Enhancing energy harvesting in low-frequency rotational motion by a quad-stable energy harvester with time-varying potential wells

In recent years, various nonlinear energy harvesters have been designed and investigated for efficiently harvesting energy in rotational motions, and they were aimed to provide suitable power supply for wireless sensors in Internet of Things (IoT). However, few of them could effectively work in low-frequency rotational motion (less than 120 rpm). In this paper, combining with the advantages of lower potential barriers and time-varying potential wells, a quad-stable piezoelectric energy harvester (PEH) is proposed to enhance the energy harvesting performance especially in low-frequency rotational motion. Additionally, a corresponding theoretical model is derived, and the related calculation model of the magnetic force is established to analyze the influence of potential barriers and nonlinear characteristics. What's more, the influence of external magnets and configuration parameters on the potential wells for different PEHs are numerically and experimentally investigated. Furthermore, the corresponding experiments are conducted and verify that the quad-stable PEH with time-varying potential wells exhibits a wider operational frequency range (1–7 Hz) in rotational motion, compared with that of the bi-stable PEH (3–7.3 Hz) and the tri-stable PEH (4–7.3 Hz), respectively. The parametric studies are carried out to explore the influence of the load resistance and the rotational radius on the energy harvesting performance, providing valuable insights into energy harvesting in rotational motion. Overall, the proposed quad-stable PEH is numerically and experimentally verified to be effective for harvesting energy in low-frequency rotational environment.