Fact Sheet

The phone you can charge with your voice

Scientists have come up with a way to harness the energy in sound waves to power electronic gadgets

Normally, chatting aimlessly is a surefire way to wind up with a dead cellphone battery. But researchers at South Korea's Sungkyunkwan University have discovered a technique that could use the sound of your voice to charge your phone. Here, a brief guide:

Can you really power a cellphone by talking into it?In theory, yes. Although for now you really have to shout to give your battery much of a boost. A prototype needed 100 decibels — the equivalent of noisy traffic or a jet passing overhead — to generate 50 millivolts of electricity. That's enough to give a smartphone battery a lift, but far from the 5 to 12 volts needed to properly charge the typical mobile device. So don't expect to find voice-charged phones in stores any time soon. But the lead researcher, Sang-Woo Kim of Sungkyunkwan University's nanotechnology institute, is confident that tinkering with the design will make this technology more practical.

How does it work?The scientists trapped nano-scale strands of zinc oxide between two flexible electrodes. Incoming sound waves hit a sound-absorbing pad on top of the device, causing the tiny zinc wires to compress and release. The movement generates a tiny electrical current. And your voice isn't the only sound the nanogenerator can convert into power. Music or any background noise, such as the sound of traffic, will also work.

Would this only work with phones?No, there are plenty of other possible applications. The same technology, once perfected, also could be used to recharge electric cars by tapping into the energy in traffic noise. Sound-insulating walls along highways also could trap and store the sound of passing vehicles, both reducing noise levels and capturing wasted energy.

Is sound the only untapped source of electricity out there?Hardly. As the hunt for alternative energy intensifies, "energy scavenging" is becoming a hot pursuit. In two of Tokyo's busiest subway stations, scientists are using power-absorbing floor tiles that store energy generated every time a passenger steps on them. Researchers have also figured out how to use the human heartbeat to charge MP3 players. "Our nanogenerators are poised to change lives in the future," says Zhong Lin Wang of Georgia Institute of Technology, whose team harnessed the energy of the human heart using nanowires so small that 500 could fit in a human hair. "Their potential is only limited by one's imagination."

Sources: Telegraph (2), Yahoo! News, PCWorld, Fast Company, Daily Mail

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