Exploiting ultralow-frequency energy via vibration-to-rotation conversion of a rope-spun rotor

Ultralow-frequency kinetic energy mainly in the form of vibrations is omnipresent in the environment, but its effective exploitation remains a challenge. To tackle this problem, this paper presents a rope-spun rotor structure to transform ultralow-frequency vibrations/linear motions to rapid rotations through a piece of rope. The superior performance of the rotor is demonstrated by applying it to electromagnetic energy harvesting from ultralow-frequency vibrations and irregular human body motions. When the rope-spun rotor based harvester is periodically pushed down 10.5 mm at 1.5 Hz, it produces 9.7 mW electric power. When embedded in a shoe insole, the harvester delivers 8 mW power to a matched load as a male participant walks with the shoe at 6.5 km/h. When positioned under a piece of floorboard, the harvester can charge a supercapacitor (220 mF) from 0 to 3.5 V within 8 min. The harvester can also sustain the continuous operation of multiple electronics simultaneously by scavenging energy from gentle finger tapping motions. This study demonstrates a new mechanism for realizing vibration-to-rotation conversion and a promising way for efficient harvesting of ultralow-frequency energy.