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Textile Integration for Wearable Energy Harvesting and ECG.
Keywords: Textile, Energy harvesting, ECG
The addition of sensors and electronics into a wearable package poses several key challenges including but not limited to size of the wearable device, long term durability and flexibility of the sensors and how to power said device whilst worn. Advances in flexible electronics integration on fabrics help to enable the integration of electronics into a wearable package. In this study, we investigate integration of a printed circuit board based main sensing system that is capable of collecting thermoelectric generated power and electrocardiogram (ECG) data. We also present our individual studies on each modules of the main acquisition system, which are thermal energy harvesting and heat sink design, flexible interconnect fabrication on fabrics and printed dry electrodes for ECG sensing. At higher level visualization, the main board interfaces with thermal energy harvesters and dry fabric based printed electrodes through our novel printed flexible interconnects. Combination of all modules creates a body-worn smart system when all modules are brought together. In thermal energy harvesting module, particular emphasis is placed on the use of energy harvesters to power the wearables. In this study, 16 small thermoelectric generators (TEGs) are integrated into a wearable package that is coupled with dry electrodes for electrocardiogram (ECG) sensing. The TEGs are connected in series on a flexible Pyralux® substrate that can then harvest usable amounts of power, up to 250 µW, from the surface of the skin via integration with a shirt or armband. The addition of a heat sink and heat spreader help maintain the temperature differential between the skin and ambient air, which allows the TEGs to provide consistent power to the wearable device. Stretchable interconnects are studied to route the harvested power to corresponding circuits and also connect individual TEG components. The stretchable interconnects on garment are made of thermoplastic polyurethane film, which is integrated on textiles via direct heat lamination. These flexible interconnects are much cheaper relative to the designs that are made of Kapton® film, and also present high flexibility due to their low Young’s modulus. Various trace designs, straight, zig-zag and meandering have been studied to determine the effect of strain on the interconnect resistance. The printed lines maintain their electrical conductivity even in 100% strain. Our last module is on Ag/AgCl printed dry electrodes, which are connected to main board through stretchable interconnects. In this study, we investigate the skin-electrode impedance and also effect of electrode form factor and on body placement on ECG signal quality. Overall, this study explores the corresponding challenges in each modules of our wearable system and presents integration techniques and challenges of the final main sensing board onto a garment based wearable platform.
Jesse S. Jur, Assistant Professor
North Carolina State University
Raleigh , NC

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