Monitoring human health in real-time using wearable motion sensors has become one of the most promising and rapidly growing technologies in the health industry. In most cases, these sensors are powered by batteries that require periodic replacement and maintenance over their lifetime. To prolong the operation of these sensors, they should have zero post-installation maintenance. In order to make these sensors battery-less and self-powered, various energy harvesting techniques have been studied in the last several years. Many energy harvesting technologies currently available are limited by their generated power, energy densities, and efficiency at lower frequency, making them unsuitable for human motion-sensing applications. Within the last decade, reverse electrowetting-on-dielectric (REWOD) based mechanical motion energy harvesting has been demonstrated to efficiently generate electrical current at lower frequency range (\< 3 Hz), which is the range of motion for various human activities such as walking, running, and physical workouts. However, the current generated from the REWOD without external bias source is quite insufficient to power such sensors. In this work, with the objective of implementing a fully self-powered wearable motion sensors, we demonstrate alternating current generation from REWOD energy harvester without any external bias source and its rectification to DC power at the frequency range of 1-3 Hz. Electrodes used in the REWOD energy harvesting are fabricated with \~100 nm thick Al~2~O~3~ dielectric layer with an additional layer of CYTOP for surface hydrophobicity and 1.0 M NaCl aqueous solution is used as an electrolyte. Approximately 40 - 60 mV of AC voltage for a frequency range of 1-3 Hz from a 50 μL electrolyte and 2.5 mm of electrode displacement is amplified using a commercial instrumentation amplifier from Texas Instruments (INA126). The differential voltage gain of the amplifier is set to be 100 V/V using a resistive feedback network. A commercial component-based seven-stage rectifier is implemented using Schottky diodes from Skyworks (SMS3922-079LF) which has a forward voltage drop of 280-340 mV with 1 mA of forward current to convert the generated AC signal to DC voltage. A DC output of \~3 V is measured enabling the system to self-power such motion sensors. Additionally, a linear relationship of frequency and displacement with output DC voltage is demonstrated showing how increasing frequency and displacement increases the output power. Such linear relationships signify the potential application of REWOD energy harvesting to reliably and fully self-power wearable motion sensors without any external bias source.


Reverse Electrowetting-on-Dielectric Energy Harvesting Integrated With Charge Amplifier and Rectifier for Self-Powered Motion Sensors

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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