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

Nanogenerators could serve in medical, defense and consumer electronics' applications

Charles J. Murray, Senior Technical Editor -- Design News, February 23, 2009

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

Zhong Lin Wang, a Regent's professor at the school, says a sheet containing tens of thousands of the nanogenerators could fit beneath a Blackberry's touch screen, enabling the handheld device to draw power from a user who taps a finger against it. The wires could also be used to power sensors that measure blood sugar level or to augment batteries in implantable medical devices, such as defibrillators and pacemakers.

"The whole reason we did this is that batteries run out of power," Wang says. "If you have a small generator, you can integrate it together with the battery and then you don'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 small electronic product.

To be sure, Wang's nanogenerators are tiny. The wires, made from zinc oxide, are between 100 and 800 nm in diameter, and 100 to 500 microns (µm) in length. Put another way, their diameter is about 1/50^th of a human hair; length is about 10 hair-widths.

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

The nanogenerators accomplish that through a piezoelectric effect - a common phenomenon in which a material creates a small amount of current in response to mechanical stress. Wang's nanogenerators are different from other piezoelectric devices, however, in their ability to draw current from virtually any mechanical motion.

"Most piezo materials use a resonant frequency to generate current," Wang says. "Ours is much smaller and we don't need a resonant frequency."

Wang's research team can make the nanogenerators in sheets. They encapsulate the single zinc-oxide wires in a flexible polymer substrate. Wires are anchored at the ends 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 draw current from virtually any mechanical frequency - from a few hertz up to kilohertz - makes it possible for the technology to serve in a variety of medical applications, including blood pressure sensors, blood sugar sensors, and possibly one day in pacemakers and implantable defibrillators. Defense experts are also looking at the technology as a way to power tiny gas sensors for soldiers.

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

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

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

Nanogenerators could serve in medical, defense and consumer electronics' applications

Charles J. Murray, Senior Technical Editor -- Design News, February 23, 2009

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