The idea of self-powered wearable devices is being looked at by several research centers. One group feel they have a breakthrough, based on drawing on the body heat of the wearer and converting this into energy of a sufficient level to power the device.
The research comes from North Carolina State University. Technologists there have come up with a novel design for harvesting body heat. As well as a proof-of-concept development, the technologists have come up with experimental prototypes. These test devices are reported to be lightweight and conform to the shape of the body.
In test the devices have generated more electricity than any previous lightweight heat harvesting technologies. The devices have been shown to generate 20 microwatts of power per centimeter squared. This has been achieved with the researchers identifying the optimal site on the body for heat harvesting. This turns out to be the upper arm. Although the wrist produces more heat the shape of the wrist is not conducive for a continuing supply of heat (since the device moves around).
In an interview with Controlled Environments, Professor Daryoosh Vashaee explains: “Wearable thermoelectric generators generate electricity by making use of the temperature differential between your body and the ambient air.”
Professor Vashaee goes on to explain that the devices are fitted with a film of thermally conductive material which rests on the skin and spreads out the heat. The conductive material has an outer polymer layer that prevents eat from dissipating. This layer instead directs body heat through a generator. The generator is very tiny (one centimeter squared) and this has proved sufficient to power the device continuously.
In addition to the upper arm, experiments have taken place with devices located on the chest (embedded into a T-shirt). These have also produced sufficient levels of power, although at a rate below that of the arm.
The main application with the new heat capturing technology is to develop devices that can monitor for health vital signs, like the heart.
The findings are published in the journal Applied Energy, in a paper titled “Wearable thermoelectric generators for human body heat harvesting.”
