On the performances of a nonlinear hybrid piezoelectric and electromagnetic energy harvester

A nonlinear energy harvester combined piezoelectric (PE) and electromagnetic (EM) is studied for the low vibration frequency excitation, and its resonant frequency can be tuned by magnetic force. In the paper, analytical solutions of amplitude, output voltage, current and power under sinusoidal and stochastic excitations are derived by the methods of harmonic balance and Fokker-Planck theory respectively. The theoretical analysis is carried out, and output performance is tested by the experiment. It can be concluded that the resonant frequency and bandwidth of harvester can be adjusted through magnetic force, and nonlinear energy harvester can improve output power compared with the corresponding linear harvester. In addition, coupling effect of PE element has influence on stiffness and damping of harvester simultaneously, while EM element coupling effect mainly affects the damping. When the harvester excited at the resonant frequency and connected with optimal PE and EM load simultaneously, the output power and 3 dB bandwidth can reach the maximum. Furthermore, mean power is linearly proportional to spectral density of acceleration at random excitation. Through analysis results, the ways that can boost the output power at low frequency excitation are found.