Improving Functionality of 2DOF Piezoelectric Cantilever for Broadband Vibration Energy Harvesting Using Magnets

This paper presents a 2DOF nonlinear piezoelectric energy harvester for improving the efficiency of energy harvesting in low frequency range.The device consisted of an L-shaped piezoelectric cantilever with a magnet at the tip of the first beam and two external magnets on the pedestal.The distance between the magnets which generated nonlinear magnetic attraction was adjusted such that the system can exhibit monostable or bistable characteristics.First,the model of this piezoelectric energy harvester was established and the dynamic equation was derived based on the magnetic attractive force.Then,the nonlinear dynamic responses of the system subject to harmonic excitation were explored by a numerical method and validated by experiments.At an excitation level of 4 m/s^(2)in reverse sweep test for the proposed nonlinear harvester,nearly 240%increase in frequency bandwidth was obtained compared to 2DOF linear one in the first two resonance regions under both monostable and bistable states.Moreover,the nonlinear device yielded a closer frequency band gap between the first two resonance regions.The findings provide insight for the design of a broadband energy harvester when there is nonlinearity using magnets.