Wearable thermoelectric energy harvesters

Post date: Jul 8, 2015 10:49:02 PM

Despite the explosive growth of wearable electronics and sensors on the market in recent years, most of the wearable devices are still powered by batteries that are subject to frequent recharging and replacement. Often these devices require energy autonomy for an extended service time without the need for the user’s intervention. Examples include preventive healthcare for elderly people with wearable medical sensors that monitor the wearer’s physiological parameters. These medical sensors need to be preferentially wireless, and operational during the patient’s daily activities for a long time up to many years without maintenance or the doctor’s direct assistance. 

Several types of wearable flexible TEGs for human body-heat energy harvesting.

Medical sensors can be powerd by the TEGs for preventive health monitoring.(Figure from JMCC 2015)

One possible solution for powering these wearable devices without a battery is to harvest energy from human body to generate electricity using a thermoelectric generator. A thermoelectric generator (TEG) is a solid-state device that can convert heat into electricity. When a TEG is attached directly onto the skin, heat from the human body flows through the TEG due to the temperature difference between the skin and the ambient. This heat flow, or the temperature gradient, creates a voltage in the TEG by the Seebeck effect, which performs useful work when connected to an external circuit.

Heat dissipation from a human body largely vary depending on the body location and surrounding conditions, typically heat flow available from the skin under indoor sedentary conditions is 1 ~ 10 mW/cm2 on the average at 22 °C ambient temperature, and a higher heat flow of 10 ~ 20 mW/cm2 is possible on the wrist, where the heat-carrying radial artery is located near the skin. 

According to our calculations, a power output on the order of hundreds microWatts can be achieved using a wearable TEG of wrist-band type made of the existing polymeric or paste-type inorganic materials. Read our recent paper published in J. Mater. Chem. C for more information and complete review of the state-of-the-art flexible thermoelectric materials and devices.  

• J.-H. Bahk, H. Fang, K. Yazawa, and A. Shakouri, “Flexible thermoelectric materials and device optimization for wearable energy harvesting,” J. Mater. Chem. C, accepted manuscript (2015). DOI: 10.1039/C5TC01644D