Sloshing liquid-metal mass for widening the bandwidth of a vibration energy harvester

Abstract Linear vibrational energy harvesting devices typically have narrow bandwidths, which limits their practical use, because the resonant frequency needs to match the frequency of the vibration source in order to maximize power generated. This paper presents a method of widening the bandwidth by using a highly dense liquid metal filled mass, which creates a sloshing effect that changes the center of gravity of the cantilever device during motion. The shift in center of gravity causes the resonant frequency of the cantilever to change. Since the resonant frequency of the device is constantly changing during oscillation of the cantilever, this results in a widening of the bandwidth. The displacement of the dense liquid metal has more influence on the center of gravity compared to other less dense liquids thus increasing the bandwidth. The paper demonstrates a 6.5× increase in bandwidth for the liquid metal filled mass compared to a typical air-filled mass with only a 9.6% reduction in power at 1 g acceleration. Acceleration effects and mechanical damping were also investigated and presented within the paper.