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Among various parameters of 3D CNTs as a conductive sulfur host material in LSB cathodes, high surface area, high porosity, and small pore size distribution, among others, are the most critical parameters, enhancing LSB performance.

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.

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

This paper presents a motion-sensing device with the capability of harvesting energy from low-frequency motion activities that can be utilized for long-term human health monitoring. The energy harvester used in the proposed motion sensor is based on the mechanical modulation of liquid on an insulated electrode, which utilizes a technique referred to as reverse electrowetting-on-dielectric (REWOD). The generated AC signal from the REWOD is rectified to a DC voltage using a Schottky diode-based rectifier and boosted subsequently with the help of a linear charge-pump circuit and a low-dropout regulator (LDO). The constant DC voltage from the LDO (1.8 V) powers the motion-sensing read-out circuitry, which converts the generated charge into a proportional output voltage using a charge amplifier. After amplification of the motion data, a 5-bit SAR-ADC (successive-approximation register ADC) digitizes the signal to be transmitted to a remote receiver. Both the CMOS energy harvester circuit including the rectifier, the charge-pump circuit, the LDO, and the read-out circuit including the charge amplifier, and the ADC is designed in the standard 180 nm CMOS technology. The amplified amplitude goes up to 1.76 V at 10 Hz motion frequency, following linearity with respect to the frequency. The generated DC voltage from the REWOD after the rectifier and the charge-pump is found to be 2.4 V, having the voltage conversion ratio (VCR) as 32.65% at 10 Hz of motion frequency. The power conversion efficiency (PCE) of the rectifier is simulated as high as 68.57% at 10 Hz. The LDO provides the power supply voltage of 1.8 V to the read-out circuit. The energy harvester demonstrates a linear relationship between the frequency of motion and the generated output power, making it suitable as a self-powered wearable motion sensor.

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.

This paper presents a reverse electrowetting-on-dielectric (REWOD) energy harvester integrated with rectifier, boost converter, and charge amplifier that is, without bias voltage, capable of powering wearable sensors for monitoring human health in real-time. REWOD has been demonstrated to effectively generate electrical current at a low frequency range (< 3 Hz), which is the frequency range for various human activities such as walking, running, etc. However, the current generated from the REWOD without external bias source is insufficient to power such motion sensors. In this work, to eventually implement a fully self-powered motion sensor, we demonstrate a novel bias-free REWOD AC generation and then rectify, boost, and amplify the signal using commercial components. The unconditioned REWOD output of 95–240 mV AC is generated using a 50 μL droplet of 0.5M NaCl electrolyte and 2.5 mm of electrode displacement from an oscillation frequency range of 1–3 Hz. A seven-stage rectifier using Schottky diodes having a forward voltage drop of 135–240 mV and a forward current of 1 mA converts the generated AC signal to DC voltage. ∼3 V DC is measured at the boost converter output, proving the system could function as a self-powered motion sensor. Additionally, a linear relationship of output DC voltage with respect to frequency and displacement demonstrates the potential of this REWOD energy harvester to function as a self-powered wearable motion sensor.

This paper presents the integration of an AC-DC rectifier and a DC-DC boost converter circuit designed in 180 nm CMOS process for ultra-low frequency (

This paper presents a self-powered motion sensor based on reverse-electrowetting on dielectric (REWOD) energy harvesting having the capability of remotely keeping a track of any motion activity. The energy harvester includes a rectifier and a voltage regulator to provide the DC supply voltage to the analog front-end and the transmitter to wirelessly transfer the data from the motion sensor. The on-chip circuitry includes a seven-stage voltage-doubler based rectifier, an amplifier, an analog-to-digital converter (ADC), and a transmitter, and is designed in standard 180 nm CMOS process with a supply voltage of 1.8 V. The recycled folded cascode (RFC) based charge amplifier has a closed-loop gain of 53 dB within the bandwidth of 1–150 Hz, which is suitable to detect any low-frequency motion signal. An 8-bit SAR-ADC is designed to digitize the amplified signal with a sampling rate of 1 ksamples/s. The transmitter used for this application operates in the 3.1–5 GHz frequency band with an energy efficiency of 8.5 pJ/pulse at 100 kbps data rate. The wireless motion sensing device with the REWOD can be suitable for quantitatively monitoring the motion-related data as a wearable sensor.

Reverse electrowetting-on-dielectric (REWOD) is a novel energy harvesting technology with a significant advantage over other energy harvesting technologies due to its effective performance at a low-frequency range and not requiring resonance frequency of solid structures. However, REWOD energy harvesting based on planar electrodes has a limited surface area and therefore a lower power output. In this work, we present a novel approach for enhancing power output from a REWOD energy harvester by significantly increasing the total available surface area using perforated silicon wafer electrodes. Without applying any external bias voltage, maximum current and voltage densities per unit planar area were measured to be 3.77 μA/cm2 and 1.05 V/cm2, respectively, for a 38 μm pore-size electrode at 5 Hz modulation frequency. RMS power density output was 4.8 μW/cm2, which is ∼23 times higher than that from our prior work on planar electrodes showing the significance of porous electrodes in REWOD energy harvesting. A simple capacitive theoretical model validating experimental results was developed and justified. The novelty of this work lies in the combination of a bias-free approach to REWOD energy harvesting coupled with significant enhancement in electrode surface area per planar area to increase the output power density.

Lithium-sulfur batteries (LSBs) represent a promising energy storage technology with a potential for next-generation high-energy storage systems due to their high specific capacity, abundant resources, low cost, non-toxicity, and environmentally friendly characteristics. However, due to many critical limitations such as insulating nature of elemental sulfur, poor lithium polysulfide (LiPS) conversion kinetics, polysulfide shuttle effect resulting in capacity fading, and low cyclic stability, commercialization of LSBs are far from realization. One of the most essential strategy to mitigate the issues with LSBs is to prevent polysulfide shuttling thereby maximizing the sulfur utilization and enhance the overall Li-S battery performance. In this work, we develop a binder free three-dimensional hybrid cathode for Li-S battery using multiwall carbon nanotubes (CNTs) and molybdenum sulfide (MoS2) as a catalyst, collectively enhancing LiPS conversion and ion transport ability and hence increased energy density, both gravimetric and volumetric. Different uniform mixtures of CNTs, MoS2, and conductive carbon black are prepared and loaded with high sulfur loading of ~6 mg cm-2. Various electrochemical performance parameters influencing cathode performance with respect to both gravimetric and volumetric energy densities are studied. Parameters that help improve the overall battery performance are identified and discussed.

Manipulating a liquid droplet with applied electrical fields has long been studied and is known as electrowetting on dielectric (EWOD). In recent years, a new approach of energy harvesting that is related to EWOD has been demonstrated and it is termed reverse electrowetting energy harvesting or simply reverse electroactuation. Reverse electroactuation is opposite to electrowetting in which energy is generated by converting mechanical energy of the liquid motion into electrical energy. The amount of energy generated using this technique mainly depends on the contact area of the electrode-electrolyte interface. The contact area can be varied by applying a bias voltage to decrease the surface tension of the electrolyte resulting into a surface area increase. As an alternative, the contact area can also be varied by applying pulsating external pressure. In this study, we plan to model and experimentally demonstrate an AC current generation by applying pulsating external pressure to move the electrolytic fluid in and out of porous materials with high surface to volume ratio. The model is based on a simple solution to the Washburn equation which establishes the pressure dependency of fluid height in the pores. Various porous materials with both uniform and non-uniform pores are used in the analysis.

A number of new developments have taken place over the years with respect to mechanical energy harvesting. However, significant progress is yet to be made to improve the energy density to sufficiently and reliably power our everyday mobile devices and other applications. Recently, a new approach in energy harvesting based on the principles of reverse electroactuation has been reported and is drawing much interest. Reverse electroactuation can be considered the opposite of electrowetting-on-dielectric, which is the manipulation of liquid droplets on dielectric with applied voltage. The reverse electroactuation approach of energy harvesting adopts a fundamental principle that the movements of liquid droplets on a dielectric film generate power by dynamically modulating the liquid-solid interfacial dielectric capacitance. The amount of power generated using this approach depends on various factors such as the type of conducting liquid used, dielectric coating type and thickness, and droplet pinning. Power densities up to 103 W/m2 have been reported using reverse electroactuation with Mercury as electrolyte, but using Mercury for real applications is not feasible due to its toxicity. In this study, we test a number of alternative conducting liquids as well as dielectric coatings in reverse electroactuation. The main objective is to observe and analyze the effect electrolyte and dielectric coatings have on power density and to compare the experimental results to previously published theoretical models. In addition to improving energy harvesting, this research contributes to fundamental understanding of how liquid movement under the combined influence of pressure, surface tension, and electric fields affect charge density. This may impact the design and development of porous materials for applications such as supercapacitors, electrodialysis, and reverse osmosis. Figure 1. In reverse electroactuation, a conducting liquid droplet is placed between two electrodes, one of which is insulated (A). A dynamic mechanical loading deflects the droplet, resulting in a modulating capacitance and therefore an electrical current (B). Figure 1