Few studies have successfully achieved high-efficiency energy harvesting in ultralow-frequency rotational motion where the rotational frequency is less than 2 Hz (120 rpm). In order to solve this challenge, this paper proposes a novel energy harvester with the centrifugal softening effect (CSE) and the magnet-induced nonlinearity. In a rotational coordinate system, the corresponding theoretical model is derived to reveal the mechanism of the CSE and to analyze the influence of the nonlinear magnetic force on the output power of the proposed harvester. Furthermore, the mechanism of the centrifugal stiffening effect (C_stiffen_E) is also theoretically analyzed. The analysis results indicate that based on the C_stiffen_E, the self-tuning harvester with a wider bandwidth can be obtained, and the CSE is better than the C_stiffen_E in enhancing the ultralow-frequency rotational energy harvesting. Meanwhile, the derived model is experimentally validated via comparisons among different piezoelectric energy harvesters (PEHs) including the linear inverse PEH, the nonlinear inverse PEH and the nonlinear forward PEH. The experimental results show that the nonlinear inverse PEH combining the magnet-induced nonlinearity and the CSE is capable of realizing high-efficiency energy harvesting in the rotational speed range of 60-120 rpm. The corresponding RMS output voltage is larger than 4 V, which is promising to provide the continuous power source for a wireless sensor. In addition, the parametric studies are conducted to provide theoretical guidance for the further optimization design of the proposed PEH.

很少有研究成功地实现了旋转频率小于2 Hz（120 rpm）的超低频旋转运动中的高效能量收集。为了解决这一挑战，本文提出了一种新型的具有离心软化作用（CSE）和磁感应非线性的能量收集器。在旋转坐标系中，推导了相应的理论模型以揭示CSE的机理，并分析了非线性磁力对所提出的收割机输出功率的影响。此外，还从理论上分析了离心加劲作用（C_stiffen_E）的机理。分析结果表明，基于C_stiffen_E，可以获得带宽较宽的自整定收割机，在增强超低频旋转能量采集方面，CSE优于C_stiffen_E。同时，通过对包括线性逆PEH，非线性逆PEH和非线性正向PEH在内的不同压电能量采集器（PEH）进行比较，对导出的模型进行了实验验证。实验结果表明，将磁感应非线性和CSE相结合的非线性逆PEH能够在60-120 rpm的转速范围内实现高效的能量收集。相应的RMS输出电压大于4 V，这有望为无线传感器提供连续电源。此外，进行了参数研究，为拟议的PEH的进一步优化设计提供了理论指导。