Embroidery as Low-Cost Solution for Making Wearable Electronics

Technology News -- November 22, 2022: Researchers were able to incorporate a self-powered numerical touchpad and movement sensors onto garments by embroidering

power-generating yarns into fabric. The method offers a potentially low-cost, scalable way to create wearable technology.

Researchers examined a variety of power-generating yarn designs in the study that was published in Nano Energy. They  combined five commercially available copper wires with a thin polyurethane coating to make them strong enough to withstand the stress and bending of the embroidery stitching process. Then, using a different substance called PTFE, they stitched them onto cotton cloth.

The researchers used a technique for producing electricity known as the "triboelectric effect," which involves utilizing the exchange of electrons between two distinct materials, similar to static electricity. In comparison to other types of fabric they examined, such as cotton and silk, they discovered that the PTFE fabric had the best performance in terms of voltage and current when in contact with the polyurethane-coated copper wires. To enhance the effect, they also tried plasma-coating the embroidery sample pieces.

"“Our technique uses embroidery, which is pretty simple – you can stitch our yarns directly on the fabric,” said the study’s lead author Rong Yin, assistant professor of textile engineering, chemistry and science at North Carolina State University. “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.”

By sewing PTFE fabric onto denim, researchers put their yarns to the test as motion sensors. To track electrical signals produced while a person moves, the embroidery patches were positioned on the palm, beneath the arm, at the elbow, and at the knee. They also tested the effectiveness of a shoe's insole as a pedometer by attaching fabric with their embroidery to it. They discovered that the electrical impulses varied depending on whether the subject was walking, running, or leaping.

Finally, they put their yarns to the test in a textile-based numeric keypad they created by sewing a piece of cotton fabric with embroidered numerals to a piece of PTFE cloth. The user pushed a number on the keypad, and they observed various electrical signals being produced for each number.

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

Since textile products will unavoidably be cleaned, they put their embroidery pattern through a series of rubbing and washing tests to see how long it will last. After manually washing, rinsing, and drying the embroidery in an oven with detergent, they discovered no difference or a little increase in voltage. They discovered weakened but still superior performance for the prototype when compared to the original sample for the plasma coating. Following an abrasion test, they discovered that after 10,000 rubbing cycles, their designs' electrical output performance had not significantly changed.

They intend to combine their sensors with other devices in subsequent work to offer more features.

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

The study, “Flexible, durable and washable triboelectric yarn and embroidery for self-powered sensing and human-machine 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.

The study abstract follows.

Flexible, durable and washable triboelectric yarn and embroidery for self-powered 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.

Published: online Oct. 27, 2022, Nano Energy

DOI: 10.1016/j.nanoen.2022.107929

Abstract: The novel combination of textiles and triboelectric nanogenerators (TENGs) successfully achieves self-powered 17 wearable electronics and sensors. However, the fabrication of Textile-based TENGs remains a great challenge 18 due to complex fabrication processes, low production speed, high cost, poor electromechanical properties, and 19 limited design capacities. Here, we reported a new route to develop Textile-based TENGs with a facile, low-cost, 20 and scalable embroidery technique. 5-ply ultrathin enameled copper wires, low-cost commercial materials, were 21 utilized as embroidery materials with dual functions of triboelectric layers and electrodes in the Textile-based 22 TENGs. A single enameled copper wire with a diameter of 0.1 mm and a length of 30 cm can produce over 60 V 23 of open-circuit voltage and 0.45 µA of short circuit current when in contact with polytetrafluoroethylene (PTFE) 24 fabric at the frequency of 1.2 Hz and the peak value of contact force of 70 N. Moreover, the triboelectric 25 performance of enameled copper wire after plasma treatment can be better than that without plasma treatment, 26 such as the maximum instantaneous power density can reach 245 μW/m which is ~ 1.5 times as much as the 27 untreated wire. These novel embroidery TENGs possess outstanding triboelectric performance and super design capacities. A 5×5 cm2 28 embroidery sample can generate an open-circuit voltage of 300 V and a short circuit current 29 of 8 μA under similar contact conditions. The wearable triboelectric embroidery can be employed in different 30 parts of the wear. A self-powered, fully fabric-based numeric keypad was designed based on triboelectric 31 embroidery to serve as a human-machine interface, showing good energy harvesting and signal collection 32 capabilities. Therefore, this study opens a new generic design paradigm for textile-based TENGs that are 33 applicable for next-generation smart wearable devices.

article information credit

NC State University Research and Innovation

Nano Energy Study

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