Passive Wireless Human Motion Monitoring Using Flexible Piezoelectric Sensors and Harmonic RFID

This paper introduces a novel passive and wireless motion sensor that integrates a flexible piezoelectric substrate with a harmonic radar transponder to enable both motion and pressure sensing. A prototype circuit was developed to validate the concept, utilizing the voltage generated by the piezoelectric sensor to bias a diode. Transmission and reception experiments were carried out using a signal generator and a spectrum analyzer. The piezoelectric sensor was then integrated with the harmonic transponder, enabling the wireless transmission of motion frequency and pressure magnitude data. Experimental results demonstrated that when a 50 kg individual performed repetitive heel movements, the transmitted signal exhibited sidebands with an amplitude increase of approximately 20 dB and frequency shifts ranging from 1 Hz to 5 Hz. These findings confirm the feasibility of a fully passive, flexible, wireless sensor capable of detecting both motion and pressure, marking significant progress in the development of advanced sensing technologies.