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Science Technology

Glass Invisibility Cloak Shields Infrared 115

An anonymous reader writes with the latest advance in the quest for a cloak of invisibility (Michigan Tech University's press release). We've been following this research as it develops; here are stories from each of the last four years. "Invisibility cloaks are slowly working their way up to shorter wavelengths — starting at millimeter-long microwaves and working their way to the nanometer wavelengths of visible light. EETimes says we are about half way there — micrometer wavelengths — in this story about using chalcogenide glass to create invisibility cloaks in the infrared. Quoting: 'Invisibility cloaks cast in chalcogenide glass can render objects invisible to infrared frequencies of light, according to researchers at Michigan Technological University... Most other demonstrations of invisibility cloaks have used metamaterials composed of free-space split-ring resonators that were constructed from metal printed-circuit board traces surrounded by traditional dielectric material. The Michigan Tech researchers... claim that by substituting nonmetallic glass resonators made from chalcogenide glass, infrared cloaks are possible too...'"
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Glass Invisibility Cloak Shields Infrared

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  • by RsG ( 809189 ) on Sunday July 25, 2010 @08:34PM (#33024646)

    Infrared also poses additional problems above and beyond what you've stated, because the light isn't coming from an external source.

    Any hot object is going to radiate infrared radiation. That isn't something external being reflected off of it, that's coming from the surface of the radiating object itself. Infrared sensors work on contrast, so if you've got, say, a skin temperature object like a human being in a room temperature environment, it'll show up. Same applies for a room temperature object in an arctic environment - what matters is contrasting temperatures between the object to hide and the world around it.

    So how do you mask this? Okay, you keep the infrared from escaping. Totally stopping it is impossible, but reducing it isn't, and "good enough" if it's reduced to the point where it no longer contrasts with its surroundings. Thing is, radiating heat is one of the ways internally heated objects (like human bodies) cool down, so depending on a number of factors, overheating will be an issue.

    But you can lose heat in other ways. Conduction and convection dissipate more heat than radiation, at least in a terrestrial environment (space is another story). Except that the medium you're dumping heat into will itself heat up and start radiating in the IR spectrum, just like your hidden whatever would have. So you've mitigated the problem, but not eliminated it.

    Now an important thing to note is that all of this applies to complete invisibility to IR. Partial stealth is another matter. Mitigating the problem is good enough if the intent is to make the job of whoever is looking for you harder. Stealth aircraft aren't invisible either, but are stealthy enough to give them an edge over the competition. OTOH, this pretty much kills any chance of making a Star Trek style cloaking device, especially if you want it to work in space.

  • Thermal protection (Score:3, Interesting)

    by La Gris ( 531858 ) * <(ten.eduarion) (ta) (sirg.ael)> on Sunday July 25, 2010 @09:33PM (#33024926) Homepage

    I know it is premature speculation on lab technologies but, well Infra-reds invisibility could mean improved heat isolating glasses windows for buildings. Keep visible light enter the building, let infra-reds refract though the other side and keep inside radiating heat bouncing the glass with perfect reflection. Would be a boon for vehicles where most windows face side to side. Would this be more efficient or combinable with athermic design?

  • Re:Military (Score:4, Interesting)

    by the_other_chewey ( 1119125 ) on Sunday July 25, 2010 @09:39PM (#33024942)
    Except that this doesn't cloak an objects infrared emissions, it makes it invisible to surrounding IR light.
    There's nothing at all hiding the infrared emissions of the object hidden by the cloak.

    Unless you find a way to break a couple of thermodynamic laws, there's no real way to completely hide an
    object's thermal emissions if it is warmer than its surroundings.
  • No: not really (Score:3, Interesting)

    by Required Snark ( 1702878 ) on Sunday July 25, 2010 @09:39PM (#33024946)
    If this can be made to work at the frequencies used by infrared targeting sensors it could be extremely useful. It doesn't have to 'match' anything. All it has to do is make the platform not emit in the expected direction, but in a direction that will make tracking difficult. Remember that these kind of meta-materials have a negative index of reflection, so they can act like unusual lenses. It doesn't even have to do this for the entire vehicle, just the hot parts used for targeting. For example, this could be a big winner for UAV platforms.
  • Re:Military (Score:4, Interesting)

    by Pharmboy ( 216950 ) on Sunday July 25, 2010 @11:18PM (#33025550) Journal

    Unless you find a way to break a couple of thermodynamic laws, there's no real way to completely hide an
    object's thermal emissions if it is warmer than its surroundings.

    Not exactly true. Military jet nozzles are designed to create a smaller IR footprint, and there are several ways to reduce your thermal print. Obviously creating less heat, storing heat to prevent it from being emitted, pushing it in a direction 180 degrees away from the radar source, etc. It starts with having more imagination. The goal is NOT to make IR emissions "disappear", only to create the illusion that they have by controlling where they go. To buy time.

    Sometimes, you can fool a system into thinking you are much smaller than you are, or depending on the threshold of the system, drastically increase the amount of time before you are noticed at all. Even stealth aircraft are not invisible to radar, but by the time the radar sees them, the radar site has been taken down by air to surface munitions. Same idea, only giving you a larger window before you are noticed, thus defeating better radar systems. We can already absorb and deflect microwaves fairly well, adding IR to aircraft defense would be a very big deal, for protection from radars, and from air to air and surface to air munitions. ie: Air superiority.

  • by Dunbal ( 464142 ) * on Monday July 26, 2010 @12:17AM (#33025952)

    The only way this will work to evade military grade infra red detection is if 1) you are not moving - people tend to notice a "cold patch" moving against a background - it's almost as good as a hot one; and 2)if you can manage to match the background heat exactly, thus masking your shape. Unfortunately if you're being viewed by something that's moving (like a helicopter or drone), you have no idea at what angle you are being viewed from at any point in time. This complicates matters.

  • Knew that already (Score:3, Interesting)

    by Drakkenmensch ( 1255800 ) on Monday July 26, 2010 @08:13AM (#33028126)
    Didn't the mythbusters already prove you can foil a heat-sensing alarm by holding a pane of glass in front of you?

The last thing one knows in constructing a work is what to put first. -- Blaise Pascal