Scientists have developed a type of "yarn," made from carbon nanotubes that can harvest energy from twisting or stretching motions. Such a method could be useful for developing motion sensors or harvesting energy from ocean waves, among other sources. Converting mechanical energy into electricity is an appealing means to create self-powered devices and harness energy from natural sources.

However, efforts to harness energy from stretching or torsional motion have been limited to circuits with very small currents. Here, Shi Hyeong Kim and colleagues discovered that adding some extra twist to a material can go a long way. They took sheets of multiwalled carbon nanotubes and spun them into high-strength yarns.

Instead of simply twisting them a bit, the researchers twisted the sheets so tightly that they formed coils. In analyzing the ability of these coils to transfer spring-like motion into energy, they found it be much more effective than material that is just twisted but not coiled.

Untwisting the coiled yarn by a small amount does not result in coil loss but instead increases coil diameter, boosting its conducting ability. The researchers combined the coiled nanotubes into a cell to create an energy harvesting device, which they dubbed a twistron harvester.

They tested the ability of the twistron to harvest energy from ocean waves, off the coast of South Korea; the 10-centimeter-long device achieved a voltage of 46 mV and an average output power of 1.79 mW.

As well, they demonstrate how the device could act as a motion sensor, for example by being sewn into a shirt to monitor motion associated with breathing.

Research paper

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