Patent ID: 7501952

Claim:
A radio-frequency identification (RFID) tag for use with a reader that generates activation energy, the RFID tag comprising: an RFID circuit for modulating tag energy when activation energy is received and for modulating tag energy when tag energy is received from another RFID tag; a first antenna configured to receive and provide activation energy to the RFID circuit and radiate modulated tag energy received from the RFID circuit; a second antenna configured to radiate activation energy received by the first antenna and receive and provide tag energy radiated by antenna from another RFID tag to the RFID circuit; a transmission line for operatively coupling the RFID circuit to the first and second antennas; whereby when a plurality of the RFID tags are positioned in sequence in operative proximity with each other, activation energy is propagated through the sequence from one RFID tag to another in one direction, and tag energy is propagated through the sequence from one RFID tag to another in another direction; wherein the RFID circuit comprises an RFID chip having a variable input impedance, the variable input impedance including a first state in which the RFID chip absorbs energy from the transmission line, a second state in which energy from the transmission line is reflected back, and a third state in which the amount of energy absorbed by the RF chip is minimized, thereby maximizing the amount of energy passed on to a next RFID tag.