Smart hat senses when traffic lights change and tells you via an app

Flexible and wear-resistant strands of conductive fibre have been used to make smart clothes with embedded computers and sensors, such as hats that can sense traffic light changes.

Previous efforts to create fibres with a hardwearing coating and a conductive core have run into problems. Materials cooling and contracting at different rates during manufacture or being twisted or washed once in a final product often cause tiny stress cracks, stopping a smart device from working.

Now, Lei Wei at Nanyang Technological University, Singapore, and his colleagues have made conductive materials that cool and contract in a similar way to the aluminosilicate glass used in smartphone screens, so that stress cracks don’t appear. The material borrows techniques for making fibre-optic cable, and Wei says the process is both cheap and “industry ready”.

The technique involves placing a semiconductor wire made of silicon or germanium into molten glass at temperatures of about 1000°C and pulling it into fine strands. The glass is later etched away with hydrofluoric acid and replaced with a polymer coating, which allows for a more flexible material. The fibres can stretch for up to 10 kilometres.

Small amounts of this fibre are then woven into a fabric using standard weaving machines and normal cotton. Wei says cotton is needed to make the clothes comfortable because the new material alone feels like “fishing line” against the skin.

The researchers have used the fibre to make several prototype items that also include electronic sensors and chips that communicate via the conductive material, such as a hat that senses when traffic lights change colour and passes the information to a smartphone app, a jumper that can receive and decode images transmitted by light pulses rather than radio waves, and a watch strap that measures its wearer’s heart rate.

In tests over six months in which the clothes were worn, washed and dried repeatedly, the fibres held up and continued to conduct electricity.

There is still a weakness, however: the link between the flexible material and the rigid circuit boards that hold computer chips and other components tends to fail after a few months, causing the smart features to stop working.

“The only part that always leads to the failure of the test is the connection between the fibre and the outer circuit,” says Wei. “To find a stable way to make the connection, that’s the challenge now.”