[engrByDayPianstByNight (OP)]

Hi,

   Do you think in our lifetime we may see the production of a practical cloaking device prototype? A cloaking device that may be as large as one to hide a Klingon bird of prey, or as small as Harry Potter's invisibility cloak? I understand there have been some advances in pursuing this goal in the last couple of years. Being someone with almost a complete lack of background in optics, I certainly appreciate people knowledgeable on this topic to "shed some light" on it. I'm interested to get some discussion how likely a cloaking device is realizable, what are the current physical limitations, etc.
   
   I also came across an interesting article today:

http://technology.newscientist.com/article/dn14659-anticloak-gives-vision-to-the-invisible.html?DCMP=ILC-hmts&nsref=news3_head_dn14659

It proposes a new theory of "anti-cloaking device." Namely, the theory of a cloaking device blocks out all the lights that shine upon some object, rendering it invisible. This also would mean that the object would be in total darkness and would not be able to see outside either. That would limit the applicability of the cloaking device.
This article proposes a theoretical approach that allows some light to go through the cloaking device in a smart way that, on one hand, maintains the invisibility of the object, and on the other hand, allows the object to see the outside world as well.

    I find this article interesting, and I never thought about this "anti-cloaking" idea before. I would like get some feedback on this forum to enlighten myself on this subject.

    Thanks.

[lyner]

As far as optical cloaking goes, then I think it would have to depend upon what sort of performance you expected from such a device. To work from one particular viewpoint then it would not be too hard to do, even now, under some conditions of illumination - a TV camera  and a big TV screen to stand behind would almost fool the casual viewer. To make it work perfectly over a wide range of angles (even to fool binocular vision) would be v difficult.
But, when you think how effective camauflage paint can be in concealing stationary objects, it will certainly be possible to have something which would work 'well enough.
I imagine that the press have exaggerated reports of any recent developments.

For radar cloaking there is a much better chance - it's already possible to suppress reflections from a target if you know where the radar pulse is coming from and send an appropriate signal back to cancel the true reflected signal. This can reduce / eliminate radar visibility.

[engrByDayPianstByNight (OP)]

You're right about the radar cloaking used by stealth fighters. What I have in mind is more of the "optical cloaking," the kind of things that currently exist in sci-fi only. That is, an object is truly invisible even if you stare right at it, because it "bends" the light around it. Has there been any research on that sort of cloaking? If so, how far along the road?

I understand the media might have hyped up the developments in this field that still largely remain theoretic.

Also, to toss in my two cents on the anti-cloaking things: judging by the diagram and the accompanying text in the URL link in my original post, my guess is that if this indeed allows the object under cloak to be able to see the outside world, the visibility is probably going to be very poor. More likely it'll be just an outline of the outside world, not unlike today's night-vision goggles, but more likely to be in poorer quality.

[lyner]

If the cloaking device is 'active'  (i.e with amplification) then there shouldn't be a significant problem for the person behind it to see through it - it could appear to be passing all the light which is going 'through it' but be generating more light on the way. This would mean that the person in the cloak would be able to see.
For effective cloaking, as I implied before, I think there is much more future in treating the problem as one of Psychology and producing the 'effect' of your not being there rather than eliminating your image completely.
Flat fish do a great job already by mimicking the  sea bottom. A pretty good all round cloaking system is, surely, better value than a perfect system which only works in some directions. Adaptive camauflage has got to be the way to go - for the soldier in the field.

[engrByDayPianstByNight (OP)]

If the cloaking device is 'active'  (i.e with amplification) then there shouldn't be a significant problem for the person behind it to see through it - it could appear to be passing all the light which is going 'through it' but be generating more light on the way. This would mean that the person in the cloak would be able to see.

Perhaps I misunderstood you. Did you say the light going through the object under the cloak as if the object were transparent? I thought the principle of optical cloaking is to somehow bend the light around the object under cloak, so as to make it invisible, not through it. Or is what you're saying a different approach in the research? Could you clarify? Thanks.

[engrByDayPianstByNight (OP)]

Wait, I just re-read your post, sophiecentaur, and I think I understand it now. I think you and I are agreeing on the same principle of the cloaking technology. You're merely describing the observer can see Object B that's directly behind Object A, which is under cloak, as if A is not there. Is that what you mean?

 

[lyner]

Yes - that's the model I had in mind. There is no problem with subject A seeing out if the system provides amplification of the light as it goes through / round; there is energy left which can be channeled 'inside' the cloak.
I am thinking in terms of a TV based system, which would, essentially, have cameras facing all round, producing images diametrically opposite them. The geometry might be a bit dodgy -
it may be fundamentally flawed, actually, if you wanted all round transparency but you should be able to make such a system work over a limited range of angles.

The microwave equivalent could, just as easily, have amplifiers in the 'channels' which take the signals round the hidden object. The nice thing about a microwave model is that you have a chance of making the components physically smaller than the wavelength with which you are dealing. Unlike the optical equivalent.
I don't know the size of the proposed device but I should have thought that there would be a detectable  phase change / distortion due to transit times and path differences and that you couldn't get round that problem (Fermat's Principle applies, I believe)

[paul.fr]

You may find this interesting.
http://www.sciencefriday.com/program/archives/200808156

[LeeE]

There are two solutions to cloaking: passive and active.  The active solution is easy but complex whereas the passive solution is really still in the realms of possibility but not actuality.

The degree of cloaking needs to be qualified too - long wavelengths (radio) are generally easier to deal with than short wavelengths (visual).