This High-Tech Yarn Generates Electricity Through Movement
Energy comes from all sorts of places, and every day, a lot of that energy is wasted. As you read this, the heat from your body, the mechanical movement of your finger on your device, and even the pressure waves produced from your speech are lost to the chaos of the universe. Scientists are keenly aware of this, and hard at work coming up with ways to generate electricity from the energy that's already there. In August of 2017, they came up with what might be the most brilliant version yet: yarn that generates electricity just by being pulled or twisted. If that makes you think "smart clothing," you're right — but think bigger.
It Was The Best Of Twines, It Was The Worst Of Twines
The yarns are made of carbon nanotubes, which are hollow tubes of carbon measuring 10,000 times thinner than a human hair but 100 times stronger than steel. They're also very good at conducting electricity. To create their "twistron harvesters," as they're being called, the researchers twisted bundles of nanotubes until they had turned into yarn — and then they twisted them even more to make them springy and elastic.
The only thing is that in order to generate electricity, the yarns need an electrolyte. That is, they either need to be coated or submerged in an ionically conducting material, which could be something as simple as salt water. But once they have their electrolyte, the yarns are good to go. "Fundamentally, these yarns are supercapacitors," said Dr. Na Li, a research scientist at the NanoTech Institute and co-lead author of the study, in a press release. "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."
With the electrolyte charging the yarn, it just takes some pulling or twisting to get the voltage up. That's because stretching reduces the yarn's volume and brings the electric charges close together, which boosts the energy level and thereby the voltage. That's how you can harvest the yarn's stored energy.
Bop It, Twist It, Pull It
So we know how they work, but what can they do? All sorts of things. To start with, the researchers attached a piece of yarn weighing less than a housefly to an LED, which lit up with each stretch of the yarn.
They also sewed the yarns into a shirt, and showed how normal breathing stretched the yarns enough to generate enough electricity to potentially power a breathing sensor.
Next, the researchers wanted to know this: if the yarns can charge in basic salt water, can they charge in the ocean? To see, co-lead author Dr. Shi Hyeong Kim from the NanoTech Institute submerged a single twistron harvester in the ocean off the coast of South Korea, held up by a balloon and weighed down by a sinker. The ocean waves stretched the yarn enough to generate electricity, showing that if they add more yarns or make the harvesters thicker, all sorts of things could be powered by the ocean. Right now, however, the yarns are best suited for powering wearable sensors and Internet of Things devices — technologies that are only becoming more widespread.