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Posted: February 13, 2008

Nanotechnology shirt may someday power your iPod

(Nanowerk News) Nanotechnology researchers at the Georgia Institute of Technology are developing a shirt that harvests energy from the wearer's physical motion and converts it into electricity for powering small electronic devices worn by soldiers in the field, hikers and other users.
Harvesting energy from such mundane disturbances as heartbeats, footsteps and light winds is an enticing prospect. This week, Nature reports a step towards fashioning energy-scavenging fabrics, with nanoscale technology that converts low-frequency vibrations into electricity - a stitch towards fashioning mechanical energy-scavenging fabrics.
Zhong Lin Wang and colleagues grow zinc oxide nanowires around textile fibres and entwined the fibres into yarns. Electricity was generated when the piezoelectric nanowires around different fibres entangled with each other and were deflected as a result of low frequency mechanical oscillations. They show that the system acts as a flexible power source, which in principle could be scaled up into fabrics for power tents, curtains or clothes.
a 'bottle-brush' structure shows nanowires arranged around a fiber
A schematic illustration of a "bottle-brush" structure shows nanowires arranged around a fiber. Microfibers coated with gold (yellow) scrub uncoated microfibers to produce electricity via a coupled piezoelectric-semiconducting process. (Image: Dr. Wang, Georgia Institute of Technology)
The authors estimate their nanogenerator output at up to 80 milliwatts per square metre of fabric - enough for personal electronics and some small-scale defence applications, they suggest.
The research, funded by the National Science Foundation (NSF) and described in the Feb. 14 issue of Nature ("Microfibre–nanowire hybrid structure for energy scavenging"), details how pairs of textile fibers covered with zinc oxide nanowires generate electricity in response to applied mechanical stress. Known as "the piezoelectric effect," the resulting current flow from many fiber pairs woven into a shirt or jacket could allow the wearer's body movement to power a range of portable electronic devices. The fibers could also be woven into curtains, tents or other structures to capture energy from wind motion, sound vibration or other mechanical energy.
"The two fibers scrub together just like two bottle brushes with their bristles touching, and the piezoelectric-semiconductor process converts the mechanical motion into electrical energy," says Zhong Lin Wang, a Regents professor in the School of Materials Science and Engineering at the Georgia Institute of Technology. "Many of these devices could be put together to produce higher power output."
Wang and collaborators Xudong Wang and Yong Qin have made more than 200 of the fiber nanogenerators. Each is tested on an apparatus that uses a spring and wheel to move one fiber against the other. The fibers are rubbed together for up to 30 minutes to test their durability and power production.
The researchers have measured current of about four nanoamperes and output voltage of about four millivolts from a nanogenerator that included two fibers that were each one centimeter long. With a much improved design, Wang estimates that a square meter of fabric made from the special fibers could theoretically generate as much as 80 milliwatts of power.
So far, there is only one wrinkle in the fabric, so to speak - washing it. Zinc oxide is sensitive to moisture, so in real shirts or jackets, the nanowires would have to be protected from the effects of the washing machine.
The research was funded by NSF's Division of Materials Research. "This multi-disciplinary research grant enables materials scientists and engineers from varied backgrounds to work together towards translating basic and applied research into viable technologies," said NSF Program Manager Harsh Deep Chopra.
The research was also sponsored by the U.S. Department of Energy and the Emory-Georgia Tech Nanotechnology Center for Personalized and Predictive Oncology.
Source: National Science Foundation; Nature
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