Piezoelectric MEMS vibration energy harvester using BiFeO₃ film and dynamic magnifier for impulsive forces

Resonant-type piezoelectric vibration energy harvesters (pVEHs) can achieve high energy conversion efficiency and output power density by using resonance phenomena with external vibrations at constant frequencies. However, this approach is less effective for the random vibrations commonly encountered in real-world environments, thus limiting its practical applications. This study employs impulsive forces and a two-degree-of-freedom system with a dynamic magnifier (DM) to enhance the output power of a nonresonant microelectromechanical systems-based pVEH (MEMS-pVEH). Lead-free BiFeO₃ (BFO) was selected as the piezoelectric thin film due to its considerable figure of merit in energy conversion applications. We investigated the electromechanical properties of the BFO-based MEMS-pVEH using DM under various impulsive force durations. The results revealed that incorporating a DM increased the output energy of the MEMS-pVEH from 0.17 nJ/G² to 3.97 nJ/G² (where G represents gravitational acceleration) for a 23.8-fold enhancement. The findings demonstrate that the output energy of conventional MEMS-pVEH structures using lead-free piezoelectric BFO film can be significantly amplified with the integration of a simple DM.