People-powered nanogenerator

researchers have developed a new technique for powering nanoscale devices by converting muscle movements or water flow into electricity.

The nanogenerators produce current by bending and then releasing zinc oxide nanowires, which are both piezoelectric (they generate electricity by applying force to crystals) and semiconducting. The National Science Foundation (NSF), the NASA Vehicle Systems Program and the Defense Advanced Research Projects Agency (DARPA) sponsored the research

“There is a lot of mechanical energy available in our environment,” said Zhong Lin Wang, a Regents Professor in the School of Materials Science and Engineering at the Georgia Institute of Technology. “Our nanogenerators can convert this mechanical energy to electrical energy. This could potentially open up a lot of possibilities for the future of nanotechnology.”

The nanogenerators developed by Wang and graduate student Jinhui Song use the very small piezoelectric discharges created when zinc oxide nanowires are bent and then released. By building interconnected arrays containing millions of such wires, Wang believes he can produce enough current to power nanoscale devices.

To study the effect, the researchers grew arrays of zinc oxide nanowires, and then used an atomic-force microscope tip to deflect individual wires. As a wire was contacted and deflected by the tip, stretching on one side of the structure and compression on the other side created a charge separation due to the piezoelectric effect.

The nanowires are made from gold and zinc oxide, meaning they are non-toxic and could be used inside the body. But they could also be used wherever mechanical energy, such as hydraulic motion of seawater, wind or the motion of a foot inside a shoe, is available.

“You could envision having these nanogenerators in your shoes to produce electricity as you walk,” Wang said. “This could be beneficial to soldiers in the field, who now depend on batteries to power their electrical equipment. As long as the soldiers were moving, they could generate electricity.”

Placing the nanowire arrays into fields of acoustic or ultrasonic energy could also produce current. Though they are ceramic materials, the nanowires can bend as much as 50 degrees without breaking.

The next step in the research will be to maximize the power produced by an array of the new nanogenerators. Wang estimates that they can convert as much as 30 per cent of the input mechanical energy into electrical energy for a single cycle of vibration. That could allow a nanowire array just 10 microns square to power a single nanoscale device, if all the power generated by the nanowire array can be successfully collected.

“Our bodies are good at converting chemical energy from glucose into the mechanical energy of our muscles,” Wang said. “These nanogenerators can take that mechanical energy and convert it to electrical energy for powering devices inside the body. This could open up tremendous possibilities for self-powered implantable medical devices.”