Design and development of a rotational energy harvester for ultralow frequency vibrations and irregular human motions

This paper presents a rotational energy harvester (REH) that is realized based on a rope-driven rotor. Featuring simple structure, low fabrication difficulty and high power density, the proposed REH can do high-speed rotation under ultralow frequency excitations, enabling efficient exploitation of ubiquitous ultralow frequency vibrations and human motions. The REH is modeled, and both simulations and experiments reveal that the performance of the REH has a positive relationship with the cross-sectional area of the elastic rope but a negative correlation with the original length of the elastic rope. Moreover, the output power exhibits a monotonous increase trend when the actuation frequency rises from 1 Hz to 5 Hz. The power generated by the REH under the manual operation at a frequency of around 4 Hz is 5.3 mW, whereas the power converted from the arm swing at a walking speed of 6.5 km/h is 0.65 mW. The REH also produces 0.45 mW power when it is actuated by the treadmill vibration triggered by human jogging. With the energy harvested by the REH from various human motions, the normal operation of some commercial electronics is continuously sustained, which demonstrates the promising potential of the REH in implementing self-powered portable/wearable personal electronics.