These nanogenerators could help power nanoscale devices without the need for unwieldy batteries, finding use in everything from portable electronics and wireless nanosensors to medical implants, said researcher Zhong Lin Wang, a nanotechnologist at the Georgia Institute of Technology in Atlanta.

"There is a lot of mechanical energy available in our environment," Wang said. The generators could, for instance, harvest energy from body motions, muscle stretching and blood pressure or from sea, wind or acoustic waves or air flowing through a pipe.

"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."

Implanted biomedical devices and wireless devices should ideally be capable of powering themselves without relying on batteries, Wang said. Moreover, the power sources for nanotechnology should ideally be the size of the devices they are energizing, he added.

The nanogenerators Wang and graduate student Jinhui Song created rely on the infinitesimal electrical discharges released when zinc oxide wires 20 to 40 nanometers wide and 200 to 500 nanometers long are bent and then released. The nanowires are piezoelectric, which means they can convert mechanical energy to electrical energy or vice versa. Although they are ceramic, each nanowire can bend as much as 50 degrees without breaking.

Zinc oxide is non-toxic, making these generators potentially appealing for use in the body. Wang said researchers could not only grow the nanowires on crystal surfaces, but also on metal foils, ceramic foundations or flexible plastic films as well.

Wang next hopes to maximize the power each array produces. He estimates they can convert as much as 30 percent of the input mechanical energy into electrical energy. This could allow a nanowire array 10 microns square to power a single nanoscale device, providing all the power the nanowire array generated can successfully get collected.

"This work is landmark progress in making nanomaterials, discovering novel properties, and utilizing these materials and properties in ways scientists have not even envisioned," said Jun Liu, a staff scientist at Pacific Northwest National Laboratory in Richland, Wash.

"The results described in this paper are extremely exciting since they address a critical issue in nanotechnology -- how to power the nanodevices that many groups have been working on," said Charles Lieber, a chemist at Harvard University in Cambridge, Mass. "Of particular interest to my own research would be the coupling of this advance to our work on making ultrasensitive but low power consuming chem-Bio sensors. For example, one could imagine linking the nanowires arrays to a human body such that normal movements generate the power needed to run either implanted or external nanosensors needed for monitoring medical conditions or threats."

Devices could reach the market in five years or more, Wang said. He and Song reported their findings in the April 14 issue of the journal Science.

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