Advancing Reverse Electrowetting-on-Dielectric from Planar to Rough Surface Electrodes for High Power Density Energy Harvesting.

Reverse electrowetting-on-dielectric (REWOD)-based energy harvesting has been studied over the last decade as a novel technique of harvesting energy by actuating liquid droplet(s) utilizing applied mechanical modulation. Much prior research in REWOD has relied on planar electrodes, which by its geometry possess a limited surface area. In addition, most of the prior REWOD works have applied a high bias voltage to enhance the output power that compromises the concept of self-powering wearable motion sensors in human health monitoring applications. In order to enhance the REWOD power density resulting from an increased electrode-electrolyte interfacial area, high surface area electrodes are required. Herein, electrical and multiphysics-based modeling approaches of REWOD energy harvester using structured rough surface electrodes are presented. By enhancing the overall available surface area, an increase in the overall capacitance is achieved. COMSOL and MATLAB-based models are also developed, and the empirical results are compared with the models to validate the performance. Root mean square (RMS) power density is calculated using the RMS voltage across an optimal load impedance. For the proposed rough electrode REWOD energy harvester, maximum power density of 3.18 µW cm-2 is achieved at 5 Hz frequency, which is ≈4 times higher than that of the planar electrodes.

A self-powered wireless motion sensor based on a high-surface area reverse electrowetting-on-dielectric energy harvester.

This paper presents a motion-sensing device with the capability of harvesting energy from low-frequency motion activities. Based on the high surface area reverse electrowetting-on-dielectric (REWOD) energy harvesting technique, mechanical modulation of the liquid generates an AC signal, which is modeled analytically and implemented in Matlab and COMSOL. A constant DC voltage is produced by using a rectifier and a DC-DC converter to power up the motion-sensing read-out circuit. A charge amplifier converts the generated charge into a proportional output voltage, which is transmitted wirelessly to a remote receiver. The harvested DC voltage after the rectifier and DC-DC converter is found to be 3.3 V, having a measured power conversion efficiency (PCE) of the rectifier as high as 40.26% at 5 Hz frequency. The energy harvester demonstrates a linear relationship between the frequency of motion and the generated output power, making it highly suitable as a self-powered wearable motion sensor.