Zero-Power Vibration Sensor for Wireless Harmonic Systems based on a Reflection-type Phase Shifter and a Piezoelectric Transducer

This paper presents a passive wireless vibration sensor capable to transmit the information related to both vibration frequency and amplitude. These information are encoded in the interrogation carrier phase using a varactor phaseshifter (acting as the phase modulator) directly connected to a piezoelectric transducer (which senses the mechanical vibrations). The phase shifter consists of a 90-degree hybrid junction in which the direct and coupled ports are closed on identical reactive impedances: a voltage-controlled variable capacitance (varactor diode) and a fixed inductor. The sensor is intended to be part of a passive wireless harmonic transponder able to retrieve the sensor information from the re-transmitted modulated signal. The sensor demonstrated to sense vibration up to 400 Hz with a 2 g peak acceleration. For the re-transmitted signal, the sidebands amplitude increases of about 10 dB as the acceleration of the mechanical system under test varies between 0.5-2.0 g at 100 Hz.