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ScienceDaily (July 9, 2012) — Researchers have discovered yet another way to harvest small amounts of electricity from motion in the world around us -- this time by capturing the electrical charge produced when two different kinds of plastic materials rub against one another. Based on flexible polymer materials, this "triboelectric" generator could provide alternating current (AC) from activities such as walking.
The triboelectric generator could supplement power produced by nanogenerators that use the piezoelectric effect to create current from the flexing of zinc oxide nanowires. And because these triboelectric generators can be made nearly transparent, they could offer a new way to produce active sensors that might replace technology now used for touch-sensitive device displays.
"The fact that an electric charge can be produced through this principle is well known," said Zhong Lin Wang, a Regents professor in the School of Materials Science & Engineering at the Georgia Institute of Technology. "What we have introduced is a gap separation technique that produces a voltage drop, which leads to a current flow, allowing the charge to be used. This generator can convert random mechanical energy from our environment into electric energy."
Because the devices can be made approximately 75 percent transparent, they could potentially be used in touch screens to replace existing sensors. "Transparent generators can be fabricated on virtually any surface," said Wang. "This technique could be used to create very sensitive transparent sensors that would not require power from a device's battery."
While smooth surfaces rubbing together do generate charge, Wang and his research team have increased the current production by using micro-patterned surfaces. They studied three different types of surface patterning -- lines, cubes and pyramids -- and found that placing pyramid shapes on one of the rubbing surfaces generated the most electrical current: as much as 18 volts at about 0.13 microamps per square centimeter.
"The entire preparation process is simple and low cost, making it possible to be scaled up for large scale production and practical applications," Wang said.