A nonlinear magnetic and torsional spring coupling piezoelectric energy harvester with internal resonance

Magnetically coupled dual-beam energy harvesters have been presented by several researches to achieve a broader response bandwidth. However, 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. In this paper, a nonlinear magnetic and torsional spring coupling energy harvester is proposed. The stiffness of the torsional spring can be easily adjusted to make the designed harvester suitable for low frequency vibrations. The introduction of torsion springs provides an extra degree of freedom to the system and broadens the response band of the system from 8.7 Hz to 15 Hz. Furthermore, the presence of the 1:3 internal resonance phenomenon in the harvester considerably achieves frequency enhancement and bandwidth extension, significantly improving the harvesting performance in low frequency environments. Numerical analysis, simulation, and experimental are carried out to verify that the proposed energy harvester is capable of harvesting low frequency wideband vibration energy. The results show that magnetic and torsional spring coupling piezoelectric energy harvester is capable of broadband energy harvesting in the range of 5-20 Hz (i.e. 15 Hz bandwidth).