Modeling and experiment of bistable two-degree-of-freedom energy harvester with magnetic coupling

The operating bandwidth of energy harvesters is one main concern in vibration energy harvesting due to the random and time-varying nature of most vibration sources. Recent research efforts have been made to address this issue including exploiting multimodal structures and nonlinear dynamics. These ideas have yielded some exciting results to leverage the broadband performance. Hybrid configurations combining these ideas are expected to provide an even better operating bandwidth and yet to be studied. In this paper, a bistable two-degree-of-freedom (2-DOF) piezoelectric energy harvester (PEH) with magnetic coupling is proposed, in which a linear parasitic oscillator attached to the main energy harvesting beam is used to generate two resonant peaks and the magnetic coupling is used to generate nonlinear dynamics, thus to achieve broadband electrical outputs. A nonlinear electromechanical model of the proposed harvester is established and the parametric study is conducted for various parasitic oscillator configurations. Experiment is subsequently performed to validate the theoretical analysis. The results indicate that nonlinear responses can appear at any of the two peaks or at both. One strong nonlinear peak in addition to a quasi-linear peak can be achieved by adequate adjustment of the parasitic oscillator. This is advantageous over the optimal linear 2-DOF PEH in terms of wider bandwidth thanks to the involved nonlinear dynamics. In addition, the load resistance has significant influence around the peak with strong nonlinear responses, resulting in evident peak shift. The best power output is accompanied with a shrunk bandwidth due to the peak shift.