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Invisibility: Possibilities / Science / Technology

Invisibility undone: Chinese scientists demonstrate how to uncloak an invisible object

Harry Potter beware! A team of Chinese scientists has developed a way to unmask your invisibility cloak. According to a new paper in the latest issue of Optics Express, the Optical Society's (OSA) open-access journal, certain materials underneath an invisibility cloak would allow invisible objects be seen again.


"Cloaking is an important problem since invisibility can help survival in hostile environment," says Huanyang Chen of Shanghai Jiao Tong University in China. He and his colleagues have proposed a theoretical "anti-cloak" that would partially cancel the effect of the invisibility cloak, which is another important problem as it turns out.

If this sounds like more movie magic, it's no accident. From the 1933 classic The Invisible Man to the more recent installment in the Harry Potter series, devices that achieve invisibility have long been the stuff of film fantasy. In recent years, however, scientists using special types of "meta" materials have shown that these Hollywood fantasies could one day become reality after all.

These materials are effectively invisible because of the way they interact with light. All materials scatter, bounce, absorb, reflect and otherwise alter light rays that strike them. We perceive color, for instance, because different materials and coatings interact with light differently. Transformation media cloaks are special materials that can bend light so much that it actually passes around the object completely. In 2006, scientists at Duke University demonstrated in the laboratory that an object made of metamaterial is partially invisible when viewed using microwaves.

Sounds cool? Not so fast. Invisibility as it has been achieved so far in the laboratory is very limited. It works, but only for a narrow band of light wavelengths. Nobody has found a way yet to make an object invisible to the broad range of wavelengths our eyes are attuned to seeing, says Chen, and doing so would be a challenge.

An even greater problem for anyone who has aspirations to be concealed in public one day is that invisibility achieved through transformation media is a two-way street. With no light penetrating a perfect invisibility cloak, there would be no way for an invisible person to see outside. In other words, invisible people would also be blind—not exactly what Harry Potter had in mind.

But now, Chen and his colleagues have developed way to partially cancel the invisibility cloak's cloaking effect. Their "anti-cloak" would be a material with optical properties perfectly matched to those of an invisibility cloak. (In technical jargon, an anti-cloak would be anisotropic negative refractive index material that is impedance matched to the positive refractive index of the invisibility cloak).

While an invisibility cloak would bend light around an object, any region that came into contact with the anti-cloak would guide some light back so that it became visible. This would allow an invisible observer to see the outside by pressing a layer of anti-cloak material in contact with an invisibility cloak.

"With the anti-cloak, Potter can see outside if he wants to," says Chen, who conducted the research together with his colleagues at Shanghai Jiao Tong University and The Hong Kong University of Science and Technology.

Paper: "The Anti-Cloak," Huanyang Chen et al, Optics Express, Vol. 16, Issue 19, September 15, 2008, pp. 14577 – 14582.

Source: American Institute of Physics

http://www.physorg.com/printnews.php?newsid=139625813
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can't they just use a can of spray paint like they did in the old doctor who episodes with the invisible daleks?
 
Seems like the Americans are already there;

(Misleading link removed by WJ)

Could be CGI but my money is on real
 
Scientists have created the first device to render an object invisible in three dimensions.

The "cloak", described in the journal Science, hid an object from detection using light of wavelengths close to those that are visible to humans.
Previous devices have been able to hide objects from light travelling in only one direction; viewed from any other angle, the object would remain visible.
This is a very early but significant step towards true invisibility cloaks.
Tolga Ergin, a scientist from the Karlsruhe Institute of Technology in Germany led the study.

He told BBC News that his team's cloak was based on the concept that you can "transform space" with a material.
He and his colleagues designed a photonic metamaterial, which influenced the behaviour of light rays.
"You can think of any transformation that you would like to have, and tailor your material to mimic this," he explained.
The basis of the design is known as a "carpet cloak". This was first proposed by Professor Sir John Pendry from Imperial College London, who also took part in this study.

"He proposed the theoretical design of having an object hidden under a bump and making the bump disappear," said Mr Ergin.
"It's like a carpet mirror," he continued. "If you hide an object under it, there is a bump, so you see a distortion in the reflected image.
"We put the carpet cloak on top of that bump and it bends the light so that the distortions disappear.
"You have the impression that the mirror you're looking at is flat."
Bending light
The trick is to change the speed and direction in which light travels through the material - that is, to change the material's refractive index.
The researchers achieved by this using a polymer crystal made up of very tiny rods. "By changing the thickness of the rods, you can change the ratio of air to polymer," explained Dr Ergin.
"Since the refractive index of air is about one and the refractive index of the polymer is about 1.52," he explained, "in principle, we can get any refractive index between those two numbers," he said.
By tailoring the refractive index of the surface of the bump, the scientists rendered it invisible to a wide range of light wavelengths slightly longer than those that we can see.

As a result, under this light, the reflective surface appeared to be flat.
A similar effect has been achieved previously in two dimensions - changing the refractive index of a piece of silicon by drilling tiny holes in its surface.
But, these holes can only be drilled in one direction.
"So if you at look at the thing from [any other] angles, you immediately see it," said Mr Ergin.
In this case, the team used a technique called laser writing to create their 3-D cloak. This uses a very finely focused laser, to "write" into a light-sensitive material.
"Wherever you put the focus spot into the material, it will harden," explained Dr Ergin. "It's a similar process to photography - when you develop it, whatever hasn't been exposed to the laser will be washed away."
Third dimension
The carpet cloak was originally designed to work in two dimensions. But when Dr Ergin and his colleagues calculated how the rays of light would travel through an object, they realised that they could use their technique to build a structure that would work in three dimensions.
In this case, the researchers use the device to cloak a bump one micrometre (one thousandth of a millimetre) high.
"But in theory there are no limits [to the size of the object you could hide], said Dr Ergin. "You could blow this up and hide a house.

"But it took us three hours to make this structure, so if you wanted to make it even one millimetre in size you would have to wait a very long time."
Professor Ortwin Hess from the University of Surrey in the UK said that this study was a "huge step forward".
"The really remarkable aspect is the demonstration of invisibility in three dimensions."
One of the major challenges that remains in the design of cloaking devices is hiding objects from wavelengths of light that are visible to humans.
"Photonic crystals usually work because the constitutive elements are not visible to the wavelength by which one observes them," Professor Hess explained.
"So if you look at the desk in front of you, you don't see the individual atoms because they are so small. You just see whole structure - the wood or the plastic."
This means that cloaking devices for visible light would have to be made up of much smaller rods. So for this technique, the laser beam would have to be made even smaller.
Currently, the rods can be made as small as 200 nanometres. To hide a bump from visible light would require rods as small as 10 nanometres.
And, as Mr Ergin explained, there is a limit to how small a point light can be focused down to.
"You could say, 'why not just make [the rods] smaller?' but it's not that easy to scale these structures down. Fabrication techniques have their limits," he said.
But Professor Hess said that this was a great achievement and these photonic materials could be used in the development of lenses and in light storage and optical circuitry.
He added: "We won't have a body-sized invisibility cloak tomorrow but this has demonstrated a remarkable proof of principle."

http://news.bbc.co.uk/1/hi/sci/tech/8574923.stm

Intriguing...
 
Invisibility cloak enters the real world
http://www.telegraph.co.uk/science/scie ... world.html

Scientists are a step closer to creating a Star Trek-style cloaking device after making an object visible to the naked eye disappear for the first time.
Invisibility cloak enters the real world

The research works by using a naturally forming crystal called calcite which has extraordinary light bending abilities Photo: CORBIS

By Richard Alleyne, Science Correspondent 4:00PM GMT 01 Feb 2011



In the past researchers have only been able to "cloak" microscopic objects using extremely complicated physics and so-called meta-materials made on a tiny scale.

But a new study at the University of Birmingham has taken a massive step forward by making a paper clip invisible – an object thousands of times bigger than previous experiments.

The research works by using a naturally forming crystal called calcite which has extraordinary light bending abilities.

By placing the crystals over an object it "bounces" light around it rendering it totally invisible to the naked eye.

Dr Shuang Zhang, a physicist and lead investigator from the University of Birmingham, said: ‘‘This is a huge step forward as, for the first time, the cloaking area is rendered at a size that is big enough for the observer to ‘see’ the invisible object with the naked eye.

"By using natural crystals for the first time, rather than artificial meta-materials, we have been able to scale up the size of the cloak and can hide larger objects, thousands of times bigger than the wavelength of the light."

The new technique is only limited by the size of the naturally formed crystals.

Calcite crystals can be up to 21ft long so it could be used on a car or a military vehicle.

It may also be possible to manufacture crystals with similar qualities.

Dr Zhang said: "Previous cloaks have succeeded at the micron level – much smaller than the thickness of a human hair – using a nano- or micro-fabricated artificial composite material.

"It is a very slow process to make these structures and they also restrict the size of the cloaking area.

"We believe that by using calcite, we can start to develop a cloak of significant size that will open avenues for future applications of cloaking devices."

The research is published in the journal Nature Communications.
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"No sign of the enemy, Captain, just a load of giant crystals!"
 
Hmm; calcite has a bizarre optical quality called 'birefringence' which causes a double image to appear when viewing objects through a crystal of that material. I expect this birefringence might be used to make things difficult to see...
http://en.wikipedia.org/wiki/Birefringence
but making macroscopic objects invisible? I can't see that...
 
ramonmercado said:
Timble2 said:
"No sign of the enemy, Captain, just a load of giant crystals!"
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Its the Crystaline Entity! Fire Photon Torpedoes!
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No...wait...hang on...it's just a giant paper clip. Cancel red alert.
 
Toward the end of a longer article about camouflage:

In 2006, the Duke University engineering professors David Smith and David Shurig, working with the British physicist John Pendry, developed a method to bend microwaves. Three years ago, professor Xiang Zhang and a team at UC Berkeley managed to bend infrared waves. But nobody had yet figured out how to bend waves of visible light. I figured Guy Cramer was blowing smoke.

Months passed. Then, this spring, Cramer invited me to his workshop. When I entered, he lowered the shades. Then he pulled up his iPad and showed me a video that depicted a cream-colored wall with a dark baseboard. In front of the wall stood something resembling a Japanese shoji screen, with panes as clear as Saran Wrap: I could see the wall behind it. In the video, a woman entered the room and walked behind the screen so that her head stuck out above it. And then I watched as her body disappeared. Her head floated above the screen, and I could see the wall. But nothing of her body. “We’re bending the entire spectrum of light—infrared, ultraviolet, thermal,” Cramer told me. “People are disappearing. It doesn’t use cameras or mirrors or require power.”

I didn’t know what to make of what I had seen (and Cramer wasn’t explaining). In his work, he maintains a constant tension between concealment and revelation. His video was tantalizing proof of nothing. A kid could achieve the same effect with video-editing software. The notorious optical-camouflage poncho had seemed mind-altering when it was caught on tape too. But nothing came of it. Could Cramer have really taken such a huge leap into the realm of the invisible?

Amy Coyne thinks maybe. Coyne is vice president for program management at ADS, a Virginia-based military-equipment contractor that helps bring Cramer’s ideas to market (ADS connected the Afghans with Cramer when new army camo was needed). “We have confidence in the quantum-stealth technology,” she said. “When you think of its potential, it’s staggering.”
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I'd say BS - if it wasn't for the fact that the guy (Cramer) has an excellent name in military circles...

Source: http://www.theatlantic.com/magazine/arc ... nc/8523/1/
 
http://autos.yahoo.com/blogs/motora...ngs-james-bond-technology-life-171557818.html
n a promotion for its first production fuel-cell vehicle in Germany, Mercedes-Benz turned a B-Class hatchback invisible -- at least, from a distance, using the same idea behind the invisible car in the James Bond film "Die Another Day." See if you can see it before it sees you.

The invisibility cloak had its tryout this week on the streets of Stuttgart, Germany. To make Q's idea of an invisible car real, Mercedes employed dozens of technicians and some $263,000 worth of flexible LED mats covering one side of the car. Using a camera mounted on the opposite side of the vehicle, the LEDs were programmed to reproduce the image from the camera at the right scale, blending the vehicle into the background from a few feet away. Doing so required power sources, computers and other gear totaling 1,100 lbs. of equipment inside the B-Class.

Mercedes' point was to show how the F-Cell hydrogen fuel cell powered car would be invisible to the environment, producing only water vapor and heat for emissions. For an invisible car, it's getting a lot of stares.
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Makes me think of Predator. And its scary to think the military have probably had this kind of stuff for a good number of years.
 
Does this mean you wouldn't be caught by speed cameras and be able to travel without paying on the freeways?
 
"I never saw him officer!" said after rear ending this car.
 
It still only makes something invisible from one particular direction, but I suppose that if you are approaching enemy lines or something like that you might expect them to only have one point of view. If they have any scouts off to one side then the system is pretty much useless. In modern asymmetric warfare it probably wouldn't be much cop.

The technology to make something invisible from all angles is many decades off, and would use phenomenal processing power; the heat produced by all-round invisibility tech would make it an easy target in IR, so there would have to be several different leaps in technology before it was really useful.
 
Still it's a very impressive effect, and even on film to know you're looking at it for real (even if it is from very specific angles) is strange.

Ironic really that it's been done by a company known for their wonky electronics.
 
A breakthrough in creating invisibility cloaks, stealth technology
March 31st, 2014 in Physics / Optics & Photonics

Assistant Professor Chanda works with students in his lab at the UCF NanoScience Technology Center. Credit: UCF

Controlling and bending light around an object so it appears invisible to the naked eye is the theory behind fictional invisibility cloaks.

It may seem easy in Hollywood movies, but is hard to create in real life because no material in nature has the properties necessary to bend light in such a way. Scientists have managed to create artificial nanostructures that can do the job, called metamaterials. But the challenge has been making enough of the material to turn science fiction into a practical reality.

The work of Debashis Chanda at the University of Central Florida, however, may have just cracked that barrier. The cover story in the March edition of the journal Advanced Optical Materials, explains how Chanda and fellow optical and nanotech experts were able to develop a larger swath of multilayer 3-D metamaterial operating in the visible spectral range. They accomplished this feat by using nanotransfer printing, which can potentially be engineered to modify surrounding refractive index needed for controlling propagation of light.

"Such large-area fabrication of metamaterials following a simple printing technique will enable realization of novel devices based on engineered optical responses at the nanoscale," said Chanda, an assistant professor at UCF.

The nanotransfer printing technique creates metal/dielectric composite films, which are stacked together in a 3-D architecture with nanoscale patterns for operation in the visible spectral range. Control of electromagnetic resonances over the 3-D space by structural manipulation allows precise control over propagation of light. Following this technique, larger pieces of this special material can be created, which were previously limited to micron-scale size.

By improving the technique, the team hopes to be able to create larger pieces of the material with engineered optical properties, which would make it practical to produce for real-life device applications. For example, the team could develop large-area metamaterial absorbers, which would enable fighter jets to remain invisible from detection systems.

Provided by University of Central Florida

"A breakthrough in creating invisibility cloaks, stealth technology." March 31st, 2014. http://phys.org/news/2014-03-breakthrou ... ology.html
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Here's a new approach to the 'invisibility cloaking' technology that multiple research teams are pursuing ...

'Beam of Invisibility' Could Hide Objects Using Light

Once thought of as the province of only "Star Trek" or "Harry Potter," cloaking technologies could become a reality with a specially designed material that can mask itself from other forms of light when it is hit with a "beam of invisibility," according to a new study.

Theoretically, most "invisibility cloaks" would work by smoothly guiding light waves around objects so the waves ripple along their original trajectories as if nothing were there to obstruct them. Previous work found that cloaking devices that redirect other kinds of waves, such as sound waves, are possible as well.

But the new study's researchers, from at the Technical University of Vienna, have developed a different strategy to render an object invisible — using a beam of invisibility.
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FULL STORY: http://www.livescience.com/60649-beam-of-invisibility-cloaks-objects-with-light.html
 
If technology starts out at the forefront of human ability and ends up popularised among the masses, can we expect a lot of invisible people wandering the streets in thirty years time? Or sooner? To what end?
 
GNC said:
If technology starts out at the forefront of human ability and ends up popularised among the masses, can we expect a lot of invisible people wandering the streets in thirty years time? Or sooner? To what end?
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No good can come of that.
 
I think people have lost sight of what this technology is for.
 
This UK startup company has mounted a Kickstarter campaign to support its invisibility shield product.
InvisabilityShield.jpg
This Startup Made a Functioning 'Invisibility Shield'. Here's How It Works

In recent years, there have been many attempts to devise some sort of invisibility tech. Now, UK-based startup Invisibility Shield Co. has come onto the scene with a new product to help you fulfill that dream of becoming invisible… kind of.

A ... person standing behind the shield truly does seem to disappear. This happens thanks to a really fun optical phenomenon called lenticular lensing, where a series of thin, cylinder-shaped lenses are arranged parallel on a surface.

There's one common use for lenticular lensing you've likely encountered: in tilt cards which change the picture depending on angle. ...

Of course, using lenticular lensing will be a little more complicated when we're talking about an entire invisibility shield, rather that just a postcard, but the basic principles are the same.

"Each shield uses a precision engineered lens array to direct much of the light reflected from the subject away from the observer, sending it sideways across the face of the shield to the left and right," the startup writes on their Kickstarter for the product.

"Because the lenses in this array are vertically oriented, the vertically oriented strip of light reflected by the standing/crouching subject quickly becomes very diffuse when spread out horizontally on passing through the back of the shield. "

The lenses in this case are very similar to the rows of horizontal bumps on those tilt cards, but instead of light entering and exiting the card at different angles from the front, here light comes from behind the shield.

As it enters the array, light hitting the sides is stretched out to cover the entire surface, making the image behind it blurry. Meanwhile, the more central light from behind the shield, where the 'disappeared' object is, is reflected back and out the sides.

The shield is particularly good at maintaining the integrity of horizontal lines, but because the lenses on the shield are vertical, it's less effective at showing vertical lines behind a person – instead creating a kind of smudge of background light. ...

The principles behind the product Invisibility Shield Co. is pitching on their Kickstarter have actually been around for several years. A 2019 showcase video by military stealth company Hyperstealth quickly inspired crafty folk on YouTube to try and replicate what they saw, with excellent success.

There is even a freely available instruction manual by engineer and YouTuber Ian Charnas on how to craft your own. ...
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FULL STORY: https://www.sciencealert.com/these-...ing-invisibility-shield-all-thanks-to-physics
 
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