Wireless Harmonic Transponder Based on Piezo-Varactor Direct Phase Modulation

Abstract

This paper presents a passive wireless harmonic transponder capable of transmitting information acquired by its vibration sensor. The system is equipped with a Schottky diode frequency doubler which converts the received signal from f
₀ to its second harmonic 2 f
₀. The sensed information is then encoded in the 2 f
₀ carrier phase using a varactor phase-shifter (acting as the phase modulator) biased through a piezoelectric transducer (which senses the mechanical vibrations). The transponder operation is demonstrated with particular focus on piezoelectric transducer vibrating resonance frequency. The side-band amplitude of the backscattered signal increases by about 10 dB for an increment of the acceleration of the mechanical system under test of 1.5 g 128 Hz.