An eccentric mass-based rotational energy harvester for capturing ultralow-frequency mechanical energy

The omnipresent ultralow-frequency vibrations and swings contain a huge amount of mechanical energy, but the low harvesting efficiency hinders their application as a practical power source. To address this issue, this paper reports an innovative eccentric mass-driven rotor (EMDR) that is capable of transforming ultralow-frequency excitations to uni-directional rotation. This motion transformation is enabled by a two-layered cantilevered plectrum that provides a sufficiently large driving stiffness for the anticlockwise rotation of a rotator but a very small sliding friction resistance during its clockwise rotation with respect to the rotator. A rotational energy harvester (REH) based on the EMDR is designed and fabricated, which exhibits remarkably improved electric outputs under ultralow-frequency excitations as compared with the conventional REH without the EMDR. Moreover, the designed REH has a comparatively long duration of electric outputs after the applied excitation vanishes, making it adapt well to the real-world excitations featuring intermittent availability. When the designed REH is attached to the human arm or leg, the generated electric energy under jogging is sufficient for running some small electronic devices. This study demonstrates the promising application foreground of the proposed EMDR in realizing high-output ultralow-frequency energy harvesters.