Piezoelectric generator with nonlinear structure

Abstract

Motion in nature is usually a low-frequency vibration such as walking, running, swinging arms, and so on, but traditional piezoelectric cantilever structures are inefficient at harvesting energy from low-frequency vibrations in the environment. To overcome this, a novel piezoelectric generator was designed. A cantilevered bimorph with a tip mass and a pair of preloading springs were fixed on its base to form a nonlinear piezoelectric generator. The energy transmission in the structure was analyzed. The harvester was modeled as a Euler–Bernoulli beam, and the piezoelectric material was assumed to be linear. The bending vibration was calculated using the Rayleigh–Ritz procedure, and the frequency characteristics of the output voltage were analyzed under different preloading distances. It was found that changing the preloading of the spring helped reduce the natural frequency of the cantilever, which facilitated conversion of ambient low-frequency vibrations into electrical energy. Then, the characteristics of low frequency energy harvesting were investigated experimentally. The theoretical results were consistent with the experimental data; moreover, the resonance frequency, which changes with the preloading distance, reduced from 43 to 35 Hz when the preloading distance was increased from 0 to 1 mm. In this paper, an effective structure to control the resonant frequency is proposed and its motion equation stated. The structure has potential for applications in predicting the effect of preloading distance on resonance frequency.