Chalmers University of Technology researcher with kinetic energy fabric

Stretchy material generates electricity under strain and as it becomes moist

Image credit: Chalmers University of Technology

Researchers at Chalmers University of Technology have developed a fabric that converts kinetic energy into electric power.

The textile generates more energy as the load applied to it increases in weight and also as it gets wetter.

The fabric can currently generate enough power to light an LED, send wireless signals or drive small electrical units, such as a pocket calculator or a digital watch.

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

In the study, the researchers created a textile by weaving a piezoelectric yarn together with an electrically conducting yarn, which is required to transport the generated electric current.

“The textile is flexible and soft and becomes even more efficient when moist or wet,” said Anja Lund who worked on the project. “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 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.”

The piezoelectric yarn is made up of twenty-four fibres, each as thin as a strand of hair.

When the fibres are sufficiently moist they become enclosed in liquid and the yarn becomes more efficient, since this improves the electrical contact between the fibres.

The technology is based on previous studies by the researchers in which they developed the piezoelectric fibres, to which they have now added a further dimension.

“The piezoelectric fibres 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.”

Previous work by the researchers on piezoelectric textiles has so far mainly focused on sensors and their ability to generate electric signals through pressure sensitivity. Using the energy to continuously drive electronic components is unique.

“Woven textiles from piezoelectric yarns makes the technology easily accessible and it could be useful in everyday life. 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,” Lund added.

The researchers believe the technology is ready for larger-scale production and are looking for industrial product developers to make use of it.

The cost of manufacture is relatively low and is comparable with the price of Gore-Tex - the established waterproof, windproof, breathable fabric - the researchers believe.

They have already 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.

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