U.S. scientists have developed a microfiber fabric that generates its own electricity, making enough current to recharge a cell phone 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 recently in the journal Nature.
"The fiber-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 fibers 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 in a telephone interview. "What the fabric does is it translates the mechanical movement of your body into electricity."
His team made the nanogenerator by first coating fibers 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 fibers.
"They automatically grow on the surface of the fiber," Wang said. "In principal, you could use any fiber 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 fibers, which works as a conductor.
To ensure all that friction was not just generating static electricity, the researchers conducted several tests. The fibers 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 meter of this fabric. This is enough to power a little iPod or charge a cell phone 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 fibers to protect the fabric in the laundry.