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Science Technology

Building an 'Invisibility Cloak' With Electromagnetic Fields 71

Posted by Soulskill
from the easier-than-building-them-with-corn-fields dept.
Nerval's Lobster writes "University of Toronto researchers have demonstrated an invisibility cloak that hides objects within an electromagnetic field, rather than swaddling it in meta-materials as other approaches require. Instead of covering an object completely in an opaque cloak that then mimics the appearance of empty air, the technique developed by university engineering Prof. George Eleftheriades and Ph.D. candidate Michael Selvanayagam makes objects invisible using the ability of electromagnetic fields to redirect or scatter waves of energy. The approach is similar to that of 'stealth' aircraft whose skin is made of material that absorbs the energy from radar systems and deflects the rest away from the radar detectors that sent them. Rather than scattering radio waves passively due to the shape of its exterior, however, the Toronto pair's 'cloak' deflects energy using an electromagnetic field projected by antennas that surround the object being hidden. Most of the proposals in a long list of 'invisibility cloaks' announced during the past few years actually conceal objects by covering them with an opaque blanket, which becomes 'invisible' by displaying an image of what the space it occupies would look like if neither the cloak nor the object it concealed were present. An invisibility cloak concealing an adolescent wizard hiding in a corner, for example, would display an image of the walls behind it in an effort to fool observers into thinking there was no young wizard present to block their view of the empty corner. 'We've taken an electrical engineering approach, but that's what we are excited about,' Eleftheriades said in a public announcement of the paper's publication. (The full text is available as a free PDF here.)"
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Building an 'Invisibility Cloak' With Electromagnetic Fields

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  • Error, Error. (Score:5, Interesting)

    by girlintraining (1395911) on Wednesday November 13, 2013 @04:28PM (#45417169)

    Invisibility cloaks like this only work within a certain range of EM frequencies. Outside of that range, it won't work; in fact it may even amplify the signal and make it more obvious whatever is being cloaked. And there are some thing no amount of cloak can deal with. You can alter the optical properties of a thing, but if it's out-gassing several thousand degree plumes... you cannot mask the infra red signature of that. These new meta materials may help in communications, but I highly doubt they will ever be able to make large human-sized physical objects disappear to any current multi-sensor technology.

    • Re:Error, Error. (Score:4, Insightful)

      by i kan reed (749298) on Wednesday November 13, 2013 @04:36PM (#45417261) Homepage Journal

      Sure, pragmatic constraints affect every design. But if you're worried about being spotted by cosmic rays, that's a lot better than being worried about being spotted by guards or radar.

      • Re:Error, Error. (Score:4, Interesting)

        by girlintraining (1395911) on Wednesday November 13, 2013 @04:56PM (#45417523)

        Sure, pragmatic constraints affect every design. But if you're worried about being spotted by cosmic rays, that's a lot better than being worried about being spotted by guards or radar.

        I'd be more worried about dying of cancer, honestly. And metamaterials do offer the promise of light-weight shielding against radioactivity in space -- as has been pointed out, they do operate over certain ranges of frequencies. I'm just tired of people calling them 'invisibility cloaks', when all they're doing is reflecting emissions at certain frequencies in a novel fashion. There are a great many useful applications for this... but "invisibility cloak" doesn't make the list. Sorry. That's bad science.

    • Re:Error, Error. (Score:4, Insightful)

      by nospam007 (722110) * on Wednesday November 13, 2013 @04:44PM (#45417379)

      "Invisibility cloaks like this only work within a certain range of EM frequencies. "

      Just like a concrete or brick wall. It works only within a certain range of EM frequencies.
      With the right viewing system, you can see right through.

    • And this isn't even an "invisiblity" shield-- what it is, is a radar-scattering device.

      From the article, apparently it scatters an incident radar beam so that the backscattered part (the part that returns to the transmitter) is zero. Specifically, they "then carefully modulated the current on each element to modify the field such that it deflected microwaves aimed at an aluminum cylinder in every direction except back toward the source of the microwaves, where the object could be detected."

      So the object i

      • by mcgrew (92797) *

        You can't scatter one beam of light with another one!

        No, but you can cancel light out [wikipedia.org] with more light [angryflower.com]. And this does make an object invisible, if tuned to the wavelength you want it to be invisible in.

        The trouble is, you could tune it to work in visible light but only if that light were coherent (as in, comes out of a laser). You can't get incoherent light out of phase with itself because it's a wide range of frequencies and all completely incoherent, like snow on an analog TV.

        • You can't scatter one beam of light with another one!

          No, but you can cancel light out with more light.

          You can cancel light out in specific directions, but the price of nulling the interference in some directions is increasing the intensity in others. It's that conservation of energy thing. On the average, you make the object brighter

          And that really isn't "invisibility"-- you can't see through the object. It's just a complicated way of achieving the same effect as painting the object black. Except it's only "black" for a selected wavelength in a selected direction.

          ...The trouble is, you could tune it to work in visible light but only if that light were coherent (as in, comes out of a laser). You can't get incoherent light out of phase with itself because it's a wide range of frequencies and all completely incoherent, like snow on an analog TV.

          Right.

    • You can alter the optical properties of a thing, but if it's out-gassing several thousand degree plumes... you cannot mask the infra red signature of that.

      Meaning, "The thing's got to have a tailpipe." So, you've seen Star Trek VI: The Undiscovered Country [wikipedia.org] ...

      • by Boronx (228853)

        But they never established that Enterprise was studying gaseous anomalies, only Excelsior

    • by slick7 (1703596)

      but I highly doubt they will ever be able to make large human-sized physical objects disappear to any current multi-sensor technology.

      Two words, Philadelphia Experiment.

    • Works in the microwave band eh? Can I get one of these in the K/Ka band for my automobile?
  • Just as I thought! (Score:5, Insightful)

    by DontBlameCanada (1325547) on Wednesday November 13, 2013 @04:29PM (#45417181)
    Canada is harbouring dissident Romulan scientists brought here by James T. Kirk (Canadian William Shatner).
    • by Anonymous Coward

      It's all fun and games until INVISIBLE ZAMBONIS

    • by mcgrew (92797) *

      William Shatner is Canadian, but James T. Kirk is from Iowa. Sheesh, you never watched any Star Trek movies? Besides, Captain James Kirk is now captain of the USS Zumwalt [cnn.com], a navy destroyer that has a cloaking device! TFA: "When its begins missions, the Zumwalt will be the largest stealth ship in the Navy."

  • by Lumpio- (986581) on Wednesday November 13, 2013 @04:30PM (#45417191)
    I think it's only justified to call something an "invisibility cloak" when it does what people actually expect an invisibility cloak to do, that is, make things actually not visible. How about calling it a "stealth cloak" because that's what I imagine most people would associate with being invisible to a radar, as opposed to the naked eye.
    • by Anonymous Coward

      I think it's only justified to call something an "invisibility cloak" when it does what people actually expect an invisibility cloak to do, that is, make things actually not visible. How about calling it a "stealth cloak" because that's what I imagine most people would associate with being invisible to a radar, as opposed to the naked eye.

      Won't you please think of the clickbait?

    • by JeanCroix (99825)
      They're quick to point out that it's not actually a cloak, either. Shades of the Holy Roman Empire...
    • Can you be wrapped in invisibility? I think not.

      Doesn't matter, someone will just come along with a uninvisiblity uncloaker and sell it to the enemy. Isn't that how it always goes?
    • by radtea (464814)

      After that, maybe they could try writing a remotely accurate summary, too! The summary is borderline gibberish, as it is impossible (in linear materials) for EM fields to "deflect" each other.

      This "cloak" is interference-based, using active dipoles to generate a field that cancels the scattered field in the forward (0 degree) and backward (180 degree) directions. It's a clever piece of work, but there are fairly hard limits to the how wide an angle such techniques can cover, and moving from an essentially

    • by Anonymous Coward

      but you won't get as many hits and advertising revenue if you do it that way, son

      Go ahead and stick your dick right in those dollar bills you whores

    • I think it's only justified to call something an "invisibility cloak" when it does what people actually expect an invisibility cloak to do, that is, make things actually not visible. How about calling it a "stealth cloak" because that's what I imagine most people would associate with being invisible to a radar, as opposed to the naked eye.

      How about flying cars? Or cure for cancer? Or pioneer probe in interstellar space? The list goes on.

    • by AK Marc (707885)
      And all it'll do is change radar to be separate radiators from receivers. With that done, active radar will "penetrate" the cloak without issue, and passive detection would be mostly unaffected.
  • by Anonymous Coward

    Invisible : Invisible to Radar :: Edible : Edible by Sperm Whales

  • I may be missing how this works, but it looks like they are driving a bunch of antennas to cancel the scattered radiation from an object in one direction. While this works, the trick is to know exactly what the input signal is and the react in time to cancel - something that can only work for very narrowband sources or sources where you know the input field (including its phase) in advance.

    I don't see how this could work for radar or light.

    • by Mr D from 63 (3395377) on Wednesday November 13, 2013 @05:18PM (#45417761)

      I don't see how this could work for radar or light.

      Of course you can't see it working. Thats the point.

      • Magnetic stealth is the perfect cloaking mechanism -- just as long as the enemy never launches anything metallic at it, they are home free!

    • by Zorpheus (857617)
      So "the ability of electromagnetic fields to redirect or scatter waves of energy" means that they just send out electromagnetic waves that interfere with the waves around the object? Was already wondering since when electromagnetic fields can redirect electromagnetic waves. That only works in Star Trek.
      • I think you are right. The cross-section for photon / photon scattering at low energies is really tiny - maybe never observed at optical wavelengths or longer. (there might be some result I don't know about).

        The article makes it sound much cooler than it is - but its still kind of a nice demonstration and not easy.

        • by Zorpheus (857617)
          Yes, it is more obvious in classical electrodynamics. For all waves and electromagnetic fields the superposition principle can be applied because the Maxwell equations are linear. This means that if you add any fields or other waves to an incoming wave you can describe the result mathematically as the sum of the incoming wave and whatever you generate.
          According to the Maxwell equations the incoming wave is influenced by susceptibility and permeability of the materials it is going through, and by charges a
  • I just don't see this working......

  • by Anonymous Coward

    Instead of trying to make something invisible (isn't that hyper-impossible anyway?), why don't we just put an SEP field over it?

  • Oh, wait... I guess the absence of pictures is proof that they succeeded. Bravo!

  • by Rotag_FU (2039670) on Wednesday November 13, 2013 @05:36PM (#45417889)

    And I thought it was just the mayor smoking crack, apparently the whole town is now. :)

    • by fishicist (777318)
      The word "invisible" does not appear in the paper. The authors call this cloaking, not invisibility.
  • We have had this tech for over 40 years! Track Break Notch will do similar things by either walking a radar off you, or move your position according to what the radar can see.
    The bigger problem is millimeter band radar, you need really funky waveguides to broadcast these as a normal antenna can't cope the small wave frequency.
    The A6 from the Navy and the EF-111A from the USAF both could manage similar things to this, I can only hope they have managed to it smaller as the units for each section of bandwidth

  • Good luck scattering and redirecting the rocks I start throwing in every direction once this technology is widely available.
  • I already have a more practical invisibility capability. I just talk to management about actual technical topics. I become invisible to them almost immediately.

  • Yet another link to an internal slashdot.org story under the datacenter topic... http://slashdot.org/topic/datacenter/invisibility-using-force-field-not-cloak/ [slashdot.org]

    Looks like slashdot is trying to be theverge or engadget...

  • I mean, didn't his cause havoc already?
  • For those of you asking "Why no picture" there actually is one.
    1. go to google
    3. type "empty field"
    Tada, picture of an invisible car.
    • What the hell?! It seriously ate step 2 for absolutely no reason! What kind of stupid filter does Slashdot have? Let's try again:
      2. click on images

      Ironic that a step about invisibility disappeared btw.
  • Sounds an awful lot like the Philadelphia Experiment except on a smaller scale. Not surprising that the work of Nikola Tesla,which in a lot of ways was way ahead of its time,is being re-examined.How many more of his discoveries will finally see the light of day after being suppressed for 60 or 70 years? All I can say is this -> "You Ain't seen Nothing Yet"
  • Seriously, the paper does not report on anything like visible light invisibility. That's not what this is. This is a case of misleading labelling.
  • It goes back to stealth technology in microwave region.

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