Piezoelectric energy harvester converting strain energy into kinetic energy for extremely low frequency operation

In this study, we developed a flexible energy harvester that uses the frequency up-conversion mechanism. The harvester is composed of a flexible piezoelectric cantilever and substrate, and it can scavenge energy from deformation or strain by converting it into a mechanical vibration of the cantilever. We found experimentally that the output voltage of the harvester not affected by an input frequency as long as the strain was large enough, and there was no lower limit of the input frequency. The critical strain, i.e., the threshold radius of curvature of the harvester, could be modulated by adjusting magnetic force; therefore, it is possible to optimally apply the harvester to various deformation ranges. The maximum and average power density at 0.5 Hz of input frequency was measured to be 320 μW/cm² and 6.8 μW/cm² for a resistive load of 10 MΩ.