Zero-Power Temperature Sensor for Wireless Harmonic Systems based on a Reflection-type Phase Shifter and a Bimorph Cantilever

This work presents a passive temperature sensor, able to encode a temperature variation in a phase variation. This is achieved combining, for the first time, a reflection-type phase shifter and a bimorph cantilever. The sensor is intended to be part of a passive wireless harmonic transponder able to retrieve the sensor information from the phase difference between the signals re-transmitted in vertical and horizontal polarizations. The temperature-controlled phase shifter is firstly designed and modeled. Then, a prototype, working at 2 GHz, is manufactured assembling the bimorph cantilever with a planar microstrip circuit and tested. A phase difference of about 47circ is observed for a temperature variation from $25^{\circ}{C}$ to $50^{\circ}{C}$, showing the high sensitivity of the proposed device, which opens the door to a new class of passive phase-encoded sensors.