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Invisibility cloak possible? how close are we?

  1. Mar 3, 2010 #1
    Dear readers,

    Is it possible to make a human being invisible using metamaterials?, if so then how close are we to making this possible as i need to make a withdrawal from my bank without the bank manager knowing!

    People can see objects because they scatter the light that strikes them, reflecting some of it back to the eye. Cloaking uses materials, known as metamaterials, to deflect radar, light or other waves around an object, like water flowing around a smooth rock in a stream.

    how can a photon pass through a metamaterial without changing its direction with no reflection?
     
  2. jcsd
  3. Mar 3, 2010 #2

    Demystifier

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    See the book
    Michio Kaku, Physics of the Impossible
     
  4. Mar 3, 2010 #3
    thankyou Demystifier, i will have to buy it as i need to go to the bank next week!
    thankyou
    Rob060870
     
    Last edited: Mar 3, 2010
  5. Mar 3, 2010 #4

    ZapperZ

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    This is not a strictly QM topic. It is more on classical E&M, and thus, will be moved into the Classical Physics forum.

    You may also want to do a search on this topic in this forum. It has been discussed already several times.

    Zz.
     
  6. Mar 3, 2010 #5

    Born2bwire

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    A true invisibility cloak as they have proposed of late would be nothing more than a giant hamster ball. Not the most practical thing to use when robbing a bank. It's not going to happen any time soon. The metamaterials that we are currently producing have losses, very narrow bandwidth, and low frequency ranges of operation. All three of these problems will need to be overcome before they can think about being able to make an invisibility cloak. They have demonstrated it in the microwave regime for the 2D case but those results are still fairly limited.
     
  7. Mar 3, 2010 #6

    ZapperZ

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    In addition to what Born2bwire has said, there is a paper that proposed that even for a "perfect" cloaking, one can still defeat such a cloaking by simply shooting a stream of charged particles at it[1]!

    So you play with your cloaking device, while I will continue playing with my particle accelerator.

    Zz.

    [1] B. Zhang and B.-I. Wu, Phys. Rev. Lett. v.103, p.243901 (2009).
     
  8. Mar 3, 2010 #7

    Born2bwire

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    Haha, I remember reading that paper. It was an interesting method. My recollection is that the paper proposed that if you shot an electron through the cloak then the electron would undergo acceleration, causing it to emit radiation. But really, I mean, if you're going to be shooting a beam of electrons out into space, why not just do it with tennis balls or bullets?
     
  9. Mar 3, 2010 #8

    marcusl

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    Born2bwire mentions narrow bandwidth, which appears to be a fundamental limitation of cloaks. Note that a light wavefront passing through the cloak must, when it exits, exactly match the wavefronts that missed the cloak and passed by in vacuo. That's how the cloaked object is rendered undetectable. But the path length through the cloak is longer, so the phase velocity must exceed c in the cloak, and that happens only in the vicinity of resonances--which are narrow band by definition. So we'll never have a cloak that works at all frequencies.

    For more see sect. 5.2 of Leonhardt and Philbin, Transformation Optics and the Geometry of Light, in Prog. Opt., available as a preprint here: http://arxiv.org/pdf/0805.4778"
     
    Last edited by a moderator: Apr 24, 2017
  10. Mar 3, 2010 #9
    Clearly the solution to a perfet cloak of invisibility is sustained orbital bombardment. :rofl:
     
  11. Mar 4, 2010 #10

    i have now ordered the book from amazon. i cant wait to read it but i do hope its in layman's terms?
    after ive read it i can then pay a visit to my local bank !
    thanks again.
     
    Last edited: Mar 4, 2010
  12. May 22, 2010 #11
    Hi all, Just to add a few more words about the invisible device to the posts of Born2bwire.
    Actually the invisibility is a solution of Hemholtz equation, which is second order deferential equation. From Mathematic we know that the solution of deferential equation is unique with a given initial conditions. So the real invisibility is if there is noting there, otherwise the device will work only for a human eyes but not for coherent light detectors, due to the unique theorem….
     
  13. May 22, 2010 #12
    ahem, but why do you need a godforsaken invisibility cloak, u'd hav to loot the bank to pay for it..... :|
    you could just use your brains and a bunch good processors to make a lumpsum transfer, study codebreaking, not classical E&M for this...:)
     
  14. May 15, 2011 #13
    Last edited by a moderator: Apr 25, 2017
  15. May 15, 2011 #14
    Well; if you cannot see the target, you're gonna be killing alot of innocent bystanders spewing bullets out in all directions until you finally 'hit' something invisible, not to mention wasting lots of metal (or tennis balls) in the process.

    I'll stick with Zapper's minimally fatal particle accelerator; however, I could probably defeat that also by wrapping myself in a very strong magnetic field.
    Maybe. ;))

    Creator
     
    Last edited: May 15, 2011
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