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 1/50th 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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