Piezoelectric transformers for ultra-low voltage energy harvesting applications

This work shows the possibility to exploit piezoelectric transformers (PTs) for implementing step-up oscillators for ultra-low DC voltage energy harvesting (EH) applications. Oscillation is achieved by coupling a common source stage made up of n-channel JFETs with a piezoelectric transformer acting like a high gain notch filter. A voltage doubler is used to store energy in a capacitor. A mathematical model of the whole system is developed and matches experimental measurements. The minimum activation voltage is 73 mV. This value decreases if higher mechanical quality factors of piezoelectric transformers are provided along with a corresponding design of the input stage.