Engineers Devise Invisibility Shield 316
GerritHoll points out an article in Nature according to which "researchers at the University of Pennsylvania 'say that a "plasmonic cover" could render objects "nearly invisible to an observer.' Earlier attempts at invisibility worked by colouring a screen to match its background, like a chameleon. The described technique is new, because it works by the concept of reducing light scattering. It is not a 'magic cloak,' however, because it will not work for the full range of visible light and needs to be adjusted precisely for the shape of the object. However, the concept could find an application in stealth technology."
Indeed, it's pretty far from advertised... (Score:5, Informative)
This technology would only work for microscopic objects (as they must be the same size as the wavelength of light hitting it), and only a single wavelength. So in other words, for you to get a nice, new cloak of invisibility you'll need to be microscopic in size and constantly in environments with only one wavelength of visible light hitting you. =)
Well, back to the drawing board.
Re:Invisibility cloaking (Score:3, Informative)
ergo, it doesn't do a damn thing this is just photoshop of an "artist conception".
been investigated a bit before (Score:5, Informative)
Russian electrodynamicists are also infamously known for proposing "plasma stealth" devices, which have yet to be demonstrated veritably well. Every few months something pops up about how they've solved high power requirements, reduced weight of the devices, eliminated interferce with the aircraft's EM devices (radar and comm/nav, which critical to everything) and problem Y. And then, you see nothing of it in any journal or trade publication. Just claims, and it seems, nothing more.
Notably, plasma radar stealth has an opposite effect of the optical stealth. The aircraft would glow like a lightbulb, and leave a trail of glowing plasma in its wake. Also notably, aircraft at high hypersonic speeds induce a local plasma air environment, due to the tremendous energy of the aerodynamics.
Re:Sounds like someone's been tokin' the hookah (Score:5, Informative)
"Could a small-sized object be hidden from radar by this "invisibility" shield?"
Millimeters to centimeters typical for radar. If you're looking to hide a large object, as in plane/ship length, you need to get into HF radio wavelengths (10-160m).
So you could hide it from... ham radio operators. On a single section of one band. Yeah, the Romulans ain't sweatin' this one. :-)
Research abstract (Score:5, Informative)
http://arxiv.org/abs/cond-mat/0502336 [arxiv.org]
Achieving transparency with plasmonic coatings
Andrea Alu, Nader Engheta [upenn.edu]
The possibility of using plasmonic covers to drastically reduce the total scattering cross section of spherical and cylindrical objects is discussed. While it is intuitively expected that increasing the physical size of an object may lead to an increase in its overall scattering cross section, here we see how a proper design of these lossless metamaterial covers near their plasma resonance may induce a dramatic drop in the scattering cross section, making the object nearly invisible to an observer, a phenomenon with obvious applications for low observability and non invasive probe design. Physical insights into this phenomenon and some numerical results are provided.
Re:Invisibility cloaking (Score:5, Informative)
500 Nanometer Romulan Warbirds, perhaps... (Score:4, Informative)
Visible light is around 400nm (violet) to 800nm (red). So, this is only effective for sufficiently tiny battleships.
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Re:Invisibility cloaking (Score:3, Informative)
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Re:Everybody knows (Score:4, Informative)
BTW plasmons are not my area of expertise but I am pretty sure that the above is correct in principle.
Re:Everybody knows (Score:2, Informative)
Chameleons (Score:5, Informative)
Grrr...
Chameleons don't change their colors for this reason. It's a myth. Stop spreading it.
http://www.wsu.edu/DrUniverse/chamel.html [wsu.edu]
Re:Indeed, it's pretty far from advertised... (Score:2, Informative)
2.2 mb PDF
Look on page 11 (numbered page, not the PDF's page) at the bottom, at TPS-43E.
The placement of those diagrams is annoying, that sentence isn't finished untill page 16. Here's what it says:
I boldfaced the really important parts. That sounds like a LOT of energy. It all depends on the class of radar. When i said beam above, I meant that they narrow their sweep path and shorten the period.
Re:Everybody knows (Score:5, Informative)
Most scientifically literate people probably haven't heard of plasmons because they only form when the surface of a metal is milled with a regular array of nanostructures. In this case you have an array of holes on the scale of tens to hundreds of nanometers in diameter. When there's some such repeating nanoscale structure it changes the electron energetics so that the energy to frequency ratio is similar to that of the electromagnetic spectrum, at which point light can couple with the surface electrons and form these longitudinal surface waves (I'm not a physicist yet, so some of this may be a bit shakey).
As the parent said it's these waves that can then travel through the holes milled in the surface out onto the other side, where for some reason or another, they'll reemit the energy stored in them as light. It's pretty cool because they've done tests and the light doesn't just come out of the holes. It's as if the light passes straight through the metal film. Furthermore, they know the light's not simply passing through the film, because they've also measured it and found a very slight delay due to the formation, propagation, and reemission of the plasmons.
The story I heard about the discovery of this phenomenon is kind of amusing. Apparently an English speaking chemist wanted an array of micro wells for some polymer reaction, asked a Chinese chemist if he could do make one. The Chinese chemist thought he was crazy and said it would take six months. Due to the language barrier, the "you're crazy" bit didn't make it through, and six months later the English speaker picked it up looked through it, and said, hey, there's nothing here.
One use they're currently looking into is very specific optical filters which can be built for any wavelength. The grad student I worked with mentioned way down the line the possibility for essentially infinite resolution displays, although how that'd work isn't quite clear.
Dazzle Camouflage (Score:3, Informative)
Re:Indeed, it's pretty far from advertised... (Score:5, Informative)
That would mean the average power (average power would dictate heating effects) is 6500W (4MW * 0.1625%), which is roughly equivalent to 4 decent microwave ovens.
Now take that amount of power and point it at an aircraft 200km away (well within the range of 481km). Without doing the calculation to find out the exact value of the intensity at 200km, I will just say that the intensity of the radar beam at 200km will be 0.000025 times smaller than at 1km. And at 1km it would be 0.000001 times smaller than at 1m, which is comparable to the range of a household microwave. So you want to stack 4 or 5 microwave ovens together, collate their radiators so that all of the energy is radiating in one general beam, and try to heat up an aircraft far away...
In short, radars do not cause significant heating on aircraft, even if the aircraft absorbs every photon that hits it. Radars do not run at 100% duty cycle, or even at 5% duty cycle. When you're generating 4 MW at those frequencies you make a lot of heat in the resonator/amplifier (klystron, twystron, etc.), so you can't just keep it on all the time or it would melt.
Re:Dazzle Camouflage (Score:3, Informative)
Re:Restrictions far too great (Score:1, Informative)
That's not even close to true. The wavelengths used are much smaller than an the plane. Usually it's microwaves. You can't get a reflection off an object smaller than a wavelength, really.
Re:Indeed, it's pretty far from advertised... (Score:3, Informative)
Which was exactly why it took a computer to be able to design stealth aircraft. The F-117 is an ugly faceting monstrosity, but it is faceted because at the time that it was designed, the computers were not powerful enough to do continuous surfaces. But advancing computing power has enabled the design of the F-22 and F-35.
But one key of stealth design is to avoid any 90-degree angles -- between ANY two surfaces. If you accomplish this, then you have done much to reduce the radar signature.
Re:Indeed, it's pretty far from advertised... (Score:4, Informative)
I found a free space loss calculator and put in 3 GHz and 100km and it came up with about -142dB, so let's play with that. You've got an +80db gain antenna and -142dB loss due to distance, which totals up to a system loss of -62dB, or -20.67 times loss.
Assuming the aircraft at 100km absorbs the whole beamwidth's worth of energy, that amounts to (6500W / 20.67)=315W. So the total heating of an aircraft illuminated by this particular radar, assuming total absorption of the beam by the aircraft, an unreasonably high 80dB gain of the dish antenna, and the airplane being the target of the beam for an extended period of time would be like putting 3 100W lightbulbs near it.
Re:Everybody knows (Score:2, Informative)
I'm studying nanoscale science (still at the beginning) and we visited the institute where the guy you mentioned is working. He introduced us to the institute and some technical aspects and we were led through the laboratories, which was very interesting.
Of course he told us the story about the misunderstanding, too. Here's the guy: http://www-isis.u-strasbg.fr/nano/ [u-strasbg.fr] Here are several publications about the phenomenon and other topics: http://www-isis.u-strasbg.fr/nano/pub.html [u-strasbg.fr]