A MEMS electrostatic energy harvester with quasi-zero stiffness control for ultra-low-frequency operation

This paper presents a MEMS electrostatic energy harvester capable of achieving the output power of the optimal velocity-damped-generator (VDRG) under time-harmonic excitations at ultra-low frequencies. The electromechanical zero stiffness of the compliant structure is precisely controlled using a unique combination of a bistable curved and folded beam structure along with a shifting transducer. Tuning transducers with various comb-drive finger geometries are employed to adjust the effective resonance from the linear-off region, enabling the harvester to adapt to different drive frequencies. The bias voltages of the harvesting and tuning transducers are analytically determined to achieve the maximum possible output power, even when the drive acceleration amplitude exceeds the critical threshold within the displacement constraint. The findings can provide a prospective design strategy to make microgenerators adaptable to ultra-low frequency operation, particularly those excited by human motion.