A Step Toward an Invisibility Cloak 197
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."
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.
Blindness (Score:5, Insightful)
Re:wavelength = length (Score:5, Insightful)
Re:Extraordinary claims require extraordinary proo (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:Summary is wrong (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:Invisibility cloak bullshit again (Score:1, Insightful)
Quite to the contrary, there are published papers that counter the claim of lenses that can beat the diffraction limit. However, there is no real counter to cloaking.
I don't understand how they can claim that there is no obstacle to a visible light cloak, though. An infrared cloak requires e-beam lithography. How the hell are we supposed to get more resolution than that? Neutron lithography?
Re:Invisibility cloak bullshit again (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 just can't resist this kind of idiotic hyperbole.
"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.
Re:Why not let a bit through? (Score:3, Insightful)
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.
Re:One color invisibility certainly could be of us (Score:1, Insightful)
It's funny how slashdotters complain about invented words such as ain't which have been used before we were all born, however have no problem with invented words such as "blog".
Re:wavelength = length (Score:3, Insightful)