Using body heat to power wearable devices can eliminate lapses in uninterrupted operation

Wearable sensors, ranging from fitness trackers to electrocardiogram monitors, have become ubiquitous in the age of smart devices. A shortcoming of these devices, however, is the need to recharge or replace their batteries, causing a lapse in continuous tracking.

Khan et al. provide a review on flexible thermoelectric generators (FTEGs) as a solution for this problem.

“TEGs can be integrated with flexible batteries to store power and supply continuous power for uninterrupted measurement,” said author Woochul Kim.

However, as the authors also point out, the technology still exhibits optimization challenges that need to be addressed before it can be used in practical applications.

TEGs suffer a tradeoff between flexibility and utility. Conventional TEGs are bulky and rigid, but FTEGs are limited in their stability and power and, while flexible, remain thick. Adding a heat sink to the FTEG can increase its stability by maintaining a consistent temperature difference between the wearer and the environment. The primary challenge, therefore, is ensuring the heat sink is of a reasonable size.

“Size matters in wearable devices,” Kim said. “A clever idea is needed to overcome this.”

Once this is accomplished, the researchers suggest further improvements that can be made to the technology. This includes storing any surplus to the continuous power supplied by the FTEG for later access, in case of temperature fluctuations for example, to guarantee uninterrupted operation, and integrating a voltage booster to ensure sufficient power.

Kim said the group is working on applying FTEGs to develop an insulin injection system operated using body heat, which can replace bulky insulin pumps.

Source: “Review on the operation of wearable sensors through body heat harvesting based on thermoelectric devices,” by Salman Khan, Jiyong Kim, Somnath Acharya, and Woochul Kim, Applied Physics Letters (2021). The article can be accessed at https://doi.org/10.1063/5.0049347 .

This paper is part of the Organic and Hybrid Thermoelectrics Collection, learn more here .