Enhanced Performance of a Frequency Up-converted Piezoelectric Energy Harvester for Wideband Vibration
This paper demonstrates enhanced performance of a mechanical impact driven frequency up-converted piezoelectric vibration energy harvester to scavenge energy from a wide range of low frequency ambient vibration. Increased bandwidth of the harvester has been obtained by increasing the stiffness of its power generating elements. The harvester structure comprises a low-frequency flexible driving beam with laterally expanded rectangular tip mass and two high-frequency unimorph piezoelectric generating beams which are struck by the driving beam mass upon excitation, and generate power. This impact mechanism results in a hindrance of the vibration motion of the driving beam, and its frequency response diverges from normal behavior, introducing wideband operation. Increase in generating beams' stiffness causes an increase in the effective stiffness of driving beam after impact which, in turn, allows bandwidth enhancement. Two different sets of unimorph generating beams have been used. Among those, use of relatively stiffer beams, made of stainless steel support layer, offers 60% increased half-power bandwidth (8Hz) and almost 3 times increased peak power (377μW) than the other, made of styrene support layer. It generates significant power within the entire operating frequency range (6Hz to 15Hz) implying its potential to be implemented in human and machine motion applications.