Abstract:
An RFID tag includes: a base sheet in which a plurality of first slits are formed to extend alternately from two opposite sides from an end of the base sheet; an antenna pattern provided on the base sheet by folding the antennal pattern to avoid the first slits; an RFID chip provided over the base sheet and electrically connected to the antenna pattern; an elastic sheet provided over any one of a top surface and a bottom surface of the base sheet; and a protective sheet provided on a surface of the elastic sheet opposite to the surface that is in contact with the base sheet and including second slits formed to correspond in position to the first slits of the base sheet.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2012-162456 filed on Jul. 23, 2012, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein are related to an RFID (Radio Frequency IDentification) tag that exchanges information with an external device in a non-contact manner. 
     BACKGROUND 
     Recently, various RFID tags have been proposed exchanging information with an external device, represented by a reader/writer, in a non-contact manner through a radio wave. 
     As a kind of such RFID tags, there has been proposed an RFID tag configured such that an antenna pattern and a circuit chip for a radio communication are mounted on a base sheet made of plastic or paper. The RFID tag of this type may be attached to, for example, a product to exchange information on the product with an external device so as to perform, for example, an identification of the product. 
     In general, when such an RFID tag is attached to a surface of a product made of an easily deformable material such as, for example, rubber, the antenna pattern in the RFID tag may be broken because of the deformation in the RFID tag such as an elongation or a flexure caused by the deformation of the product material. Also, when the temperature around the product changes, the difference in linear expansion coefficient among the product itself, and the cladding and the base sheet of the RFID tag may produce stresses between the product and the RFID tag so that the antenna pattern in the RFID tag may be broken. 
     In addition, when the RFID tag is extended and attached to a product having a curved portion or a corner portion on a surface thereof, the difference in the radius of the curvature between the product itself, and the cladding and the base sheet of the RFID tag may produce tensile stresses between the product and the RFID tag so that the antenna pattern in the RFID tag may be broken. 
     The following is reference document:
     [Document 1] Japanese Laid-open Patent Publication No. 2006-268090.   

     SUMMARY 
     According to an aspect of the embodiments, an RFID tag includes: a base sheet in which a plurality of first slits are formed to extend alternately from two opposite sides from an end of the base sheet; an antenna pattern provided on the base sheet by folding the antennal pattern to avoid the first slits; an RFID chip provided on the base sheet to be electrically connected to the antenna pattern; an elastic sheet provided on any one of a top surface and a bottom surface of the base sheet; and a protective sheet provided on a surface of the elastic sheet opposite to the surface that is in contact with the base sheet and including second slits formed to correspond in position to the first slits of the base sheet. 
     The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view illustrating a system using an RFID tag according to the present exemplary embodiment; 
         FIG. 2A  and  FIG. 2B  are views illustrating the structure of a conventional RFID tag; 
         FIG. 3A  and  FIG. 3B  are views illustrating the structure of an RFID tag according to a first exemplary embodiment; 
         FIG. 4A  and  FIG. 4B  are views illustrating the structure of an RFID tag according to a second exemplary embodiment; 
         FIGS. 5A to 5D  are views illustrating modified examples of an antenna pattern and slits; 
         FIGS. 6A and 6B  are views illustrating the steps of forming an antenna pattern and an inductance pattern, and the steps of cutting openings and a base sheet using a laser in a method of manufacturing an RFID tag according to the first exemplary embodiment; 
         FIG. 7  is a view illustrating the steps of adhering a lower rubber sheet and an upper rubber sheet to the base sheet in the method of manufacturing the RFID tag according to the first exemplary embodiment; 
         FIG. 8  is a view illustrating the steps of adhering a lower reinforcement film and an upper reinforcement film to a bottom side of the lower rubber sheet and a top side of the upper rubber sheet, respectively, in the method of manufacturing the RFID tag according to the first exemplary embodiment; 
         FIGS. 9A to 9C  are views illustrating an example where the RFID tag according to the first exemplary embodiment is mounted on a product; and 
         FIGS. 10A and 10B  are views illustrating an example where the RFID tag according to the first exemplary embodiment is mounted on a product. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First,  FIG. 1  illustrates an example of a system using an RFID tag according to the present exemplary embodiment. 
     An RFID tag  100  receives electromagnetic field energy emitted from a reader/writer  200  as electric power by an antenna pattern, and a circuit chip (RFID chip) in the RFID tag  100  is driven by the electric power to perform a communication operation. The reader/writer  200  reads data recorded in the RFID chip in the RFID tag  100  attached to a product  300 . The read data are sent to an information device such as, for example, a computer connected to the reader/writer  200  to perform a product management. Also, the data may be sent to the reader/writer  200  from the information device such as, for example, a computer, and recorded in the RFID chip in the RFID tag  100 . 
     Subsequently, as a comparative example, an example of the structure of a conventional RFID tag  100  will be described with reference to  FIGS. 2A and 2B .  FIG. 2A  illustrates a plan view of the conventional RFID tag  100  in a state where a cover sheet and a part of a protective cladding on the cover sheet are removed, and  FIG. 2B  illustrates the cross-sectional view of the conventional RFID tag  100 . 
     The RFID tag  100  illustrated in  FIG. 2A  includes an antenna pattern  2  provided on a base sheet  10 , a circuit chip  1  that is adhered to the base sheet  10  by an epoxy-based adhesive and electrically connected to the antenna pattern  2  via a bump (not illustrated), and an inductance pattern  4  that is electrically connected to the antenna pattern  2  to generate inductance. 
     Referring to  FIG. 2B , the RFID tag  100  includes a cover sheet  8  that is adhered to the base sheet  10  to cover the antenna pattern  2 , the circuit chip  1 , and the inductance pattern  4 . The cover sheet  8  is typically made of a material selected from the group comprising, for example, a PET material, a polyester material, a polyolefin material, a polycarbonate material, and an acrylic based material. Also, the base sheet  10  and the cover sheet  8  are covered with a protective cladding  90  made of, for example, a resin. 
     Hereinafter, exemplary embodiments according to the technology of the present disclosure will be described in detail with reference to accompanying drawings. 
       FIGS. 3A and 3B  are view illustrating the structure of an RFID tag according to the first exemplary embodiment to which the disclosed technology is applied.  FIG. 3A  illustrates a plan view of an RFID tag  110  according to the first exemplary embodiment in a state where an upper rubber sheet and an upper reinforcement film are removed, and  FIG. 3B  illustrates a cross-sectional view of the RFID tag  110 . The RFID tag  110  according to the first exemplary embodiment includes an antenna pattern  2  provided on a base sheet  10 , a circuit chip  1  adhered to the base sheet  10  by an epoxy-based adhesive and electrically connected to the antenna pattern  2  via a bump (not illustrated), and an inductance pattern  4  that is electrically connected to the antenna pattern  2  to generate inductance. 
     In the RFID tag  110  according to the first exemplary embodiment, a plurality of slits  20  are formed to extend alternately from the top and the bottom sides of the base sheet  10  in the widthwise direction of the base sheet  10  (in the vertical direction in the drawing). The reason why the slits  20  are alternately formed is to suppress the strength of the base sheet  10  from being weakened when the widthwise length of the base sheet  10  is locally shortened. 
     The antenna pattern  2  is wired in such a manner that it is folded in a meandering shape to avoid the slits  20 . Also, since the slits  20  are also formed from an end portion of the base sheet  10  in the portion where the inductance pattern  4  is wired, the inductance pattern  4  is also wired in such a manner that it is folded in a meandering shape to avoid the slits  20 . Also, openings  22  are formed in the central portion of the base sheet  10  which is surrounded by the antenna pattern  2  and the inductance pattern  4 . 
     Subsequently, referring to  FIG. 3B , the base sheet  10  is sandwiched in a vertical direction between a lower rubber sheet  50  and an upper rubber sheet  52  which are made of an elastic body such as, for example, silicon rubber. The slits  20  and the openings  22  of the base sheet  10  are also occupied by the lower rubber sheet  50  and the upper rubber sheet  52 . Also, the lower rubber sheet  50  and the upper rubber sheet  52  are sandwiched between a lower reinforcement film  60  and an upper reinforcement film  62  which are disposed on the bottom surface of the lower rubber sheets  50  and the top surface of the upper rubber sheet  52 , respectively, and made of, for example, a PET material. Also, in the lower reinforcement film  60  and the upper reinforcement film  62 , slits  70  and openings  72  are formed to correspond, in position, to the slits  20  and the openings  22  of the base sheet  10 . 
     As described above, the plurality of alternate slits  20  and the openings  22  are formed in the base sheet  10 . Thus, even if expansion and contraction stresses are applied to the base sheet  10  as the RFID tag  110  is expanded or contracted in the lengthwise direction (in the horizontal direction in the drawing), the widths of the slits  20  and the openings  22  are changed in response to the stresses and thus, stresses are not substantially applied to the antenna pattern  2  and the inductance pattern  4 . 
     Also, since the lower rubber sheet  50  and the upper rubber sheet  52  disposed on the bottom surface and top surface of the base sheet  10 , respectively, to sandwich the base sheet  10  therebetween are expanded or contracted in response to the lengthwise expansion or contraction of the base sheet  10 , stresses are not substantially applied to the base sheet. 
     Also, since the plurality of alternate slits  70  and the openings  72  are formed in the lower reinforcement film  60  and the upper reinforcement film  62  disposed on the bottom surface of the lower rubber sheet  50  and the top surface of the upper rubber sheet  52 , respectively, to sandwich the lower rubber sheet  50  and the upper rubber sheet therebetween, the widths of the slits  70  and the openings  72  are changed in response to the stresses even if the expansion and contraction stresses are applied to the lower reinforcement film  60  and the upper reinforcement film  62  as the RFID tag  110  is expanded and contracted lengthwise (in the horizontal direction in the drawing). Accordingly, stresses are not substantially applied to the lower rubber sheet  50  and the upper rubber sheet  52 . 
     Thus, even if the RFID tag  110  is expanded or contracted lengthwise (in the horizontal direction in the drawing), the stresses are not substantially applied to the antenna pattern  2  and the inductance pattern  4 . Thus, there is an effect that the antenna pattern  2  and the inductance pattern  4  are not broken easily. 
       FIG. 4A  illustrates a plan view of an RFID tag  120  according to a second exemplary embodiment in a state where an upper rubber sheet and an upper reinforcement sheet are removed, and  FIG. 4B  illustrates a cross-sectional view of the RFID tag  120 . The RFID tag  120  of the second exemplary embodiment and the RFID tag  110  of the first exemplary embodiment are different from each other in terms of the shape of the inductance pattern  4 . 
     A circuit chip  1  is connected to an antenna pattern  2  via a bump (not illustrated). Herein, since an adhesive (not illustrated) is filled in the connecting portion, a small capacitor that is unnecessary in design is formed between the circuit chip  1  and the antenna pattern  2 . The parasitic capacitance of such a capacitor disturbs the input of power from the antenna pattern  2  to the circuit chip  1 , which may cause a problem such as degradation of a communication range of the RFID tag. 
     Accordingly, an inductance pattern  4  is provided to generate inductance so that the inductance and the parasitic capacitance generate resonance to counterbalance the parasitic capacitance. Since the parasitic capacitance changes depending on the relative position relationship between the circuit chip  1  and the antenna pattern  2 , it is required to change the shape of the inductance pattern  4  that generates the resonance. 
     Subsequently, referring to  FIGS. 5A to 5D , descriptions will be made as to modified examples in which the folded shape of the antenna pattern  2  in which the slits  20  formed in the base sheet  10  vary in shape. 
     The slits  20  may be formed alternately from left and right with respect to the longitudinal direction of the base sheet  10  (in the vertical direction in the drawing), and the shape, width, and interval of the slits  20  may be variously modified. Also, the antenna pattern  2  and the inductance pattern  4  may be variously changed in shape and may be wired to avoid the slits  20 . 
       FIG. 5A  illustrates a modified example in which the folded shape of the antenna pattern  2  takes a sine wave shape. The shape and interval of the slits  20  are the same as those in the above described RFID tag  110  of the first exemplary embodiment. 
       FIG. 5B  illustrates a modified example in which the slits  20  take a wedge (triangular) shape, and the folded antenna pattern  2  takes a sine wave shape. Here, the end side of each of the slits  20  is largely opened to be capable of coping with torsion as well as the bending in the longitudinal direction. 
       FIG. 5C  illustrates a modified example in which the width and interval of the slits  20  vary. As to the slit width, W1 and W2 coexist in which W2 is wider than W1. Also, as to the interval of the slits  20 , L1 and L2 coexist in which L2 is narrower than L1. 
       FIG. 5D  illustrates a modified example in which the cut depths of the slits  20  vary, and the folded widths of the antenna pattern  2  vary according to the cut depths. As to the cut depths of the slits, D1 and D2 coexist in which D2 is deeper than D1. Also, the folded width (in the vertical direction in the drawing) of the antenna pattern  2  varies according to the cut depth of the slits  20 . 
     Hereinafter, a method of manufacturing the RFID tag according to the present exemplary embodiment will be described with reference to  FIGS. 6A ,  6 B,  7  and  8 . 
     First, referring to  FIG. 6A , a mask is disposed on a PET sheet  12 , and the PET sheet  12  is screen-printed using an Ag paste, and then the mask is removed. Subsequently, an antenna pattern  2  and an inductance pattern  4  which are made of the Ag paste are formed. 
     Then, referring to  FIG. 6B , the PET sheet  12  is cut by a laser in the portion surrounded by the antenna pattern  2  and the inductance pattern  4  to form openings  22 . Then, the PET sheet  12  is cut by the laser in the vicinity of the antenna pattern  2  and the inductance pattern  4  to obtain a base sheet  10 . 
     Then, a circuit chip  1  is fixedly bonded to the antenna pattern  2  by, for example, soldering with a bump interposed therebetween. Also, the vicinity of the circuit chip  1  is reinforced by curing an epoxy-based adhesive. 
     Then, referring to  FIG. 7 , a lower rubber sheet  50  and an upper rubber sheet  52  are adhered to the bottom and top surfaces of the base sheet  10 . 
     Subsequently, referring to  FIG. 8 , a lower reinforcement film  60  and an upper reinforcement film  62  are prepared in which slits  70  and openings  72  are formed in advance and then adhered to the bottom surface of the lower rubber sheet  50  and the top surface of the upper rubber sheet  52 , respectively. 
     Finally, referring to  FIGS. 9A to 9C  and  10 A and  10 B, examples will be described in which a RFID tag  110 ,  120  according to the first and second exemplary embodiments of the present disclosure is mounted on a product  300 . Although the RFID tag  110  is exemplified in the following description, the RFID tag  120  may be mounted in the same manner. 
     In a case where the surface of the product  300  is flat, an adhesive sheet may be adhered to one of the lower reinforcement film  60  and the upper reinforcement film  62  in the outside of the RFID tag  110 , and then may be attached to the product  300 . However, in a case where the surface of the product  300  is curved and thus, it is difficult to attach the RFID tag  110  by the adhesive sheet, a band  80  as illustrated in  FIGS. 9A to 9C  may be used to fix the RFID tag  110  on the product  300 . 
       FIG. 9A  illustrates an example where the RFID tag  110  of the first exemplary embodiment is attached on the band  80 . At one end of the band  80  (left side in the drawing), a plurality of buttons  84  are attached, and at the other end of the band (right side in the drawing), a button  82  to be fitted into one of the buttons  84  is attached. 
       FIG. 9B  is a top plan view illustrating a state where the RFID tag  110  is attached on the cylindrical product  300  using the band  80 .  FIG. 9C  is a side view illustrating the state where the RFID tag  110  is attached on the cylindrical product  300  by using the band  80 . 
     The band  80  is wound to surround the circumference of the cylindrical product  300 , and then at the ends of the band  80 , the button  82  is fitted into one of the plurality of buttons  84  in accordance with the circumferential length of the product  300  so as to fix the band  80  on the product  300 . 
       FIGS. 10A and 10B  illustrate an example where the RFID tag  110  of the first exemplary embodiment is embedded in an elastic body such as, for example, rubber, which in turn is formed in a ring-shaped band  86 .  FIG. 10A  is a top plan view illustrating a state where the band  86  embedded with the RFID tag  110  is attached to the cylindrical product  300 .  FIG. 10B  is a side view illustrating the state where the ring-shaped band  86  is attached to the cylindrical product  300 . Since the contractible RFID tag  110  is embedded in the elastic body, the whole band  86  has contractibility. Accordingly, the RFID tag  110  may be attached even on various products  300  having different circumferential lengths using the contractible band  86 . 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.