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  • Advanced Bias-Free Energy Harvesting Based on High-Dielectric Flexible Electrodes With Reverse Electrowetting-on-Dielectric
Title: Advanced Bias-Free Energy Harvesting Based on High-Dielectric Flexible Electrodes With Reverse Electrowetting-on-Dielectric
A unique method for capturing energy from mechanical electrolyte modulation is known as reverse electrowetting-on-dielectric (REWOD). Prior REWOD studies relied on rigid electrodes which demand a high bias voltage to maximize harvested power, hindering the advancement of self-powered wearable health-monitoring sensors. In addition, the amount of energy harvested via the REWOD technique can be improved to a greater extent with the utilization of a high-dielectric (high-k) metal oxide (HDMO) layer on flexible electrodes. In this study, two distinct sets of electrodes that are flexible are utilized for harvesting energy with the REWOD phenomenon. The samples were coated with HDMO layers, namely, hafnium oxide (HfO2) and manganese dioxide (MnO2), respectively. The material deposition on a polyimide sheet is employed via a sputtering-based physical vapor deposition (PVD). The utilization of MnO2 samples with the proposed flexing REWOD test measurement generated 476.21 μW/cm2 an utmost power density value with an encapsulated electrolyte between electrodes.  more » « less
Award ID(s):
2246559
PAR ID:
10537583
Author(s) / Creator(s):
; ; ; ;
Publisher / Repository:
IEEE
Date Published:
Journal Name:
IEEE Sensors Journal
Volume:
24
Issue:
7
ISSN:
1530-437X
Page Range / eLocation ID:
9480 to 9488
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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    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−2is achieved at 5 Hz frequency, which is ≈4 times higher than that of the planar electrodes. 
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  2. ; ; ; (, Scientific Reports)
    Abstract Increasing demand for self-powered wearable sensors has spurred an urgent need to develop energy harvesting systems that can reliably and sufficiently power these devices. Within the last decade, reverse electrowetting-on-dielectric (REWOD)-based mechanical motion energy harvesting has been developed, where an electrolyte is modulated (repeatedly squeezed) between two dissimilar electrodes under an externally applied mechanical force to generate an AC current. In this work, we explored various combinations of electrolyte concentrations, dielectrics, and dielectric thicknesses to generate maximum output power employing REWOD energy harvester. With the objective of implementing a fully self-powered wearable sensor, a “zero applied-bias-voltage” approach was adopted. Three different concentrations of sodium chloride aqueous solutions (NaCl-0.1 M, NaCl-0.5 M, and NaCl-1.0 M) were used as electrolytes. Likewise, electrodes were fabricated with three different dielectric thicknesses (100 nm, 150 nm, and 200 nm) of Al2O3and SiO2with an additional layer of CYTOP for surface hydrophobicity. The REWOD energy harvester and its electrode–electrolyte layers were modeled using lumped components that include a resistor, a capacitor, and a current source representing the harvester. Without using any external bias voltage, AC current generation with a power density of 53.3 nW/cm2was demonstrated at an external excitation frequency of 3 Hz with an optimal external load. The experimental results were analytically verified using the derived theoretical model. Superior performance of the harvester in terms of the figure-of-merit comparing previously reported works is demonstrated. The novelty of this work lies in the combination of an analytical modeling method and experimental validation that together can be used to increase the REWOD harvested power extensively without requiring any external bias voltage. 
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  3. ; ; ; ; (, IEEE Sensors Journal)
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  5. ; ; ; ; ; ; (, Scientific Reports)
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