The Centrifugal Softening Effect of an Inverse Nonlinear Energy Harvester in Low-frequency Rotational Motion for Enhancing Performance

Recently, various nonlinear energy harvesters, which is aimed to provide the power supply for wireless sensors, are designed to harvest rotational energy. However, there are few studies for energy harvesting from rotational motion when the rotational speed is less than 120 rpm (2 Hz). In this paper, an inverse nonlinear piezoelectric energy harvester (PEH) is proposed for enhancing performance in low-frequency rotational motion via the centrifugal softening effect. In addition, according to Lagrange equation, the related theoretical model is derived. Furthermore, the experiments between the forward and inverse configurations in rotational motion are conducted under the rotational speeds ranging from 60 rpm to 160 rpm. The experimental results demonstrate that in low-frequency rotational motion the inverse PEH exhibits outstanding performance with the RMS voltage as high as 5 V, which is enough for powering some wireless sensors. Overall, the centrifugal softening effect is verified to be an effect method for energy harvesting in low-frequency rotational motion.