Researchers in the US and China have teamed up to develop what they deem to be power-generating yarns capable of charging textile technologies. Academics at NC State, in North Carolina, worked alongside the Ocean University of China, the South China University of Technology and Hong Kong Polytechnic University to establish their concept.
It is based on the ‘triboelectric effect’, through which electrons are passed between two materials to generate a current.
In this instance, the team used copper wires wrapped in a thin polyurethane coating and a PTFE (polytetrafluoroethylene) fabric as this pair – unlike trialled alternatives including cotton and silk – performed best in terms of generating the greatest voltage.
“In our design, you have two layers — one is your conductive, polyurethane-coated copper wires, and the other is PTFE, and they have a gap between them,” explained Rong Yin, Assistant Professor of Textile Engineering, Chemistry and Science at NC State.
“When the two non-conductive materials come into contact with each other, one material will lose some electrons, and some will get some electrons. When you link them together, there will be a current.”
The academics used the embroidery process to integrate their two materials into apparel, something they say can be done to a finished article rather than an item in production.
This was tested by applying the coated wire and PTFE fabric to items so that they could operate like sensors across the body. It was also trialled in the form of a numbered keypad, where numbers were embroidered and pressed to gauge the current they’d generate.
“When we put the embroidery in a shoe, if you are running, it generates a higher voltage than if you were just walking. When we stitched numbers onto fabric, and press them, it generates a different voltage for each number. It could be used as an interface,” Yin noted.
Whilst the premise looks promising, the research team has also been buoyed by its performance after laundering – as any textile-based technology would need to be durable enough to withstand multiple wash cycles.
After hand washing and rinsing the embroidery with detergent, and drying it in an oven, they found no difference or a slight increase in voltage.
“The next step is to integrate these sensors into a wearable system,” Yin said.
