Achieving high electric outputs from low-frequency motions through a double-string-spun rotor

The pervasive low-frequency mechanical energy is important for realizing self-powered electronics, but its efficient exploitation is still a highly challenging task due to the mismatch between the motion frequencies and the working frequencies of already reported energy harvesters. To tackle this issue, we propose in this paper a new motion-conversion mechanism (which we name ‘double-string-spun rotor’) to transform low-frequency motions (mechanical vibrations and irregular human body motions) to uni-directional and high-speed rotation. Consisting of a rotatable shaft and a ratchet, the rotor structure first converts low-frequency motions to bi-directional rotation of the shaft through two strings and then drives the ratchet to do uni-directional rotation via curved plectra. The promising application of the rotor in capturing low-frequency mechanical energy is examined through an electromagnetic generator (harvester) constructed with the rotor, which generates 46 mW power when actuated by a crank-slider mechanism at 7 Hz. The generator has also been utilized to scavenge irregular human body motions and low-frequency vibrations engendered by daily jogging, and the collected energy allows the continuous work of various commercial electronics. This study provides a new strategy for efficiently exploiting ambient low-frequency motions and exhibits the high probability of realizing self-sustained electronics with the captured low-frequency mechanical energy.