Human and Environment Influences on Thermoelectric Energy Harvesting Toward Self-Powered Textile-Integrated Wearable Dev
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Human and Environment Influences on Thermoelectric Energy Harvesting Toward SelfPowered Textile-Integrated Wearable Devices Amanda Myers1, Ryan Hodges2, and Jesse S. Jur2 Department of Mechanical and Aerospace Engineering, North Carolina State University, 911 Oval Drive, Raleigh, NC 27695, U.S.A. 2 Department of Textile Engineering, Chemistry and Science, North Carolina State University, 1000 Main Campus Drive, Raleigh, NC 27695, U. S. A. 1
ABSTRACT The study of on-body energy harvesting is most often focused on improving and optimizing the energy harvester. However, other factors play a critical factor in the energy harvesting integration techniques of the harvester to close-to body materials of the wearable device. In addition, one must recognize the wide array of human factors and ergonomic factors that lead a variation of the energy harvesting. In this work, key affecting variables at varying onbody locations are investigated for commercial thermoelectric generators (TEGs) integrated within a textile-based wearable platform. For this study, a headband and an armband is demonstrated with five TEGs connected in series in a flexible form factor via Pyralux®. These platforms enable comparison of the amount of energy harvested from the forehead versus the upper arm during various external conditions and movement profiles, e.g. running, walking, and stationary for periods of up to 60 minutes. During these tests, ambient temperature, ambient humidity, accelerometry, and instantaneous power are recorded live during the activity and correlated to the energy harvested. Human factors such as skin temperature and application pressure were also analyzed. Our analysis demonstrates that vigorous movement can generate over 100 μW of instantaneous power from the headband and up to 35 μW from the armband. During the stationary movement profile, the instantaneous power levels of both the headband and the armband decreased to a negligible value. Our studies show that for higher intensities of movement, air convection on the cool side of the TEG is the dominating variable whereas the temperature gradient has a significant effect when the subject is stationary. This work demonstrates key materials and design factors in on-body thermoelectric energy harvesting that allows for a strategic approach to improving the integration of the TEGs. INTRODUCTION The focus of on-body energy harvesting is of particular interest due to the sensing and wearability limitations that batteries impose. Eliminating the use of a battery makes the long term adoption of wearable devices more feasible due to improved ease of use and continuous sensing reliability [1]. A study performed by Starner and Paradiso [2] defined a range of power values that can be harvested from the body using various techniques. Notably, the largest amount of energy harvesting potential is found in human motion, or kinetic energy harvesting, through the use of piezoelectric materials. However, the energy harvesting potential drops significantly when movement ceases, yielding an uns
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