A sweater can keep warm the person who is wearing it, but in future it may even generate electricity to power small devices. You don't think it is possible? Check out the article "Harvesting electrical energy from carbon nanotube yarn twist" (submitted in February, but published in Science, 25 Aug 2017: Vol. 357, Issue 6353, pp. 773-778 DOI: 10.1126/science.aam8771). In the essay a group of researchers from The University of Texas at Dallas and the Hanyang University in South Korea (in collaboration with researchers from Virginia Tech, the Wright-Patterson Air Force Base and China) analyse the possibilities of what they call "twistron harvesters", a new kind of yarn capable of converting movement into an electrical current.
The yarns were constructed from carbon nanotubes, which are hollow cylinders of carbon 10,000 times smaller in diameter than a human hair. The nanotubes were twist-spun into high-strength, lightweight yarns. To make the yarns highly elastic, the researchers introduced so much twist that the yarns coiled like an over-twisted rubber band.
The yarn must be either submerged in or coated with an ionically conducting material - or electrolyte - which can be as simple as a mixture of ordinary table salt and water. When the twistron is stretched the internal friction sets the charges from the carbon nanotubes free, releasing electricity.
"Fundamentally, these yarns are supercapacitors," states Dr. Na Li, a research scientist at the NanoTech Institute and co-lead author of the study, in a press release on the University of Dallas site. "In a normal capacitor, you use energy - like from a battery - to add charges to the capacitor. But in our case, when you insert the carbon nanotube yarn into an electrolyte bath, the yarns are charged by the electrolyte itself. No external battery, or voltage, is needed."
As explained by Dr. Ray Baughman, director of the NanoTech Institute and a corresponding author of the study, stretching the coiled twistron yarns 30 times a second generated 250 watts per kilogram of peak electrical power when normalized to the harvester's weight.
In the lab, the researchers showed that a twistron yarn weighing less than a housefly could power a small LED, which lit up each time the yarn was stretched. Co-lead author Dr. Shi Hyeong Kim, a postdoctoral researcher at the NanoTech Institute, went to test the yarn on the field: he waded into the surf off the east coast of South Korea to deploy a coiled twistron in the sea. He attached a 10 centimeter-long yarn weighing only 1 milligram (about the weight of a mosquito), between a balloon and a sinker that rested on the seabed. Every time an ocean wave arrived, the balloon would rise, stretching the yarn up to 25 percent, thereby generating measured electricity.
The inspiration for this research is all around us and more or less under our eyes: the researchers were indeed interested in finding alternative sources of power for small-scale, portable electronics and wearable devices.
At present, these harvesters could be employed for powering applications where changing batteries is impractical, such as sensors and sensor communications. "Based on demonstrated average power output, just 31 milligrams of carbon nanotube yarn harvester could provide the electrical energy needed to transmit a 2-kilobyte packet of data over a 100-meter radius every 10 seconds for the Internet of Things," added Baughman.
Yet there are different applications for such a yarn: while it would indeed be possible harvesting energy from the motion of ocean waves or from temperature fluctuations that could be used to charge a storage capacitor or use the waste energy to power IoT applications, when sewn into a shirt, the yarns could be employed as a self-powered breathing monitor (that could generate useful data for medical devices), but could also be woven into electronic textiles to harvest electrical energy from human motion.
The real challenge now is to make the yarn less expensive and harvest the enormous amount of energy available from ocean waves. It would be interesting to see if twistron could be taken out of the lab and to a yarn fair: it is about time that such events started featuring not just artisanal products, but a combination of luxury yarns and synthetic products based on innovative scientific and technological discoveries.
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