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Reverse electrowetting-on-dielectric (REWOD) energy harvesting is an effective energy harvesting method at low frequencies such as the frequencies of human motion. Various REWOD energy harvester designs have been presented in prior works, but these generally use rigid and often expensive substrates and time-consuming and/or costly fabrication methods. To address these challenges, in this work REWOD energy harvesters were fabricated consisting of aluminized polyester sheets as the functional layers and with polycarbonate sheets for added mechanical support. The fabrication of these samples eliminates the need for costly materials, clean room technologies, and high-end equipment. Samples were characterized using a flat arrangement and on a test fixture that simulates the repeated bending that occurs on the back of a bending knee. Without applying any external bias voltage, the maximum voltage and current output for the bending samples were determined to be 25.1 mV and 230 nA, respectively, and the corresponding maximum power is 5.77 nW at a bending frequency of 5 Hz. With an estimated cost of U.S. $ 0.28 for each REWOD harvester (U.S. $ 0.03/cm2), the cost per nanowatt of power is U.S. $ 0.05/nW, which is approximately 380 times lower than the approximately U.S. $ 19/nW of our previous REWOD energy harvesters. Our simple devices provide a low-cost, easily fabricated flexible approach to wearable motion sensing and energy harvesting that can be useful for various healthcare applications. 

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. 

Abstract 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. 

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. 

Monitoring human health in real-time using wearable and implantable electronics (WIE) has become one of the most promising and rapidly growing technologies in the healthcare industry. In general, these electronics are powered by batteries that require periodic replacement and maintenance over their lifetime. To prolong the operation of these electronics, they should have zero post-installation maintenance. On this front, various energy harvesting technologies to generate electrical energy from ambient energy sources have been researched. Many energy harvesters currently available are limited by their power output and energy densities. With the miniaturization of wearable and implantable electronics, the size of the harvesters must be miniaturized accordingly in order to increase the energy density of the harvesters. Additionally, many of the energy harvesters also suffer from limited operational parameters such as resonance frequency and variable input signals. In this work, low frequency motion energy harvesting based on reverse electrowetting-ondielectric (REWOD) is examined using perforated high surface area electrodes with 38 µm pore diameters. Total available surface area per planar area was 8.36 cm2 showing a significant surface area enhancement from planar to porous electrodes and proportional increase in AC voltage density from our previous work. In REWOD energy harvesting, high surface area electrodes significantly increase the capacitance and hence the power density. An AC peak-to-peak voltage generation from the electrode in the range from 1.57-3.32 V for the given frequency range of 1-5 Hz with 0.5 Hz step is demonstrated. In addition, the unconditioned power generated from the harvester is converted to a DC power using a commercial off-theshelf Schottky diode-based voltage multiplier and low dropout regulator (LDO) such that the sensors that use this technology could be fully self-powered. The produced charge is then converted to a proportional voltage by using a commercial charge amplifier to record the features of the motion activities. A transceiver radio is also used to transmit the digitized data from the amplifier and the built-in analog-to-digital converter (ADC) in the micro-controller. This paper proposes the energy harvester acting as a self-powered motion sensor for different physical activities for wearable and wireless healthcare devices.