A magnetically coupled two-degrees-of-freedom piezoelectric energy harvester using torsional spring

Two-degrees-of-freedom magnetically coupled energy harvesters have been presented by several researches to achieve a broader response bandwidth. However, most two-degrees-of-freedom systems are composed of two piezoelectric beams, while in the low frequency operating environment with limited space, the dimension of the piezoelectric beam is limited which leads to high stiffness of the generated beam. Therefore, the output of dual-beam system is relatively low under low frequency and amplitude vibrations. This paper presents a magnetically coupled two-degrees-of-freedom energy harvester by using torsional spring. The proposed harvester consists of a piezoelectric beam with a tip magnet and an interacting magnet mounted on a rotatable bar with a torsional spring. The shape of the potential well changes with the rotation of the bar, facilitating the occurrence of the snap-through motion under low amplitude and wideband vibration excitation. What’s more, the stiffness of the torsional spring can be easily adjusted to make the designed harvester suitable for low frequency vibrations. Compared with the conventional bi-stable harvester, the presented harvester could easily overcome the potential barrier and generate larger power under low excitation intensity. Analytical, simulation, and experimental results demonstrate that the proposed energy harvester is capable of harvesting low frequency wideband vibration energy.