Nanowires generate energy from muscle movement

PORTLAND, Ore. — The demonstration required a hamster to wear a jacket with a built-in nanogenerator, but the running critter showed that almost any movement can be harnessed to generate electricity to power electronic devices.

Researchers at Georgia Tech, which conducted the demonstration, predict nanoscale piezoelectric energy generators could power mobile phones and other handhelds using the energy harvested from the environment. In the near term, researcher Zhong Lin Wang said he wants to power medical nanodevices with muscle movements such as flexing fingers and vibrating vocal cords.

"Millions of our piezoelectric nanowires will be needed to produce enough energy to power a consumer electronic device like a Blackberry," said Wang. "But our demonstration here has proven the principle that any type of muscle movements in humans or animals can be used to generate power."

Most efforts to harvest energy have used sources of cyclic motion, such as a turning wheel. Wang investigated whether the irregular motion of muscles also could be harnessed. If so, then muscle motion could be used to power, for instance, medical implants that dispense drugs or sense conditions like high blood pressure.

To test the theory, Wang built two energy-harvesting devices with embedded piezoelectric nanowires: a finger sleeve that spanned the first joint and a tiny hamster jacket that contained four parallel nanowires that flexed whenever the hamster ran on its treadmill. Both were shown to reliably produce about 50 to 100 millivolts, with an output current of 0.5 nanoamps.

The piezoelectric nanowires were made from zinc oxide, which generate electricity whenever bent. By arranging the wires so that bending caused by human and animal movements generated energy, power was harvested that could someday be channeled into batteries. Each piezoelectric nanowire measured from 100 to 800 nanometers in diameter and 100 to 500 micrometers long.

To generate sufficient voltage and current to run electronics devices, the tiny nanowires would have to be combined to generate enough electricity to power a device like a Blackberry. Since the direction in which they bend determines the direction of the current generated, bending must be synchronized so that currents in different directions do not cancel each other out.

Surmounting these engineering hurdles will take at least five years, according to Wang. The next milestone, which Wang hopes to reach within a year, will be demonstrating fabrication of parallel, aligned nanowires that bend in unison.

"Our current research is to make millions of our nanowires work together in a sheet, and demonstrate that they can all be aligned and synchronized " said Wang.

For the hamster jacket, four nanowires sewn into the fabric were synchronized by embedding them in a substrate that could bend in only one direction. A similar technique will be used for the next demonstration, which will encapsulate millions of parallel nanowires in a flexible polymer.