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A Step Toward an Invisibility Cloak
Technology Review has a writeup on the latest advance in the lab towards an invisibility cloak made of metamaterials, described this week in Science. We've been following this technology since the beginning. The breakthrough is software that lets researchers design materials that are both low-loss and wideband. "The cloak that the researchers built works with wavelengths of light ranging from about 1 to 18 gigahertz — a swath as broad as the visible spectrum. No one has yet made a cloaking device that works in the visible spectrum, and those metamaterials that have been fabricated tend to work only with narrow bands of light. But a cloak that made an object invisible to light of only one color would not be of much use. Similarly, a cloaking device can't afford to be lossy: if it lets just a little bit of light reflect off the object it's supposed to cloak, it's no longer effective. The cloak that Smith built is very low loss, successfully rerouting almost all the light that hits it."
Similarly, a cloaking device can't afford to be lossy: if it lets just a little bit of light reflect off the object it's supposed to cloak, it's no longer effective.
Why would that be no longer effective? If the cloak reroutes 90% of the light, then you're left with 10% opacity, right? Sure, something that translucent would be very difficult to see, especially from a distance.
Direct link please!
http://www.technologyreview.com/computing/21971/?a=f
Garbage javascript broke for me and the page didn't get past a white page.
If visible light is being routed around the cloak, it could cause some serious navigation issues for the cloaked object. Maybe some objects (ships/aircraft) will only need a cloak that routes radar, leaving pilots to navigate by sight and dead reckoning (GPS uses radio frequencies, right?)
"works with wavelengths of light ranging from about 1 to 18 gigahertz"
frequency is in hertz.
wavelength is a length, so it will be in meters or feet or inches or volkswagen bugs.
that is all. </pedantic>
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and not in what he is capable of receiving."
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Pics or it didn't happen.
Metamaterials are interesting enough _whithout_ that stupid invisibility shit everytime.
I mean, lenses without diffration limit are also interesting. And opposed to the inisibility stuff, they might really work.
HI O WISE PRINCE. WHT TOOK U SO DAM LONG?
Now I can see what happens inside the Girls' dorm!
Giggity-giggity-goo.
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1-18 ghz is way way broader than a very thin swat of visible light. Just looking at the spectra should show it. Mod me actually uninformative or overrater.
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"Now [that] this is becoming a more feasible technology, we will start to see a lot more of it."
Heh, i thought the goal was to see a lot less of it :)
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...and I ain't an engineer.
I bet you've a schoolteacher.
It is dangerous to be right when the government is wrong.
Bah, "ain't" is a perfectly valid contraction for "am not", and has been since at least 1706. (See http://www.etymonline.com/index.php?search=ain't&searchmode=none) Proscriptionists object to it largely because it's often used for "is not", or "are not", which was seen as somehow "perverting" the English language.
In fact, though, "ain't" has been used that way since at least the 19th century.
About the worst that you can say of "ain't" is that it's inappropriate for a formal register, but so are most contractions.
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7000 -> f = lambda/c -> 4.28275E+14
5000 -> f = lambda/c -> 5.99585E+14
Difference -> 1.713E+14 Hz -> 1.713E5 GHZ
About 171,000 GHZ not 17
Sigh, here we go again! Radars and optical vision do not work in remotely the same way. Creating invisibility in the two different realms is a completely different problem.
In most vision situations there are two critical factors which don't occur in the great majority of radars. The first is illumination of the target from angles other than the viewing angle (OK, there are bistatic radars, but they are not common) and the other is a background which is illuminated. Try to think about this for just a few moments. Why can't we all make ourselves invisible just by wearing matt black clothing? Well, obviously because we will stand out against the background unless we happen to be standing in front of black wall or wandering around in a coal mine. The whole point of the fictional 'invisibility cloak' is that it works in all circumstances. We can already be invisible in certain carefully controlled environments, that after all is what camouflage is all about.
But, a radar is rather like wandering about in the above mentioned coal mine, or perhaps a dark forest with a miner's lamp fixed to your head. The background is basically black and the illumination comes from the viewing direction. In this scenario, someone dress entirely in black would be effectively invisible. And that is the key point to grasp. In the world or radar we can achieve invisibility simply by making sufficiently 'black' 'paint'. The weird ability of these meta-materials to allow the illumination to pass through the target un-disturbed is of no benefit. Since we don't have a receiver on the other side of the target to detect this energy it isn't relevant. Now, sure, we can all dream up complex bistatic radars which rely on the obscuration of the signal to detect the target, but I remain to be convinced that such a thing can be made sufficiently versatile to be useful.
Can I stress that I am not suggesting the these meta-materials don't have an application in the world of radar. They seem to me to be particularly useful where one wants to remove a fixed object which obscures the view of your radar. For example, consider a radar on a ship. It may well find that in some directions its view is obscured by other parts of the superstructure. If the could cover these other bits of the ship with meta-materials such that the radar pulses could pass 'through' and back again undisturbed, then our radar's field of view would be increased. Such an application would work perfectly well with even the relatively narrow band materials presented previously.