Wireless Passive Temperature Sensor based on a Harmonic Transponder and a Thermistor

This paper presents a novel wireless zero-power temperature sensor. Through the combination of harmonic radio frequency identification (RFID) technology and the concept of amplitude modulation, it was possible to create a transponder, which can therefore also be used for sensing applications. The prototype was obtained by combining a Schottky-diode for the frequency doubler with a negative temperature coefficient (NTC) thermistor. The thermistor controls the self-bias point of the diode, thereby changing the backscattered signal amplitude to the reader. Since the thermistor only impacts on the dc signal self-generated by the diode, the transponder performance does not depend on the NTC parasitics. The quantity monitored in this particular application is the temperature, and the task is achieved by modulating in amplitude the output port of a frequency doubler with the NTC thermistor. Therefore, the proposed sensor is able to transmit the information about the quantity of interest wirelessly and without power supply batteries.