Abstract:
A test fixture and electronic tag assembly includes an electronic tag comprising an electronic device and a half wave dipole antenna of antenna length L. The antenna is configured as first and second coiled dipole antenna segments connecting with and extending in opposite directions from the electronic device. The assembly further includes a support frame; first and second electrically conductive pads positioned in spaced apart relationship within the support frame; and apparatus for fixedly holding end segments of the first and second coiled dipole antenna segments respectively against the first and second conductive pads in an overlapping relationship. A combined length of the first and second coiled dipole antenna segments and the conductive pads less the length of the overlapping end segments define a calculated effective antenna length for operative utility in performance measurement of the electronic tag in air analogous with the performance of the performance of the tag in a non-air medium such as in a tire. The spacing between the conductive pads may be selectively altered to accommodate the testing of tags of varying lengths within the fixture.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to an RFID tag test fixture and method and, more specifically, a testing fixture and method for a RFID tire tag. 
       BACKGROUND OF THE INVENTION 
       [0002]    RFID tags are incorporated into a range of products for the purpose of allowing an identification of the product by a remote reading device. It is important that tags of variable lengths and configurations be tested in order to verify that they are operating correctly within system specifications for the particular product and application for which they are intended. In addition, it is desirable to determine the minimum read and write power characteristics of the tag so that testing will provide a reliable quality control assessment. Furthermore, it is desirable to test the tags under controlled environmental conditions to improve the reliability and relevance of the test results. 
       SUMMARY OF THE INVENTION 
       [0003]    According to an aspect of the invention, a test fixture and electronic tag assembly includes an electronic tag comprising an electronic device and a half wave dipole antenna of antenna length L. The antenna is configured as first and second coiled dipole antenna segments connecting with and extending in opposite directions from the electronic device. The assembly further includes a support frame; first and second electrically conductive pads positioned in spaced apart relationship within the support frame; and apparatus for fixedly holding end segments of the first and second coiled dipole antenna segments respectively against the first and second conductive pads in an overlapping relationship. 
         [0004]    Pursuant to another aspect of the invention, a combined length of the first and second coiled dipole antenna segments and the conductive pads define a calculated effective antenna length for operative utility in performance measurement of the electronic tag in air. Verification of the minimum read and write power levels required by tags of varying lengths may be established. 
         [0005]    In a further aspect, the retention apparatus comprises abutting first and second blocks defining a block cavity dimensioned and shaped for receipt of the electronic tag and conductive pads therein. The spacing between the conductive pads may be selectively altered to accommodate testing tags of varying lengths. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The invention will be described by way of example and with reference to the accompanying drawings in which: 
           [0007]      FIG. 1A  is a perspective view of a tag assembly. 
           [0008]      FIG. 1B  is a perspective view of the tag in an encapsulating protective medium. 
           [0009]      FIG. 2  is a perspective view of a support stand sub-assembly of the test fixture apparatus. 
           [0010]      FIG. 3  is a partial exploded perspective view of the test fixture apparatus. 
           [0011]      FIG. 4  is a partial exploded perspective view of an upper portion of the support stand 
           [0012]      FIG. 5  is a partial perspective view of an upper portion of the support stand. 
           [0013]      FIG. 6  is a top plan view of the tag support block component of the apparatus. 
           [0014]      FIGS. 7A ,  7 B, and  7 C are plan view of a substrate insert component of the apparatus showing alternative conductive pad schematic configurations. 
           [0015]      FIG. 8A  is a top plan view of the tag support block and loaded tag with insert substrate components of the apparatus configured to provide a longer conductive pad extension to the tag antenna. 
           [0016]      FIG. 8B  is a top plan view of the tag support block and loaded tag with the insert components of the apparatus configured to provide comparatively shorter conductive pad extension to the tap antenna. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    Referring first to  FIGS. 1A and 1B , an electronic tire tag  10  is of a conventional commercially configured type and includes an antenna formed by a pair of coiled antenna segments  12 ,  14 . An integrated circuit package (IC)  16  is mounted to a carrier substrate  18  and includes interconnection leads  20 ,  22  extending from opposite IC package sides respectively. The antenna  12 ,  14  is conventionally electrically connected to the IC leads  20 ,  22  and is suitably tuned to a predetermined radio frequency “f” substantially within a range of 902 to 928 MHz, for receiving RF signals, referred to herein as interrogation signals, from an external transceiver (not shown). 
         [0018]    Operatively, the interrogation signal is received by the antenna  12 ,  14  from a remote transponder (not shown) and transmitted to the integrated circuitry within the package  16 . The integrated circuit within the package  16  processes the RF interrogation signal into a power signal for powering a logic circuit that includes conventional ROM, RAM, or other known types of memory storage devices and circuitry. Data transmission from the storage devices is thereby enabled and stored data is transmitted by the antenna  12 ,  14  back to an external reader or transponder (not shown). The tag  10  may be incorporated within various products and utilized to communicate stored data relating to such products to the remote reading device. 
         [0019]    The electronic tire tag  10  may be encapsulated in a rigid or semi-rigid material, such as a urethane, epoxy or polystyrene resin, hard rubber compound or the like in a configuration such as the cylindrical package  24  shown in  FIG. 1B . Thereafter, the encapsulated electronic tire tag  10  is preferably wrapped with a suitable green rubber material (not shown) to form a green rubber patch (not shown) that is vulcanized and fixedly secured to a tire (not shown). Alternatively, the tag  10  may be incorporated within the green tire prior to tire cure. 
         [0020]    Accordingly, the RFID tire tag must be tuned to rubber for efficient operation. However, testing (minimum read and minimum write power) the tag  10  within a rubber material is problematic. Placing the tag in close contact to cured rubber does not provide the optimal coupling method and as the cured rubber sample ages, the testing data may become unreliable. Also, in order to test RFID tire tags  10  with different antenna lengths, different sized rubber samples would need to be employed to accommodate the antenna length differences. Testing the tag  10  in air would, ordinarily, not achieve satisfactory and reliable results because the tag  10  is not tuned for air. That is, its length (and impedance) is designed to transmit in rubber and not air. 
         [0021]    The subject invention varies the effective length (and consequently its impedance) of a tag antenna in a testing apparatus and methodology disclosed herein. By so doing, the RFID tag  10  may be tested in air yet yield results analogous to a rubber transmission test environment. The testing apparatus is shown in  FIGS. 2-5 . As shown, the apparatus includes a support from assembly  26  formed having a base  28 , vertically extending spaced-apart legs  30 ,  32  affixed at one end to the base by suitable means such as bolts  31 . A test fixture assembly  34  includes a cover member or block  36  having a cover cavity  37  within an underside. The block  36  may be formed of any suitably rigid material such as a thermoplastic resin. A holding plate or second block  38  is provided having indented sides  39  A, B. The holding plate or block  38  fits closely within the cover cavity  37  such that a bottom surface of the cover and a top surface  44  of the holding plate are in abutment. The holding plate attaches to vertical slots  42  extending along the upper spans of legs  30 ,  32  by suitable means such as bolts  40  whereby the holding plate  38  is vertically adjustable along the support legs  30 ,  32  to a preferred height. For example, a testing height for a tag  10  may place the tag at a level simulating a mounting location of the tag within a tire. 
         [0022]    Within the upper plate surface  44  of the holding plate  38  are spaced apart, generally rectangular, cavities  46 ,  48  connected by a centrally disposed tag cavity  50 . The tag cavity  50  has a geometric profile for receipt of the IC package  16  of tag  10  as will be explained. A pair of substrate insert bodies  52 ,  54  are further provided have a generally rectangular form dimensioned for close receipt within respective holding plate cavities  46 ,  48 . Positioned within each substrate body  52 ,  54  are a pair of adjustment slots  56  that receive bolts  58 . The bolts  58  extend through sockets  60  within the floor of the cavities  46 ,  48  to secure the substrate bodies within the holding plate cavities. Each substrate body  52 ,  54  is laterally repositionable within a respective holding plate cavity  46 ,  48  to the extent of the slots  56 . 
         [0023]    The substrate bodies  52 ,  54  each are preferably although not necessarily multi-level, having a raised shelf region  62  along one side of the body. The raised shelf region  62  of each body  52 ,  54  supports a conductive pad  64  that is affixed by appropriate means to a top surface of the shelf region. The conductive pad  64  connected to each substrate body  52 ,  54  may comprise a conductive plate member (not shown) of suitably conductive material. In the embodiment shown, the conductive pads  64  are formed by foil tape having a conductive copper metallic surface. The foil tape comprising the conductive pads is affixed by adhesive to the shelf region  62  of each body  52 ,  54 . The coverage of the shelf region  62  may be varied as illustrated in the alternatively-sized pads of  7 A, B, and C. The sizing of the pads  64  determines the extent to which the test fixture assembly can accommodate tags of varying sizes. 
         [0024]    To conduct a test on a tag  10 , the tag  10  is positioned over the holding plate  38  and loaded into the cavities  46 ,  48  and  50 . So situated, as shown best by  FIG. 8B , the coiled antenna segments  12 ,  14  of the tag  10  overlap the conductive pads  64  on substrate bodies  52 ,  54 . It will be noted that the extent of overlap may differ from tag to tag, depending on the length of the antenna segments  12 ,  14  of a given tag and the position of the substrate bodies  52 ,  54  within the cavities  46 ,  48 . Bodies  52 ,  54  may be adjusted laterally within and to the extent of slots  56  to alter the extent of overlap with the antenna segments  12 ,  14 . The shape and size of the central cavity  50  is somewhat oversized to accommodate receipt of the IC package  16  of a range of tag devices. 
         [0025]    The cover  36  is thereafter assembled upon the holding plate  38  to enclose the tag  10  within the cavities  46 ,  48 , and  50  in a sandwich configuration. The tag  10  is thereby rendered relatively immobile for the testing procedure. The testing procedure includes sweeping the sandwiched tag  10  at varying power levels from a transmitting device (not shown) to determine the minimum read and write power characteristics of the tag. At the conclusion of the test procedure, the cover  36  is removed and tag  10  withdrawn. 
         [0026]      FIG. 8B  shows the tag placed in the testing fixture assembly  34 . The number of coils of the tag antenna touching the copper tape foil may be varied. The substrate inserts  52 ,  54  are screwed down by the screws  58  so that they do not shift during testing. The tag  10  for incorporation into a tire is designed such that the tag length and impedance are tuned to transmit in rubber. Testing the tag in a rubber medium, however, is difficult for the reasons previously explained. For the tag to be able to transmit in air, its effective length and consequently its impedance requires variation. The copper tape pads  64  on the inserts  52 ,  54  facilitate a variation to the length of the antenna of tag  10 , as will be appreciated from the following example. 
         [0027]    Since the antenna is a half-wave dipole antenna, its length can be computed according to the formula: 
         [0028]    Length (L)=468/f (MHz) feet, where f=Frequency of transmission (for the subject example 902-928 MHz). Selecting a mean frequency of, as an example, 915 Hz, the effective length of the antenna was calculated to be 6.13 inches. A tag of approximately 3.1 inches in length was employed. The effective length of antenna represents the combination of conductive pad and tag length. Therefore, the conductive pad length required to total 6.13 inches is approximately 3.0 inches, or, 1.5 inches of conductive pad on either side within the testing fixture assembly.  FIGS. 8A and 8B  show the apparatus having conductive pads  64  of differing lengths,  FIG. 8A  pads being comparatively longer than those of  FIG. 8B . The effective length of the antenna may be changed by sliding the substrates that carry the conductive pads within respective cavities  46 ,  48 . Screws  58  within slots  56  are tightened when the requisite position required for the desired effective length of antenna is established. 
         [0029]    From experimental results, it was concluded that the length of the copper tape affected the test results as the impedance of the tag varied with the length of the copper pad employed. Minimum power requirement at a range of test frequencies verified that the median and the mode nearly coincided and the standard deviation of the data was low, implying that the data obtained was accurate and precise. The testing of the tag in air utilizing the test fixture assembly  34  thus was concluded to be accurate. 
         [0030]    The subject test fixture assembly  34  can accommodate different length tags. The copper foil taped pads  64  are laterally adjustable and may cover more or less of the surface area of the substrate inserts in order to accommodate a range of tag lengths. The pads act to extend the length of the antenna of the tag  10  to a requisite extent necessary to achieve a requisite effective antenna length. The testing assembly  34  eliminates the need for customized apparatus because tags of varying sizes and lengths may be accommodated. In addition, the assembly  34  eliminates the problem of testing an RFID tire tag in a rubber medium. Testing the tag within fixture assembly  34  and in air proved to be an accurate indicator that the tag  10  was performing according to predetermined minimum and maximum power criteria. Issues relating to testing within cured rubber and aging rubber accordingly may be avoided. The apparatus and assembly  34  thus provides a flexible fixture for testing tags having antenna segments of varied lengths by utilizing the conductive pads to extend the antenna length to a required extent. In addition, the sandwich configuration of the fixture assembly  34  acts to render a tag undergoing testing immoveable at a desired height for reliable and repeatable test results. 
         [0031]    Variations in the present invention are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described which will be within the full intended scope of the invention as defined by the following appended claims.