Stability State Transition and Dynamics Modeling of an Elliptical Pendulum-Inspired Energy Harvester with Dynamic Axial Load

Vibration energy harvesting techniques provide a solution for the continuous powering of wireless sensor networks. Nevertheless, the limited energy conversion efficiency of low-frequency and large-amplitude vibrations remains a significant challenge. We propose an elliptical pendulum-inspired piezoelectric energy harvester (EP-PEH) for harvesting ultra-low frequency and large-amplitude vibration. This device couples magnetic, gravitational, and inertial forces through an elliptical pendulum mechanism, enabling their synergistic action to apply dynamic axial loads to the piezoelectric beam. This significantly enhances the strain level of the piezoelectric beam, thereby improving the energy conversion efficiency under ultra-low frequency. Based on the Lagrange equation, the electromechanical coupling dynamics model of the system is established, and the synergy mechanism between magnetic force, gravity and inertial force is revealed by using the dynamic bifurcation theory. Phase diagrams were utilized to characterize the influence of geometric nonlinearity on electrical performance. From the standpoint of output power, we explored the effects of flexible piezoelectric polymer polyvinylidene fluoride (PVDF) film thickness and external resistance on the electrical performance of EP-PEH. Theoretical calculations show that the output power of the proposed harvester is 38% higher than that of the traditional harvester. An EP-PEH prototype was fabricated, and the accuracy of the model was experimentally verified. In summary, this work provides new insights into wireless power supply for sensor networks in low-frequency, high-amplitude environments.