Performance estimation of a piezoelectric energy harvester with rotatable external magnets.

This study estimates the performance of a piezoelectric energy harvester (PEH) with rotatable external magnets from the viewpoint of global dynamics. According to static analysis of the PEH dynamic system, the monostable and bistable potential wells are configured under different values of the inclined angle of the external magnets. In the monostable case, the method of multiple scales is applied for the analysis of periodic responses, while the extended averaging method and the Melnikov method are utilized to analyze the periodic and chaotic responses in the bistable case. Numerical results are in great agreement with the theoretical ones. It follows from the comparison of the dynamical behaviors in the two cases that the bistable-well configuration is more efficient in harvesting vibration energy under low-frequency or low-level ambient excitation. In the bistable case, sequences of the coexisting attractors and basins of attraction (BAs) with the increase in the excitation strength are presented, illustrating that the inter-well periodic and chaotic responses can be successively triggered by the rise in the excitation level, and which attractor will contribute to increasing the voltage output depends on the location and size of their BAs. With the increase in the excitation level, rich nonlinear dynamic phenomena, such as multistability, period-2 attractors, chaos, fractal BAs, and hidden attractors, can be observed.