Abstract:
A combined EAS/RFID tag including an EAS circuit and a first RFID circuit is disclosed. The EAS circuit has at least one capacitor and the RFID circuit has a main antenna wherein at least a part of the capacitor of the EAS circuit provides at least a part of the main antenna of the RFID circuit. The EAS circuit may include two capacitors and each capacitor may include first and second plates on first and second sides of a substrate wherein one plate of each capacitor forms part of the main antenna of the RFID circuit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 61/067,308 filed Feb. 27, 2008, the disclosure of which is hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to an electronic tag having combined Electronic Article Surveillance (EAS) and Radio Frequency Identification (RFID) functions. 
         [0003]    There exists a need for combining EAS and RFID functions in a retail environment. Many retail outlets that make use of EAS for deterring shoplifting also rely on information obtained via RFID technology for inventory control purposes. Retail outlets already spend considerable money for EAS hard tags that are re-useable. Adding an RFID function to the EAS tags may be easily justified due to improved productivity in inventory control as well as deterring shoplifting. 
         [0004]    In order to minimize interactions between EAS and RFID elements, prior art attempts at combining EAS and RFID functions have placed the EAS element and the RFID element far apart in an end-to-end or side-by-side relationship in an effort to minimize the interactions between the elements. However, this leads to an increase in size of the combined tag which is undesirable. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention may provide a combined EAS and RFID tag that at least alleviates the problem of increased size of a combined EAS/RFID tag while maintaining acceptable levels of performance for tracking articles in inventory (RFID function) as well as securing articles leaving a retail outlet (EAS function). 
         [0006]    According to one aspect of the present invention there is provided a combined EAS/RFID tag including an EAS circuit and a first RFID circuit, said EAS circuit having at least one capacitor and said RFID circuit having a main antenna wherein at least a part of said capacitor of said EAS circuit provides at least a part of said main antenna of said RFID circuit. 
         [0007]    The combined EAS/RFID tag is arranged such that the EAS circuit shares at least one common element with the RFID circuit. Typically the EAS circuit has a resonator including a coil (inductor) and a capacitor. Typically the RFID circuit includes a primary antenna and an integrated circuit (IC). To increase reading range of the RFID circuit, the RFID circuit typically includes a (larger) main or secondary antenna. Components of the EAS and RFID circuits are preferably formed on opposite sides of a common substrate. At least one capacitor plate of the EAS circuit may be provided on a first side of the substrate. At least one capacitor plate of the EAS circuit may be provided on a second side of the substrate. The capacitor plates may be positioned relative to each other on the substrate such that the substrate provides a dielectric between the plates. The capacitor plate on the first side of the substrate may form a part of the EAS circuit. The capacitor plate on the second side of the substrate may form a part of the RFID circuit such as an antenna part. The capacitor plate on the second side of the substrate may also form a part of the EAS circuit. The capacitor plates on the first and second sides of the substrate may form a capacitor of the EAS resonator. 
         [0008]    The antenna part and the capacitor parts each require substantial portions of the available area of the substrate to be devoted to their realization and hence a substantial portion of the overall size of the tag. By arranging the EAS and RFID circuits such that they share a common part that may require a substantial portion of the substrate to be devoted to it, the size of the combined EAS and RFID circuits may be correspondingly reduced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Preferred embodiments of the present invention will now be described with reference to the accompanying drawings wherein: 
           [0010]      FIGS. 1  ( a ) and ( b ) show a layout of components of a combined EAS/RFID tag according to the present invention; 
           [0011]      FIGS. 2  ( a ) and ( b ) show schematic diagrams corresponding to  FIGS. 1  ( a ) and  1  ( b ); 
           [0012]      FIG. 3  shows a schematic diagram of an EAS circuit; 
           [0013]      FIGS. 4  ( a ) to  4 ( d ) show layers of a combined EAS/RFID tag according to an embodiment of the present invention; 
           [0014]      FIGS. 5(   a ) to  5 ( d ) show layers of a combined EAS/RFID tag according to a further embodiment of the present invention; 
           [0015]      FIGS. 6(   a ) to  6 ( d ) show layers of a combined tag according to an embodiment of the present invention; 
           [0016]      FIGS. 7(   a ) to  7 ( d ) show layers of a combined tag according to a further embodiment of the present invention; 
           [0017]      FIGS. 8(   a ) to  8 ( c ) show schematic diagrams of the EAS circuit corresponding to  FIG. 6 ; and 
           [0018]      FIG. 9  shows layers of a combined EAS/RFID tag according to a further embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      FIG. 1(   a ) shows a first layer of a combined EAS/RFID tag. The first layer includes parts of an EAS circuit including first plates  10 ,  11  of respective capacitors  30 ,  31  (refer  FIG. 3)  of an EAS resonator. The first layer includes coil  12  of inductor  32  of the EAS resonator. One end  13  of coil  12  terminates outside coil  12  and is connected to capacitor plate  10 . The other end  14  of coil  12  terminates inside coil  12  and is connected to capacitor plate  11  as described below. The first layer is provided on a first side of a substrate in any suitable manner and by any suitable means such as by acid etching a suitable conductive material applied to the substrate. 
         [0020]      FIG. 1(   b ) shows a second layer of the combined EAS/RFID tag. The second layer includes parts of the EAS circuit including second plates  15 ,  16  of capacitor  30 ,  31  of the EAS resonator. The second layer includes conductive track  17  linking second plates  15 ,  16 . One function of track  17  is to provide a connection between second plates  15 ,  16  to complete a series circuit for the EAS resonator (refer  FIGS. 2 and 3) . The second layer is provided on a second side of the substrate in any suitable manner and by any suitable means such as by acid etching a suitable conductive material applied to the substrate. Another function of track  17  is to complete a U-shaped dipole antenna on the second side of the substrate. The dipole antenna may provide a secondary antenna for the RFID circuit as described below. 
         [0021]    The second layer includes a bridge  18  for linking end  14  of coil  12  to capacitor plate  11 . Bridge  18  includes terminal lands  19 ,  20  for joining to terminal lands  14 ,  21  on the first layer. The terminal lands on the first and second layers may be electrically joined in any suitable manner and by any suitable means such as by means of mechanical crimping through a relatively thin substrate. The crimping should be performed with sufficient pressure to deform the lands and break through the substrate to provide an interference connection between the lands. The substrate may include any suitable insulating material such as oriented polypropylene (OPP). 
         [0022]      FIG. 2(   a ) shows a schematic diagram of components in  FIG. 1(   a ) and  FIG. 2(   b ) shows a schematic diagram of components in  FIG. 1(   b ).  FIG. 2(   a ) corresponds to the upper half of the EAS resonator shown in  FIG. 3  and  FIG. 2(   b ) corresponds to the lower half of the EAS resonator shown in  FIG. 3 . 
         [0023]      FIG. 4(   a ) shows a first layer of a combined EAS/RFID tag. The first layer includes first plates  40 ,  41  of respective capacitors of an EAS circuit and coil  42  of an inductor of the EAS circuit. The first layer is provided on a first side of OPP substrate  43 . 
         [0024]      FIG. 4(   b ) shows a second layer of the combined EAS/RFID tag. The second layer includes second plates  44 ,  45  or the respective capacitors of the EAS circuit and track  46  linking second plates  44 ,  45 . The second layer is provided on a second side of OPP substrate  43 . The second layer includes bridge  49  for linking lands  47 ,  48  on the first layer. Land  47  is associated with one end of coil  42  and land  48  is associated with first capacitor plate  41 . 
         [0025]      FIG. 4(   c ) shows the first and second layers provided on substrate  43  and crimpings  47   a ,  48   a  applied to lands  47 ,  48  of the first layer and associated ends of bridge  49  to complete the series circuit for the EAS resonator. 
         [0026]      FIG. 4(   d ) shows a view similar to  FIG. 4(   c ) and includes a separate primary antenna loop  50  associated with a UHF RFID circuit. The RFID circuit includes a separately formed adaptive kernel (AK) module (UHF tag) manufactured by Tagsys SAS. 
         [0027]      FIG. 5(   a ) shows a first layer of a combined EAS/RFID tag including first plates  51 ,  52  of respective capacitors of an EAS circuit and coil  53  of the EAS circuit not unlike  FIG. 4(   a ). The first layer is provided on one side of OPP substrate  54 . 
         [0028]      FIG. 5(   b ) shows a second layer of the combined EAS/RFID tag including second plates  55 ,  56  of the respective capacitors of the EAS circuit and track  57  linking second plates  55 ,  56 . The second layer also includes bridge  58  for linking lands  59 ,  60  on the first layer not unlike  FIG. 4(   b ). The second layer is provided on an opposite side of OPP substrate  54 . The second layer includes a C-shaped antenna  61  that is integrally linked with track  57  to provide a primary antenna loop for an RFID circuit (the loop is completed via track  57 ). 
         [0029]      FIG. 5(   c ) shows the first and second layers provided on substrate  54  and crimpings  59   a ,  60   a  applied to lands  59 ,  60  of the first layer and associated ends of bridge  58  to complete the series circuit for the EAS resonator. The RFID circuit includes IC module  62  as shown in  FIG. 5(   d ). 
         [0030]      FIGS. 6(   a ) to  6 ( d ) show a modification of the EAS/RFID tag of  FIGS. 5(   a ) to  5 ( d ) to provide a HF RFID function in addition to the EAS and UHF RFID functions provided by the embodiment of  FIGS. 5(   a ) to  5 ( d ). 
         [0031]      FIG. 6(   a ) shows a first layer of a combined tag including first plates  63 ,  64  of respective capacitors of an EAS circuit and coil  65  of the EAS circuit not unlike  FIG. 5(   a ). The first layer is provided on one side of OPP substrate  66 . 
         [0032]      FIG. 6(   b ) shows a second layer of the combined tag including second plates  67 ,  68  of the respective capacitors of the EAS circuit and track  69  linking second plates  67 ,  68 . The second layer includes bridge  70  for linking lands  71 ,  72  of the first layer. The second layer is provided on an opposite side of OPP substrate  66 . The second layer includes C-shaped antenna  73  that is integrally linked with track  69  to provide a primary antenna loop for the RFID circuit. The RFID circuit includes IC module  73   a  as shown in  FIG. 6(   d ). 
         [0033]    The modification includes cutting  70   a  applied via a laser, or the like to bridge  70  (refer  FIGS. 8(   a ) and  8 ( b )) to receive an RFID strap  74  comprising a small substrate and IC chip  75  connected to conductive pads  76 ,  77  to enable the pads to be attached to lands  71 ,  72  via crimpings  71   a ,  72   a  or the like. 
         [0034]    The modified EAS/RFID tag may provide three functions, namely: 
         [0035]    an EAS anti-theft circuit; 
         [0036]    a HF RFID circuit using coil  65  of the EAS circuit as an antenna; and 
         [0037]    a UHF RFID circuit. 
         [0038]      FIG. 7(   a ) to  7 ( d ) show a modification of the EAS/RFID tag of  FIGS. 4(   a ) to  4 ( d ) to provide a HF RFID function in addition to the EAS and UHF RFID functions provided by the embodiment of  FIGS. 4(   a ) to  4 ( d ). 
         [0039]      FIG. 7(   a ) shows a first layer of a combined tag including first plates  78 ,  79  of respective capacitors of an EAS circuit and coil  80  of the EAS circuit not unlike  FIG. 4(   a ). The first layer is provided on one side of OPP substrate  81 . 
         [0040]      FIG. 7(   b ) shows a second layer of the combined tag including second plates  82 ,  83  of the respective capacitors of the EAS circuit and track  84  linking second plates  82 ,  83 . The second layer includes bridge  85  for linking lands  86 ,  87  on the first layer. The second layer is provided on an opposite side of OPP substrate  81 . 
         [0041]      FIG. 7(   c ) shows the first and second layers provided on substrate  81  and crimpings  86   a ,  87   a  applied to lands  86 ,  87  of the first layer and associated ends of bridge  85  to complete the series circuit for the EAS resonator. 
         [0042]      FIG. 7(   d ) shows a view similar to  FIG. 7(   c ) and includes a separate primary antenna loop  88  associated with an RFID circuit included with a separately formed AK module (UHF tag) manufactured by Tagsys SAS. 
         [0043]    The modification includes laser cutting  85   a  of bridge  85  to receive an RFID strap  89  comprising a small substrate and an IC chip. The modified embodiment may provide three functions including an EAS circuit, a HF RFID circuit and a UHF RFID circuit. 
         [0044]      FIGS. 8(   a ) to  8 ( c ) are schematic diagrams of the EAS circuit shown in  FIGS. 6(   a ) to  6 ( d ) wherein parts labelled with like reference numerals correspond to like parts in  FIGS. 6(   a ) to  6 ( d ). 
         [0045]      FIG. 9  shows layers of a combined EAS/RFID tag. A first layer includes first plates  90 ,  91  of respective capacitors of an EAS circuit and coil  92  of an inductor of the EAS circuit. The first layer is provided on a first side of PET substrate  92 . A second layer includes second plates  93 ,  94  of the respective capacitors of the EAS circuit and track  95  linking second plates  93 ,  94 . The second layer is provided on a second side of PET substrate  92 . 
         [0046]    The second layer includes bridge  96  for linking lands  97 ,  98  on the first layer, land  97  being associated with one end of coil  92  and land  98  being associated with first capacitor plate  90 . Bridge  96  may be linked with lands  97 ,  98  in any suitable manner and by any suitable means such as crimping. 
         [0047]    Plates  93 ,  94  and track  95  of the second layer also form a C-shaped UHF dipole antenna for an RFID circuit. The RFID circuit includes a separately formed AK module (UHF tag) including primary antenna loop  99  and IC chip  100  provided on separate insulating substrate  101 . The long edge of loop  99  couples electromagnetically to track  95  of the second layer via substrate  101  and an adhesive. The second layer may be thicker than the first layer. 
         [0048]    Plates  93 ,  94  include respective slots  102 ,  103  for tuning the dipole antenna to a correct frequency (e.g. 866 MHZ). The slots  102 ,  103  may be made longer by laser trimming to tune the antenna to a lower frequency. 
         [0049]    If slots  102 ,  103  were shorter the antenna would be tuned to a higher frequency. Hence plates  93 ,  94  may be considered to be blanks which may be laser trimmed to a correct operating frequency. Plates  93 ,  94  may be trimmed to enable the dipole antenna to operate at a higher frequency (915 or 950 MHz) to compensate for packaging that tends to lower frequency. Laser trimming of plates  93 ,  94  may also be used to correct tolerances inherent in materials and assembly. Plates  90 ,  91  include corresponding notches  104 ,  105  to enable plates  93 ,  94  to be trimmed without changing HF capacitance. 
         [0050]    Separation  106  between capacitor plates  93 ,  94  and coil  92  preferably is substantially constant to maintain parasitic capacitance between plates  93 ,  94  and coil  92  which at UHF frequencies resembles a slab of conductor rather than a coil. Plates  93 ,  94  are slightly larger than plates  90 ,  91  as this may better maintain parasitic capacitance between coil  92  and the UHF antenna. The parasitic capacitance is undesired but may be compensated. It may also allow plates  90 ,  91  to be laser trimmed without affecting parasitic capacitance between the UHF antenna and coil  92  and without affecting UHF structure outline in general. 
         [0051]    Coil  92  is connected to plate  91  via elongate track  107 . The other end of coil  92  is connected to plate  90  via elongate track  108 . The width of each track  107 ,  108  is chosen such that it may operate as a micro-stripline with the UHF antenna as its ground plane even in regions where the UHF antenna is a track itself. The length of each track  107 ,  108  may be a quarter wavelength at the UHF operating frequency in the substrate. In the example shown it is 61.5 mm long for 866 MHz operation. 
         [0052]    Tracks  107 ,  108  are a key to making the HF EAS circuit invisible to the UHF RFID circuit when operating at UHF frequencies. UHF current distribution is such that current flowing on the main UHF parts makes its way towards the end of each capacitor plate, its magnitude reducing from a maximum as path length increases from a point of symmetry of the dipole. However, when the current reaches capacitive hats  93   a ,  94   a  it sees the HF capacitor plate and some current flows across the capacitors and thus in the HF layer. As mentioned above, coil  92  with small spaces between its windings tends to have the appearance of a slab of conductor so UHF capacitive hats  93   a ,  94   a  are somewhat shorted together and a low impedance path appears between UHF capacitive hats  93   a ,  94   a  via the HF layer. By placing connection between capacitor plate  91  and HF coil  92  over the UHF dipole as a quarter-wave micro-stripline, currents that enter the HF layer capacitor plate via the UHF layer capacitor plate see coil  92  connected through this quarter-wave line and thus see coil  92  as a high impedance (virtual open circuit). Hence minimal current flows through the HF coil and thus minimal parasitic impedance appears between the UHF antenna capacitive hats  93   a ,  94   a  and the UHF antenna operates without seeing the HF capacitor or coil  92 . By making the antenna symmetrical with reference to the micro-stripline, capacitive hats  93   a ,  94   a  may be isolated from the HF capacitors and HF coil  92 . When operating at HF, the micro-striplines just add to HF layer capacitive plate area. 
         [0053]    The dimensions of the tag may be 47 mm×47 mm overall conductor on a 50 mm×50 mm substrate. 
         [0054]    A HF RFID chip may be inserted in series with coil  92  at a gap somewhere in coil  92 . The HF capacitor layer may be adjusted and the HF feature may be RFID instead of EAS. 
         [0055]    Finally, it is to be understood that various alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention.