Researchers Plan Embroidery as Low-Cost Solution for Making Wearable Electronics – ScienceDaily

Embroidering energy-generating threads onto the fabric allowed the researchers to embed a self-powered digital touchpad and motion sensors into the garments. This technology offers a potentially low-cost, scalable way to make wearable devices.

“Our technology uses embroidery, which is very simple — you can sew our yarn directly onto the fabric,” said the study’s lead author Rong Yin, assistant professor of textile engineering, chemistry and science at North Carolina State University. “While producing the fabric, you don’t need to think about anything about the wearables. You can incorporate the energy-generating threads after the piece of clothing is made.”

In the study published in nano energy, the researchers tested multiple power generation filament designs. To make it sturdy enough to withstand the stress and bending of the embroidery stitching process, they eventually used five commercially available copper wires, which had a thin layer of polyurethane on them, held together. Then they sewed it onto cheesecloth with another material called PTFE.

“This is a low-cost way to make wearable electronics using commercially available products,” Yin said. “The electrical characteristics of our prototypes were comparable to other designs that relied on the same power generation mechanism.”

The researchers relied on a method of generating electricity called the “frictional effect,” which involves harnessing electrons that are exchanged by two different materials, such as static electricity. They found that PTFE fabric had the best performance in terms of voltage and current when in contact with polyurethane-coated copper wire, compared to other types of fabric tested, including cotton and silk. They also tested coating embroidery samples with plasma to increase the effect.

“In our design, you have two layers — one is conductive copper wire that’s coated with polyurethane, and the other is PTFE, and there’s a gap between them,” Yin said. “When the two non-conducting materials come into contact with each other, one material will lose some electrons, and the other will gain some. When you connect them together, there will be a current.”

The researchers tested their threads as motion sensors by embroidering them with PTFE fabric onto denim. They placed embroidery patches on the palm of the hand, under the arm, elbow, and knee to track the electrical signals generated as the person moved. They also attached fabric with their embroidery to the sole of the shoe to test its use as a pedometer, and found that their electrical signals varied depending on whether a person was walking, running, or jumping.

Finally, they tested their leads in a fabric-based numeric keypad on the arm, which they made by embroidering numbers on a piece of cheesecloth, and attaching it to a piece of PTFE fabric. Depending on which number the person pushed on the keypad, they saw different electrical signals generated for each number.

“You can embroider our threads on clothes, and when they move, they generate an electrical signal, and these signals can be used as a sensor,” Yin said. “When we put the embroidery into the shoe, if you’re running, it generates a higher voltage than if you’re just walking. When we sewed the numbers onto the fabric, and pressed it, it generated a different voltage for each number. It could be used as an interface.”

Since textile products would inevitably be washed, they tested the durability of their embroidery design in a series of wash and rub tests. After hand washing, rinsing the embroidery with detergent, and drying it in the oven, they found no difference or slight increase in effort. For the plasma-coated prototype, they found poor but still superior performance compared to the original sample. After abrasion testing, they found that there was no significant change in the electrical output performance of their designs after 10,000 rubbing cycles.

In future work, they plan to combine their sensors with other devices to add more functionality.

“The next step is to integrate these sensors into a wearable system,” said Yin.

The study, “Flexible, Durable, and Washable Electrophoresis Threads and Electrophoresis for Self-Sensing and Human-Machine Interaction” is published online in nano energy. Co-authors include Yu Chen, Erdong Chen, Zihao Wang, Yali Ling, Rosie Fisher, Mingjiao Li, Jacob Hart, Willie Mo, Wei Zhao, Xiaoming Tao, and Bao Yang. Funding was provided by North Carolina State University through the NC State Faculty Research and Professional Development Fund and the NC State REU Summer Program.

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