Make your own electricity...
2008-02-14 14:50
Chicago - US scientists have
developed a microfibre fabric that generates its own
electricity, making enough current to recharge a cellphone or
ensure that a small MP3 music player never runs out of power.
If made into a shirt, the fabric could harness power from
its wearer simply walking around or even from a slight breeze,
they reported on Wednesday in the journal Nature.
"The fibre-based nanogenerator would be a simple and
economical way to harvest energy from the physical movement,"
Zhong Lin Wang of the Georgia Institute of Technology, who led
the study, said in a statement.
The nanogenerator takes advantage of the semiconductive
properties of zinc oxide nanowires - tiny wires 1 000 times
smaller than the width of a human hair - embedded into the
fabric.
The wires are formed into pairs of microscopic
brush-like structures, shaped like a baby-bottle brush.
One of the fibres in each pair is coated with gold and
serves as an electrode. As the bristles brush together through
a person's body movement, the wires convert the mechanical
motion into electricity.
"When a nanowire bends it has an electric effect," Wang
said. "What the fabric does is it
translates the mechanical movement of your body into
electricity."
His team made the nanogenerator by first coating fibres
with a polymer, and then a layer of zinc oxide. They dunked
this into a warm bath of reactive solution for 12 hours. This
encouraged the wires to multiply, coating the fibres.
"They automatically grow on the surface of the fibre," Wang
said. "In principal, you could use any fibre that is
conductive."
They added another layer of polymer to prevent the zinc
oxide from being scrubbed off. And they added an ultra-thin
layer of gold to some fibres, which works as a conductor.
To ensure all that friction was not just generating static
electricity, the researchers conducted several tests. The
fibres produced current only when both the gold and the zinc
oxide bristles brushed together.
So far, Wang said the researchers had demonstrated the
principle and developed a small prototype.
"Our estimates show we can have up to 80 milliwatts per
square metre of this fabric. This is enough to power a little
iPod or charge a cellphone battery," he said.
"What we've done is demonstrate the principle and the
fundamental mechanism."
Wang said the material could be used by hikers and soldiers
in the field and also to power tiny sensors used in biomedicine
or environmental monitoring.
One major hurdle remains: zinc oxide degrades when wet.
Wang's team is working on a process that would coat the fibres
to protect the fabric in the laundry.