A variable-capacitance vibration-to-electric energy harvester

Past research on vibration energy harvesting has focused primarily on the use of magnets or piezoelectric materials as the basis of energy transduction, with few experimental studies implementing variable-capacitance-based scavenging. In contrast, this paper presents the design and demonstration of a variable-capacitance vibration energy harvester that combines an asynchronous diode-based charge pump with an inductive energy flyback circuit to deliver 1.8 mu W to a resistive load. A cantilever beam variable capacitor with a 650-pF dc capacitance and a 348-pF zero-to-peak ac capacitance, formed by a 43.56 cm(2) spring steel top plate attached to an aluminum base, drives the charge pump at its out-of-plane resonant frequency of 1.56 kHz. The entire harvester requires only one gated MOSFET for energy flyback control, greatly simplifying the clocking scheme and avoiding synchronization issues. Furthermore, the system exhibits a startup voltage requirement below 89 mV, indicating that it can potentially be turned on using just a piezoelectric film.