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Tag responsive to high frequency for varying capacitance of capacitor in power source

  • US 5,721,535 A
  • Filed: 05/30/1995
  • Issued: 02/24/1998
  • Est. Priority Date: 05/27/1994
  • Status: Expired due to Term
First Claim
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1. A tag responsive to high frequency for receiving a high frequency wave from an interrogator to derive electrical power from the high frequency wave and for communicating with the interrogator, comprising:

  • a tuning circuit that receives a high frequency wave having a tuning frequency;

    a power source that includes rectifying capacitors and rectifies output of the tuning circuit to output a source voltage;

    a voltage detector circuit that detects the source voltage output from the power source; and

    a capacitance varying circuit that varies the capacitance of the rectifying capacitors according to the source voltage detected by the voltage detector circuit.

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