Topic: Metamaterials: a real invisibility cloak

[Thucydides]

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.

[warspite]

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?

[Beadwindow 7]

Could you imagine?

This would be an amazing resource for ECW. Imagine hiding your CPs or RRBs from Directional Finding?

[MCG]

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.

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).

[Trinity]

How much energy would this thing need.   

Definitely NOT feasible for the next 20-30 years?

[Klc]

As the article said. You can hide a small copper rod from microwaves. If you can find a use for that... 

[MCG]

Today it's a rod.  In 25 years it could be a tank, destroyer or attack fighter that is hidden.

[warspite]

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.

[Bert]

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.

[MCG]

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.

[Bert]

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.

[MCG]

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.”

[andreit1]

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. 

[Aden_Gatling]

Outta' control  ... just came across a video of this technology (wait for the end to check out the jacket): http://www.youtube.com/watch?v=VVi7mZ6XX3w

[warspite]

http://projects.star.t.u-tokyo.ac.jp/projects/MEDIA/xv/oc.html
It's actually quite ingenious. As far as I can tell the reflective material only reflects the image you project, hence with an image of the background it masks the object behind it. Not an expert but should have potential for base security or security for any fixed location in general.

[geo]

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."

[army08]

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.

[Thucydides]

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.

[GAP]

Especially in various forms of covert ops, etc.....

[Thucydides]

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.

[tomahawk6]

Cant have a cloak without an energy shield.
All we need for our space ship is a warp drive.

[Ecco]

All we need for our space ship is a warp drive.

Here is your warp drive.
http://dsc.discovery.com/news/2008/07/28/warp-speed-engine.html

[Thucydides]

A broadband invisibility cloak is now within reach. Given that lightwaves are much smaller than sound or radio waves, it will be easier in theory to "cloak" aircraft and AFV's from radar, and submarines from sonar than to make objects disappear in the visible spectrum. My main question now is how well does this stuff work in controlling leakage of energy from the shielded object? (Damn, what is that thermal hotspot in the middle of the open field?)

Exciting stuff

http://www.technologyreview.com/computing/21971/?nlid=1694&a=f

Friday, January 16, 2009
Invisibility-Cloak Breakthrough
New software has enabled metamaterials to work with a broad band of frequencies.
By Katherine Bourzac

Metamaterials interact with light in ways that appear to violate the laws of physics. They can bend light around an object as if it weren't there, or narrow the resolution of light microscopes down to a few nanometers. But metamaterials must be painstakingly structured at the nano- and microscales in order to achieve these exotic effects. Now the Duke University researcher who built the first invisibility cloak in 2006 has created software that speeds up the design of metamaterials. He and his colleagues have used the program to build a complex light cloak that's invisible to a broad band of microwave light--and they did it in only about 10 days.

David R. Smith of Duke and Tai Jun Cui of Southeast University, in Nanjing, China, led the work, which is a landmark in the field of metamaterials. 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.

"Their cloak . . . answers the naysayers who predicted that cloaks would always be narrowband and lossy," says John Pendry, chair in theoretical solid-state physics at Imperial College London. Pendry did the theoretical work upon which both the first invisibility cloak and its new successor are based. "Needless to say, I am delighted with this development," says Pendry. He and his Imperial College colleague Jensen Li proposed a theoretical version of a broadband cloak just last year, and at that time, he says, he "did not expect such rapid experimental progress."

The broadband cloak is a rectangular structure measuring about 50 by 10 centimeters, with a height of about 1 centimeter. It's made up of roughly 600 I-shaped copper structures. Making each structure is a simple matter, says Smith. "They're copper patterns on a circuit board, cut up and arranged. It's a well-known, inexpensive technology." The hard part is determining the dimensions of each of these 600 structures and how to arrange them. With the first light cloak, which had only 10 such pieces, "we had to design each element by numerical simulations," Smith says. Applying the same approach to the more complicated cloak would have eaten up months.

Even for physicists and engineers, the math involved in the theoretical design of cloaking devices is very difficult, says Nicholas Fang, a professor of mechanical science and engineering at the University of Illinois at Urbana-Champaign. The way that a material interacts with light's magnetic and electric components is taken into account in determining the size, shape, and orientation of each structure in a metamaterial. Pendry and Li's theoretical work described how to make a broadband cloak by using materials structured so that they have an electrical response to light, but not a magnetic one. But it wasn't clear how to put this idea into practice. The Southeast University researchers developed new algorithms to greatly speed up the process, says Smith. These algorithms make it possible to quickly predict how a structure with a particular shape will interact with light.

The cloak itself, described this week in Science, is indeed impressive, says Fang, who's working on metamaterials for super-resolution biological imaging. But what's more exciting is that the new approach to design will accelerate the development of other metamaterials. Smith says that he and his group have already moved beyond the cloak reported in Science, but because their latest work is unpublished, he can't specify what they've made. "Now [that] this is becoming a more feasible technology," he says, "we will start to see a lot more of it."

Other applications of metamaterials, says Smith, include optical devices that take light energy and concentrate it, instead of turning it away--conceptually, the opposite of a cloak. "You could improve solar cells by making structures to increase the field strength of the light," he says. The new work suggests that this could be done over the whole spectrum of wavelengths found in sunlight. Similarly, broadband "hyperlenses" that gather up light missed by normal lenses could revolutionize biological imaging. Fang and others have developed narrowband hyperlenses with resolutions of only a few nanometers, which make the molecular workings of cells visible. A broadband hyperlens could work with all colors of visible and infrared light.

The ultimate goal, says Pendry, is cloaking in the visible-light spectrum, and Smith's latest work points the way forward. "There are no insuperable obstacles to making a cloak work at optical frequencies," Pendry says. "The Duke paper brings this goal a step closer."

Copyright Technology Review 2009.

[Thucydides]

Notice this is a flat plate of material. This form factor is much easier to work with when building an actual object:

http://www.technologyreview.com/blog/arxiv/23270/?nlid=1908

Acoustic superlens could cloak objects from sonar

First experimental demonstration of a technology that could trigger a new game of cat and mouse beneath the waves
Wednesday, April 01, 2009

Researchers have been messing about with optical metamaterials and invisibility cloaks for a few years now. And while progress has been rapid, nobody's going to be fooling Voldemort any time soon.

But the same exotic tricks that apply to light can equally be applied to sound. And potentially more easily too because sound has a longer wavelength. The business parts of acoustic metamaterials should therefore be significantly easier to build than their optical counterparts.

And that's just what Nicholas Fang and buddies from the University of Illinois at Urbana- Champaign have done: create a flat slab of acoustic metamaterial that focuses sound with a negative refractive index. They've even fashioned a design that works as a "superlens" that focuses the so-called evanescent sound waves that form within a single wavelength of the source-- a world first apparently.

Fang and co have created an acoustic metamaterial by carving an array of holes into an aluminium sheet and filling the holes with water. The holes then resonate when water moves over them, like wind over the mouth of a bottle.

In theory, superlenses can far outperform the resolution of conventional lenses but Fang's lens isn't super just yet: its resolution is only about half the length of the incident waves. But that's pretty good and among the best that has ever been possible with purely passive focusing elements. And while conventional optics can never beat this kind of resolution, Fang's superlenses can almost certainly be improved.

Another big advantage is the shape of the lens which is entirely flat and just a few centimetres square. That makes it much easier to make than the spherical optics that have been necessary in the past.

Obviously, the new technique will be handy for medical imaging and nondestructive testing but the authors hint at a more exotic application. They say:

    "This design approach may lead to novel strategies of acoustic cloak for camouflage under sonar.

Tantalising! What on Earth could they mean?

[Recon 3690]

This brings to mind the 2 Philadelphia Experiment movies