Atlanta (GA) - Zhong Lin Wang and a team of researchers from Georgia Institute of Technology (GIT) have developed a super-tiny zinc-oxide alternator that generates power through vibrations. Wang believes that someday an energy source of this kind may provide power for nano-devices operating inside the human body - those powered by internal vibrations coming from blood flow. Such a device may also be worn as clothing, generating power through regular daily activity.





Zinc-oxide alternator



One significant problem in using zinc-oxide inside or outside the human body is that the material is somewhat water soluble and breaks down. This is especially true in an acidic or basic environment. This undesirable trait makes it somewhat difficult to manufacture, store and conduct tests with. It also makes it very impractical for general use as the materials wear out over time with regular atmospheric exposure. Wang has figured out a way to get by that, however. He manufactures the alternator and then immediately encases it in a plastic coating, like a form of anodizing. This seals it from the environment and away from any water vapor and body fluids.








Power generation



The device generates alternating current through something resembling a slinky. A coiled wire of 3-5 microns in diameter and 200-300 microns long (relatively large in size compared to previous versions of the power source) expands and contracts through environmental vibrations or artificial sources (as was used for testing). This results in an alternating current charge generated, which is as high as +/- 45 millivolts (though with very low amperage). All of this is derived through a well-known property of zinc-oxide. In fact, zinc-oxide is being eyed by many scientists because because of its interesting and wide properties in the areas of optical, magnetic, electric and semiconductor applications.



This is Wang's 4th generation zinc-oxide alternator. Each revision has been refined as a converter of mechanical energy into electrical, and he calls this model the "flexible charge pump." Previous generations were notably smaller though. Wang chose the larger size for this model to make it easier to manufacture through a 600 degree Celsius deposition process. Wang says there's no reason the device and manufacturing methodology couldn't scale down to the true nano-sizes of molecules, though for his research it wasn't practical. He wanted to prove it worked first, was easily replicated, and then if needed reduce its size.

According to Wang, his new creation "adds to the family of very small-scale generators able to power devices used in medical sensing, environmental monitoring, defense technology and personal electronics." And all of the members of his family are potentially powered by vibratory sources.





Low efficiency, but more than enough



The flexible charge pump operates at only 7% efficiency, making it fall relatively low on the efficiency spectrum. Car alternators, for example, achieve 50% or greater efficiency - and some claim 70% or higher. Still, considering the fact that Wang's design generates low quantities of power from available vibratory sources, it's very likely efficiency will go up with continued research. While 7% is enough when several devices are connected in series, future applications with 30% (or greater) would greatly reduce cost and size, making them more desirable solutions for applications.


Thank you, doctor



This very small device may turn out to be exactly what the doctor ordered for drug dispensers and other future battery-free applications inside the body. If affixed to a major blood vessel, for example, the hair-sized alternator could vibrate solely by the power of the heart as it pushes blood cells right by on the other side of the vessel wall.

In addition, if thousands of strands were sewn into clothing, a type of constantly-generating power source would be available to run PDAs, cell phones, or other devices - especially if there was a mild breeze making every "tiny slinky" active and vibrating like lawn spinners.

Such a device would really be like implementing wind power on an extremely small scale. And by most any standard that is very cool.





Additional information



Funding for this project is from the U.S. Department of Energy, National Science Foundation, the Air Force Office of Scientific Research and the Emory-Georgia Tech Center for Cancer Nanotechnology Excellence.



Read more at Georgia Tech's research news site, or in the November 9, 2008 issue of the Nature Technology journal.