A new fabric designed to convert kinetic energy into electric power works in ways that are curiously counterintuitive: the greater the load applied, the more electricity it generates; the more it gets exposed to moisture, the more efficient the generation becomes.
The material was created by researchers at Chalmers University of Technology, in cooperation with the Swedish School of Textiles at the University of Borås and the Swedish Research Institute for Industrial Renewal and Sustainable Growth (Swerea IVF). In developing the woven fabric, researchers made use of the piezoelectric effect — the ability of certain materials to generate an electric charge in response to applied mechanical stress — by weaving a piezoelectric yarn together with an electrically conducting yarn. When the thin fibers of the piezoelectric yarn become moist, electrical contact is improved. Woven together, the two yarn types constitute an electric circuit in series.
Currently, the material can generate enough power to light an LED, send wireless signals or drive small electric units such as a pocket calculator or digital watch.
"To demonstrate the results from our research, we use a piece of the textile in the shoulder strap of a bag," said Chalmers researcher Anja Lund. "The heavier the weight packed in the bag and the more of the bag that consists of our fabric, the more electric power we obtain. When our bag is loaded with 3 kilos of books, we produce a continuous output of 4 microwatts. That's enough to intermittently light an LED. By making an entire bag from our textile, we could get enough energy to transmit wireless signals."
Lund says that, with modification, it is also possible to add more materials to the weave, or to use it as a layer within a multi-layer product. The researchers' collaboration with the Borås school has demonstrated that the yarn can be woven in industrial looms and cope with the harsh conditions of mass production. The cost is relatively low, as well — comparable in price to Gore-Tex.
The researchers consider their technology to be ready for larger-scale production, at least in theory; it's now up to industrial product developers to figure out how to make use of it.