Touchscreens could generate their own power, thanks to the discovery of a new method of energy harvesting.
US scientists have discovered that it's possible to capture the electrical charge produced when two different kinds of plastic materials rub against one another.
Based on flexible polymer materials, this 'triboelectric' generator could also provide alternating current from activities such as walking. And because they can be made nearly transparent, they could offer a new way to produce active sensors for touch-sensitive device displays.
"The fact that an electric charge can be produced through this principle is well known," says Zhong Lin Wang of 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."
The triboelectric generator is based on a sheet of polyester rubbing against a sheet made of polydimethysiloxane (PDMS). The polyester tends to donate electrons, while the PDMS accepts them. Immediately after the polymer surfaces rub together, they are separated, creating an air gap that isolates the charge on the PDMS surface and forms a dipole moment.
If an electrical load is then connected between the two surfaces, a small current will flow to equalize the charge potential. By continuously rubbing the surfaces together and then quickly separating them, the generator can provide a small alternating current.
The technique could be used, says the team, to create a very sensitive self-powered active pressure sensor - even the touch of a feather could be enough to produce a small current.
And because the devices can be made 75 percent transparent, they could potentially be used in touch screens to replace existing sensors.
"Transparent generators can be fabricated on virtually any surface," says Wang. "This technique could be used to create very sensitive transparent sensors that would not require power from a device's battery."
The production process, says Wang, is simple and low cost, meaning it could be scaled up for large scale production and practical applications.
And the generators are pretty robust, continuing to produce current even after days of use and more than 100,000 cycles of operation.
The next step for the team will be to create systems that include energy storage.
"Friction is everywhere, so this principle could be used in a lot of applications," says Wang.
"We are combining our earlier nanogenerator and this new triboelectric generator for complementary purposes. The triboelectric generator won't replace the zinc oxide nanogenerator, but it has its own unique advantages that will allow us to use them in parallel."