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Passive tag identification system and method

  • US 4,663,625 A
  • Filed: 12/20/1985
  • Issued: 05/05/1987
  • Est. Priority Date: 11/30/1983
  • Status: Expired due to Fees
First Claim
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1. An identification system for use in association with a set of objects, such as persons, animals, packages or the like, whereby any member of said set may be identified while said member is located within a predetermined interrogation zone, wherein said system comprises:

  • interrogation field means whereby at least one oscillating electromagnetic interrogation field may be established in said interrogation zone;

    response signal detection means operable to monitor said interrogation zone;

    an identification tag associated with each member of said set, each tag comprising;

    a response member formed of a magnetically permeable material adapted to reach saturation abruptly at a predetermined level of magnetic flux and responsive to half cycles of said interrogation field when present in said interrogation zone, upon abrupt magnetic saturation thereof, to abruptly distort said field thereby generating a series of field distortion pulses corresponding to successive half cycles of said interrogation field and detectable during said half cycles;

    an electromagnetic masking coil around the said response member selectively operable to magnetically mask the same and thereby prevent saturation of said response member and adapted to be rendered inoperable whereby no such masking takes place;

    switch means in circuit with said masking coil selectively operable during a half cycle to control said masking coil;

    circuitry means connected with said switch means and operable to control opening and closing of said switch means according to a predetermined sequence in timed relation to said half cycles of said interrogation field thereby establishing during the presence of said interrogation field a series of interrogation field distortion pulses caused by abrupt saturation of said response member, said series of interrogation field distortion pulses being interrupted by a unique series of discontinuities in said series of distortion pulses which defines an identification code for said tag;

    power means for said circuitry means whereby the same may be operated, and,signal processing means connected to said detection means for processing and decoding said series of distortion pulses.

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