A yarn made from carbon nanotubes can generate power when stretched, with the material harvesting mechanical energy from its environment and converting it to electricity.
Energy harvesters have been made before, but they often generate only low power, or require an external voltage to function. Seon Jeong Kim at Hanyang University in Seoul, Ray Baughman at the University of Texas at Dallas in Richardson and their colleagues made a device from yarns of hollow, nanometre-scale cylinders of carbon, which they twisted into tightly bound coils. Immersing the yarns in an ionic solution — such as salt water — or coating them in an electrolyte gel caused charges to build up on the surface. When a spring-like piece of yarn was stretched, these charges were squeezed together, increasing the yarn’s voltage. This caused electricity to flow between it and a separate electrode, without the need for an external voltage.
The team demonstrated that, when stretched, a yarn weighing less than 20 milligrams — about the mass of a housefly — can power a light-emitting diode. And it produces more than 100 times more electrical power per unit of weight than other weavable fibres or yarns.