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Bulk wave transponder

  • US 5,359,250 A
  • Filed: 03/04/1992
  • Issued: 10/25/1994
  • Est. Priority Date: 03/04/1992
  • Status: Expired due to Fees
First Claim
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1. A transponder, comprising:

  • (a) an antenna; and

    (b) a bulk wave transducer, coupled to said antenna, comprising a substrate, first and second bus electrodes, a plurality of interdigital transducers (IDTs) so disposed upon said substrate as to generate, in response to an interrogation signal received by said antenna, a response signal conveying an identifying code, and a layer of piezoelectric film in contact with said IDTs;

    wherein each of said IDTs is coupled to at least one of said first and second bus electrodes;

    wherein said plurality of IDTs comprises a series of connected and unconnected IDTs (T1, T2, T3 . . . TN) so disposed as to generate a response signal in which is encoded a prescribed sequence of digits, wherein the connected IDTs are connected to both said first and second bus electrodes and the unconnected IDTs are unconnected to said second bus electrode;

    wherein all of said IDTs are disposed on a single surface of said substrate;

    wherein each digit (digiti) corresponds to a unique IDT (Ti) and is capable of representing at least two conditions, including the connected/unconnected state of its corresponding IDT;

    wherein each digit is carried via a unique frequency (fi); and

    wherein the inter-IDT spacings Di are related to the frequencies fi as follows;

    
    
    space="preserve" listing-type="equation">D.sub.i =2d/tan(arcos(ν

    a/Lf.sub.i)),where ν

    a represents the velocity of the bulk waves in the substrate, d represents the thickness of the substrate, and L represents two times the spacing between adjacent electrodes of the IDTs plus the width of an electrode.

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