Abstract:
A contactless communication medium includes: a base material made of an insulating material; an antenna coil portion formed by winding a conductor in a plane on the base material; a capacitor connected to the antenna coil portion; a communication processing section connected to the antenna coil portion and the capacitor to perform a contactless communication process; and a metal pattern having a predetermined area and disposed in a region surrounded by the antenna coil portion, the metal pattern being not electrically connected to the antenna coil portion or the capacitor.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. JP 2010-108803 filed in the Japanese Patent Office on May 10, 2010, the entire content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a contactless communication medium that performs contactless wireless communication with a reader/writer in proximity, an antenna pattern arrangement medium provided in the contactless communication medium, a communication apparatus incorporating the contactless communication medium, and a communication method for contactless wireless communication. 
     2. Description of the Related Art 
     So-called contactless IC cards are commonly used as a contactless communication medium that performs contactless wireless communication with a reader/writer in proximity. The contactless IC cards are widely used, for example, for ticket examination systems in railway stations, payment systems in convenience stores and so forth, room entry/exit systems, and so forth. The contactless IC cards are also referred to as RFID (Radio Frequency Identification) tags or wireless IC tags. 
     Such a contactless IC card includes an IC chip embedded inside the card, which allows quick reaction and processing for room entry/exit and billing management, and thus enhances the convenience of the card compared to a magnetic card. 
       FIGS. 11A and 11B  show an exemplary configuration of a contactless IC card according to the related art.  FIG. 11A  shows a circuit for contactless communication disposed on a resin base material. In a contactless IC card as an actual product, the circuit is concealed by an outer shell material such as a film disposed on the front surface of the card. 
     The configuration shown in  FIG. 11A  is described. An antenna coil portion  20  is disposed on the front surface of a base material  10  close to the outer periphery of the base material  10 . The antenna coil portion  20  is formed by winding a conductor pattern made of a conductor such as copper or aluminum and having a constant width in a plurality of turns (in the example, four turns) at constant intervals on the surface of the base material  10  close to the outer periphery of the base material  10 . 
     A first end portion  21  and a second end portion  22  of the antenna coil portion  20  are connected to an IC chip  11  serving as an integrated circuit component that performs a communication process. In this case, the first end portion  21  of the antenna coil portion  20  is led to the back surface of the base material  10  to be connected to the IC chip  11 , which performs a communication process, via a conductor pattern  14  provided on the back surface. The second end portion  22  of the antenna coil portion  20  is connected to the IC chip  11  via a conductor pattern  13 . 
     The first end portion  21  and the second end portion of the antenna coil portion  20  are also connected to a capacitor  12  and an adjustment capacitor  30 . The first end portion  21  of the antenna coil portion  20  is connected to the capacitor  12  and the adjustment capacitor  30  also via the conductor pattern  14  provided on the back surface. 
     The capacitor  12  accumulates charge generated by a carrier wave received by the antenna coil portion  20  to obtain electric power for driving the IC chip  11 , and includes a first electrode portion formed by a conductor pattern provided on the front surface and a second electrode portion formed by a conductor pattern provided on the back surface. The capacitor  12  accumulates charge with the first electrode portion and the second electrode portion, which face each other via the base material  10 . Each of the electrode portions forming the capacitor  12  has a relatively large area so as to be able to accumulate a relatively large amount of charge. 
     The adjustment capacitor  30  is configured to change the resonant frequency. The adjustment capacitor  30  includes a first conductor pattern  31  provided on the front surface and connected to the second end portion  22  of the antenna coil portion  20  and a second conductor pattern  32  provided on the back surface and connected to the conductor pattern  14 . The first conductor pattern  31  provided on the front surface is formed to include comb-teeth conductor patterns. The second conductor pattern  32  provided on the back surface is formed to orthogonally intersect the comb-teeth portions. Charge is accumulated at each of the intersections. The adjustment capacitor  30  has a small capacitance compared to the capacitor  12 . The adjustment capacitor  30  increases the resonant frequency by cutting off some of the comb-teeth conductor patterns to reduce the condenser capacitance during adjustment of the resonant frequency in a contactless IC card manufacturing process. 
       FIG. 11B  shows a circuit that is equivalent to the configuration of the contactless IC card shown in  FIG. 11A . 
     As shown in  FIG. 11B , the IC chip  11  and the capacitor  12  and the adjustment capacitor  30  are connected in parallel with the antenna coil portion  20 . 
     The adjustment process for increasing the resonant frequency using the adjustment capacitor  30  is performed by cutting off portions of the first conductor pattern  31  and the second conductor pattern  32 . In the process, for example, a hole is formed in the base material  10  at a point at which the first conductor pattern  31  is cut, and the first conductor pattern  31  and the second conductor pattern  32  are removed. 
     The resonant frequency adjustment process in the manufacturing process is performed automatically using an adjustment device (not shown). That is, the adjustment device is provided with data on a cutting position for correcting the resonant frequency of a communication medium in advance, and performs adjustment by determining a cutting position on the basis of a resonant frequency obtained through actually measurement and forming a hole in a base material at the determined position. By performing the adjustment, a contactless IC card with an appropriate resonant frequency is obtained. 
       FIGS. 12A and 12B  show an exemplary configuration of a contactless IC card, which is different from the example of  FIGS. 11A and 11B , with an intermediate tap. 
     The configuration shown in  FIG. 12A  is described. An antenna coil portion  20 , which is formed by winding a conductor pattern in a plurality of turns, is disposed on the front surface of a base material  10  close to the outer periphery of the base material  10 . A first end portion  21  and a second end portion  22  of the antenna coil portion  20  are connected to an IC chip  11  serving as an integrated circuit component that performs a communication process. The first end portion  21  of the antenna coil portion  20  is connected to the IC chip  11 , which performs a communication process, via a conductor pattern  14  provided on the back surface. 
     The capacitor  12  is connected to the first end portion  21  of the antenna coil portion  20  on the back surface, and to an end portion  24  of an antenna extension portion  23  extending from the second end portion  22  of the antenna coil portion  20  on the front surface. 
     Regarding the adjustment capacitor  30 , the second conductor pattern  32  provided on the back surface is connected to the conductor pattern  14  provided on the back surface, and the first conductor pattern  31  provided on the front surface is connected to the end portion  24  provided on the front surface. 
       FIG. 12B  shows a circuit that is equivalent to the configuration of the contactless IC card shown in  FIG. 12A . 
     As shown in  FIG. 12B , the IC chip  11  is connected to the antenna coil portion  20 , and the capacitor  12  and the adjustment capacitor  30  are connected to the antenna coil portion  20  via the antenna coil portion  20  and the extension portion  23 . The second end portion  22 , at which the antenna coil portion  20  and the extension portion  23  are connected to each other, serves as an intermediate tap. The adjustment process performed using the adjustment capacitor  30  is the same as the example of  FIGS. 11A and 11B . 
     In the case of the configuration shown in  FIGS. 12A and 12B , adjustment performed using the adjustment capacitor  30  makes it possible to change the overall inductance value without changing the inductance value of components connected to the IC chip  11 . 
     Japanese Unexamined Patent Application Publication No. 2007-102348 discloses an RFID tag in which a dummy pattern is provided outside an antenna coil. 
     SUMMARY OF THE INVENTION 
     While some cellular phone terminals incorporate a contactless IC card that provides an electronic money function or the like, there are a large number of cellular phone terminals and portable music players that do not have an electronic money function, and there is a great desire to add an electronic money function to such cellular phone terminals and portable music players. Therefore, in order to conveniently provide an IC card function to the cellular phone terminals, casings that are capable of storing an IC card and that match the housing of a terminal are currently commercially available. With such casings, however, the IC card is merely placed in close proximity to the cellular phone terminal, which may increase the thickness and the volume of the terminal to deteriorate the usability for users. In addition, the contactless IC cards themselves are designed and manufactured on the assumption of use in a free space (an environment in which there is no metal or the like in proximity), and therefore the presence of any housing for a cellular phone terminal or the like that contains metal in proximity may significantly reduce the communication distance. 
     According to the related art, it is conceived to provide a magnetic sheet between an electronic device and a contactless IC card affixed to the housing of the electronic device in order to satisfy the communication characteristics of the card, which enables improvement in communication distance. Even if the communication distance is improved, however, there may be a region in which communication may not be performed (hereinafter referred to as a communication dead zone) depending on the combination between a reader/writer and a contactless IC card (contactless communication medium). 
     In view of the foregoing, it is desirable to eliminate a communication dead zone in communication performed between a contactless communication medium and a reader/writer. 
     According to an embodiment of the present invention, there is provided a contactless communication medium including: a base material made of an insulating material; an antenna coil portion formed by winding a conductor in a plane on the base material; a capacitor connected to the antenna coil portion; and a communication processing section connected to the antenna coil portion and the capacitor to perform a contactless communication process. 
     The contactless communication medium additionally includes a metal pattern having a predetermined area and disposed in a region surrounded by the antenna coil portion, the metal pattern being not electrically connected to the antenna coil portion or the capacitor. 
     With the metal pattern, which has a predetermined area and which is not electrically connected to the antenna coil portion or the capacitor, disposed in a region surrounded by the antenna coil portion, it is possible to eliminate a communication dead zone without changing the maximum distance over which communication with a reader/writer may be made. 
     According to the present invention, with the metal pattern disposed in a region surrounded by the antenna coil portion, it is possible to eliminate a communication dead zone without changing the maximum distance over which communication with a reader/writer may be made. This allows to favorably perform contactless wireless communication with the reader/writer in the case where the contactless communication medium is affixed to the housing of an electronic device, for example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a plan view showing an exemplary configuration of a contactless communication medium according to an embodiment of the present invention; 
         FIG. 1B  shows a circuit that is equivalent to the configuration of the contactless communication medium of  FIG. 1A ; 
         FIG. 2  is a perspective view showing the front surface and the back surface of the contactless communication medium according to the embodiment of the present invention; 
         FIG. 3  is an exploded perspective view showing the overall configuration of the contactless communication medium according to the embodiment of the present invention; 
         FIG. 4  is an exploded side view showing the contactless communication medium according to the embodiment of the present invention assembled to a terminal device; 
         FIG. 5  shows exemplary communication distance characteristics according to the embodiment of the present invention; 
         FIG. 6  is a plan view showing another example (a first modification with a single metal pattern) of the contactless communication medium according to the embodiment of the present invention; 
         FIG. 7  is a plan view showing another example (a second modification with an increased number of divided metal patterns) of the contactless communication medium according to the embodiment of the present invention; 
         FIG. 8A  shows exemplary communication distance characteristics according to the modification of  FIG. 7 ; 
         FIG. 8B  shows exemplary communication distance characteristics according to the modification of  FIG. 7 ; 
         FIG. 9  is a plan view showing another example (third modification with metal patterns divided in two directions) of the contactless communication medium according to the embodiment of the present invention; 
         FIG. 10A  shows exemplary communication distance characteristics according to the modification of  FIG. 9 ; 
         FIG. 10B  shows exemplary communication distance characteristics according to the modification of  FIG. 9 ; 
         FIG. 11A  is a plan view showing an exemplary configuration of a contactless IC card according to the related art; 
         FIG. 11B  shows a circuit that is equivalent to the configuration of the contactless IC card of  FIG. 11A ; 
         FIG. 12A  is a plan view showing another example (an example with an intermediate tap) of the contactless IC card according to the related art; and 
         FIG. 12B  shows a circuit that is equivalent to the configuration of the contactless IC card of  FIG. 12A . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present invention will be described in the following order. 
     1. Exemplary Configuration of Medium according to Embodiment ( FIGS. 1A ,  1 B, and  2 ) 
     2. Exemplary Overall Configuration ( FIGS. 3 and 4 ) 
     3. Characteristics of Medium according to Embodiment ( FIG. 5 ) 
     4. First Modification ( FIG. 6 ) 
     5. Second Modification ( FIGS. 7 ,  8 A, and  8 B) 
     6. Third Modification ( FIGS. 9 ,  10 A, and  10 B) 
     7. Other Modifications 
     [1. Exemplary Configuration of Medium According to Embodiment] 
     The configuration of a contactless IC card according to an embodiment will be described below with reference to  FIGS. 1A ,  1 B, and  2 . In the embodiment, a conductor pattern to be discussed below is disposed on a base material formed by a resin sheet to form an antenna coil arrangement medium, to which components such as an IC chip are attached to form a contactless communication medium  110 . As discussed later, the contactless communication medium  110  is completed as a contactless IC card by disposing other sheets and so forth on the front and rear sides of the base material. 
       FIG. 1A  is a plan view showing the front surface of the contactless communication medium  110 .  FIG. 2  shows a front surface  110   a  and a back surface  110   b  of the contactless communication medium  110 . It should be noted, however, that the back surface  110   b  shown in  FIG. 2  is as seen from the front side to facilitate understanding the correspondence with the front surface  110   a . Thus, the back surface  110   b  as actually seen from the back side is vertically inverted from that shown in  FIG. 2 . 
     As shown in  FIGS. 1A and 2 , the contactless communication medium  110  is formed by a rectangular base material that is similar to various types of cards, and an antenna coil portion  120  is disposed on the front surface of the contactless communication medium  110  close to the outer periphery of the contactless communication medium  110 . The antenna coil portion  120  is formed by winding a conductor pattern made of a conductor such as copper or aluminum and having a constant width in a plurality of turns (in the example, about four turns) on the front surface  110   a  of the contactless communication medium  110  close to the outer periphery of the contactless communication medium  110 . 
     A first end portion  121  and a second end portion  122  of the antenna coil portion  120  are connected to an IC chip  111  serving as an integrated circuit component that performs a communication process. In this case, the first end portion  121  of the antenna coil portion  120  is led to the back surface of the base material to be connected to the IC chip  111 , which performs a communication process, via a conductor pattern  113  provided on the back surface. As shown in  FIG. 2 , the conductor pattern  113  provided on the back surface is led from the back surface to the front surface of the base material at an IC chip connection point  114  to be connected to the IC chip  111 . The second end portion  122  of the antenna coil portion  120  is directly connected to the IC chip  111 . 
     The first end portion  121  and the second end portion  122  of the antenna coil portion  120  are also connected to a capacitor  112  and an adjustment capacitor  130 . The capacitor  112  is connected to the first end portion  121  of the antenna coil portion  120  via the conductor pattern  113  on the back surface of the base material, and to an end portion  124  of an antenna extension portion  123  extending from the second end portion  122  of the antenna coil portion  120  on the front surface. 
     The capacitor  112  accumulates charge generated by a carrier wave received by the antenna coil portion  120  to obtain electric power for driving the IC chip  111 . As shown in  FIG. 2 , the capacitor  112  includes a first electrode portion  112   a  formed by a conductor pattern provided on the front surface and a second electrode portion  112   b  formed by a conductor pattern provided on the back surface. The capacitor  112  accumulates charge with the first electrode portion  112   a  and the second electrode portion  112   b , which face each other via the base material. Each of the electrode portions  112   a  and  112   b  forming the capacitor  112  has a relatively large area so as to be able to accumulate a relatively large amount of charge. 
     The adjustment capacitor  130  is configured to change the resonant frequency. As shown in  FIG. 2 , the adjustment capacitor  130  includes a first conductor pattern  131  provided on the front surface and connected to the second end portion  122  of the antenna coil portion  120  and a second conductor pattern  132  provided on the back surface and connected to the second electrode portion  112   b . The first conductor pattern  131  provided on the front surface is formed to include a plurality of comb-teeth conductor patterns. The second conductor pattern  132  provided on the back surface is formed to orthogonally intersect the comb-teeth portions. Charge is accumulated at each of the intersections. The adjustment capacitor  130  has a small capacitance compared to the capacitor  112 . The adjustment capacitor  130  increases the resonant frequency by cutting off some of the comb-teeth conductor patterns to reduce the condenser capacitance during adjustment of the resonant frequency in a contactless IC card manufacturing process. 
     The configuration described so far is similar to that of the contactless IC card according to the related art shown in  FIGS. 12A and 12B . 
     In the embodiment, metal patterns  201 ,  202 , and  203  are disposed on the base material forming the contactless communication medium  110 . In the embodiment of  FIG. 1A and 2 , the metal patterns  201 ,  202 , and  203  are disposed on the same surface of the base material as the surface on which the antenna coil portion  120  is formed, inside the antenna coil portion  120 . 
     The metal patterns  201 ,  202 , and  203  are formed from a conductive metal material such as a copper or aluminum foil, and are not electrically connected to other circuit components such as the antenna coil portion  120  and the capacitor  112 . For example, the metal patterns  201 ,  202 , and  203  may be made of the same metal material as the material of the conductor pattern forming the antenna coil portion  120 , and may be formed at the same time as the antenna coil portion  120  is formed by etching or the like. 
     In the embodiment of  FIGS. 1A and 2 , the three metal patterns  201 ,  202 , and  203  have the same size as each other, and are arranged in the vertical direction in the case where the contactless communication medium  110  is a horizontally long card. A straight gap with a relatively narrow width of about 1 mm is provided between the three metal patterns  201 ,  202 , and  203 . 
     The metal patterns  201 ,  202 , and  203  are disposed on the front surface of the base material inside the innermost turn of the antenna coil portion  120  and in a region other than regions in which the IC chip  111 , the capacitor  112 , and the adjustment capacitor  130  are disposed to occupy as large an area as possible. 
     That is, in the embodiment, as shown in  FIG. 1A , the IC chip  111 , the capacitor  112 , and the adjustment capacitor  130  are disposed in a left corner region inside the pattern forming the antenna coil portion  120 . Then, the three metal patterns  201 ,  202 , and  203  are disposed in a relatively large region extending from the approximate center to the right corner inside the pattern forming the antenna coil portion  120 . 
     With the presence of the three metal patterns  201 ,  202 , and  203 , in the case where the contactless IC card is brought into proximity to a reader/writer, most of an antenna of the reader/writer overlaps the metal patterns  201  to  203 . That is, most of the antenna of the reader/writer, which is generally smaller than the antenna of the IC card, overlaps the metal patterns  201  to  203  during contactless proximity communication. 
     A reader/writer antenna position  300  indicated by the phantom line in  FIG. 1A  indicates the position of the antenna of the reader/writer in the case where the contactless IC card according to the embodiment is brought into proximity to the approximate center of the reader/writer. The metal patterns  201  to  203  are thus positioned to overlap the antenna of the reader/writer. 
       FIG. 1B  shows a circuit that is equivalent to the circuit of the contactless communication medium  110  shown in  FIGS. 1A and 2 . The equivalent circuit is basically the same as the equivalent circuit shown in  FIG. 12B . 
     As shown in  FIG. 1B , the IC chip  111  is connected to the antenna coil portion  120 , and the capacitor  112  and the adjustment capacitor  130  are connected to the antenna coil portion  120  via the extension portion  123 . The second end portion  122 , at which the antenna coil portion  120  and the extension portion  123  are connected to each other, serves as an intermediate tap. 
     [2. Exemplary Overall Configuration] 
     Next, an exemplary overall configuration of a contactless IC card including the contactless communication medium  110  described so far will be described. 
       FIG. 3  shows the overall contactless IC card in an exploded state. In the contactless IC card, an outer shell material  160  is disposed on the front surface  110   a  of the contactless communication medium  110 . Although the outer shell material  160  is formed by a relatively thick resin material in the embodiment, the outer shell material  160  may be formed by a thin resin sheet. 
     A magnetic sheet  180  and an adhesive sheet  170  are sequentially disposed on the back surface  110   b  of the contactless communication medium  110 , and integrated with each other to be assembled into a contactless IC card. 
     The magnetic sheet  180  is a sheet formed by a magnetic material. The magnetic sheet  180  may be a sheet formed by mixing magnetic powder with a high magnetic permeability into a resin material such as a polymer material, for example. 
     The adhesive sheet  170  provided on the back surface  110   b  facilitates attaching the contactless IC card to other electronic devices to be assembled into a communication apparatus. That is, as shown in  FIG. 4 , for example, the contactless IC card according to the embodiment may be affixed to the back surface of a terminal device  200  such as a cellular phone terminal, a smart phone, an information terminal, or an audio/video playing device to form a communication apparatus with a contactless communication function. In this case, the presence of the magnetic sheet  180  allows the contactless IC card to favorably perform contactless communication without interference by circuit components in the terminal device  200  when the contactless IC card is brought into proximity to a reader/writer (not shown) to perform contactless communication. 
     Specifically, with the magnetic sheet  180  disposed in proximity to the antenna coil portion  120 , magnetic flux from the reader/writer concentrates on the magnetic sheet  180  during contactless wireless communication, which improves the state of transmission and reception performed by the antenna coil portion  120  disposed adjacent to the magnetic sheet  180 . In particular, with the contactless IC card affixed to the terminal device  200  which is separate from the card as shown in  FIG. 4 , the presence of a relatively large metal component is highly likely to degrade the transmission/reception performance of the antenna coil portion  120  because of the influence of the metal component. With the magnetic sheet  180  disposed between the antenna coil portion  120  and the terminal device  200 , magnetic flux concentrates on the magnetic sheet  180  to prevent a reduction in wireless communication sensitivity due to the influence of the terminal device  200 . 
     Further, in the case of the embodiment, as shown in  FIGS. 1A and 2 , the metal patterns  201 ,  202 , and  203  are disposed inside the antenna coil portion  120  to further improve the wireless communication characteristics. 
     [3. Characteristics of Medium According to Embodiment] 
     Next, improvement in wireless communication characteristics achieved by the contactless IC card according to the embodiment will be described. 
       FIG. 5  shows a comparison between the characteristics (on the right side of  FIG. 5 ) of the contactless IC card (with the metal patterns  201  to  203 ) according to the embodiment and the characteristics (on the left side of  FIG. 5 ) of a contactless IC card with no metal patterns (according to the example of  FIG. 12A ). 
     In  FIG. 5 , the vertical axis indicates the distance D [mm] from the reader/writer to the contactless IC card, and a range in which the correct communication response rate is 100% is defined as a communicable range. 
     As shown in  FIG. 5 , in either case, communication is possible in a range in which the distance D is up to more than 50 mm. In the case of the contactless IC card with no metal patterns, however, there is a communication dead zone in which the correct communication response rate is less than 100% in a range in which the distance D is several millimeters. 
     In the case of the contactless IC card with the metal patterns  201  to  203  according to the embodiment, in contrast, there is no communication dead zone in a range in which the correct communication response rate is 100%, which allows reliable communication if the distance between the reader/writer and the contactless IC card is from 0 mm to about 50 mm. Thus, according to the configuration of the embodiment, the wireless communication performance is improved over the related art. 
     This effect is attributable to the fact that the antenna of the reader/writer is relatively small and overlaps the metal patterns  201  to  203  as indicated by the reader/writer antenna position  300  shown in  FIG. 1A . 
     The effect shown in  FIG. 5  may be obtained both in the case where the magnetic sheet  180  shown in  FIG. 3  is provided and in the case where no such magnetic sheet  180  is provided. 
     [4. First Modification] 
       FIG. 6  shows a first modification of the embodiment. In  FIG. 6 , components corresponding to those in  FIGS. 1A and 2  are denoted by the same reference numerals. 
     In the modification of  FIG. 6 , a single metal pattern with a large area is disposed on the base material on which the antenna coil portion  120  is disposed to serve as a metal pattern  211 . 
     That is, the single metal pattern  211  is disposed on the front surface of the base material inside the innermost turn of the antenna coil portion  120  and in a region other than regions in which the IC chip  111 , the capacitor  112 , and the adjustment capacitor  130  are disposed to occupy as large an area as possible. 
     In the modification of  FIG. 6 , the area of the single metal pattern  211  is substantially the same as the total of the areas of the three metal patterns  201  to  203  in the embodiment of  FIG. 1A . 
     Although not shown, the wireless communication characteristics according to the modification of  FIG. 6  are substantially the same as the characteristics of the contactless IC card with no metal patterns shown in  FIG. 5 . 
     [5. Second Modification] 
       FIG. 7  shows a second modification of the embodiment. In  FIG. 7 , components corresponding to those in  FIGS. 1A and 2  are denoted by the same reference numerals. 
     In the modification of  FIG. 7 , seven metal patterns divided in the vertical direction are disposed on the base material on which the antenna coil portion  120  is disposed to serve as metal patterns  221  to  227 . 
     That is, the seven metal patterns  221 ,  222 ,  223 , . . . , and  227  divided in the vertical direction in case of a horizontally long card are disposed on the front surface of the base material inside the innermost turn of the antenna coil portion  120  and in a region other than regions in which the IC chip  111 , the capacitor  112 , and the adjustment capacitor  130  are disposed. 
     In the modification of  FIG. 7 , the total of the areas of the seven metal patterns  221  to  227  is substantially the same as the total of the areas of the three metal patterns  201  to  203  in the embodiment of  FIG. 1A . 
       FIGS. 8A and 8B  show the wireless communication characteristics according to the modification of  FIG. 7 . 
       FIG. 8A  shows the characteristics for a case where the contactless IC card is disposed at the center of an antenna of a reader/writer. In  FIG. 8A , the vertical axis indicates the distance D [mm] from the reader/writer to the contactless IC card, and a range in which the correct communication response rate is  1001  is defined as a communicable range. 
     As shown in  FIG. 8A , wireless communication may be made over a distance that is substantially the same as with the characteristics shown in  FIG. 5 , and there is no dead zone. 
       FIG. 8B  shows the characteristics for cases where the contactless IC card is shifted in X and Y directions from the center of the antenna of the reader/writer. The X and Y directions are orthogonal to each other. 
     In  FIG. 8B , the bar indicated as XY 0  corresponds to a case where the card is disposed at the center of the reader/writer. The graph also shows bars corresponding to cases where the card is displaced by +10 mm and −10 mm in the X direction (respectively indicated as X+10 and X−10) and by +10 mm and −10 mm in the Y direction (respectively indicated as Y+10 and Y−10). 
     Substantially no variations are observed in the characteristics even if the card is displaced except for the case where the card is shifted by −10 mm in the Y direction, in which case there is a slight dead zone in a range in which the distance D from the reader/writer to the card is several millimeters. 
     Thus, the configuration according to the modification of  FIG. 7  also provides favorable wireless communication characteristics. 
     [6. Third Modification] 
       FIG. 9  shows a third modification of the embodiment. In  FIG. 9 , components corresponding to those in  FIGS. 1A and 2  are denoted by the same reference numerals. 
     In the modification of  FIG. 9 , four metal patterns  231  to  234  divided in the vertical direction and four metal patterns  235  to  238  divided in the horizontal direction are disposed on the base material on which the antenna coil portion  120  is disposed to serve as metal patterns  231  to  238 . 
     That is, the four metal patterns  231 ,  232 ,  233 , and  234  divided in the vertical direction in case of a horizontally long card are disposed on the front surface of the base material inside the innermost turn of the antenna coil portion  120  and in a region other than regions in which the IC chip  111 , the capacitor  112 , and the adjustment capacitor  130  are disposed. A space is provided between the metal pattern  232  and the metal pattern  233 . Then, the four metal patterns  235 ,  236 ,  237 , and  238  divided in the horizontal direction, which is orthogonal to the vertical direction, are disposed in the space between the metal patterns  232  and  233 . 
     In this case, of the four metal patterns  235 ,  236 ,  237 , and  238  divided in the horizontal direction, the metal pattern  235  on the rightmost side has a larger area, and the three remaining metal patterns  236 ,  237 , and  238  have the same area which is smaller than the area of the metal pattern  235 . The metal patterns  231 ,  232 ,  233 , and  234  divided in the vertical direction have the same area as each other. 
       FIGS. 10A and 10B  show the wireless communication characteristics according to the modification of  FIG. 9 . 
       FIG. 10A  shows the characteristics for a case where the contactless IC card is disposed at the center of an antenna of a reader/writer. In  FIG. 10A , the vertical axis indicates the distance D [mm] from the reader/writer to the contactless IC card, and a range in which the correct communication response rate is 100% is defined as a communicable range. 
     As shown in  FIG. 10A , wireless communication may be made over a distance that is substantially the same as with the characteristics shown in  FIG. 5 , and there is no dead zone. 
       FIG. 10B  shows the characteristics for cases where the contactless IC card is shifted in X and Y directions from the center of the antenna of the reader/writer. The X and Y directions are orthogonal to each other. 
     In  FIG. 10B , the bar indicated as XY 0  corresponds to a case where the card is disposed at the center of the reader/writer. The graph also shows bars corresponding to cases where the card is displaced by +10 mm and −10 mm in the X direction (respectively indicated as X+10 and X−10) and by +10 mm and −10 mm in the Y direction (respectively indicated as Y+10 and Y−10). 
     In the configuration according to the modification of  FIG. 9 , as seen from  FIG. 10B , there is no dead zone at all even if the card is shifted. 
     Thus, the configuration according to the modification of  FIG. 9  also provides favorable wireless communication characteristics. In particular, favorable characteristics are secured to a degree even if the card is shifted from the center of the reader/writer to some degree. 
     [7. Other Modifications] 
     The embodiment shown in  FIG. 1A  and the modifications are formed by providing metal patterns in a circuit configuration with a so-called intermediate tap (the configuration shown in  FIGS. 12A and 12B ). On the contrary, metal patterns may also be provided in the configuration with no intermediate tap shown in  FIGS. 11A and 11B , inside the antenna coil portion. 
     In addition, although the metal patterns are disposed on the same surface as the surface on which the antenna coil portion is disposed in the embodiment and the modifications, the antenna coil portion and the metal patterns may be disposed on the front surface and the back surface, respectively, of the base material. 
     Further, the metal patterns may be disposed on a sheet that is separate from the base material on which the antenna coil portion is disposed as long as the metal patterns are disposed inside the antenna coil portion as the resulting IC card is seen in plan (that is, in the state shown in  FIG. 1A , etc.). It should be noted, however, that the sheet with the metal patterns is preferably disposed between the base material forming the contactless communication medium  110  and the magnetic sheet  180 , or between the base material forming the contactless communication medium  110  and the outer shell material  160 , when illustrated with reference to  FIG. 3 . If the sheet with the metal patterns is disposed on the outer side (lower side in  FIG. 3 ) of the magnetic sheet  180 , improvement in communication performance is not expected. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.