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Nanotech Clothing Produces Power From Motion

Joab Jackson
for National Geographic News
February 13, 2008
 
Nanotech fabric that can harvest energy from motion could one day lead to clothing that can power portable electronics, researchers say.

Zhong Lin Wang and colleagues at Georgia Institute of Technology designed the new fabric based on a phenomenon called the piezoelectric effect.

This effect occurs when mechanical pressure is applied to certain materials that have crystalline structures in such a way that it produces a small electric charge.

Wang's team lined textile fibers with piezoelectric nanowires arranged like the bristles on a bottlebrush. When a person walks around wearing the material, the wires rub together and generate electricity.

"Bending the wires creates a piezoelectric field potential," Wang said. (Related news: "Knee-Brace Generator Offers Portable 'Power Plant'" [February 7, 2008].)

The researchers estimated that their material could eventually generate up to 80 milliwatts of power for each square meter (about 11 square feet) of fabric.

An average digital music player or cell phone, by contrast, uses a few hundred milliwatts or more.

So while your future sweat suit may not charge up your iPod, it could power tiny sensors that keep track of your vital signs as you run.

And the use is not limited to clothing, Wang added. The technique can be applied to any surface that picks up vibration, such as engines, tires, or even swaths of cloth catching the wind.

Growing Wires

For their research, which is described in tomorrow's issue of the journal Nature, the Georgia Tech team first grew nano-size wires of zinc oxide around Kevlar fibers.

The wires were 50 nanometers thick, or about a thousand times thinner than a single human hair.

"You can grow this wire on any substrate, even on your hair," Wang said. The wires would make your hair look gray, he added, but it would feel largely the same.

The enhanced Kevlar was then woven to create fabric. As the material stretched, the wires bent, creating electric potential.

Electrodes at the bases of the fibers collected the charge.

Min-Feng Yu is a nanoelectronics expert at the University of Illinois, Urbana-Champaign.

While Wang's team is not the first to harness the piezoelectric effect, they have found a way to produce such material in large quantities, Yu noted.

Last year, Yu demonstrated how a single nanowire could harvest mechanical energy by a similar means.

But the new research shows that millions of such wires could be easily produced.

"Dr. Wang's team has a simple and low-cost process," Yu said. "It opens a new frontier."

Powering the Small

For decades nanotech researchers have speculated about potential applications for tiny electronics.

(Read "Nanotechnology's Big Future" in National Geographic magazine [June 2006].)

Nano-size sensors placed in the bloodstream could better detect early onset of diseases, for example.

Such devices could also be woven into soldiers' uniforms to monitor their health during combat.

Other work has focused on a fleet of tiny sensors that could be spread across a geographic area to monitor environmental health.

"One thing [nano-sensors have] in common is that each of these things needs power," Wang said, explaining why he chose nano-scale power generation as an area of study.

Conventional batteries are still too large, but piezoelectric generation would be perfect for these applications, Wang and others have reasoned.

"Any nano-device will consume very little power. Why don't we take an advantage of that?" Wang said.

David Nagel, a research professor at George Washington University, noted that if the team's nanowires work as predicted, then they could indeed power tiny systems, given enough material.

The fabric could even be useful for larger devices if the power is stored up and the devices are used sparingly.

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