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Scientists Make Item Invisible to Microwaves 219

Vicissidude writes "A team of American and British researchers has made a cloak of invisibility. In their experiment the scientists used microwaves to try and detect a copper cylinder. Like light and radar waves, microwaves bounce off objects making them visible and creating a shadow, though it has to be detected with instruments. If you can hide something from microwaves, you can hide it from radar and visible light. In effect the device, made of metamaterials — engineered mixtures of metal and circuit board materials, which could include ceramic, Teflon or fiber composite materials — channels the microwaves around the object being hidden. When water flows around a rock, co-author David R. Smith explained, the water recombines after it passes the rock and people looking at the water downstream would never know it had passed a rock. The first working cloak was in only two dimensions and did cast a small shadow, Smith acknowledged. The next step is to go for three dimensions and to eliminate any shadow."
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Scientists Make Item Invisible to Microwaves

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  • meta-materials (Score:5, Informative)

    by lgw ( 121541 ) on Thursday October 19, 2006 @02:02PM (#16504625) Journal
    If you can hide something from microwaves, you can hide it from radar and visible light.

    I don't think this follows, at least when we're talking about metamaterials []. So far no one has invented metamaterials for optical wavelengths, as metamaterials rely on complex structure that's somewhat wavelength specific. It's easier to play "fool the photon" with microwaves (because of the longer wavelength) or X-rays (because of the higher energy) than it is with visible light. (Xiang Zhang's experiments in extending near-field effects of visible light are a very different mechanism, and are lumpedin with metamaterials simply for lack of a better term.)
  • by thermopile ( 571680 ) on Thursday October 19, 2006 @02:24PM (#16505005) Homepage
    I was on a selection committee for DARPA to look into this stuff a few years ago.

    Negative Index of refraction Materials (NIMs), metamaterials, or whatever you want to call them, are relatively easy to make in the microwave region, since the wavelengths are on the order of centimeters. Thus, using a special arrangement of rings, loops, and wires, you can craft a lattice-like material that exhibits negative refraction. Technically, it has a negative magnetic permeability (mu) and negative permittivity (epsilon).

    This has all kinds of weird implications. The group velocity is still in the forward direction, but the phase velocity goes in reverse. Evanescent waves propogate, not die off. Perfect lenses can be made. Measurements LESS than the wavelength of light can be taken. There was a list of implications in the August issue of Scientific American, I believe.

    Anyhow, this works great at the ~cm scale. Visible light is hard as hell: the scale there is on the order of nanometers. And the copper or silver or tungsten wires used to make the metamaterials have MISERABLE magnetic losses at these small scales, so mu is no longer negative. The energy no longer propagates in the medium. As of three years ago, there were no promising candidates for solving this problem. There was an outside hack at using carbon nanotubes -- which may or may not maintain their permeability down to small scales -- but it was a long shot at best. Arranging the little guys would have been devilishly difficult.

    Glad to see that Pendry, who's been in this field almost as long as Veselago, is still making good strides. Even if they can't get to the visible wavelength, NIM's have spectacular applications for microwave antennae.

  • Re:Color me dubious (Score:1, Informative)

    by Anonymous Coward on Thursday October 19, 2006 @02:26PM (#16505059)
    Actually, 1 and 3 are precisely what these metamaterials can achieve. This one might not achieve 3, however they have worked out spherical structures that will do precisely that.
  • Fermat's principle (Score:4, Informative)

    by Anonymous Coward on Thursday October 19, 2006 @02:50PM (#16505583)
    To expand: light following the path of least time is known as Fermat's principle []. Fermat's principle can in turn be derived from Feynman's path integral formulation of quantum mechanics []; it is related to [] the principle of least action []. Feynman's book QED: The Strange Theory of Light and Matter has a lay derivation of Fermat's principle from path integrals (due to constructive superposition of quantum phase differences).
  • by ScaryFroMan ( 901163 ) <> on Thursday October 19, 2006 @04:23PM (#16507515)
    Technically, Romulans are Vulcan.
  • Re:meta-materials (Score:2, Informative)

    by Anonymous Coward on Thursday October 19, 2006 @04:29PM (#16507643)
    Actually that's not true. Metamaterials *have* been invented that work in the visible (although at the red end of the spectrum where wavelengths are longer) and there have been metamaterials which work in the near-IR for some time now. You are absolutely correct that fooling a microwave is easier, however fooling X-rays will be enormously difficult - x-rays have wavelengths on the order of the spacing between atoms in a solid, hence creating nanostructures with a "repeat unit" on this order is virtually impossible. It still may be possible to create something with scattering features on this wavelength using exotic arrangements of subatomic particles (complicated interfering standing waves in an electron resonator possibly) but this increases the difficulty by orders of magnitude further!
  • by mcrbids ( 148650 ) on Thursday October 19, 2006 @04:46PM (#16507977) Journal
    There's this thing called a pinhole camera, it's a relatively new advance.

    And, folks, here's a case indicating the limits of moderation by the unwashed masses. A pinhole camera [] is the very oldest type of camera. Having no lens, it can be made with a box and (gasp!) a nail. It is known to have been known about by the Chinese somewhere in the 5th century B.C, and Aristotle in 4th century B.C. [] Oh, how a small bit of research in widely available knowledge could have saved the parent poster from looking like a dolt!

    But this worthless (and incorrect) piece of wisdom gets moderated up by the clueless who don't take the time to understand what the !@# they're reading.

    Just when I start to get hope for mankind, I see something like this...
  • Re:Quite some time. (Score:2, Informative)

    by gnomino ( 975992 ) on Thursday October 19, 2006 @09:20PM (#16511325)
    What's the use of that if everyone else has the same thing?
  • Re:Quite some time. (Score:3, Informative)

    by c6gunner ( 950153 ) on Friday October 20, 2006 @08:04AM (#16514649)
    Nonsense. Well, the Hague convention art. 23 bit is nonsense anyway. You could argue that we already "kill treacherously" because we employ camouflage, snipers, artillery, landmines, etc. Any such argument would be just plain silly though. The treachery part of the Hague conventions refers more to things like poisoning, or getting your prostitutes to "distract" them while you sneak up and slit their throats (sound unlikely? think about how old these conventions are). As to the GC, you're absolutely right. However, the reason that these convention came about was in order to protect civilian lives. Basically, we, as soldiers, deliberately make ourselves into targets. While our uniforms may come in camouflage colours they're also extremely easy to identify once seen, so what we're really doing in any built up area is strapping giant bullseyes onto ourselves saying "shoot me, and not the guy in the blue jeans and 'fuck you' shirt". What terrorists do, by not identifying themselves in a similar manner, is place civilian lives at greater risk. If I can't tell an enemy from a non-combatant I'm more likely to shoot at anyone that looks threatening, whereas when the bad guys all wear the same colour there's really no excuse for shooting a civ. So, the cloak, while possibly violating the word of those specific Geneva Conventions, would uphold their spirit. While soldiers would no longer be easily identifiable, you also wouldn't be likely to mistake a civilian for a soldier. Why? Because the soldier would, when in combat, always be either in uniform or invisible. Either way he'd look nothing like the civilians around him. Based on that, I could see those conventions being modified to work with the new technology.

"We shall reach greater and greater platitudes of achievement." -- Richard J. Daley