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A Step Toward an Invisibility Cloak
Posted by
kdawson
on Sun Jan 18, 2009 03:41 PM
from the can-you-see-me-now dept.
from the can-you-see-me-now dept.
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."
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Why not let a bit through? (Score:5, Insightful)
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.
Re:Why not let a bit through? (Score:5, Funny)
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.
The Predator still got his ass shot up good with that hand-held vulcan gun, because the soldier saw the 10% of light that he couldn't cloak.
Parent
Re:Why not let a bit through? (Score:5, Funny)
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.
The Predator still got his ass shot up good with that hand-held vulcan gun, because the soldier saw the 10% of light that he couldn't cloak.
Yes, but if you look at it from a D&D point of view, you get a 90% miss chance, which is a game-breaking advantage.
Parent
Re:Why not let a bit through? (Score:5, Funny)
Yes, but if you look at it from a D&D point of view, you get a 90% miss chance, which is a game-breaking advantage.
I put on my robe and wizard hat.
Parent
Re:Why not let a bit through? (Score:4, Funny)
I put on my cloak and tinfoil hat.
There, fixed that for you. ;)
Parent
Re:Why not let a bit through? (Score:5, Informative)
For those of you who have wondered where the "robe and wizard hat" thing came from:
http://bash.org/?104383 [bash.org]
Parent
Re: (Score:3, Informative)
Except that full concealment or invisibility only grants you 50% miss chance and you can't gain more than that.
Learn the rules!
California > Minnesota (Score:4, Funny)
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.
The Predator still got his ass shot up good with that hand-held vulcan gun, because the soldier saw the 10% of light that he couldn't cloak.
That's what you get for pissing off Jesse "the future Governor of Minnesota" Ventura.
Cloaking device or not.
Parent
Re: (Score:3, Insightful)
Funny? (Score:3, Funny)
I fail to see what is so funny about that.
Re: (Score:2)
It's all a mix up when the told the geeks "makes me an invisible cloak"
They made the cloak invisible meaning that when you put it on you can see under the cloak.
FUUUU (Score:5, Informative)
Direct link please!
http://www.technologyreview.com/computing/21971/?a=f [technologyreview.com]
Garbage javascript broke for me and the page didn't get past a white page.
Re:FUUUU (Score:5, Funny)
It's not broke... it's cloaked!
Parent
Re:FUUUU (Score:5, Funny)
Parent
Blindness (Score:5, Insightful)
Re:Blindness (Score:5, Funny)
Parent
1 to 18 gigahertz (Score:2)
Re: (Score:3, Funny)
You must be thinking of the 16k visual spectrum. This is referring to the Spectrum 128k.
wavelength = length (Score:5, Informative)
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>
Re:wavelength = length (Score:5, Insightful)
Parent
Re:wavelength = length (Score:5, Funny)
Not for those of us who don't live in a vacuum, you insensitive clod!
Parent
Re: (Score:3, Funny)
Not for those of us who don't live in a vacuum, you insensitive clod!
C is still constant. C is the speed of light _in_a_vacuum_ not the speed of light in your parent's basement. And by the way I am a clod, you insensitive pedantic.
Re: (Score:3, Informative)
No, the refractive index does depend on the frequency for dispersive media, which are effectively all real media. See
http://en.wikipedia.org/wiki/Dispersion_(optics) [wikipedia.org] and http://en.wikipedia.org/wiki/Refractive_index [wikipedia.org] . Different frequencies have different phase velocities in a given dispersive medium and thus different refractive indices (see chart in "refractive index" link)
Also you can't do the calculation you describe for different frequencies unless you take into account the Abbe number of the material.
h [wikipedia.org]
Re:wavelength = length (Score:5, Funny)
Parent
Re: (Score:3, Informative)
Given the radius of a circle you can calculate its area, but that doesn't mean they're the same thing or that you can use them interchangeably. Convertibility is not equivalence, and the article as written is wrong.
Re: (Score:3, Insightful)
invisibility schmisibility (Score:5, Funny)
Re: (Score:3, Funny)
Re: (Score:3, Funny)
NSFW: http://tinyurl.com/9hn2ba [tinyurl.com]
Invisibility cloak bullshit again (Score:5, Interesting)
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.
Re: (Score:3, Insightful)
The 'invisibility cloak' thing is right up there with 'teleportation'. Every time someone manages to 'teleport' the state of a single subatomic particle, we get a bunch of articles likening the process to Star Trek teleporters.
Do ANY of the researchers involved in these things really expect them to have invisibility or teleportation capabilities at macro scales someday? I was under the impression that neither of them had any relevance at larger scales, and while I could be wrong, it seems like the media j
At last! (Score:5, Funny)
Now I can see what happens inside the Girls' dorm!
Giggity-giggity-goo.
Re: (Score:2)
Now I can see what happens inside the Girls' dorm!
Who needs a cloak for that? [yikers.com]
NOT Invisibility Cloak: RADAR Cloak (Score:4, Interesting)
Is it just me, or would this stuff work VERY well as a RADAR cloaking device?
1-18 GHz is solidly in the microwave (millimeter-wave RADAR anyone?) range...
Re:NOT Invisibility Cloak: RADAR Cloak (Score:5, Insightful)
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.
Parent
from TFA (Score:5, Funny)
"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 :)
Extraordinary claims require extraordinary proof (Score:2)
Re: (Score:3, Insightful)
Actually, all claims require adequate support for provisional acceptance. Differing standards for differing claims derives from the concept of canon which has more of a place in religion than science.
I agree it would have been nice if they'd included a demonstration vid.
Re: (Score:2)
"one color" (whatever that means)
A basic understanding of the spectrum (and absolutely no RTFA on my behalf) would suggest that they mean one colour of the spectrum. So if they can cloak, say, the red spectrum, you'd show up looking a different colour than your normal sort.
Imagine looking at some purple paper and then removing the red visibility/light from it. Is it still purple to your eyes?
No Photo No Talk! (Score:4, Funny)
I look forward to the photo of the prototype.
Re: (Score:2)
"But a cloak that made an object invisible... (Score:3, Insightful)
...to light of only one color would not be of much use."
It would be exceptionally useful if that colour was infra-red.
Why all the work? (Score:3, Informative)
I don't see why they're overdoing this so much. I've been able to become invisible for a long time--all I have to do is cover my eyes!
Try it today!
18 GHZ is NOT the width of the visible specturm (Score:5, Informative)
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
Re: (Score:3, Informative)
That was some confusing math. First of all 1 Angstrom is 10^-10. you're thinking nm. And the equation should be:
f = c/lambda
I guess you meant that as the frequencies come out correctly.
The sentence above is wrong (Score:5, Informative)
Parent
Re: (Score:3, Insightful)
Yep, that's the one. Frequencies should be thought of logarithmically. You can use the musical concept of octaves in this case. 1-18 GHz is about 4.17 octaves, whereas 400-750 THz is about 0.9 octaves.
Re:One color invisibility certainly could be of us (Score:5, Funny)
...and I ain't an engineer.
I bet you've a schoolteacher.
Parent
Re:One color invisibility certainly could be of us (Score:5, Informative)
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 [etymonline.com]) 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.
Cheers,
Your Friendly Neighborhood Pedant
Parent
Re: (Score:2)
"But a cloak that made an object invisible to light of only one color would not be of much use." If the color corresponded closely with the wavelength of laser weapons resistant/protective eye-wear could be developed of such materials.
We have simpler and cheaper absorptive filters for that already. But, making it invisible to the IR lasers used for laser rangefinders could come in handy, although it wouldn't take long to train tank crews to lase something next to the tank rather than the tank itself.
Maybe you could make it wideband enough to defeat IR heat sensitive cameras. That would be interesting. Would it look like an absolute zero patch rather than a hot engine? Probably wouldn't take long to reprogram the missiles to home in o