ABSTRACT

Self-powered sensors capable of zero-maintenance monitoring and data collection over days to weeks are currently not available for many applications that do not have regular access to solar energy or wireless power transmission. The goal of this research project is to use the high surface area advantage of a liquid-based energy harvesting concept called reverse electrowetting to harvest energy from low-frequency movement and to develop a self-powered motion sensor to detect various movements such as walking and running. A miniaturized integrated circuit (IC) chip will also be developed that will make the energy harvester highly suitable for other industrial and biomedical applications. This technology will make it possible to develop self-powered devices capable of long-term motion sensing that can be useful for monitoring post-operative elderly patients who are recovering from procedures such as joint replacement surgery. The self-powered motion sensor will rely on the harvested kinetic motion as its external energy source and will be capable of long-term operation. Such a wireless sensor has not previously been demonstrated for low-frequency kinetic energy harvesting. Also, as a part of this project, energy harvesting, and circuit design experiences will be added to the University of North Texas (UNT) College of Engineering summer camp for the K-12 youth as well as providing sponsorship for an undergraduate senior design team.
High surface area reverse electrowetting depends on reversible electrolyte movement within a porous electrode with applied pressure or an electric field. Key limiting parameters that have not been previously verified experimentally include electrode pore size, electrolyte conductivity, dielectric type or thickness, surface finish, and the pressure and voltage magnitude or frequency. These parameters will be modeled, optimized, and experimentally validated to achieve the maximum available energy or power for a cm-sized transducer. The hypothesis is: reverse electrowetting is capable of producing 1 mW/cm2 at <10 Hz oscillation frequency through the use of high surface area materials and parameter optimization. These design parameters will be used in the selection and integration of highly porous electrode materials (e.g. sintered metal and buckypaper) with electrolyte, electret, and housing components for maximum low-frequency energy harvesting in a ~5 cm3 package. An integrated circuit (IC) will be developed to convert the harvested energy into a usable constant DC power supply. The system will be integrated with a low-power wireless data transmission circuitry and miniaturized antenna on a flexible PDMS substrate for developing a self-powered, conformable motion sensor. This wearable sensor will be unique as it will be self-powered and low-cost and will demonstrate high surface area reverse electrowetting's ability to harvest enough energy from low-frequency motion to entirely self-power a wearable motion sensor. Specific contributions from this research include: fundamental understanding of high surface area reverse electrowetting, demonstration of reverse electrowetting in a flexible system, highly efficient rectifier and DC-DC converter topologies that can start with as low as 30 mV input voltages, and an integrated self-powered motion sensor with wireless data transmission capability.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

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