Keynote Speakers

Powering IoT Sensors with Body Heat

Abstract

The temperature difference between human body and the ambient provides a potential energy source to generate electrical power for IoT sensors.  This presentation will give two approaches converting body heat into electricity.  One is based on the traditional thermoelectric effect relying on the electron transport in semiconductors and the other is based on ion transport in hydrogels.  For the traditional thermoelectric generators using rigid semiconductors, key challenges are how to make the device flexible and how to maximize the power output.  We design flexible thermoelectric generators (f-TEG) using multifunctional copper electrodes for flexibility, heat concentration and dissipation, and fabrics for comfort and heat-leakage reduction.  When worn on the forehead, our f-TEG's maximum output power density (based on the device's area) reaches 48 µW/cm² at a wind speed of 2 m/s and an ambient temperature of 15°C. An LED powered by our f-TEG headband with 100 pairs of thermoelectric pillars can illuminate a paper for reading in a dark room at 16.5°C without an external heat sink or forced convection at the cold side.  In a different approach, we achieve flexibility using ion transport in hydrogels under a temperature gradient.  Thermopower as high as 17 mV/K, which is two orders of magnitude higher than traditional thermoelectric materials, has been achieved.  Such materials make it possible to use only small number of legs to achieve high voltage.  A proof-of-concept wearable device consisting of 25 unipolar elements generated over 2V and a peak power of 5 mW using body heat.  This talk is based on the following two published papers: Han et al., “Giant thermopower of ionic gelatin near room temperature,” Science, 368, 1091; Qian et al., “High-performance, flexible thermoelectric generator based on bulk materials,” Cell Reports Physical Science, 3, 100780, 2022.