|
Monday, October 15, 2007 Invisibility Made EasierA new method for creating metamaterials that bend light in unusual ways may bring practical applications closer. By Kevin Bullis
In the past year, the media have been abuzz with talk of an exotic class of materials, called metamaterials, that could be used to make flat and distortion-free lenses, powerful microscopes, and even cloaking devices that make objects invisible. But versions of the materials suitable for practical applications have been difficult to make. Now researchers at Princeton University have demonstrated metamaterials that are both higher performing and much easier to manufacture, perhaps bringing these applications closer to reality. "It's quite an important step," says Igor Smolyaninov, a research scientist at the University of Maryland who works with metamaterials. "It's much less expensive than anything else that people are doing." Light passing from one ordinary material into another bends slightly--think of how a straight stick in water looks bent--but light passing into a metamaterial bends in the opposite direction. Metamaterials thus have what's called a negative index of refraction. A lens made from such a material wouldn't have to be curved. (It's the curvature of an ordinary lens that enables it to focus incoming light.) Metamaterials could also be used to route electromagnetic waves around an object, rendering it invisible. Already, researchers have demonstrated a cloaking device that makes objects invisible to microwaves, and others have created materials that negatively refract electromagnetic waves in the visible part of the electromagnetic spectrum. But until now, metamaterials have had to be patterned with intricate shapes smaller than the wavelength of light they're meant to manipulate. Consequently, materials that work with light of microscopic wavelengths, such as infrared and visible light, have been difficult to make. Because of the way they produce negative refraction, existing metamaterials have also had a strong tendency to absorb light, making them impractical for use in optics. The materials developed at Princeton retain the property of negative refraction, yet they're much easier to make. Rather than requiring intricate structures, such as the split rings used in the microwave cloaking device, the materials can be made simply by stacking up extremely thin layers of semiconductor material. What's more, that stacking can be done by the same tools now used to make semiconductor materials for lasers used in telecommunications, says Claire Gmachl, the Princeton researcher who led the work. The new materials consist of alternating layers of indium gallium arsenide and aluminum indium arsenide, and they're tuned to work in the infrared region of the spectrum. Like other metamaterials, the new materials affect light differently than ordinary materials do because they are made of structures significantly smaller than the wavelength of the light passing through them. In this case, however, it is the layers of semiconductors themselves that are thinner than the wavelength of light. Consequently, a wave passing through the material encounters multiple layers at once, responding to them as if they were a single material with properties quite unlike those of either semiconductor in isolation. |
Audio »
Share »
Digg this
Add to del.icio.us
Add to Reddit
Add to Facebook
Slashdot It!
Stumble It!
Add to Newsvine
Add to Connotea
Add to CiteUlike
Add to Furl
Googlize this
Add to Rojo
Add to MyWeb
Favorite
Print
E-mail
Acoustic Cloak Designed
06/17/2008
Comments
kitk on 10/15/2007 at 1:52 AM
52
GeckoOBac on 10/15/2007 at 7:21 AM
2
But just think about the flat lenses... With metamaterials you can achieve a greater concentration of light than with conventional lenses, thus improving laser technology, astronomic telescopes and any application that needs focused EM waves (maybe even very focused long range radio communications? Or even long distance transfer of power through EM waves? Ok maybe this is a bit to far :P).
You could improve conventional microscopes (if they manage to make metamaterials able to concentrate a large range of very short wavelenght radiations), which would probably remain cheaper than electronic microscopes and more used all around.
About "cloaking" technology, I find a hard time trying to think of something that isn't strictly militarily related, but I guess it could have its uses too.
cjwoodcock on 10/15/2007 at 9:05 AM
1
dmm on 10/15/2007 at 1:07 PM
136
2. Allow police to hide at the side of the road.
3. Fashion. For example, dresses that make fat women look skinny.
4. High-rises in residential areas wouldn't have to be eye-sores.
5. Cloaking clothes for hunters and wildlife photographers (but unfortunately also for criminals and paparrazzi).
6. Cloaked utility poles, cell phone towers, windmills, etc. (only visible up close) would reduce "sight pollution."
7. One word: Toys.
dmm on 10/15/2007 at 1:12 PM
136
2. Wavelength-specific, not broadband.
3. Still rather absorptive.
Nevertheless, cool.
evolvingwheel on 10/16/2007 at 12:57 AM
5
cretin001 on 10/18/2007 at 8:48 PM
35
dmm on 10/22/2007 at 5:36 PM
136
Lots of science has a long lead time before it sees practical applications. For example, Fleming first observed the antibacterial action of Penicillium mold in 1928, but penicillin was not ready for use until 1945. That's a 17-year delay, for something that in retrospect should have been a no-brainer for fast-track development.
Another example is electricity. Faraday demonstrated electromagnetic induction in 1831, but electricity was not put to "practical" use in society until Edison invented the lightbulb and started his electric company. That wasn't until the end of 1880 -- 50 years later. And of course, Faraday's discoveries didn't come out of nowhere. He was building on research into electricity and magnetism that went back at least to Franklin a century before him. So you could make the case that electricity had a 150-year development time, from initial scientific research to first practical application.
A more modern example: general relativity was proposed by Einstein in 1915. It did not see practical use until the GPS system was completed, in 1995. That's an 80-year gap. Another modern example: the structure of DNA was figured out in 1953. The first practical use, DNA testing for genetic defects (or forensics), was not available to the public until about 1983, 30 years later.
In summary, it is unrealistic to expect exciting discoveries to result immediately in consumer applications. There is generally a delay of anywhere from 20 to 100 years. Scientists work for our grandchildren.