Yarns that generate electricity when they are stretched or twisted have been created by a research team led by scientists at The University of Texas at Dallas and Hanyang University in South Korea.

According to the researchers, 'twistron' yarns could potentially harvest energy from the motion of ocean waves or from temperature fluctuations.

The yarns are constructed from carbon nanotubes. To generate electricity, the nanotubes were either submerged in or coated with an ionically conducting material, or electrolyte, which can be as simple as a mixture of ordinary table salt and water.

"Fundamentally, these yarns are supercapacitors," said UT Dallas scientist Dr Na Li. "In a normal capacitor, you use energy – like from a battery – to add charges to the capacitor. But in our case, when you insert the carbon nanotube yarn into an electrolyte bath, the yarns are charged by the electrolyte itself."

According to the team, when a harvester yarn is twisted or stretched, the volume of the carbon nanotube yarn decreases, bringing the electric charges on the yarn closer together and increasing their energy. This increases the voltage associated with the charge stored in the yarn, enabling the harvesting of electricity.

Stretching the coiled twistron yarns 30times/s is said to generate 250W/kg of peak electrical power when normalised to the harvester's weight.

"No other reported harvester provides such high electrical power or energy output per cycle as ours for stretching rates between a few cycles per second and 600 cycles/s," said UT Dallas Dr Ray Baughman.

" Based on demonstrated average power output, just 31mg of carbon nanotube yarn harvester could provide the electrical energy needed to transmit a 2KByte packet of data over a 100m radius every 10s."

"There is a lot of interest in using waste energy to power the IoT, such as arrays of distributed sensors," Dr Li said. "Twistron technology might be exploited for such applications where changing batteries is impractical."