Liquid-based electrostatic energy harvester with high sensitivity to human physical motion

This paper presents a new liquid-based electrostatic energy harvester that converts the mechanical energy of human-motion-induced vibrations to electrical energy. The basic design uses a conducting liquid to enhance sensitivity to human motion, the frequency of which is typically as low as several hertz; it also uses a hydrophobic coating to provide a broad frequency bandwidth. As liquid slops in accordance with external motions, proposed energy harvester shows large capacitance variations. The device was tested under various conditions with periodic and nonperiodic movements. The maximum capacitance obtained from the fabricated device was about 10 nF, whereas the minimum capacitance was 5 pF, resulting in an extremely high capacitance ratio of 2000. The hydrophobic treatment enables the fabricated device to work well for periodic motions with a frequency range of 2–5 Hz. The power generated from a human running motion at a speed of 8 km h−1 is theoretically estimated to be 35.3 µW with charge-constrained conversion and an auxiliary voltage of 1 V.