A dual impact driven frequency up-conversion piezoelectric energy harvester for ultralow-frequency and wide-bandwidth operation

In the view of the limitation of traditional frequency up-conversion piezoelectric energy harvesters (FUC-PEH) which has a narrow operating frequency range and is difficult to adapt to the ultralow frequency excitation, this study presents a dual impact driven FUC-PEH composed of two piezoelectric energy harvester units (PEHUs). The electromechanical model of the FUC-PEH is established based on the single degree of freedom system and piezoelectric coupling factor. An experimental prototype is made and tested under different excitation frequencies and accelerations. The dynamic characteristics and energy output characteristics of the system are analyzed by theoretical calculation and experimental tests. The results show that the proposed energy harvester can provide efficient energy output in a wide frequency range of 3.5 Hz–15 Hz under different excitation accelerations. When the excitation acceleration is 6 m/s² and the excitation frequency is 9.8 Hz, the average output power of the lower PEHU across optimum load resistance can reach 1.17 mW. When the excitation frequency is 15 Hz, the average output power of the upper PEHU across optimum load resistance can reach 1.86 mW. The theoretical and experimental results show that the proposed energy harvester has potential for powering miniaturized wireless portable devices.