Spinning a yarn

A US company has put a new spin on power-scavenging clothing by creating flexible piezoelectric fibres hundreds of metres long to weave into fabrics.

Piezoelectric (PZ) materials yield an electrical current when deformed, and researchers have been searching for a way to mix them with fabrics to provide power via movement in clothing. The military are also interested in their potential as a power source according to SmartWear, which is focusing on providing power to unmanned aerial vehicles via towed fabric banners.

SmartWear has used a ‘fibre spinning’ process to create longer and more flexible PZ strands. Dr Michael Pottenger, principal investigator at SmartWear, said that conventional techniques to create PZ material are expensive and unsuitable for fabrics. ‘The fibres produced are very short and not continuous,’ said Pottenger.

‘Thin-film deposition gives flat strips that are flexible in only one direction and have to be mounted on plastic, so they can be uncomfortable to wear, whereas ceramic PZs have better performance but are brittle and will break without much deflection.’

SmartWear’s process yielded better quality PZ material, he said. ‘The PZ crystals are better aligned and they are the right type of material, unlike thin film deposition, where you have to go through an additional process called ‘poling’ to line the crystals up and at first you often don’t get the right material deposited,’ said Pottenger.

The fibre spinning process involves pushing melted polymer solution through a ‘spinnerette’ that looks like a showerhead spinning at various speeds, after which the fibres are stretched causing stress-induced crystallisation. ‘We expected the performance to be worse. When we started we thought it wasn’t possible,’ said Pottenger. But although the performance does not match ceramic PZs, it improves on thin-film polymers.

‘We’re not claiming we’re going to replace all PZs, but there are many applications that are currently just not possible because of the constraints of conventional materials,’ he said.

Pottenger predicted that the material will be available in one to two years. He said that SmartWear’s UAV power-scavenging banner needs more research, to balance the power input with the extra drag provided by towing the material, but has the potential to reduce the battery payload and extend flight time.