November 18, 2008 A micron-scale generator that uses zinc oxide wires to produce alternating current could be woven into clothing to power wireless devices or implanted in the body to monitor vital signs. A team led by Zhong Lin Wang at the Georgia Institute of Technology’s Center for Nanostructure Characterization has developed the generator, which can produce an oscillating output voltage of up to 45 millivolts.
Zinc oxide generates electric potential when put under mechanical stress, in a phenomenon known as the piezoelectric effect. By using movement in the environment to stretch and release zinc oxide wires, the miniature generators can operate self-sufficiently, and transfer 7% of the mechanical force into electricity. The “flexible charge pump” generator is the fourth generation of zinc oxide generator designed by the team, and the first one to exceed the nano scale. However, Wang claims that the design can be scaled down if necessary.
In addition to being smaller, and therefore more difficult to produce, the previous generations of zinc oxide generators depended on contact between the nanowires and an electrode, or required scrubbing of the fibers. The generators also suffered from limited lifespans, which undermined the advantage of their self-sufficiency. The flexible charge pumps are larger and more robust – the wires have diameters of three to five microns and lengths of 200 to 300 microns. The generator is also encased in polyimide to protect it from the environment.
Miniature generators like the flexible charge pump could be the enabling technology for some long-promised emerging tech like smart fabrics. It could also inspire developments in completely new fields. “Self-powered nanotechnology could be the basis for a new industry,” said Wang. “That’s really the only way to build independent systems.”
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