Electricity-Generating Yarn Makes Wearable Circuits as Simple and Cheap as Embroidery

Researchers at North Carolina State University, Ocean University of China, Hong Kong Polytechnic University, and South China University of Technology have detailed a low-cost and scalable approach to developing self-powered wearable electronics — using embroidery and a low-cost functional yarn.

"Our technique uses embroidery, which is pretty simple — you can stitch our yarns directly on the fabric," explains lead author Rong Yin, assistant professor of textile engineering, chemistry, and science at NC State. "During fabric production, you don't need to consider anything about the wearable devices. You can integrate the power-generating yarns after the clothing item has been made."

Designed for both a low production cost and a robust finished material, the embroidered wearables platform creates triboelectric nano-generators (TENGs), which harness the body's movement and convert it into usable electricity through a combination of PTFE fabric and polyurethane-coated copper wires.

"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," Yin explains. "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. This is a low-cost method for making wearable electronics using commercially available products. The electrical properties of our prototypes were comparable to other designs that relied on the same power generation mechanism."

The yarn can be used for more than just energy generation, too: The team was able to turn the material into wearable motion sensors, embroidering it onto denim and placing patches under the user's palm, arm, elbow, and knee to track their movement — while in another experiment the team used it in a functional insole, which doubled as a pedometer that could differentiate walking, running, and jumping. A third prototype turned a sleeve into a numeric keypad, acting like a keyboard matrix to serve as an input device.

"You can embroider our yarns onto clothes, and when you move, it generates an electrical signal, and those signals can be used as a sensor," Yin says. "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."

The team's work has been published under closed-access terms in the journal Nano Energy.