Embroidering researchers’ eyes as a low-cost solution for making wearable electronics

Embroidering energy-generating threads onto fabric allowed researchers to embed a self-powered digital touchpad and motion sensors into clothing. The technique offers a potential inexpensive and scalable method for fabricating wearable devices.

“Our technique uses embroidery, which is quite simple – you can sew our threads directly onto fabric,” said the study’s lead author. Rong Yin, assistant professor of textile engineering, chemistry, and science at North Carolina State University. “When producing fabrics, you don’t need to worry about portable devices. You can integrate the energy-generating threads after the garment has been made.

In the study published in Nano energy, the researchers tested several models of energy-generating wires. To make them durable enough to withstand the tension and bending of the embroidery stitching process, they eventually used five commercially available copper wires together, which had a thin polyurethane coating. Then they sewed them on cotton fabric with another material called PTFE.

“This is an inexpensive method to make portable electronic devices using commercially available products,” Yin said. “The electrical properties of our prototypes were comparable to other designs that relied on the same energy-generating mechanism.”

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

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

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

Finally, they tested their yarns in an over-the-arm textile-based numeric keypad, which they made by embroidering numbers onto a piece of cotton fabric and attaching them to a piece of PTFE fabric. Depending on the number the person pressed on the keypad, they saw different electrical signals generated for each number.

“You can embroider our threads on clothes, and when you move, it generates an electric signal, and these signals can be used as a sensor,” Yin said. “When we put the embroidery in a shoe, if you are running it generates a higher tension than if you were just walking. When we sew numbers on fabric and press them, it generates a different tension for each number It could be used as an interface.

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

In future work, they plan to integrate their sensors with other devices to add more functions.

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

The study, “Flexible, Durable, and Washable Triboelectric Yarn and Embroidery for Autonomous Sensing and Human-Computer Interaction,” was published online in Nano energy. Co-authors included Yu Chen, Erdong Chen, Zihao Wang, Yali Ling, Rosie Fisher, Mengjiao Li, Jacob Hart, Weilei Mu, Wei Gao, Xiaoming Tao, and Bao Yang. Funding was provided by North Carolina State University through the NC State Faculty Research & Professional Development Fund and the NC State Summer REU program.

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Note to Editors: The summary of the study follows.

Flexible, durable, washable triboelectric thread and embroidery for autonomous sensing and human-machine interaction

Authors: Yu Chen, Erdong Chen, Zihao Wang, Yali Ling, Rosie Fisher, Mengjiao Li, Jacob Hart, Weilei Mu, Wei Gao, Xiaoming Tao, Bao Yang and Rong Yin.

Posted: online on Oct. 27, 2022, Nano energy

DO I: 10.1016/j.nanoen.2022.107929

Summary: The novel combination of textiles and triboelectric nanogenerators (TENGs) successfully yields 17 self-powered wearable electronic devices and sensors. However, the fabrication of textile-based TENGs remains a great challenge 18 due to complex manufacturing processes, low production speed, high cost, poor electromechanical properties and 19 limited design capabilities. Here we have reported a new way to develop textile-based TENGs with an easy, inexpensive, 20 and scalable embroidery technique. Ultrafine 5-ply enameled copper wires, low-cost commercial materials, have been used as embroidery materials with dual function as triboelectric layers and electrodes in textile-based TENGs. A single enameled copper wire with a diameter of 0.1 mm and a length of 30 cm can produce more than 60 V 23 of open-circuit voltage and 0.45 µA of short-circuit current in contact with a polytetrafluoroethylene (PTFE) 24 fabric at the frequency of 1.2 Hz and the peak value of the contact force of 70 N. In addition, the triboelectric performance 25 of the enameled copper wire after plasma treatment can be better than that without treatment. plasma, 26 such that the maximum instantaneous power density can reach 245 μW/m which is ~1.5 times more than the untreated wire 27. These new embroidery TENGs possess outstanding triboelectric performance and outstanding design capabilities. A 5 x 5 cm2 embroidery sample 28 can generate an open circuit voltage of 300 V and a short circuit current 29 of 8 µA under similar contact conditions. Portable triboelectric embroidery can be used in different parts of wear. A fully cloth-based, self-powered numeric keypad was designed based on 31 triboelectric embroidery to serve as a human-machine interface, showing good energy harvesting and 32 signal gathering capabilities. Therefore, this study opens up a new generic design paradigm for textile-based TENGs that are applicable to next-generation smart wearable devices.