'Smart Cloth' Could Power Mobile Devices'Smart Cloth' Could Power Mobile Devices

Engineers at the University of California, Berkeley, have developed power-generating nanofibers that could one day be woven into clothing and used to power hand-held electronics.

The fibers, made of organic polyvinylidene fluoride, or PVDF, have properties that allow them to convert the energy created from mechanical stress, such as the stretches and twists of a human body in motion, into electricity. The material is flexible and relatively easy and cheap to manufacture.

"This technology could eventually lead to wearable smart clothes that can power hand-held electronics through ordinary body movements," Liwei Lin, professor of mechanical enginering at U.C. Berkeley and head of the research team that developed the fiber, said in a statement.

Researchers are currently testing whether more vigorous movements, such as dancing, would generate more power. Because the fiber nanogenerators are so small, engineers believe they can be weaved into clothing with no perceptible change in comfort for the user, Lin said.

Trying to harvest energy from wearable nanofibers that act as microscopic generators is not new. Other research teams have used inorganic semiconductor materials, such as zinc oxide or barium titanate, but these materials have proven to be more brittle and harder to grow in significant quantities than the organic material used by the U.C. Berkeley team.

The tiny nanogenerators developed at Berkeley are 100 time thinner than a human hair and one tenth the width of common cloth fibers. By tugging and tweaking the nanofibers, researchers were able to generate from five to 30 millivolts and 0.5 to 3 nanoamps.

In addition to developing the electric-generating fiber, Lin's team also pioneered the technique used to place the material on a surface, so positive and negative poles are on opposite ends, similar to the poles on a battery. Without this control, the negative and positive poles might cancel each other out and reduce energy efficiency.

Lin's team was able to demonstrate energy conversion efficiencies as high as 21.8%, with an average of 12.5%. Those numbers are much higher than other nanofibers made with PVDR and from zinc oxide fine wires.

"We think the efficiency likely could be raised further," Lin said. "For our preliminary results, we see a trend that the smaller the fiber we have, the better the energy efficiency. We don't know what the limit is."

The fiber nanogenerators are described in this month's issue of Nano Letters, a peer-reviewed journal published by the American Chemical Society.