Yahoo News 13 Feb 08;
US researchers have created a nano-fiber textile that harvests energy from movement, paving the way for clothing that could one day power an iPod or other wearable electronic devices, according to a study published Wednesday.
Using the same mechanical principle as a self-winding watch, but on scale measured in billionths of a meter, tiny nano-generators can scavenge "wasted" energy from sound waves, vibrations, or even the human heart beat.
The fibers, developed by a team of scientists at the Georgia Institute of Technology led by Zhong Lin Wang, are covered with pairs of zinc oxide nanowires that produce tiny pulses of electricity in response to friction.
"The two fibers scrub together just like two bottle brushes with their bristles touching," converting the mechanical motion into electrical energy, explained Wang.
"Many of the devices could be put together to produce a higher output," he said.
This method of generation energy from friction is called the "piezoelectric effect."
The fibers could also be woven into curtains, tents or other structures to capture energy from wind motion, sound vibrations or other mechanical energy, according to the study, published in the British journal Nature.
The human body contains many sources of energy that could drive nanogenerators, including blood flow pumped by the heart, exhalation from the lungs, and walking.
Even the act of typing on a computer is a potential source of nano-scale energy.
So far, Wang and his colleagues have made more than 200 of the microscopic nano-generators. The fibers assemblies were each tested for 30 minutes to check durability and power production.
Other kinds of nano-generators driven by scavenged energy aim to power biosensors to monitor a patient's glucose levels, strain sensors for bridges, and environmental sensors to detect toxins.
There remains at least one significant problem before Wang's nano-fibers can become part of our daily wardrobes.
Zinc oxide is sensitive to water, which means that clothes made from these fibers could never be washed, the study said.
Microfiber fabric makes own electricity: study
Julie Steenhuysen, Yahoo News 13 Feb 08;
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 on Wednesday 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.
(Editing by Maggie Fox and Alan Elsner)
