An Ultralow Frequency Energy Harvester With an Asymmetric-Stiffness Pendulum Inspired by Biological Grooming Behavior

Qitao Lu, Guoyuan Xia, Mingjing Cai, Xin Li, Junyi Cao, Wei-Hsin Liao

Abstract: For boosting output power, frequency-up methods like gear train and plucking are introduced into pendulum-based electromagnetic energy harvesters (EEHs). Still, the gear train and plucking methods have the problems of high-manufacturing costs and high-energy loss, respectively. To address the above issues, inspired by biological grooming behavior, we present a low-cost, high-efficiency EEH utilizing 3-D printing. This device is excited by an asymmetric stiffness pendulum, induced by an oblique cantilever beam, converting the ultralow frequency of human motion into high-speed, unidirectional rotation of the rotor. The energy density comparison between the sandwich and back iron structure of the EEH is made by the simulation, and then parameters are selected. The bench-top swing experiment system is established to test the performance of the EEH, and the established equivalent electromagnetic model discusses the load resistance result. The feasibility of human walking for powering the Internet of Things (IoT) device is explored when wearing the EEH. The bench-top test result shows that the EEH can reach the normalized power of $1.07\cdot 10{^{-}4 }$ W/(Hz $\cdot ^{\circ }$ ) and normalized power density of 6.6 W/(m ${^{{3}}} \cdot $ Hz $\cdot ^{\circ }$ ). Through human testing at a walking of 1 km/h, the IoT device can run normally, showing great potential for achieving self-power and cost-effective IoT devices.