Study on cantilever piezoelectric energy harvester with tunable function

Abstract

Piezoelectric energy harvesters tend to convert energy from ambient vibration to electricity, which can gain a higher output voltage at resonance region. How to obtain a larger working bandwidth is urgent to explore at present. In this paper, a cantilever plate energy harvester is designed, with two boxes added at two free edges along the fixed-free direction and one rolling ball placed in each boxes respectively. The natural frequency of the structure can be adjusted by changing the centroid of the structure, which is caused by the balls rolling in the box. The range of adjustment that contains from the maximum (upper limit) to minimum (lower limit) frequency, is defined as the theoretical frequency band. The mode function of tunable cantilever plate is given according to deflection curve. Considering the rigid body motion of boxes and the composite motion of the balls, the Hamilton principle and the Hertz contact theory are taken into account to derive the vibration equations of the system. The experiment is carried out to verify the correctness of the theoretical mode and the dynamic equations. The responses of the structure under different excitation frequencies are calculated by using MATLAB software and verified by frequency sweep experiment. The results show that the working bandwidth of proposed structure under different balls initial positions is wider than with that of beam structure in resonance, thus proving the better tuning ability of the designed system. In addition, the output of the energy harvester under different external excitation acceleration is given. The effects of different length of box on the working bandwidth and output power density are studied. The relationship between conversion rate and external resistance is proposed under different boxes length. A high performance energy harvester with wider operating frequency range is designed.