A fabric was developed that converts kinetic energy into electric power. The greater the load applied to the textile and the wetter it becomes, the more electricity it generates. The woven fabric generates electricity when it is stretched or exposed to pressure. The fabric can currently generate enough power to light an LED, send wireless signals, or drive small electric units such as a pocket calculator or a digital watch.
The technology is based on the piezoelectric effect that results in the generation of electricity from deformation of a piezoelectric material, such as when it is stretched. The textile was created by weaving a piezoelectric yarn together with an electrically conducting yarn, which is required to transport the generated electric current.
To demonstrate the technology, researchers used a piece of the textile in the shoulder strap of a bag. The heavier the weight packed in the bag and the more of the bag that consisted of the fabric, the more electric power was obtained. When the bag is loaded with 3 kilos of books, a continuous output of 4 microwatts was produced — enough to intermittently light an LED. By making an entire bag from the textile, enough energy could be generated to transmit wireless signals.
The piezoelectric yarn is made up of 24 fibers, each as thin as a strand of hair. When the fibers are sufficiently moist, they become enclosed in liquid and the yarn becomes more efficient, since this improves the electrical contact between the fibers. The piezoelectric fibers consist of a piezoelectric shell around an electrically conducting core. The piezoelectric yarn, in combination with a commercial conducting yarn, constitutes an electric circuit connected in series.
More materials may be added to the weave, or it may be used as a layer in a multilayer product. The yarn can be woven in industrial looms, and is sufficiently wear-resistant to cope with the harsh conditions of mass production.