An international research team has developed high-tech yarns that generate electricity when they are stretched or twisted. The team is led by scientists at The University of Texas at Dallas and Hanyang University in South Korea and includes researchers from South Korea, Virginia Tech, Wright-Patterson Air Force Base and China. They recently published their findings in Science.
The researchers have labeled the technology “twistron.” The yarns are constructed from carbon nanotubes that were twist-spun into high-strength, lightweight yarns and then twisted to create elasticity. To generate electricity, the yarns are submerged in or coated with an electrolyte, which can be a simple solution of table salt and water.
“When you insert the carbon nanotube yarn into an electrolyte bath, the yarns are charged by the electrolyte itself,” says research lead Dr. Na Li. “No external battery, or voltage, is needed.”
When a harvester yarn is twisted or stretched, the volume of the yarn decreases, bringing the electric charges on the yarn closer together and increasing their energy, says Dr. Carter Haines, associate research professor at the Alan G. MacDiarmid NanoTech Institute at UT Dallas and co-lead author of the article. This increases the voltage associated with the charge stored in the yarn, enabling the harvesting of electricity.
In the lab, the researchers showed that a twistron yarn weighing less than a housefly could light up a small LED each time the yarn was stretched. The researchers also sewed twistrons into a shirt. The wearer’s breathing stretched the yarn and generated an electrical signal, demonstrating the potential for applications such as respiration sensors.
Twistrons have further potential to harvest waste thermal energy from the environment. Li connected a twistron yarn to a polymer artificial muscle that contracts and expands when heated and cooled, and the twistron converted the polymer muscle’s mechanical energy into electrical energy.
The team predicts harvesting waste energy could help power the Internet of Things, including arrays of distributed sensors and situations where changing batteries is impractical.
Outside the lab, off the east coast of South Korea, co-lead author Dr. Shi Hyeong Kim investigated how twistrons could capture ocean wave action, testing electrolyte more chemically complex than a solution of table salt. He attached a yarn 10 centimeters in length, weighing only 1 milligram (about the weight of a mosquito), between a balloon and a sinker that rested on the seabed. Each wave forced the balloon to rise, stretching the yarn up to 25 percent and generating measured electricity.
Though the investigators used very small amounts of twistron yarn in the study, the results suggest that harvester performance is scalable, by increasing twistron diameter and by operating many yarns in parallel.
The current expense of the harvesters lends itself best to wearables, but co-author Dr. Ray Baughman suggests, “If our twistron harvesters could be made less expensively, they might ultimately be able to harvest the enormous amount of energy available from ocean waves.”
Video: University of Texas at Dallas, via Ars Technica