A Tunable Nonlinear Magnetic Piezoelectric Energy Harvester

To broaden the effective frequency band of piezoelectric energy harvesters, this paper designed a nonlinear magnetic piezoelectric energy harvester with adjustable frequency and fast switching between monostable and bi-stable mode. This harvester is composed by adding a pair of movable magnets on a piezoelectric cantilever beam with an end magnet. Firstly, the distributed parameter dynamics of the harvester was analyzed. The dynamics equation of the system was derived based on Euler-Bernoulli theory, and the expressions of kinetic energy, potential energy and electric energy of the system were analyzed according to Lagrange function. The magnetic force expression of the system was obtained according to the magnetic dipole model. The first-order reduced model of the system was obtained by Galerkin discrete method and Taylor expansion, and the analytical expression of the equations was derived via the harmonic balance method. Then, the monostable and bi-stable characteristics of the harvester were studied by simulation software, and the effects of magnet spacing, damping, load resistance and other parameters on the output voltage and output power of the system were analyzed and verified by the subsequent experiment. According to the experimental result, the nonlinear magnetic force brought by the movable magnet can significantly increase the output voltage and output power of the harvester; the resonant frequency of the energy harvester can be changed by adjusting the magnet spacing, which better widens the working frequency band; the energy harvesting system can rapidly switch between monostable mode and bi-stable mode by adjusting the magnet spacing, and use the monostable mode and and the bi-stable mode to harvest vibration energy in high-frequency environment and the low-frequency environment, respectively.