'Power shirt' generates watts as you walk
A microfibre fabric that generates enough of its own electricity to recharge a mobile phone or ensure that an mp3 player never runs out of power has been developed by US scientists.
If made into a shirt, the fabric could harness power from its wearer simply walking around or even from a slight breeze, they report today in the journal Nature.
"The fibre-based nanogenerator would be a simple and economical way to harvest energy from the physical movement," says Professor Zhong Lin Wang of the Georgia Institute of Technology, who led the study.
The nanogenerator takes advantage of the semiconductive properties of zinc oxide nanowires, tiny wires 1000 times smaller than the width of a human hair, embedded in 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 says. "What the fabric does is it translates the mechanical movement of your body into electricity."
Coating the fibres
His team made the nanogenerator by first coating fibres with a polymer and then a layer of zinc oxide.
They then 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 says. "In principle, you could use any fibre that is conductive."
They then 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.
Could it be static?
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 says the researchers have 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 [mobile] phone battery," he says.
"What we've done is demonstrate the principle and the fundamental mechanism."
Out of the lab
Wang says 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.