Double Impact-Based Piezoelectric Energy Harvester for Low-Frequency Operation

This article presents a theoretical, numerical, and experimental study of a frequency upconverting (FUC) piezoelectric vibration energy harvester with a single low-frequency resonator that impacts twice per oscillation cycle on a single high-frequency unimorph generator. The model’s relevant physical aspects are specially designed to enhance the electrical output power over a wide-frequency range in the low-frequency excitation. The proposed double impact strategy allows obtaining a nearly constant output voltage, in contrast to typical upconverting mechanisms whose output voltage decays quickly in time. The device is safe from fatigue and can be used in high acceleration scenarios because the large displacements are limited by the generating beam, which acts as a natural stopper in an upward and downward directions. The prototype is designed to obtain a low value of optimal resistance with enhanced broadband performance below 25 Hz. The double impact FUC energy harvester’s performance is improved by adjusting the gap distance, the thickness of the generating beam, and the tip mass of the driving beam. The harvester reports 1428-
$\mu \text{W}$
peak output power at 20 Hz and
$400 ~\mu \text{W}$
of average power for a usable bandwidth from 17.5 to 22 Hz in health monitoring systems.