placed in position, the non-contact IC card  20  is at a distance of 10 to 20 mm from the antenna coil  11 , the communication becomes infeasible because the non-contact IC card  20  and the matching tuning circuit  30  interfere with each other and become unstable in operation. This inconvenience may be overcome by strictly matching the resonance frequency of the non-contact IC card  20  to that of the matching tuning circuit  30  or by significantly separating the two resonance frequencies from each other.  
         [0124]      FIG. 11  shows the results of measurement of the distance for communication XY without the matching tuning circuit  30  and the results of measurement of the distance for communication XY with the matching tuning circuit  30  placed in position.  
         [0125]     In case the matching tuning circuit  30  is not used, the distance for communication XY was measured at a location separated in the vertical direction by 10 mm from the center of the antenna coil  11  of the reader/writer  10 . In case the matching tuning circuit  30  is used, the distance for communication XY was measured at a location separated 10 mm in the vertical direction from the center of the antenna coil  32  of the matching tuning circuit  30 .  
         [0126]     Meanwhile, the location of insertion of the matching tuning circuit  30  is 10 mm away from the reader/writer  10 , as set forth above.  
         [0127]     In the absence of the matching tuning circuit  30 , the distance for communication XY is such that −30≦X (mm)≦30 and −15≦Y (mm)≦15, as shown in  FIG. 11 . That is, the distance for communication XY is defined to be the inside of an ellipsis, with a long axis of 60 mm and a short axis of 30 mm, as indicated by a broken line.  
         [0128]     In case the matching tuning circuit  30  is placed in position, the distance for communication XY is such that −50≦X (mm)≦50 and −40≦Y (mm)≦40, as shown in  FIG. 11 . That is, in  FIG. 11 , the distance for communication XY is defined to be the inside of an ellipsis, with a long axis of 100 mm and a short axis of 80 mm, as indicated by a solid line.  
         [0129]     Thus, it may be seen that, by placing the matching tuning circuit  30  between the reader/writer  10  and the non-contact IC card  20 , the distance for communication XY is quadrupled.  
         [0000]     (Experiment 2)  
         [0130]     In the experiment 2, the reader/writer  10  was bonded to an iron plate  60 , which iron plate,. stuck to the reader/writer  10 , was placed so as to prove an obstacle between the reader/writer  10  and the noncontact IC card  20  to approximate the actual use state, as shown in  FIG. 12 . The distance for communication Z and the distance for communication XY were measured for the case in which the matching tuning circuit  30  was used and for the case in which the matching tuning circuit  30  was not used.  
         [0131]     In the iron plate  60 , there is bored an aperture  60 A of approximately the same shape as that of the antenna coil  1  of the reader/writer  10 . When the reader/writer  10  is stuck to the iron plate  60 , attention is to be paid so that the aperture  60 A is in register with the antenna coil  11 .  
         [0132]     In the experiment  2 , the reader/writer  10 , noncontact IC card  20  and the matching tuning circuit  30  used are to be exactly the same as those used in the experiment 1. In using the matching tuning circuit  30 , a spacer  61  is interposed between the iron plate  60  and the matching tuning circuit  30 , and the separation between the antenna coil  11  of the reader/writer  10  and the matching tuning circuit  30  is set to 5 mm, as shown in  FIG. 12 .  
         [0133]     The measured results of the distance for communication Z, shown in  FIG. 12 , and those for the distance for communication XY, shown in  FIG. 14 , are shown below. First,  FIG. 15  shows the measured results of the distance for communication Z, in the absence of the matching tuning circuit  30 , and those of the distance for communication Z with the matching tuning circuit  30  placed in position. Meanwhile, since the matching tuning circuit  30  in the experiment 2 is placed at a separation of 5 mm from the antenna coil  11  of the reader/writer  10 , the distance for communication Z was measured from the position of the matching tuning circuit  30 .  
         [0134]     In the absence of the matching tuning circuit  30 , the communication disabled state was invited, in which communication is disabled under the influence of the iron plate  60 , as shown in  FIG. 15 . The distance for communication Z, in case the matching tuning circuit  30  was placed in position, was 5 to 35 mm.  
         [0135]     Thus, by introducing the matching tuning circuit  30  between the reader/writer  10  noncontact IC card  20 , the wireless communication by the reader/writer  10  and the non-contact IC card  20  may be improved from the communication disabled state to a practically satisfactory state.  
         [0136]      FIG. 16  shows the measured results of the distance for communication XY in the absence of the matching tuning circuit  30  and those of the same distance with the matching tuning circuit  30  placed in position.  
         [0137]     In the absence of the matching tuning circuit  30 , the distance for communication XY was measured at a position 5 mm spaced apart in the vertical direction from the center of the antenna coil  11  of the reader/writer  10  and, in case the matching tuning circuit  30  was placed in position, the same distance XY was measured at a location 5 mm spaced apart from the center of the antenna coil  32  of the matching tuning circuit  30 .  
         [0138]     It is noted that the matching tuning circuit  30  is introduced at a position 5 mm spaced apart from the antenna coil  11  of the reader/writer  10 , as noted previously.  
         [0139]     In case the matching tuning circuit  30  is not used, the communication is disabled, as shown in  FIG. 16 . The distance for communication XY is such that −35≦X (mm)≦35 and −20≦Y (mm)≦20. That is, as shown in  FIG. 16 , the distance for communication XY is defined to be the inside of an ellipsis, with a long axis of 70 mm and a short axis of 40 mm, as indicated by a solid line in  FIG. 16 .  
         [0140]     Thus, it may be seen that, by placing the matching tuning circuit  30  between the reader/writer  10  and the non-contact IC card  20 , the wireless communication by the reader/writer  10  and the non-contact IC card  20  may be improved from the communication disabled state to a practically satisfactory state.