Where there’s power being produced, there are researchers looking into how it might be harvested and put to use, no matter how small the amount.
Take triboelectric charging – it’s what’s behind the shock you get when you shuffle across a carpeted room and then, say, grab the refrigerator door handle. Friction got you charged up, and your subsequent contact with the metal led to a quick discharge.
Seizing on this phenomenon, Georgia Tech University researchers report success in enhancing and capturing the electric charge produced when two transparent plastic materials rub against one another.
“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.”
What might be the point of this?
Well, the researchers suggest that their triboelectric generator could give a boost to nanogenerators that use the piezoelectric effect (that’s the generation of a charge by applying stress to certain materials) to create current from the flexing of zinc oxide nanowires (as talked about here).
One potential use: Because the 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.
That opens up the possibility that your incessant typing, sliding and tapping on your iPhone won’t take a toll on the device’s battery.
“Transparent generators can be fabricated on virtually any surface,” Wang said. “This technique could be used to create very sensitive transparent sensors that would not require power from a device’s battery.”
The key to the system working is the matching of materials of different types in order to exploit the charge differential. So Wang’s system has a sheet of polyester rubbing against a sheet made of polydimethysiloxane (PDMS); the polyester gives up electrons and the PDMS takes them.
With an electrical load connected between the two surfaces, continually rubbing the surfaces together and then separating them creates the electric current.
Wang said they’ve ratcheted up the current production in the system by putting microscopic pyramid shapes on the rubbing surfaces instead of keeping them smooth.
“The patterning enhanced the generating capacity by boosting the amount of charge formed, improving capacitance change due to the air voids created between the patterns, and by facilitating charge separation,” the university said.
The research was funded by the National Science Foundation, the Department of Energy and the U.S. Air Force, and was reported in the June issue of the journal Nano Letters.