Piggyback modulation for UHF RFID sensors

We introduce the technique of “piggybacking” sensor data onto existing commercial passive UHF RFID tags. Sensor data fed into a PIN diode modulator is coupled onto the tag and transmitted along with the tag ID via backscatter. The radar cross section (RCS) of the tag antenna is a function of the input impedance of the tag ASIC, coupling S-parameters, and the input impedance of the PIN diode modulator. Both analog and digital sensor signals coexisting with identification data are presented.