Invisibility Cloak - Currently In Design!

[Dram]

Yes, the title says it all.

 

Now before you laugh your lungs out onto your keyboard, thus preventing you from replying, read the following:

 

http://www.wired.com/news/wireservice/0,70...l?tw=wn_index_4

 

Pretty crazy. It was in the news here in Sydney. Quite interesting. Only disadvantage is that you would'nt be able to see out of it, but I guess a camera would do. Remember that no wireless tech would work as the electromagnetic radiation would just pass by it, thus any viewing media to the outside world would have to be wired.

 

Just thought some of you may be interested by this

[Domarius]

That's awesome. It works just like how they described the predator one works.

[thestemmer]

They've been talking about this for years. I'll believe it when I (don't) see it.

[sparhawk]

Don't be to overenthusiastic. While it has some use, it is quite limited in it's application.

[Ishtvan]

That's pretty interesting. Here is another article on it: http://www.msnbc.msn.com/id/12961080/

 

You might need access to Science for this, but if you are at a university or something and have that, you can read the full preprint paper here: http://www.sciencemag.org/cgi/rapidpdf/1125907v1.pdf

 

You realize the paper is theoretical, not experimental, right? They developed a method to solve for the optical constants needed to "bend" EM fields into arbitrary configurations. They applied this method to a problem of confining fields in the material to a spherical shell with none in the inner sphere (the place they want to cloak), and solved for the permittivity and permeability they would need to do this, assuming that any value of the permittivity and permeability, positive or negative, would be obtainable using "metamaterials."

 

Metamaterials are composite materials patterned to achieve arbitrary optical constants for wavelengths larger than the composite dimensions, and some progress has been made in the last few years making things like negative refractive index materials (light bends the "wrong" way compared to naturally occuring materials). I believe that's what Pendry, the first author, works on.

 

There's two main problems with this proposal, that they explain in the paper:

1. Narrow bandwidth: The simulation in the paper only works for one frequency of light, other frequencies will not be bent in the same way by these materials, and thus not see the cloaking. The prospect of cloaking over the whole visible frequency range of several hundred nanometers is pretty slim. The paper mentions something about making it broadband by immersing the entire system in a high dielectric material, but that means the observers would have to be in that material as well. Unfortunately that doesn't apply to vacuum, air, or water.

 

The cloak could work better for radar applications, since that is a narrower frequency band.

 

2. Realistic materials limits: While optical metamaterials are cool (yay materials science!) they can't necessarily do all the things they let them do in that simulation. They state in the paper that for beams of light coming in toward the center of the sphere, they must be bent very sharply, and this would require an unrealistic gradient in optical constants. Light has to "see" several composite layers of metamaterials over one of its wavelengths in order to act like it's in a material with the desired optical constant. That means if their simulation requires a huge change in optical constant over a dimension the size of a few atomic layers, it ain't gonna happen.

 

They admit that with real materials, cloaking will not work for light coming at areas near the center of the sphere. They go so far as to market the technique as "cross section reduction" rather than total invisibility. That's cool, as long as they're honest. Again it works better for microwave frequencies (radar), since the required "resolution" of the composite dimensions in the metamaterial is proportional to the wavelength of the light.

 

To realise these designs in real life, we'll have to reliably fabricate 3d metamaterials with the desired spatial distribution of optical constants, and that gets harder as the cloaking wavelength gets shorter. [Edit: Thicker shells are also better since they allow more room for the light to bend and don't require as high an index gradient.]

[thestemmer]

 

I take it you have some experience with this subject, Ishtvan?

[Dram]

@Ish: Yeah I know it's just a design. I thought it was interesting and so just posted it

 

@Spar: Yeah true, but it's still interesting to know that they're working on it at least. Of course, without making any illusions, pretty much the -only- purpose this technology would have is Military. At least for the first few years. It's kinda damning..

[Ishtvan]

I take it you have some experience with this subject, Ishtvan?

 

I'm studying optical materials for grad school. So I guess I have some, although I don't deal with negative index materials. Mainly I just read the Science paper quoted in the article. They did a good job explaining it at a fairly general level.

 

@Spar: Yeah true, but it's still interesting to know that they're working on it at least. Of course, without making any illusions, pretty much the -only- purpose this technology would have is Military. At least for the first few years. It's kinda damning..

While they did cite some other applications, it's probably true that the only people who would pay the cost for it right now are military. I wonder how well that could shield things from EMPs?

[Dram]

I wonder how well that could shield things from EMPs?

 

Well technically it should completely because it's still electromagnetic radiation. I might have gotten something mixed up though; this metamaterial, can it refract all EMR? or only in the visual range? If it can refract the whole spectrum then it means that you could use that to shield things from gamma rays etc. Now THAT would be a useful application - radiation bunkers still Military of course...

[Ishtvan]

Argh, read my post! The simulation only works at one frequency, so no it cannot cloak across an entire spectrum. It can't cloak across the whole visual spectrum, that was just the other newspapers sensationalizing it. I don't know much about EMP's, but they're probably broadband enough that it wouldn't work, now that I think about it. For an EMP shield you don't even need this design to redirect it around an object, you just need something that will absorb or reflect everything.

[Dram]

Argh, read my post!

 

ehehe...yeah it was long and you know....

 

The simulation only works at one frequency, so no it cannot cloak across an entire spectrum. It can't cloak across the whole visual spectrum, that was just the other newspapers sensationalizing it. I don't know much about EMP's, but they're probably broadband enough that it wouldn't work, now that I think about it. For an EMP shield you don't even need this design to redirect it around an object, you just need something that will absorb or reflect everything.

 

Ahh thought so. Well at least it's getting SOMEWHERE.