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Engineers Devise Invisibility Shield
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."
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.
-Vendal Thornheart
U.S. Air Force scientists looked into generating a field of plasma around an aircraft to reduce aerodynamic drag. One unexpected effect was a reduction of RCS (radar cross section, a rough measure of radar visibility), though to my knowledge the research has not been pursued (it probably continues in classified state, just like the plasma toroid ABM system 7 years ago...). Of course, this is EM radiation in the radio portin of the specturm, not optical.
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.
"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. :-)
Here's an obligatory link to the pre-print research paper and the abstract:
http://arxiv.org/abs/cond-mat/0502336
Achieving transparency with plasmonic coatings
Andrea Alu, Nader Engheta
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.
A better link would be http://projects.star.t.u-tokyo.ac.jp/projects/MEDI A/xv/oc.html
Includes some show-off videos.
I shall go and tell the indestructible man that someone plans to murder him.
"And crucially, the effect only works when the wavelength of the light being scattered is roughly the same size as the object."
Visible light is around 400nm (violet) to 800nm (red). So, this is only effective for sufficiently tiny battleships.
It's not easily possible to hide from any good EW system. They use multiple frequencies, pulse modulation, frequency hopping, staggered pulses, and a hundred other techniques that provide some really fine grained resolution - right out to the MTUR.
You also find RADAR on HF, it's annoying if your day job is to actually listen to the static, sounds a bit like a high pitched fart, transmissions are normally short duration though - less than 30 seconds then the frequency is changed - don't hear it again for a couple of minutes/hours.
Plasmons are not science fiction or a hoax. They are electron waves in the surface of conducting materials. They also allow light to pass through holes very much smaller than the wavelength by converting the light to plasmons and back again on the other side. This was previously thought to be impossible and it has applications in optical microscopy.
BTW plasmons are not my area of expertise but I am pretty sure that the above is correct in principle.
...match its background, like a chameleon.
Grrr...
Chameleons don't change their colors for this reason. It's a myth. Stop spreading it.
http://www.wsu.edu/DrUniverse/chamel.html
// file: mice.h
#include "frickin_lasers.h"
Yeah, that's all basically correct. I did research on annealing these metal films to try to change their optical properties (we ran into some problems with grain structures in the metal growing during the annealing process).
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.