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Metamaterials: a real invisibility cloak

a_majoor

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Canada is becoming a leader in the investigation of "Metamaterials". Rather than go into the physics (which is rather freaky) the effect of metamaterials is to bend light, radio and radar waves in unexpected directions. By careful control of the material, you could literally bend light  or radar around an object, rendering it effectively transparent. Rather bizzare effects could be engineered into antennas and lenses using these materials, perhaps reducing the size of the lens compared to an equally powerful conventional optical device, creating powerful surveillance systems which could be incorporated into hand held devices.

Metamaterials working in the microwave frequency range are now being studied, and in 2005, a simple prototype that works with visible light frequencies was demonstrated.

There is an introduction in the October edition of Popular Science, and http://www.nserc.ca/news/2004/p040311_bio3.htm.
 
Not sure where to post this. Please move if it's in the wrong place.
http://www.cbc.ca/technology/story/2006/10/19/invisibility-cloak.html#skip300x250

Scientists create 'invisibility' cloak that bends microwaves
Last Updated: Thursday, October 19, 2006 | 12:09 PM ET
CBC News
A team of British and U.S. scientists has demonstrated the first working "invisibility cloak," although don’t expect it to appear in the Halloween costumes aisle just yet.

The team, led by Professor Sir John Pendry of Imperial College in London, built the prototype at Duke University in North Carolina and reported its findings Thursday in Science Express, the advance online publication of the journal Science.

Little more than 12 centimetres across, the small device can redirect microwave beams so they flow around a "hidden" object inside with little distortion, making it appear almost as if nothing were there at all.

Like light, microwaves bounce off objects, making them visible and creating a "shadow," although it has to be detected with instruments.

The new work could be a baby step to an improved version that would make the Klingons and Harry Potter jealous by hiding people and objects from visible light.

Like 'water flowing around a smooth rock'

In the experiment, the scientists used microwaves to try to detect a copper cylinder "hidden" by the cloak, which is made from metamaterials — or engineered mixtures of metal and circuit board materials, which could include ceramic, Teflon or fibre composite materials.

"The waves' movement is similar to river water flowing around a smooth rock,” said cloak designer David Schurig, a research associate in Duke's electrical and computer engineering department.

The test came five months after the team published a theory that such a device was possible to design.

"By incorporating complex material properties, our cloak allows a concealed volume, plus the cloak, to appear to have properties similar to free space when viewed externally," said David Smith, a professor of electrical and computer engineering at Duke, in a release Thursday.

"The cloak reduces both an object's reflection and its shadow, either of which would enable its detection."

Wireless, radar applications

Cloaking differs from stealth technology, which doesn't make an aircraft invisible but reduces the cross-section available to radar, making it hard to track. Cloaking simply passes the radar or other waves around the object as if it weren't there.

Cloaks that render objects essentially invisible to microwaves could have a variety of wireless communications or radar applications, the researchers said.

The scientists said their cloak represents the most comprehensive approach to invisibility yet realized, with the potential to hide objects of any size or material property.

Earlier scientific approaches to achieving "invisibility" often relied on limiting the reflection of electromagnetic waves, they added.

Could this have serious military application? Even if it could only hide a target from radar etc, it would seem to me to have enormous potential. Comments?
 
Could you imagine?

This would be an amazing resource for ECW. Imagine hiding your CPs or RRBs from Directional Finding?
 
warspite said:
Could this have serious military application? Even if it could only hide a target from radar etc, it would seem to me to have enormous potential. Comments?
Eventually, yes.  Probably not for a while.
Sig_Des said:
Could you imagine?

This would be an amazing resource for ECW. Imagine hiding your CPs or RRBs from Directional Finding?
I don't think this will hide a transmitter from direction finding.  It would hide things from the ambient EM spectrum (including from detection systems that look for a return of their own EM broadcasts).
 
How much energy would this thing need.  ::) ::) ???

Definitely NOT feasible for the next 20-30 years?

 
As the article said. You can hide a small copper rod from microwaves. If you can find a use for that...  ::)
 
Today it's a rod.  In 25 years it could be a tank, destroyer or attack fighter that is hidden.
 
From theory to hiding this small copper rod, took five months. From here it would just be a matter of increasing the scale and efficiency. The main problem, as Trinity has said, will be how much power this thing will use to operate.
 
The trick to the technology is HOW it redirects microwaves, if "redirects" is the word to
accurately describe what the device does.  The article specifies microwaves but other
electromagnetic spectrums are not listed.

"Visibility" of radar usually within microwave bands rely on signal reflection or discernable
changes across a transmission field.  The technology would reduce the reflection by the
redirection of radar pulses and minimize discernable changes in RF fields.  Speculative
applications may involve radar/RF object detection countermeasures or in the reduction
of damaging solar/high power RFI fields.
 
Bert ,
You are describing stealth technology when you talk of redirecting the radar pulses.  That is not what is described above (in which the radar pulses would still be seen undisturbed on the far side of the object).  When this technology is made to work (at it may be a very many years) then you would no longer be able to detect stealth aircraft through passive stations looking for scattered EM waves.
 
Sorry McG, I'm taking this right from the article:

>
Little more than 12 centimetres across, the small device can redirect microwave beams so they flow around a "hidden" object inside with little distortion, making it appear almost as if nothing were there at all.
<

The article doesn't provide a full scientific concept or technical specifications of the wave redirection.  It does specify
"microwaves" which are a small part of the electromagnetic spectrum and redirect with "little" distortion.  The radar does
detect reflections so the device may minimize or eliminate discernable radar signatures.  I was speculating the device could also mask
objects passing through X-ray machines or lower/redirect solar RFI that affects satellites in time to come.
 
The goal of the technology is no reflection/scattering.  You noted yourself (your first post above) that "redirects" does not fit the technology description.  I agree that the device could mask objects passing through X-ray machines, and this is probably much nearer in the future that any battlefield application.

Crude invisibility cloak unveiled
Device makes microwaves slip around object
Oct. 19, 2006. 11:04 AM
RANDOLPHE E. SCHMID
ASSOCIATED PRESS

WASHINGTON - Harry Potter and Captain Kirk would be proud. A team of American and British researchers has made a Cloak of Invisibility.
Well, OK, it’s not perfect. Yet.

But it’s a start, and it did a pretty good job of hiding a copper cylinder from microwave detection.

Like light and radar waves, microwaves bounce off objects making them visible and creating a shadow, though it has to be detected with instruments.
And if you can hide something from microwaves, you can hide it from radar — a possibility that will fascinate the military — and likely from eyesight as well.

Cloaking differs from stealth technology, which doesn’t make an aircraft, ships and other objects invisible but reduces the cross-section available to radar, making it hard to track.

Cloaking simply passes the radar or other waves around the object as if it weren’t there, like water flowing around a smooth rock in a stream.
The new work points the way for an improved version that could even hide people and objects from visible light.

Conceptually, the chance of adapting the concept to visible light is good, cloak designer David Schurig said in a telephone interview.

But Schurig, a research associate in Duke University’s electrical and computer engineering department, added: “From an engineering point of view it is very challenging.”

 
I would give it a maximum of 10 years before it is applied
to actual combat. Although by then a counter measure will surely have emerged. I say we go
back to fighting with our fists.  :salute:
 
http://news.bbc.co.uk/2/hi/science/nature/7553061.stm

Scientists in the US say they are a step closer to developing materials that could render people invisible.

Researchers at the University of California in Berkeley have developed a material that can bend light around 3D objects making them "disappear".
The materials do not occur naturally but have been created on a nano scale, measured in billionths of a metre.
The team says the principles could one day be scaled up to make invisibility cloaks large enough to hide people.

Stealth operations

The findings, by scientists led by Xiang Zhang, were published in the journals Nature and Science.
The light-bending effect relies on reversing refraction, the effect that makes a straw placed in water appear bent.
Previous efforts have shown this negative refraction effect using microwaves—a wavelength far longer than humans can see.
The new materials instead work at wavelengths around those used in the telecommunications industry—much nearer to the visible part of the spectrum.
Two different teams led by Zhang made objects made of so-called metamaterials—artificial structures with features smaller than the wavelength of light that give the materials their unusual properties.

One approach used nanometre-scale stacks of silver and magnesium fluoride in a "fishnet" structure, while another made use of nanowires made of silver.
Light is neither absorbed nor reflected by the objects, passing "like water flowing around a rock," according to the researchers. As a result, only the light from behind the objects can be seen.

Cloak and shadow

"This is a huge step forward, a tremendous achievement," says Professor Ortwin Hess of the Advanced Technology Institute at the University of Surrey.
"It's a careful choice of the right materials and the right structuring to get this effect for the first time at these wavelengths."
There could be more immediate applications for the devices in telecommunications, Prof Hess says.
What's more, they could be used to make better microscopes, allowing images of far smaller objects than conventional microscopes can see.

And a genuine cloaking effect isn't far around the corner.

"In order to have the 'Harry Potter' effect, you just need to find the right materials for the visible wavelengths," says Prof Hess, "and it's absolutely thrilling to see we're on the right track."

 
I read and wrote on an article on usenet a number of years back. It was essentially just a matter of having a light absorbant material that could also reflect those colours around it - cloaking. Or in the case of invisibility take the signal then transmit the signal from one side, map the digital characteristics of the space from point A to point b and display it. I have no doubts this technology existed over 5 years ago. in a 1 meter x 1 meter sized drone.

 
Metamaterials do not absorb wavelengths of light (or sound, there are some threads on metamaterials in the navy board and elsewhere in Army.ca), but rather refract them in a controlled manner. Think of how light is refracted in a glass of water when you dunk a spoon in it; the spoon looks broken where the light is refracted.

Metamaterials control the refraction in the manner the designer plans, metamaterials already exist for radio and microwave frequencies (imagine bending a radar beam around an aircraft or ship), and have been demonstrated for light and sound as well. invisibility in all wavelengths will be difficult to achieve, since refraction is a property of the wavelength of the light, radio or sound wave you are trying to bend, but even limited invisibility would be pretty freaky.
 
Especially in various forms of covert ops, etc.....
 
More on Metamaterials:

http://www.technologyreview.com/Nanotech/21213/?nlid=1268&a=f

Bringing Invisibility Cloaks Closer
The fabrication of two new materials for manipulating light is a key step toward realizing cloaking.
By Katherine Bourzac

In an important step toward the development of practical invisibility cloaks, researchers have engineered two new materials that bend light in entirely new ways. These materials are the first that work in the optical band of the spectrum, which encompasses visible and infrared light; existing cloaking materials only work with microwaves. Such cloaks, long depicted in science fiction, would allow objects, from warplanes to people, to hide in plain sight.

Both materials, described separately in the journals Science and Nature this week, exhibit a property called negative refraction that no natural material possesses. As light passes through the materials, it bends backward. One material works with visible light; the other has been demonstrated with near-infrared light.

The materials, created in the lab of University of California, Berkeley, engineer Xiang Zhang, could show the way toward invisibility cloaks that shield objects from visible light. But Steven Cummer, a Duke University engineer involved in the development of the microwave cloak, cautions that there is a long way to go before the new materials can be used for cloaking. Cloaking materials must guide light in a very precisely controlled way so that it flows around an object, re-forming on the other side with no distortion. The Berkeley materials can bend light in the fundamental way necessary for cloaking, but they will require further engineering to manipulate light so that it is carefully directed.

One of the new Berkeley materials is made up of alternating layers of metal and an insulating material, both of which are punched with a grid of square holes. The total thickness of the device is about 800 nanometers; the holes are even smaller. "These stacked layers form electrical-current loops that respond to the magnetic field of light," enabling its unique bending properties, says Jason Valentine, a graduate student in Zhang's lab. Naturally occurring materials, by contrast, don't interact with the magnetic component of electromagnetic waves. By changing the size of the holes, the researchers can tune the material to different frequencies of light. So far, they've demonstrated negative refraction of near-infrared light using a prism made from the material.

Researchers have been trying to create such materials for nearly 10 years, ever since it occurred to them that negative refraction might actually be possible. Other researchers have only been able to make single layers that are too thin--and much too inefficient--for device applications. The Berkeley material is about 10 times thicker than previous designs, which helps increase how much light it transmits while also making it robust enough to be the basis for real devices. "This is getting close to actual nanoscale devices," Cummer says of the Berkeley prism.

The second material is made up of silver nanowires embedded in aluminum. "The nanowire medium works like optical-fiber bundles, so in principle, it's quite different," says Nicholas Fang, mechanical-science and -engineering professor at the University of Illinois at Urbana-Champagne, who was not involved in the research. The layered grid structure not only bends light in the negative direction; it also causes it to travel backward. Light transmitted through the nanowire structure also bends in the negative direction, but without traveling backward. Because the work is still in the early stages, it's unclear which optical metamaterial will work best, and for what applications. "Maybe future solutions will blend these two approaches," says Fang.

Making an invisibility cloak will pose great engineering challenges. For one thing, the researchers will need to scale up the material even to cloak a small object: existing microwave cloaking devices, and theoretical designs for optical cloaks, must be many layers thick in order to guide light around objects without distortion. Making materials for microwave cloaking was easier because these wavelengths can be controlled by relatively large structural features. To guide visible light around an object will require a material whose structure is controlled at the nanoscale, like the ones made at Berkeley.

Developing cloaking devices may take some time. In the short term, the Berkeley materials are likely to be useful in telecommunications and microscopy. Nanoscale waveguides and other devices made from the materials might overcome one of the major challenges of scaling down optical communications to chip level: allowing fine control of parallel streams of information-rich light on the same chip so that they do not interfere with one another. And the new materials could also eventually be developed into lenses for light microscopes. So-called superlenses for getting around fundamental resolution limitations on light microscopes have been developed by Fang and others, revealing the workings of biological molecules with nanoscale resolution using ultraviolet light, which is damaging to living cells in large doses. But it hasn't been possible to make superlenses that work in the information-rich and cell-friendly visible and near-infrared parts of the spectrum.

Copyright Technology Review 2008.
 
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