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Roll-to-roll production of RFID tags

  • US 10,224,902 B2
  • Filed: 05/09/2012
  • Issued: 03/05/2019
  • Est. Priority Date: 11/18/2006
  • Status: Active Grant
First Claim
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1. A radio frequency identification (RFID) tag comprising:

  • a substrate having a predetermined thickness;

    an antenna mounted on the substrate;

    a variable tank circuit coupled to the antenna;

    a tuner coupled to the variable tank circuit, wherein, when the RFID tag is not exposed to an interfering substance, the RFID tag has a first resonant frequency, and when the RFID tag is exposed to the interfering substance, impedance of the antenna is changed causing a change in resonant frequency of the RFID tag to a second resonant frequency, wherein the tuner adjusts impedance of the variable tank circuit to substantially compensate for the antenna impedance change thereby adjusting the resonant frequency of the RFID tag to be substantially the first resonant frequency, and wherein the tuner generates a digital value indicative of an amount of impedance adjustment of the variable tank circuit, wherein the digital value is operable to be interpreted by a radio frequency (RF) reader to determine characteristics of the interfering substance, wherein the characteristics include one or more of a proximity of the interfering substance to the RFID tag, an environmental condition, a metal, a free space, and a liquid; and

    a transmitter operable to convert the digital value into an outbound RF signal and to transmit the outbound RF signal to the RF reader.

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