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A piezoelectric fabric that generates power through the bending of its component threads could harvest useful amounts of power from a wearer's body motions.In 2007 Zhong Lin Wang, a materials scientist at the Georgia Institute of Technology in Atlanta, US, developed a generator composed of a forest of piezoelectric zinc oxide nanowires topped by a flat conductive plate. As the plate is pushed down, the wires bend, producing a voltage that induces current to flow into the plate.Now Wang has turned this idea into an electricity-generating thread, which he plans to weave into a fabric. His team figured out how to grow the nanowires on a strand of Kevlar fibre instead of a flat surface, so that the wires stick out from the fibre like the bristles on a pipe-cleaner.When two of the bristly fibres rub against one another, the nanowires deform, causing a current to flow through a thin layer of metal coating on one of the fibres.No pricklesIn tests with just two short fibres, Wang's team was able to generate a few picowatts of power, but they found that the power output increased 50-fold when three pairs of fibres are twined together into a yarn, increasing the area of contact.Wang estimates that the fabric should be capable of generating about 80 milliwatts of electricity per square metre, enough to charge a cellphone battery or other personal electronics from the ordinary motions of a shirt or a curtain blowing in the wind.
By allowing nanowire growth to take place at temperatures as low as 80 degrees Celsius, the new fabrication technique would allow the nanostructures to be grown on virtually any shape or substrate.As a next step, the researchers want to combine multiple fiber pairs to increase the current and voltage levels. They also plan to improve conductance of their fibers.However, one significant challenge lies head for the power shirt -- washing it. Zinc oxide is sensitive to moisture, so in real shirts or jackets, the nanowires would have to be protected from the effects of the washing machine, Wang noted.