Zhong Lin Wang, a professor of materials science at Georgia Tech, has been working on the problem for several years, mostly focusing on piezoelectric materials that generate an electrical voltage under mechanical stress, but this didn't yield enough power to be really useful.
Now Wang's group has demonstrated that using the triboelectric effect that creates static electricity from friction, power could be harnessed from a type of plastic, polyethylene terephthalate, and a metal. When thin films of these materials come into contact with one another, they become charged. And when the two films are flexed, a current flows between them, which can be harnessed to charge a battery. When the two surfaces are patterned with nanoscale structures, their surface area is much greater, and so is the friction between the materials and the power they can produce.
So far, the Georgia Tech nanogenerator can convert 10 to 15 percent of the energy in mechanical motions into electricity, and thinner materials should be able to convert as much as 40 percent, Wang says.
A fingernail-sized square of the triboelectric nanomaterial can produce 8mW when flexed, enough power to run a pacemaker. A patch that's five by five centimeters can light up 600 LEDs at once, or charge a lithium-ion battery that can then power a commercial cell phone. "The choice of materials is wide, and fabricating the device is easy," says Wang. Any of about 50 common plastics, metals, and other materials can be paired to make this type of device.
Now, the new nanogenerator must be proven to generate power from mechanical vibrations in real life. Wang says he is in talks with companies about developing the energy scavenger for particular applications, and envisions it being worn on an armband.
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