Nanotube yarns offer an alternative to piezoelectric and triboelectric devices for harvesting energy Illustration: Shi Hyeong Kim/Hanyang University, Seoul, South Korea Illustration of a torsionally tethered coiled harvester electrode and counter and reference electrodes in an electrochemical bath, showing the coiled yarn before and after stretch.
An international team of researchers led by researchers at the University of Texas (UT) at Dallaswhere they have been working on making carbon nanotube-based yarns for well over a decadehas devised a way to make these carbon nanotube yarns into devices that can harvest energy from stretching or twisting them.
In research described in the journal Science , the initial results show promise for immediate use in powering small sensor nodes in Internet of Things (IoT) applications. The team says its nanotube yarns could produce larger amounts of energy by flexing and twisting in response to the movement of ocean waves.
While it appears as though these nanotube yarns are exploiting a piezoelectric effect, in which a material can generate an electric charge in response to applied mechanical stress, the yarns behavior makes it more closely tied to so-called electroactive polymers (EAPs), which are a kind of artificial muscle.
Basically what's happening is when we stretch the yarn, we're getting a change in capacitance of the yarn. Its that change that allows us to get energy out, explains Carter Haines, associate research professor at UT Dallas and co-lead author of the paper describing the research, in an interview with IEEE Spectrum.
This makes it similar in many ways to other types of energy harvesters. For instance, in other research, it has been demonstratedwith sheets of rubber with coated electrodes on both sidesthat you can increase the capacitance of a material when you stretch it and it becomes thinner. As a result, if you have charge on that capacitor, you can change the voltage associated with that charge.
We're more or less exploiting the same effect but what we're doing differently is we're using an electric chemical cell to do this, says Haines. So we...