Electricity from body heat

Thermoelectric material could power portable electronics and smart wear

Do fitness armbands soon lack rechargeable batteries? BsWei / thinkstock
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Instead of battery or battery: Researchers have developed a material that can only generate electricity by using body heat. Its cotton fabric and a conductive polymer exploits the temperature difference between the skin and its surroundings, generating voltages of around 20 millivolts through thermoelectric effects. This could be used in future, for example, in clothing built-in electronics.

Clothes are no longer just for dressing: the trend is towards the "smart" textile with additional functions. T-shirts, pants and co are already functioning as a user interface for smartphones, activity trackers or even as a medical device - and the electronics built into them are getting smaller and smaller.

The technology completely disappear in the textile, but does not work. One reason: The clothes have to be powered somehow. For this purpose, so far usually accessories are used, which must be plugged by magnet, push button or Velcro to the textile. However, scientists are already working on more elegant solutions: for example, ultra-thin solar cells that could easily be printed on clothing in the future.

Thermoelectric effects

Trisha Andrews of the University of Massachusetts in Amherst and her colleagues present a different approach: They have developed a substance that uses electronic energy to supply portable electronics with energy. The principle behind it: Alone by the gap between the warm body temperature and the cooler ambient temperature so-called thermoelectric materials can generate energy. Electricity is transported from the warm to the cold region - a small but usable current flows.

However, the application of this method in practice has so far lacked cost-effective, efficient and harmless materials, as the researchers report: "However, we have now developed a cheap and biocompatible tissue with sufficient thermoelectric properties to power small devices with electricity. " Display

The tissue can generate voltages of around 20 millivolts. © UMass Amherst / Andrew lab

Yield of over 20 millivolts

Specifically, their material consists of cotton fabric, on which a conductive polymer called PEDOT-CI is printed. Integrated into a band, the power supplier can be worn, for example, on particularly warm body regions such as the wrist, the palm or the upper arm. Tests showed: When worn, the band generated at least a thermal voltage of over 20 millivolts. Schwwei even increased the energy yield.

But does the fabric withstand everyday stresses as well? How durable the PEDOT-CI coating is, the scientists studied by washing the fabric and rubbing and pulling on it - hardness tests that left the material undamaged and without any loss of performance. "This confirms the robustness and robustness of the PEDOT-CI, " writes the team. In the future, the fabric could be used in smart clothing, but could also power small, wearable devices such as wristwatches or activity trackers. (Advanced Materials Technologies, 2019; doi: 10.1002 / admt.201800615)

Source: University of Massachusetts, Amherst

- Daniel Albat