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Science Technology

A Step Toward an Invisibility Cloak 197

Technology Review has a writeup on the latest advance in the lab towards an invisibility cloak made of metamaterials, described this week in Science. We've been following this technology since the beginning. The breakthrough is software that lets researchers design materials that are both low-loss and wideband. "The cloak that the researchers built works with wavelengths of light ranging from about 1 to 18 gigahertz — a swath as broad as the visible spectrum. No one has yet made a cloaking device that works in the visible spectrum, and those metamaterials that have been fabricated tend to work only with narrow bands of light. But a cloak that made an object invisible to light of only one color would not be of much use. Similarly, a cloaking device can't afford to be lossy: if it lets just a little bit of light reflect off the object it's supposed to cloak, it's no longer effective. The cloak that Smith built is very low loss, successfully rerouting almost all the light that hits it."
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A Step Toward an Invisibility Cloak

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  • by artor3 ( 1344997 ) on Sunday January 18, 2009 @04:48PM (#26509095)

    Similarly, a cloaking device can't afford to be lossy: if it lets just a little bit of light reflect off the object it's supposed to cloak, it's no longer effective.

    Why would that be no longer effective? If the cloak reroutes 90% of the light, then you're left with 10% opacity, right? Sure, something that translucent would be very difficult to see, especially from a distance.

  • FUUUU (Score:5, Informative)

    by sakdoctor ( 1087155 ) on Sunday January 18, 2009 @04:49PM (#26509099) Homepage

    Direct link please! []

    Garbage javascript broke for me and the page didn't get past a white page.

  • Blindness (Score:5, Insightful)

    by Tubal-Cain ( 1289912 ) * on Sunday January 18, 2009 @04:54PM (#26509123) Journal
    If visible light is being routed around the cloak, it could cause some serious navigation issues for the cloaked object. Maybe some objects (ships/aircraft) will only need a cloak that routes radar, leaving pilots to navigate by sight and dead reckoning (GPS uses radio frequencies, right?)
    • Wonderful! Can I get this installed on my personal airborne transportation system? Because then I can truly say: Where is my flying car?
    • by Agripa ( 139780 )

      Invisible man stories have always bothered me because of this. How does he see if his retina and various eye structures are invisible? H. G. Wells addressed this to a limited extent.

      • The eyes themselves wouldn't be invisible, but the cloak would redirect light around them, making them useless unless there were eye holes (or camera holes) cut in the cloak.
    • by joggle ( 594025 )

      Yea, GPS currently uses 2 frequencies (eventually a third will be used too).

      The frequencies used are:

      F1: 1575.42 MHz
      F2: 1227.6 MHz

      (new frequency, not transmitted yet)
      F3: 1176.45 MHz

      So theoretically this new cloak would be invisible to these frequencies.

  • How is 1 to 18 gigahertz a swath as wide as the visual spectrum? It's much wider. This is around 4 octaves (ie, doublings of frequency). The visual spectrum is from 400 to 700 nanometers - not even a full octave.
    • Re: (Score:3, Funny)

      by CarpetShark ( 865376 )

      How is 1 to 18 gigahertz a swath as wide as the visual spectrum? It's much wider.

      You must be thinking of the 16k visual spectrum. This is referring to the Spectrum 128k.

    • That's wavelength, not frequency...

      • by TheLink ( 130905 )
        How does that make him wrong? It's still not a full octave.

        As long as the wavelength is not double at one end, it's not going to be a full octave.
  • wavelength = length (Score:5, Informative)

    by Doviende ( 13523 ) on Sunday January 18, 2009 @04:55PM (#26509133) Homepage
    "works with wavelengths of light ranging from about 1 to 18 gigahertz"

    frequency is in hertz.
    wavelength is a length, so it will be in meters or feet or inches or volkswagen bugs.

    that is all. </pedantic>
    • by John Courtland ( 585609 ) on Sunday January 18, 2009 @05:06PM (#26509235)
      Yeah, but it doesn't matter too much since c is constant. It's easy to calculate wavelength for any given frequency.
      • by ZombieRoboNinja ( 905329 ) on Sunday January 18, 2009 @05:35PM (#26509461)

        Not for those of us who don't live in a vacuum, you insensitive clod!

        • Re: (Score:3, Funny)

          by dotancohen ( 1015143 )

          Not for those of us who don't live in a vacuum, you insensitive clod!

          C is still constant. C is the speed of light _in_a_vacuum_ not the speed of light in your parent's basement. And by the way I am a clod, you insensitive pedantic.

          • by beav007 ( 746004 )

            And by the way I am a clod, you insensitive pedant.

            There, fixed that for you.

          • Well what if I was saying it's not "easy to calculate wavelength," because even though c remains constant I can't actually use it to calculate wavelength since I'm not in a vacuum? What if THAT?

            Also, it's lower-case "c," and how DARE you call me pedantic! ;-)

        • by Devil's BSD ( 562630 ) on Sunday January 18, 2009 @06:31PM (#26509923) Homepage
          Yeah, I live in a Bose-Einstein condensate, you insensitive clod!
      • Re: (Score:3, Informative)

        by edittard ( 805475 )

        Given the radius of a circle you can calculate its area, but that doesn't mean they're the same thing or that you can use them interchangeably. Convertibility is not equivalence, and the article as written is wrong.

        • Re: (Score:3, Insightful)

          ... Jesus Christ almighty. You can figure it out easily enough, plus you won't do anything meaningful about it anyhow, so what's the point of complaining?
          • by Kokuyo ( 549451 )

            Uh, it's fun?

          • Perhaps if enough people complain the quality of the editing might go up?

            What's the point in defending incompetent writers, other than to try and show off that you remember some basic physics that, incidentally, everybody knows?

      • by Sinbios ( 852437 )
        The speed of light is not constant when not in a vacuum, and the wavelength frequency conversion depends on the speed of the wave, not the speed of the wave in a vacuum. So, you can't convert the frequency in this article to wavelength without first knowing the properties of the medium the frequency was measured in.
    • VW bugs are a unit of mass.

  • by Anonymous Coward on Sunday January 18, 2009 @04:56PM (#26509143)
    Pics or it didn't happen.
  • by imsabbel ( 611519 ) on Sunday January 18, 2009 @05:02PM (#26509199)

    Metamaterials are interesting enough _whithout_ that stupid invisibility shit everytime.

    I mean, lenses without diffration limit are also interesting. And opposed to the inisibility stuff, they might really work.

    • Re: (Score:3, Insightful)

      by Rorschach1 ( 174480 )

      The 'invisibility cloak' thing is right up there with 'teleportation'. Every time someone manages to 'teleport' the state of a single subatomic particle, we get a bunch of articles likening the process to Star Trek teleporters.

      Do ANY of the researchers involved in these things really expect them to have invisibility or teleportation capabilities at macro scales someday? I was under the impression that neither of them had any relevance at larger scales, and while I could be wrong, it seems like the media j

    • ...I mean, lenses without *diffration* limit are also interesting. And opposed to the *inisibility* stuff, they might really work...

      The device DOES work: At least one 'c' and a 'v' are succesfully cloaked! Of course you DID type them...

  • At last! (Score:5, Funny)

    by commodore64_love ( 1445365 ) on Sunday January 18, 2009 @05:03PM (#26509207) Journal

    Now I can see what happens inside the Girls' dorm!


    • Now I can see what happens inside the Girls' dorm!

      Who needs a cloak for that? []

      • More dorm room kissing please. I like young libertines.

        "Coming soon to a sticky theater near you, Harry Potter and the Seven Sexy Spells!"

        RON: "But Harry we can't go in the girl's dorm. We're gonna get in trouble."
        HARRY:"Shush Ron. This is important. Look there's Hermione in her underwear."
        RON: "What's Victoria's Secret?"
        HARRY:"You really are clueless aren't you?"
        RON: (blinks) "I never knew Hermione was so... large. Wow. Like two grapefruits!"
        HARRY:"I've been helping her with engorgement spe

  • by thorndt ( 814642 ) on Sunday January 18, 2009 @05:05PM (#26509227)

    Is it just me, or would this stuff work VERY well as a RADAR cloaking device?

    1-18 GHz is solidly in the microwave (millimeter-wave RADAR anyone?) range...

    • by HuskyDog ( 143220 ) on Sunday January 18, 2009 @08:44PM (#26511145) Homepage

      Sigh, here we go again! Radars and optical vision do not work in remotely the same way. Creating invisibility in the two different realms is a completely different problem.

      In most vision situations there are two critical factors which don't occur in the great majority of radars. The first is illumination of the target from angles other than the viewing angle (OK, there are bistatic radars, but they are not common) and the other is a background which is illuminated. Try to think about this for just a few moments. Why can't we all make ourselves invisible just by wearing matt black clothing? Well, obviously because we will stand out against the background unless we happen to be standing in front of black wall or wandering around in a coal mine. The whole point of the fictional 'invisibility cloak' is that it works in all circumstances. We can already be invisible in certain carefully controlled environments, that after all is what camouflage is all about.

      But, a radar is rather like wandering about in the above mentioned coal mine, or perhaps a dark forest with a miner's lamp fixed to your head. The background is basically black and the illumination comes from the viewing direction. In this scenario, someone dress entirely in black would be effectively invisible. And that is the key point to grasp. In the world or radar we can achieve invisibility simply by making sufficiently 'black' 'paint'. The weird ability of these meta-materials to allow the illumination to pass through the target un-disturbed is of no benefit. Since we don't have a receiver on the other side of the target to detect this energy it isn't relevant. Now, sure, we can all dream up complex bistatic radars which rely on the obscuration of the signal to detect the target, but I remain to be convinced that such a thing can be made sufficiently versatile to be useful.

      Can I stress that I am not suggesting the these meta-materials don't have an application in the world of radar. They seem to me to be particularly useful where one wants to remove a fixed object which obscures the view of your radar. For example, consider a radar on a ship. It may well find that in some directions its view is obscured by other parts of the superstructure. If the could cover these other bits of the ship with meta-materials such that the radar pulses could pass 'through' and back again undisturbed, then our radar's field of view would be increased. Such an application would work perfectly well with even the relatively narrow band materials presented previously.

      • by Nahor ( 41537 )
        While absorbing the radar waves works. That doesn't make being transparent to those waves useless. It's just a different method to the same problem. It has actually the advantage, as you pointed out, to be a more generic solution. "Black paint" works well today but "transparent paint" may be necessary tomorrow.
      • Either completely absorbing or allowing the RADAR waves to pass by undisturbed are equally valuable for RADAR cloaking. The key issue is how little of the radio waves are reflected. I'm not sure which will be more viable in the future, but sufficiently absorptive paint and structures are the winners for now.

        • The key issue is how little of the radio waves are reflected.

          Indeed, I couldn't agree more, and this is a property which rarely seems to be mentioned in meta-material discussions. Supposing that such a material passed 95% of the energy undisturbed and only reflected 5%. I think that this would rightly be regarded as an excellent technical achievement, and after all some glass isn't that good, but it would seem to be of limited military value. As we know from the radar equation's R^4 term, this will only reduce detection range by a little more than 50%, and you can

  • from TFA (Score:5, Funny)

    by someone1234 ( 830754 ) on Sunday January 18, 2009 @05:13PM (#26509303)

    "Now [that] this is becoming a more feasible technology, we will start to see a lot more of it."

    Heh, i thought the goal was to see a lot less of it :)

  • I don't believe it (much as I'd like to). Show it to me. Hell, even if they made a cloak that only obstructed "one color" (whatever that means) with 10% loss, that'd still be a huge leap.
    • Re: (Score:3, Insightful)

      by fyoder ( 857358 )

      Actually, all claims require adequate support for provisional acceptance. Differing standards for differing claims derives from the concept of canon which has more of a place in religion than science.

      I agree it would have been nice if they'd included a demonstration vid.

      • by beav007 ( 746004 )
        And how would they have done that? Even TFS says that it doesn't work on visible light.
      • all claims require adequate support for provisional acceptance

        I think those that tested the hell out of relativity in the early 20th century would disagree with you. When something is so out of the ordinary or flies so much in the face of conventional wisdom, it will be tested more than something which merely "builds" on an existing concept.

        You may be right, but in your purist logical thinking you are denying a fundamental attribute of humans.

    • "one color" (whatever that means)

      A basic understanding of the spectrum (and absolutely no RTFA on my behalf) would suggest that they mean one colour of the spectrum. So if they can cloak, say, the red spectrum, you'd show up looking a different colour than your normal sort.

      Imagine looking at some purple paper and then removing the red visibility/light from it. Is it still purple to your eyes?

    • Yyeah, I'd be more inclined to see this as more than an investor-grab opportunity if they even showed a single picture of SOMETHING. And that "picture" of the nano-structure close-up doesn't count.

      I mean, couldn't they have at least wrapped a tiny piece of this material around a pencil or something to show that you can barely see the wrapped portion?

      Like C'mon... seriously.

      Scientist: Amazing news people! We've developed this material to be a THOUSAND times better than in the past! It's absolutely phenomi

  • by sam0737 ( 648914 ) < minus cat> on Sunday January 18, 2009 @05:22PM (#26509375)

    I look forward to the photo of the prototype.

    • As part of the hype, one article a while ago showed off such a photo... which was actually a normal photo of a tank, badly Photoshopped to make it look like it was fading to invisibility at one end. That kind of nonsense highlights the level of hype about this project.
  • by Peet42 ( 904274 ) <Peet42@Netscap e . net> on Sunday January 18, 2009 @06:29PM (#26509913) light of only one color would not be of much use."

    It would be exceptionally useful if that colour was infra-red.

    • by bh_doc ( 930270 )
      Infra-red is a range, not a colour.
      • by Peet42 ( 904274 )

        But most of the detectors, say for body-heat in a battle zone, detect emissions within an extremely narrow range.

  • Why all the work? (Score:3, Informative)

    by RyoShin ( 610051 ) <tukaro AT gmail DOT com> on Sunday January 18, 2009 @06:29PM (#26509915) Homepage Journal

    I don't see why they're overdoing this so much. I've been able to become invisible for a long time--all I have to do is cover my eyes!

    Try it today!

  • But a cloak that made an object invisible to light of only one color would not be of much use.

    Tell that to the Green Lantern, you insensitive clod!


  • by jschimpf ( 628722 ) on Sunday January 18, 2009 @08:17PM (#26510937)
    Visible light ~5000 - 7000 Angstroms (1X10-9 m)

    7000 -> f = lambda/c -> 4.28275E+14

    5000 -> f = lambda/c -> 5.99585E+14

    Difference -> 1.713E+14 Hz -> 1.713E5 GHZ

    About 171,000 GHZ not 17

    • Re: (Score:3, Informative)

      by bint ( 125997 )

      That was some confusing math. First of all 1 Angstrom is 10^-10. you're thinking nm. And the equation should be:

      f = c/lambda

      I guess you meant that as the frequencies come out correctly.

  • by Tom ( 822 )

    Submitter needs to re-check his assumptions.

    Why should an "invisbility cloak" only be useful if it works 100%? Camouflage is being used in pretty much every war, and it's far from perfect. A cloak that "leaks" could still be great in low-light or reduced visibility settings. It doesn't have to be "perfect" to be useful. The stealth fighters aren't really radar-invisible, either. Just very difficult to detect, and for most settings that's good enough.

  • I don't understand the focus on clothes here. Obviously, vehicles would be the first targets. And, vehicles don't care about weight, that much.

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