Paper microphone may help charge your cellphone

[Nipuna]

Screaming with rage at your dying cell phone battery doesn't help much, but that could be about to change. Researchers have developed a postage stamp-sized microphone that can harvest acoustic energy to top up your charge on the go.

Zhong Wang of the Georgia Institute of Technology in Atlanta and his colleagues created their microphone from a thin sheet of paper just a few centimetres across. They used a laser to zap a grid of microscopic holes in the paper, then coated one side in copper and laid it on top of a thin sheet of Teflon, joining the two sheets at one edge.

Sound waves vibrate the two sheets in different ways, causing them to come in and out of contact. This generates an electric charge, similar to the one made when your rub a balloon on your hair, which can charge a phone slowly.

The paper microphone could also be used as a way to recycle sound energy from the environment, getting free electricity from the "waste" sounds all around us. The charge can also be converted into a range of sound frequencies, allowing the initial sounds to be amplified.

The amount of power the microphone provides depends on its size, but it's around 121 milliwatts per square metre. "It can be made into any size you like," says Wang, though he admits a stamp-sized microphone fitted to your phone would only provide a small amount of power rather than fully charging your phone.

Journal reference: ACS Nano, DOI: 10.1021/acsnano.5b00618