Alleged invisibility cloak

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WarDaft
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Alleged invisibility cloak

Postby WarDaft » Mon Jan 07, 2013 7:52 pm UTC

So with all the developments in metamaterials as of late, enthusiastic people (including me) were saying crazy things like "in 10-15 years, we'll actually be able to make things invisible!" when (or so it seems on the surface) we should have been saying 10-15 months.

This company website (and a whole lot of news sites, some more hyperbole filled than others) claims that they've made it and have started talks with Canadian and US military departments. On the other hand, they aren't showing anyone except potential military buyers so no one can corroborate it.


Do you think this is an elaborate hoax, or are we really jumping forward in technology that fast?
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Re: Alleged invisibility cloak

Postby gmalivuk » Mon Jan 07, 2013 8:08 pm UTC

From what I've seen, those military folks were completely unenthusiastic about the technology. Which either means that they already have it, which I consider relatively unlikely given the previously slow progress of this kind of tech, or it means the company has very little to offer beyond exaggerated hype, which I consider to be extremely likely given the previous tendency for companies to oversell "groundbreaking" technology in an effort to get investors.
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Re: Alleged invisibility cloak

Postby scarecrovv » Tue Jan 08, 2013 12:31 am UTC

The complete lack of technical detail on the website, combined with the refusal to show any actual results, and the abuse of the prefixes "quantum" and "hyper" are huge red flags for a hoax.

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Re: Alleged invisibility cloak

Postby EdgarJPublius » Tue Jan 08, 2013 6:59 pm UTC

The website looks almost exactly like the sort of websites used to announce 'totally real perpetual motion, you guys don't even know, it's like, so real'.
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Re: Alleged invisibility cloak

Postby BlackSails » Wed Jan 09, 2013 2:35 am UTC

I love the badly photoshopped image at the top that says "for security reasons, we cant show you our invisible technology"

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Re: Alleged invisibility cloak

Postby MostlyHarmless » Wed Jan 09, 2013 5:32 am UTC

To be fair, although the site is pretty clearly quackery, invisibility cloaks aren't as far from reality as you might think: http://www.math.washington.edu/~gunther ... wfinal.pdf

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Re: Alleged invisibility cloak

Postby WarDaft » Wed Jan 09, 2013 7:16 am UTC

It has an amazing breadth of press coverage though. They've seriously shot their credibility in the foot if it doesn't exist, which is not good for what seems to be a real company even if it isn't selling real invisibility cloaks.
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Re: Alleged invisibility cloak

Postby Sockmonkey » Wed Jan 09, 2013 7:18 am UTC

BlackSails wrote:I love the badly photoshopped image at the top that says "for security reasons, we cant show you our invisible technology"

If it really was invisible how would we know it's in the picture in the first place? :P
Frankly if you have working invisibility you wanna keep it a secret from anyone but the military guys you're trying to sell it to.

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Re: Alleged invisibility cloak

Postby mathmannix » Wed Jan 09, 2013 6:43 pm UTC

BlackSails wrote:I love the badly photoshopped image at the top that says "for security reasons, we cant show you our invisible technology"


I love the fact that it calls each picture a "mock-up". While mockup usually means something like "working model" or "prototype", methinks the grammarlawyers could say "it said it was 'mock' didn't it?"
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Re: Alleged invisibility cloak

Postby Carlington » Thu Jan 10, 2013 6:20 am UTC

The guy's got a lot of credentials as a camouflage pattern designer, but I can find literally no scientific background, nor any work in the sort of optics you'd need to make a material like this. Add that to the fact that optical physicists have achieved similar results, but never on objects bigger than 1 cm3, and I'm pretty happy to say quack.
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Re: Alleged invisibility cloak

Postby idobox » Fri Jan 11, 2013 4:25 pm UTC

Metamaterial invisibility cloaks have two big issues:
-narrow bandwidth
-rigidity

Which means you could make a barrel shaped cloak that makes you invisible in green light, but not in blue or red. Pretty useless for personal camouflage.

I've been working on metamaterials in microwave band, and these things are tricky to design, and very sensitive. We have to use pattern tiles about one tenth of a wavelength to get decent results. In optical frequencies, it means tiles about 50 wide, so even smaller details. You don't have a lot of design options at this scale.
A few years ago, I remember reading about a radar invisibility cloak for missiles. It was heavy, and worked only for a narrow range of radar frequencies, so people preferred regular stealth technology.

Active camouflage, with flexible flat screens sewn into your clothes, appears to be a much more viable solution for this kind of issues. And you don't need to be totally invisible. Being difficult to see over the background would already be a big improvement
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Re: Alleged invisibility cloak

Postby Zamfir » Fri Jan 11, 2013 5:09 pm UTC

http://iopscience.iop.org/1367-2630/14/1/013054 looks like state of the art experimental cloaking results it has 'pictures', tough they require some interpretation.

It's a cylinder, and it apparently cloakable from all angles and for different 'lighting conditions', which really reads more like 'for different types of radar installations'.

For the moment the cloaking itself is not quite perfect, and it's microwave range, but those seem like surmountable challenges

But the object is also the size of a few wavelengths, and the working frequency (called a 'wide band' by the authors) is something like 2.9 to 3.3 gigahertz, with good performance only in the middle of that range.

As far as I can tell, those are rather fundamental problems on the road to a hypothetical Harry Potter cloak. The metamaterials seem to work on resonance-like effects, with a tight frequency dependency built into the concept.And vision-fooling cloaking would require the manipulation of the field across millions of wavelengths, which seems a completely different kind of exercise.

Weirdly enough, I can envision loads of applications for this kind of mastery of optical manipulation. In lense-like functions, or in optical electronics, say. Antennas. But it's completely unclear how one would good from here to visual cloaking of macroscopic objects, even with the best of luck.

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Re: Alleged invisibility cloak

Postby idobox » Fri Jan 11, 2013 7:26 pm UTC

Zamfir wrote:But the object is also the size of a few wavelengths, and the working frequency (called a 'wide band' by the authors) is something like 2.9 to 3.3 gigahertz, with good performance only in the middle of that range.

Just to clarify: the cloak is larger than a wavelength, but it is made of elements significantly smaller.
I just skimmed the document, but the performance appears to be good for about 100-200MHz, so between 3 and 6% relative bandwidth. The visible optical wavelengths are between 400 and 800nm, so about 33% relative bandwidth. That's a big difference.

Zamfir wrote:As far as I can tell, those are rather fundamental problems on the road to a hypothetical Harry Potter cloak. The metamaterials seem to work on resonance-like effects, with a tight frequency dependency built into the concept.And vision-fooling cloaking would require the manipulation of the field across millions of wavelengths, which seems a completely different kind of exercise.

That's exactly true. The first type of known metamaterial used split rings, resonant structures, and when in an array, and close to the resonant frequency, you get all sort of weird stuff happening. The idea is that the wave does not propagate normally, but sees a number of inductances and capacitances that result in weird behavior.
The textbook example is 1D negative refraction index cable. if you build a cable with serial capacitors and parallel inductors, at a particular frequency, the phase velocity will be negative.

Obviously, all that is highly dependent on the frequency, and tricks to widen the bandwidth have helped go from .1% to 5% bandwidth last time I checked.
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Re: Alleged invisibility cloak

Postby cphite » Fri Jan 11, 2013 8:01 pm UTC

gmalivuk wrote:From what I've seen, those military folks were completely unenthusiastic about the technology. Which either means that they already have it, which I consider relatively unlikely given the previously slow progress of this kind of tech, or it means the company has very little to offer beyond exaggerated hype, which I consider to be extremely likely given the previous tendency for companies to oversell "groundbreaking" technology in an effort to get investors.


Even if we assume that it works, the glaring problem with this sort of thing is that it's a cloak - you have to be inside of it for it to work. For a soldier, this is no small matter - they're already carrying 70-80 lbs of gear, asking them to do so under a cloak made of whatever these are made of is simply not feasible. It might make slightly more sense for a vehicle, but even there you have to consider how do you cover an entire vehicle with something and ensure that people can get in and out of it quickly, that you're aren't impeding it's ability to move, etc.

Assuming it works, how does this cloak react to rain? To dust and dirt? To wind? To fire or other damage? Does it interfere with radio/cellular reception? How quickly (if at all) can the thing being cloaked move and remain cloaked?

It doesn't surprise me at all that the military isn't jumping at this.

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Re: Alleged invisibility cloak

Postby idobox » Sat Jan 12, 2013 8:46 pm UTC

Armored vehicles are already covered in heavy cumbersome things, for example armor. Adding an invisibility cloak shouldn't be too much of a problem if it could work.
As it is a passive material, it shouldn't have any issues with rain, dirt or dust. I'm not sure about damage. Speed is not an issue unless Doppler effect is noticeable. RF communications should be able to pass through with a good design.

The biggest issue is that you wouldn't be able to see anything from inside. And that nobody knows how to make one that covers the whole visible spectrum, and even less the IR spectrum.
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Re: Alleged invisibility cloak

Postby Copper Bezel » Sat Jan 12, 2013 9:55 pm UTC

Well, I wouldn't imagine needing to worry about Doppler shift. = ) But might the cloak need to be configured in a particular way? You mentioned that real systems that have been tested are rigid; if this cloak was flexible, wouldn't there be an ideal geometry at which it would work best? So moving might temporarily deform it, causing it to be visible?

There's a pedestrian problem implied with dirt and dust - dirt and dust aren't invisible, and the surface may or may not be easy to clean, since the surface properties are going to be defined by whatever funky optical effects are needed. And wouldn't rain also cause refraction problems that could disrupt the optical properties of the metamaterial? Like those demonstrations of how Morpho butterflies turn from blue to green when wet?
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Re: Alleged invisibility cloak

Postby Technical Ben » Sun Jan 13, 2013 10:44 pm UTC

Rain would cause massive problems for the effect of splashing in the air. ;)
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Re: Alleged invisibility cloak

Postby scarecrovv » Tue Jan 15, 2013 12:35 am UTC

idobox wrote:The biggest issue is that you wouldn't be able to see anything from inside. And that nobody knows how to make one that covers the whole visible spectrum, and even less the IR spectrum.


I'm not sure why everybody seems to think that you can't see out of an invisibility cloak. I'm not a physicist, so maybe I'm missing something, but is there any reason you can't make a tiny pinhole in the cloak and put an itty bitty camera in it? Sure, the camera would be visible, but you'd reduce your visual cross section from that of a tank to that of a small camera.

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Re: Alleged invisibility cloak

Postby cphite » Tue Jan 15, 2013 4:35 pm UTC

idobox wrote:Armored vehicles are already covered in heavy cumbersome things, for example armor. Adding an invisibility cloak shouldn't be too much of a problem if it could work.


Throw a tarp over your car and try driving around town; report back with any problems you encounter ;)

As it is a passive material, it shouldn't have any issues with rain, dirt or dust. I'm not sure about damage. Speed is not an issue unless Doppler effect is noticeable. RF communications should be able to pass through with a good design.


My understanding is that these cloaks work by bending and redirecting light. If there is a layer of dirt or dust on top of the cloak, I have to assume that the enemy is going to see that layer of dirt or dust. If rain is falling on the cloak it's being to be splashing off the surface and forming a layer that the enemy can see. I seriously doubt that the Doppler effect will be a factor.

The biggest issue is that you wouldn't be able to see anything from inside. And that nobody knows how to make one that covers the whole visible spectrum, and even less the IR spectrum.


Exactly.

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Re: Alleged invisibility cloak

Postby Tass » Tue Jan 15, 2013 5:41 pm UTC

cphite wrote:Throw a tarp over your car and try driving around town; report back with any problems you encounter ;)


Throw in a small camera and a screen on the inside. The camera, while visible, is much harder to spot than a tank.

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Re: Alleged invisibility cloak

Postby elliptic » Wed Jan 16, 2013 1:33 pm UTC

If there is a layer of dirt or dust on top of the cloak, I have to assume that the enemy is going to see that layer of dirt or dust.


And even if the cloak starts off clean the natural enemy countermeasure is... a paintball gun :D

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Re: Alleged invisibility cloak

Postby idobox » Wed Jan 16, 2013 1:34 pm UTC

Although it is possible to make flexible metamaterials, their properties change when flexed, and a flexible invisibility cloak could not work. So definitely not for soldiers.

The materials in the optic wavelengths are made of small balls of an element in a a matrix of another element, nothing especially funky. Also they can be covered with a varnish or something to protect them. Obviously, anything out of the cloak will be visible, including dust or raindrops. The cloak would not be perfectly invisible, but look more like a pane of glass: you can see through it, it is very difficult to spot, but if you look carefully, you can see small deformations and stuff stuck to it. If you cover it in mud, the mud is visible.

If you put your cloak in a medium of a different refraction index, it will not work properly. I'd have to run a simulation to be sure, but I suppose it would behave a bit like a cylinder of glass: invisible when surrounded by glass, acting as a lens in other cases.

Oh, also, by definition, these systems are cylindrical or spherical. It might be possible to make them elliptic, but I'm not sure. In the end, it is much easier to put cameras and flat screens on a vehicle.
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Re: Alleged invisibility cloak

Postby Quizatzhaderac » Tue Jan 29, 2013 6:48 pm UTC

mathmannix wrote:I love the fact that it calls each picture a "mock-up". While mockup usually means something like "working model" or "prototype", methinks the grammarlawyers could say "it said it was 'mock' didn't it?"

That seems like a fairly correct use of the term "mock-up". The problem being that mock ups answer the question "what is an invisibility cloak?", not "did you really build an invisibility cloak?"
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Re: Alleged invisibility cloak

Postby CleverDick » Sun Feb 03, 2013 10:11 am UTC

Why must invisibility technology always be in Harry Potter cloak form? I'd be much more interested in a stealth field generator, ala Star Wars.

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Re: Alleged invisibility cloak

Postby tms » Sun Feb 03, 2013 2:10 pm UTC

At this point I'm guessing the latter belongs in the subforum.
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Re: Alleged invisibility cloak

Postby Quizatzhaderac » Mon Feb 04, 2013 3:43 pm UTC

CleverDick wrote:Why must invisibility technology always be in Harry Potter cloak form? I'd be much more interested in a stealth field generator, ala Star Wars.

Because that's the way it worked in Greek mythology, and those stories have had a bit more time to get around than star wars.
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Re: Alleged invisibility cloak

Postby Tass » Mon Feb 04, 2013 9:32 pm UTC

Quizatzhaderac wrote:
CleverDick wrote:Why must invisibility technology always be in Harry Potter cloak form? I'd be much more interested in a stealth field generator, ala Star Wars.

Because that's the way it worked in Greek mythology, and those stories have had a bit more time to get around than star wars.


Maybe also because one is slightly less impossible than the other.

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Re: Alleged invisibility cloak

Postby eSOANEM » Tue Feb 05, 2013 5:56 pm UTC

CleverDick wrote:Why must invisibility technology always be in Harry Potter cloak form? I'd be much more interested in a stealth field generator, ala Star Wars.


Wait, Star Wars had stealth fields? I don't remember them. Shield generators definitely but I can't remember any stealth fields.

Star Trek certainly had them though.
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Re: Alleged invisibility cloak

Postby tms » Tue Feb 05, 2013 9:25 pm UTC

eSOANEM wrote:Wait, Star Wars had stealth fields?

These were depicted in some video games.
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Re: Alleged invisibility cloak

Postby thoughtfully » Tue Feb 05, 2013 9:59 pm UTC

I seem to remember them also in the animated series from a couple years back.
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Re: Alleged invisibility cloak

Postby eSOANEM » Tue Feb 05, 2013 11:59 pm UTC

Ok, I'm not missing anything from the films then. I was worried for a second.
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Re: Alleged invisibility cloak

Postby Xenomortis » Wed Feb 06, 2013 9:49 am UTC

Cloaking devices are mentioned once in ESB (and how the Millennium Falcon could not have one).
But I don't think that's related to "stealth fields", whatever the hell they are.
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Re: Alleged invisibility cloak

Postby Jofur » Wed Feb 06, 2013 2:09 pm UTC

That does bring up another interesting use of any kind of light bending tech. Seems like it would be moderately practical on stationary objects. Say, an entrance to something. Just a thought to get rolling.
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Re: Alleged invisibility cloak

Postby ikrase » Wed Feb 06, 2013 8:11 pm UTC

CleverDick wrote:
Why must invisibility technology always be in Harry Potter cloak form? I'd be much more interested in a stealth field generator, ala Star Wars.

Because that's the way it worked in Greek mythology, and those stories have had a bit more time to get around than star wars.

Well, the Ring of Gyges was just a ring.

Also because perfect active camo might work well for a cloak.
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