Building an 'Invisibility Cloak' With Electromagnetic Fields 71
Nerval's Lobster writes "University of Toronto researchers have demonstrated an invisibility cloak that hides objects within an electromagnetic field, rather than swaddling it in meta-materials as other approaches require. Instead of covering an object completely in an opaque cloak that then mimics the appearance of empty air, the technique developed by university engineering Prof. George Eleftheriades and Ph.D. candidate Michael Selvanayagam makes objects invisible using the ability of electromagnetic fields to redirect or scatter waves of energy. The approach is similar to that of 'stealth' aircraft whose skin is made of material that absorbs the energy from radar systems and deflects the rest away from the radar detectors that sent them. Rather than scattering radio waves passively due to the shape of its exterior, however, the Toronto pair's 'cloak' deflects energy using an electromagnetic field projected by antennas that surround the object being hidden. Most of the proposals in a long list of 'invisibility cloaks' announced during the past few years actually conceal objects by covering them with an opaque blanket, which becomes 'invisible' by displaying an image of what the space it occupies would look like if neither the cloak nor the object it concealed were present. An invisibility cloak concealing an adolescent wizard hiding in a corner, for example, would display an image of the walls behind it in an effort to fool observers into thinking there was no young wizard present to block their view of the empty corner. 'We've taken an electrical engineering approach, but that's what we are excited about,' Eleftheriades said in a public announcement of the paper's publication. (The full text is available as a free PDF here.)"
Error, Error. (Score:5, Interesting)
Invisibility cloaks like this only work within a certain range of EM frequencies. Outside of that range, it won't work; in fact it may even amplify the signal and make it more obvious whatever is being cloaked. And there are some thing no amount of cloak can deal with. You can alter the optical properties of a thing, but if it's out-gassing several thousand degree plumes... you cannot mask the infra red signature of that. These new meta materials may help in communications, but I highly doubt they will ever be able to make large human-sized physical objects disappear to any current multi-sensor technology.
Re:Error, Error. (Score:4, Insightful)
Sure, pragmatic constraints affect every design. But if you're worried about being spotted by cosmic rays, that's a lot better than being worried about being spotted by guards or radar.
Re:Error, Error. (Score:4, Interesting)
Sure, pragmatic constraints affect every design. But if you're worried about being spotted by cosmic rays, that's a lot better than being worried about being spotted by guards or radar.
I'd be more worried about dying of cancer, honestly. And metamaterials do offer the promise of light-weight shielding against radioactivity in space -- as has been pointed out, they do operate over certain ranges of frequencies. I'm just tired of people calling them 'invisibility cloaks', when all they're doing is reflecting emissions at certain frequencies in a novel fashion. There are a great many useful applications for this... but "invisibility cloak" doesn't make the list. Sorry. That's bad science.
Cloaking! (Score:2)
The Klingons are going to be pissed we've got this technology too. Nothing quite as entertaining as a pissed-off Klingon, either.
Re:Error, Error. (Score:4, Insightful)
"Invisibility cloaks like this only work within a certain range of EM frequencies. "
Just like a concrete or brick wall. It works only within a certain range of EM frequencies.
With the right viewing system, you can see right through.
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Not even invisible (Score:2)
And this isn't even an "invisiblity" shield-- what it is, is a radar-scattering device.
From the article, apparently it scatters an incident radar beam so that the backscattered part (the part that returns to the transmitter) is zero. Specifically, they "then carefully modulated the current on each element to modify the field such that it deflected microwaves aimed at an aluminum cylinder in every direction except back toward the source of the microwaves, where the object could be detected."
So the object i
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You can't scatter one beam of light with another one!
No, but you can cancel light out [wikipedia.org] with more light [angryflower.com]. And this does make an object invisible, if tuned to the wavelength you want it to be invisible in.
The trouble is, you could tune it to work in visible light but only if that light were coherent (as in, comes out of a laser). You can't get incoherent light out of phase with itself because it's a wide range of frequencies and all completely incoherent, like snow on an analog TV.
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You can't scatter one beam of light with another one!
No, but you can cancel light out with more light.
You can cancel light out in specific directions, but the price of nulling the interference in some directions is increasing the intensity in others. It's that conservation of energy thing. On the average, you make the object brighter
And that really isn't "invisibility"-- you can't see through the object. It's just a complicated way of achieving the same effect as painting the object black. Except it's only "black" for a selected wavelength in a selected direction.
...The trouble is, you could tune it to work in visible light but only if that light were coherent (as in, comes out of a laser). You can't get incoherent light out of phase with itself because it's a wide range of frequencies and all completely incoherent, like snow on an analog TV.
Right.
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You can alter the optical properties of a thing, but if it's out-gassing several thousand degree plumes... you cannot mask the infra red signature of that.
Meaning, "The thing's got to have a tailpipe." So, you've seen Star Trek VI: The Undiscovered Country [wikipedia.org] ...
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But they never established that Enterprise was studying gaseous anomalies, only Excelsior
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but I highly doubt they will ever be able to make large human-sized physical objects disappear to any current multi-sensor technology.
Two words, Philadelphia Experiment.
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I'll take your two and raise you two
Magnetic mines and morons
They both exist, ergo your argument is invalid.
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Two words, Philadelphia Experiment.
The story is thought to be a hoax.[1][2][3] The U.S. Navy maintains that no such experiment was ever conducted, and details of the story contradict well-established facts about the Eldridge itself, as well as commonly accepted physics.[4] [wikipedia.org]
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Just as I thought! (Score:5, Insightful)
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It's all fun and games until INVISIBLE ZAMBONIS
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And then... the dreaded Zamboni Apocalypse....
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William Shatner is Canadian, but James T. Kirk is from Iowa. Sheesh, you never watched any Star Trek movies? Besides, Captain James Kirk is now captain of the USS Zumwalt [cnn.com], a navy destroyer that has a cloaking device! TFA: "When its begins missions, the Zumwalt will be the largest stealth ship in the Navy."
I wish they'd stop calling it that. (Score:5, Insightful)
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I think it's only justified to call something an "invisibility cloak" when it does what people actually expect an invisibility cloak to do, that is, make things actually not visible. How about calling it a "stealth cloak" because that's what I imagine most people would associate with being invisible to a radar, as opposed to the naked eye.
Won't you please think of the clickbait?
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Doesn't matter, someone will just come along with a uninvisiblity uncloaker and sell it to the enemy. Isn't that how it always goes?
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Can you be wrapped in invisibility? I think not.
You obviously never suffered through high school...
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After that, maybe they could try writing a remotely accurate summary, too! The summary is borderline gibberish, as it is impossible (in linear materials) for EM fields to "deflect" each other.
This "cloak" is interference-based, using active dipoles to generate a field that cancels the scattered field in the forward (0 degree) and backward (180 degree) directions. It's a clever piece of work, but there are fairly hard limits to the how wide an angle such techniques can cover, and moving from an essentially
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but you won't get as many hits and advertising revenue if you do it that way, son
Go ahead and stick your dick right in those dollar bills you whores
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I think it's only justified to call something an "invisibility cloak" when it does what people actually expect an invisibility cloak to do, that is, make things actually not visible. How about calling it a "stealth cloak" because that's what I imagine most people would associate with being invisible to a radar, as opposed to the naked eye.
How about flying cars? Or cure for cancer? Or pioneer probe in interstellar space? The list goes on.
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irrelevant (Score:1)
Invisible : Invisible to Radar :: Edible : Edible by Sperm Whales
Just destructive interference? (Score:2)
I may be missing how this works, but it looks like they are driving a bunch of antennas to cancel the scattered radiation from an object in one direction. While this works, the trick is to know exactly what the input signal is and the react in time to cancel - something that can only work for very narrowband sources or sources where you know the input field (including its phase) in advance.
I don't see how this could work for radar or light.
Re:Just destructive interference? (Score:5, Funny)
I don't see how this could work for radar or light.
Of course you can't see it working. Thats the point.
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Magnetic stealth is the perfect cloaking mechanism -- just as long as the enemy never launches anything metallic at it, they are home free!
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I think you are right. The cross-section for photon / photon scattering at low energies is really tiny - maybe never observed at optical wavelengths or longer. (there might be some result I don't know about).
The article makes it sound much cooler than it is - but its still kind of a nice demonstration and not easy.
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According to the Maxwell equations the incoming wave is influenced by susceptibility and permeability of the materials it is going through, and by charges a
We have been here before it went horribly wrong (Score:3, Funny)
My Summary.... (Score:2)
I just don't see this working......
Invisibility Cloak? (Score:1)
Instead of trying to make something invisible (isn't that hyper-impossible anyway?), why don't we just put an SEP field over it?
Pics or it didn't happen! (Score:2)
Oh, wait... I guess the absence of pictures is proof that they succeeded. Bravo!
Invisibility Cloak, yeah right (Score:4, Insightful)
And I thought it was just the mayor smoking crack, apparently the whole town is now. :)
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Nice try, but.. (Score:1)
We have had this tech for over 40 years! Track Break Notch will do similar things by either walking a radar off you, or move your position according to what the radar can see.
The bigger problem is millimeter band radar, you need really funky waveguides to broadcast these as a normal antenna can't cope the small wave frequency.
The A6 from the Navy and the EF-111A from the USAF both could manage similar things to this, I can only hope they have managed to it smaller as the units for each section of bandwidth
Projectile vulnerability (Score:1)
Already figured it out (Score:1)
I already have a more practical invisibility capability. I just talk to management about actual technical topics. I become invisible to them almost immediately.
How is this Datacenter related? (Score:2)
Yet another link to an internal slashdot.org story under the datacenter topic... http://slashdot.org/topic/datacenter/invisibility-using-force-field-not-cloak/ [slashdot.org]
Looks like slashdot is trying to be theverge or engadget...
Philadelphia Experiment, anyone? (Score:1)
hmmm (Score:2)
1. go to google
3. type "empty field"
Tada, picture of an invisible car.
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2. click on images
Ironic that a step about invisibility disappeared btw.
Tesla Proven Right,Again (Score:2)
Move along... nothing to see here (Score:2)
very old technology (Score:2)