From Hamsters to Vocal Chords: Material Draws Energy from Any Mechanical Motion

A materials' science professor at Georgia Institute of Technology has createdsingle-wire "nanogenerators" that could provide autonomous power forapplications ranging from PDAs to gas sensors to blood pressure monitors.

Zhong LinWang, a Regent's professor at the school, says a sheet containing tens ofthousands of the nanogenerators could fit beneath a Blackberry's touch screen,enabling the handheld device to draw power from a user who taps a fingeragainst it. The wires could also be used to power sensors that measure bloodsugar level or to augment batteries in implantable medical devices, such asdefibrillators and pacemakers.

"The wholereason we did this is that batteries run out of power," Wang says. "If you havea small generator, you can integrate it together with the battery and then youdon't need to replace the battery as often."

Indeed,Wang believes some applications could be run exclusively by his nanogenerators,although it could take thousands or even millions of the wires to run a smallelectronic product.

To be sure,Wang's nanogenerators are tiny. The wires, made from zinc oxide, are between100 and 800 nm in diameter, and 100 to 500 microns (µm) in length. Put anotherway, their diameter is about 1/50^th of a human hair; length is about10 hair-widths.

Moreover, the amount of electricalcurrent they produce is equally miniscule. When Wang and associates at GeorgiaTech recently fitted a hamster with a four-nanogenerator jacket, the hamster-powereddevice generated 0.5 nanoamps (nA) of current.

The nanogenerators accomplish thatthrough a piezoelectric effect - a common phenomenon in which a material createsa small amount of current in response to mechanical stress. Wang'snanogenerators are different from other piezoelectric devices, however, intheir ability to draw current from virtually any mechanical motion.

"Most piezomaterials use a resonant frequency to generate current," Wang says. "Ours ismuch smaller and we don't need a resonant frequency."

Wang's researchteam can make the nanogenerators in sheets. They encapsulate the singlezinc-oxide wires in a flexible polymer substrate. Wires are anchored at theends with an electrical contact and a Shottky Barrier to control current flow.A "sheet" with about 10,000 nanogenerators measures about 4 cm long, he says.

Wang says the ability to drawcurrent from virtually any mechanical frequency - from a few hertz up tokilohertz - makes it possible for the technology to serve in a variety ofmedical applications, including blood pressure sensors, blood sugar sensors,and possibly one day in pacemakers and implantable defibrillators. Defenseexperts are also looking at the technology as a way to power tiny gas sensorsfor soldiers.

Georgia Tech's study has shown thedevices can be driven by a variety of irregular mechanical motions, includingthe vibration of vocal chords, flapping of flags in a breeze, tapping offingers, or hamsters exercising on a wheel.

"All we need is mechanical bending - back and forth - any kind ofmechanical disturbance," he says. "It's a key difference, and it truly expandsthe range of applications for this technology."