Self-powered wearable garments that double as digital sensors have several advantages over battery-powered devices, primarily because they don’t require batteries. Batteries typically are rigid structures and uncomfortable to wear. Batteries also need recharging. One technological solution for an integrated power source is the triboelectric nanogenerator (TENG). The triboelectric effect produces energy by harnessing electrons when two different materials come in contact with each other. We’ve written about TENGs several times in the past five years, mentioning work by physicists and engineers at Clemson University, Purdue University, and others. Most recently, we covered a prototype battery-free wearable that measures vital signs in real-time developed by researchers at the University of California, Irvine (UCI).
According to a team of research engineers from North Carolina State University (NCSU), South China University of Technology, Ocean University of China, and Hong Kong Polytechnic University, producing woven textiles with integrated TENGs is costly, overly complex, and time-consuming. Woven fabric with self-powered sensors also have poor electromechanical properties with limited power capabilities, the research team asserts. Led by the team at NCSU, the group developed a solution to the limitations of self-powered woven textiles. The team published a study in Nano Energy that describes their technology.
Rather than try to overcome the challenges of creating power-generating woven fabric, the NCSU-led researchers created a power-generating yarn that is sufficiently durable for embroidery stitching. The yarn consists of five common copper wires, each with a polyurethane insulating coating. The team stitched the yarn onto a two-layer fabric. One layer was cotton denim. The second layer was polytetrafluoroethylene (PTFE). The team stitched the PTFE with the coated wire-based thread. The embroidered patch produced open-circuit voltage and short circuit micro amperage (µA) when the wearer moved. The team embroidered patches that acted as motion sensors on the wearer’s palm, arm, elbow, and knee as well as a numeric keypad. The varied number shapes generated different voltages when pressed. To count steps, the group also stitched an embroidered patch on the insole of a shoe.
The engineers tested the embroidered fabric patches by rubbing them 10,000 times and by hand washing and rinsing followed by drying in an oven. There was no significant change following the rubbing abrasion test and either no change or a slight voltage increase after the three-part cleaning cycle.
Rong Yin, assistant professor of textile engineering, chemistry and science at North Carolina State University, and the lead author of the study said, “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.”
Next steps include integrating the separate sensors into systems for wearables. Creating self-powering wearables with this method has the advantages of low cost and simple scalability.
