Harvesting vibrational energy with liquid-bridged electrodes: thermodynamics in mechanically and electrically driven RC-circuits

TL;DR

This paper presents a theoretical study of vibrational energy harvesting using liquid-bridged electrodes, introducing a new bias voltage engine that significantly enhances energy output across various frequencies.

Contribution

It introduces a novel energy harvesting engine with a time-dependent bias voltage, improving power output in vibrational energy harvesters with liquid-bridged electrodes.

Findings

Optimal electrode separation depends on bias potential type.

New engine increases harvested work by orders of magnitude at low frequencies.

Power can be enhanced by factors of 2-5 at high frequencies.

Abstract

We theoretically study a vibrating pair of parallel electrodes bridged by a (deformed) liquid droplet, which is a recently developed microfluidic device to harvest vibrational energy. The device can operate with various liquids, including liquid metals, electrolytes, as well as ionic liquids. We numerically solve the Young-Laplace equation for all droplet shapes during a vibration period, from which the time-dependent capacitance follows that serves as input for an equivalent circuit model. We first investigate two existing energy harvesters (with a constant and a vanishing bias potential), for which we explain an open issue related to their optimal electrode separations, which is as small as possible or as large as possible in the two cases, respectively. Then we propose a new engine with a time-dependent bias voltage, with which the harvested work and the power can be increased by orders of magnitude at low vibration frequencies and by factors 2-5 at high frequencies, where frequencies are to be compared to the inverse RC-time of the circuit.