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Electronic identification system confirming valid code

  • US 5,995,017 A
  • Filed: 11/24/1997
  • Issued: 11/30/1999
  • Est. Priority Date: 01/04/1991
  • Status: Expired due to Term
First Claim
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1. An identification system comprising:

  • an interrogator; and

    a plurality of transponders wherein;

    the interrogator comprises;

    a transmitter for transmitting an interrogation signal to the transponders,a receiver for receiving response signals from the transponders,a processor for identifying the transponders from data in the response signals, andmeans for confirming that a valid code from any one of the transponders is received and for modifying the interrogation signal to indicate confirmation of the valid code, the modifying of the interrogation signal being in response to and just after successful identification of the one of the transponders and being for a predetermined period after successfully identifying the one of the transponders, the predetermined period of time being shorter than a length of a transponder transmission;

    each of the transponders comprises;

    a receiving antenna for receiving the interrogation signal,a code generator,a transmitting antenna,a modulator connected to the code generator, so that upon receipt of the interrogation signal the transponder transmits a response signal containing data which identifies the transponder,means for repeating a transmission of the response signal at random or pseudo-random intervals to increase a probability of successful reception thereof by the interrogator, andmeans for sensing a modification in the interrogation signal and ceasing transmission of the response signal in response thereto.

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