Researchers have conjured up a trickle of electricity by zapping tiny nanowires with ultrasound. If they can grow that trickle into a stream, the technology might turn everyday vibrations into power for miniature sensors that could be sprinkled in the environment or implanted in the body.
Everyone knows that nanotechnology means really small stuff, such as sensors that could be placed inside the body to monitor blood sugar or on the battlefield to sniff out poison gas. But as sophisticated as these devices are, they are still burdened because they rely on an outside power. "The size of the entire device is determined by the size of the power source," says nanotechnologist Zhong Lin Wang of the Georgia Institute of Technology. On top of that, he says, batteries require toxic chemicals and have to be replaced periodically.
Looking to make a nanotech power source, Wang started from the fact that nanothin wires of zinc oxide are piezoelectric, meaning they develop a charge when bent. He and his team grew a forest of these wires on a semiconductor substrate and placed a corrugated silicon electrode closely above them [see image].
Ultrasound passing through the device rattles the electrode back and forth, Wang says, which in turn bends the wires to and fro like bristles on a toothbrush. The resulting charges transfer to a metal layer coating the electrode—and, voilà, a 500-nanowire array produces a nanoampere of current, the team reports in this week's Science.
Wang says that to actually power a simple electronic device such as a diode or a transistor, he has to raise the charge on the device from its current millivolt to at least half a volt. He says he plans to make the nanowires more uniform and stack multiple arrays as well as add capacitors, which accumulate charge.