FM-based piezoelectric strain voltage sensor at ultra-low frequencies with wireless capability

An FM-based ultra low frequency piezoelectric strain voltage sensing system is proposed. The sensing frequencies possible in this system are orders of magnitude lower than those of traditional methods. This method involves the conversion of changes in piezoelectric device's strain voltage to changes in capacitance with a varactor diode. This diode forms part of a feedback network in a Colpitts oscillator, converting variations in capacitance to variations in frequency. The frequency variations are demodulated using an FM demodulator. Demodulated signals as low as 1 mHz were achieved and measured. The system was also implemented and measured with a wireless transmission and demodulation of the FM signal