A pendulum-plucked rotor for efficient exploitation of ultralow-frequency mechanical energy

Harvesting the pervasive ultralow-frequency (<5 Hz) mechanical energy has been considered as a promising strategy to implement decentralized power sources for the sharply increasing number of low-power electronics, but the low output power impedes the practical application of ultralow-frequency energy harvesting technologies. To address this issue, this paper reports a pendulum-plucked rotor that can transform ultralow-frequency excitations (vibrations and swings) to uni-directional and rapid rotation. This transformation is enabled by an innovative inclined two-layered plectrum, which provides both sufficiently large driving stiffness and low friction resistance. Owing to the uni-directional and rapid rotation, an energy harvester realized with the pendulum-plucked rotor achieves 7.6 mW and 1.25 mW output power under ultralow-frequency swings and vibrations, respectively, which are approximately an order of magnitude higher than those (0.2 mW and 0.15 mW) generated by the conventional swing-based energy harvester under the same conditions. Moreover, the fabricated harvester can capture sufficient human biomechanical energy for powering a wireless temperature sensor and a wireless door bell. This study demonstrates the promising potential of the pendulum-plucked rotor in harnessing the ultralow-frequency mechanical energy as the decentralized power sources.