Anja Lund with a piece of the electric textile in the shoulder strap of a bag (the lighter-coloured part). To the right: a LED that flashes because electricity is generated when the textile is stretched. Credit: Johan Bodell/Chalmers University of Technology

Textiles that generate electricity as they stretch could be a new way to power lights or small electronic devices.

A team from Chalmers University of Technology in Sweden has created a fabric that converts kinetic energy into electric power, where the greater the load applied to the textile and the wetter it becomes the more electricity it can generate.

The new woven fabric has generated enough power to light an LED, send wireless signals or drive small electric units like pocket calculators or digital watches.

According to the study, textiles are an ideal format for low-power electronics because textiles can interact with the user as displays based on electrochromic or electroluminescent fibers or by movement, such as artificial muscles.

The technology is based on the piezoelectric effect, which results in the generation of electricity from deformation of a piezoelectric material, like when it is stretched.

The researchers weaved a piezoelectric yarn together with an electrically conducting yarn to create the new fabric.

“The textile is flexible and soft and becomes even more efficient when moist or wet,” Anja Lund, a postdoctoral researcher at Chalmers, said in a statement. “To demonstrate the results from our research we use 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 consists of our fabric, the more electric power we obtain. When our bag is loaded with three kilos of books, we produce a continuous output of four 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.”

The piezoelectric yarn is made of thin fibers that when sufficiently wet become enclosed in liquid, enabling the yarn to become more efficient because it improves the electrical contact between the fibers.

“The piezoelectric fibers consist of a piezoelectric shell around an electrically conducting core,” Lund said. “The piezoelectric yarn in combination with a commercial conducting yarn constitute an electric circuit connected in series.”

Past studies by the team have focused on sensors and their ability to generate electric signals through pressure sensitivity. However, using the energy to continuously drive electronic components is groundbreaking.

“Woven textiles from piezoelectric yarns makes the technology easily accessible and it could be useful in everyday life,” Lund said. “It's also possible to add more materials to the weave or to use it as a layer in a multi-layer product. It requires some modification, but it's possible.”

According to the researchers, the technology is ready in principal for larger scale production. The cost is relatively low. Through their collaboration with the Swedish School of Textiles, the researchers have been able to demonstrate that the yarn can be woven in industrial looms and is sufficiently wear-resistant to cope with the harsh conditions of mass production.

The study was published in NPJ Flexible Electronics.