Experimental Demonstration of Usable Power from Body Heat with Wristband Thermoelectric Energy Harvester

Wearable devices have become commonplace within today’s society, creating a new level of connectivity and ease of access to our daily lives. However, by nature of their dependency on batteries, they inherently restrict our capacity to use on a per-charge basis. Many wearable electronics and medical devices require frequent charging which can be time consuming and frustrating to the user. Recharging can be replaced by an energy harvester utilizing body heat through thermoelectric energy conversion. Untapped energy, in the form of heat is constantly generated by the human body and can be converted into a continuous electrical energy supply. Thermoelectric modules can generate electrical power from low temperature gradients in a safe and reliable manner. In the case of wearable devices, an optimized energy harvesting system generates sufficient power to free us from our dependency on the “next charge”. Inherent difficulties that arise during the development of wearable energy harvesters are low voltage and power outputs, as well as limited space. Based on our previous accomplishment of thermoelectric system optimization work, a wrist-band prototype was built using only off-the-shelf components. From system level optimization of a heat sink utilizing natural convection and a thermoelectric module, a geometric factor (-factor), which is defined as leg length over fill factor, was determined for maximum power output. Number of pairs were optimized to minimize reduced boost converting efficiency. Our prototype has demonstrated a usable amount of 0.5 mW of power generation over 45 cm2 of coverage area at 5V output voltage, which is sufficient to power a micro controller that can execute basic code, analyze data, measure temperature, and track time, amongst other things. The experimental evidence for our theoretical work will provide a guideline for a thermoelectric system design as well as thermoelectric material development