Invisibility: Possibilities / Science / Technology

[CygnusRex]

Invisibility Shields Planned by Engineers

James Owen in London
for National Geographic News
February 28, 2005

In popular science fiction, the power of invisibility is readily apparent. Star Trek fans, for example, know that the devious Romulans could make their spaceships suddenly disappear.

But is the idea really so implausible? Not according to new findings by scientists who say they have come up with a way to create cloaking device.


Electronic engineers at the University of Pennsylvania in Philadelphia are researching a device they say could make objects "nearly invisible to an observer." The contrivance works by preventing light from bouncing off the surface of an object, causing the object to appear so small it all but disappears.

The concept was reported today by the science news Web site [email protected]. It says the proposed cloaking device would not require any peripheral attachments (such as antennas or computer networks) and would reduce visibility no matter what angle an object is viewed at.

Sir John Pendry, a physicist at Imperial College, London, said the concept potentially holds several important applications "in stealth technology and camouflage."

While types of invisibility shielding have been developed before, the phenomenon described by Andrea Alú and Nader Engheta sounds like something that might have been witnessed from the bridge of science fiction's starship Enterprise.

The concept is based on a "plasmonic cover," which is a means to prevent light from scattering. (It is light bouncing off an object that makes it visible to an observer).

The cover would stop light from scattering by resonating at the same frequency as the light striking it. If such a device could cope with different wavelengths of electromagnetic radiation (including visible light), in theory, the object would vanish into thin air.

Plasmonic Covers

Alú and Engheta investigated experimental plasmonic covers that incorporated metals, such as gold and silver, to hide visible light.

When light strikes a metallic material, waves of electrons, called plasmons, are generated. The engineers found that when the frequency of the light striking the material matched the frequency of the plasmons, the two frequencies act to cancel each other out.

Under such conditions, the metallic object scattered only negligible amounts of light.

The researchers' studies show that spherical and cylindrical objects coated with plasmonic shielding material produce very little light scattering. These objects, when hit by the right wavelength of light, were seen to become so small that they were almost invisible.

The study is supported by the U.S. Defense Advanced Research Projects Agency, which researches and develops cutting edge military technology.

Some experts note, however, that cloaking devices that could enable military vehicles and aircraft, let alone spaceships, to become completely invisible to the enemy are likely to remain elusive for the foreseeable future.

John Pendry, the Imperial College physicist, said that light-shielding covers would have to be customized to match the properties of each and every object they hide.

It would be still more difficult to devise shields that could cope with all wavelengths of the visible spectrum—from red to violet light—and not just a single color.

Types of invisibility shielding previously proposed by scientists depend on advanced camouflage systems, rather than objects being made to look undetectably tiny. Such systems involve light sensors that create a mirror image of the background scene on the concealed object.

Despite the exciting possibilities raised by the new research, it may take us some time before science is able to catch up with those evasive Romulans.

Source

 

[ramonmercado]

Engineers devise invisibility shield

Engineers devise invisibility shield
Philip Ball
Electron effects could stop objects from scattering light.

The idea of a cloak of invisibility that hides objects from view has long been confined to the more improbable reaches of science fiction. But electronic engineers have now come up with a way to make one.

Andrea Alù and Nader Engheta of the University of Pennsylvania in Philadelphia say that a 'plasmonic cover' could render objects "nearly invisible to an observer". Their idea remains just a proposal at this stage, but it doesn't obviously violate any laws of physics.

"The concept is an interesting one, with several important potential applications," says John Pendry, a physicist at Imperial College in London, UK. "It could find uses in stealth technology and camouflage."

Cloak of many colours

Types of invisibility shielding have been developed before, but these mostly use the chameleon principle: a screen is coloured to match its background, so that the screened object is camouflaged.

The concept could find uses in stealth technology and camouflage.

John Pendry
Physicist, Imperial College, UK



For example, inventor Ray Alden in North Carolina has proposed a system of light detectors and emitters that project a replica of the scene appearing behind an object from its front surface. Researchers at the University of Tokyo are working on a camouflage fabric that uses a similar principle, in which the background scene is projected on to light-reflecting beads in the material.

But the invisibility shield proposed by Alù and Engheta in a preprint on arXiv1 is more ambitious than this. It is a self-contained structure that would reduce visibility from all viewing angles. In that sense it would be more like the shielding used by the Romulans in the Star Trek episode "Balance of Terror" in 1966, which hid their spaceships at the push of a button.

Scatter-brained

The key to the concept is to reduce light scattering. We see objects because light bounces off them; if this scattering of light could be prevented (and if the objects didn't absorb any light) they would become invisible. Alù and Engheta's plasmonic screen suppresses scattering by resonating in tune with the illuminating light.

Plasmons are waves of electron density, caused when the electrons on the surface of a metallic material move in rhythm. The researchers say that a shell of plasmonic material will scatter light negligibly if the light's frequency is close to the resonant frequency of the plasmons. The scattering from the shell effectively cancels out the scattering from the object.

For visible-light shielding, says Engheta, nature has already provided suitable plasmonic materials: silver and gold. To reduce the scattering of longer-wavelength radiation such as microwaves, one could make the shield from a 'metamaterial': a large-scale structure with unusual electromagnetic properties, typically constructed from arrays of wire loops and coils.

Alù and Engheta's calculations show that spherical or cylindrical objects coated with such plasmonic shields do indeed produce very little light scattering. It is as though, when lit by light of the right wavelength, the objects become extremely small, so small that they cannot be seen.

Size matters

Pendry warns, however, that the concept as it stands is "no magic cloak", because it would have to be delicately tuned to suit each different object it hides. Perhaps even more of a drawback, he points out, is the fact that a particular shield only works for one specific wavelength of light.

An object might be made invisible in red light, say, but not in multiwavelength daylight.

And crucially, the effect only works when the wavelength of the light being scattered is roughly the same size as the object. So shielding from visible light would be possible only for microscopic objects; larger ones could be hidden only to long-wavelength radiation such as microwaves. This means that the technology could not be used to hide people or vehicles from human vision.

But that need not undermine other potential uses, Engheta says. For example, the effect could be useful for making antiglare materials.

Another possible use for plasmonic screening is microscopy, he adds. Light microscopes could surpass their usual resolution limits by using tiny probes to measure the light field very close to the object being imaged. Such probes could be made 'invisible' so that they don't disturb the imaging signal.

And of course the shielding would work fine for concealing large objects such as spaceships from sensors or telescopes that used long-wavelength radiation instead of visible light.

http://www.nature.com/news/2005/050228/ ... 228-1.html

References
Alù A. & Engheta N. Preprint, http://arxiv.org/abs/cond-mat/0502336 (2005).

 

[Mal_Adjusted]

Greets

anyone else thinking "disappearing" UFOs?

making objects invisible to microwaves migth have stealth applications too.

work better at night?

mal

 

[Stormkhan]

Electronic engineers at the University of Pennsylvania in Philadelphia ...

Hmm. Now, there's a coincidence. Is it something in the water?

 

[wembley8]

"And crucially, the effect only works when the wavelength of the light being scattered is roughly the same size as the object. So shielding from visible light would be possible only for microscopic objects;"

Looks kinda limited.

Most radar operates in centimetre bands too, so it's only good for hiding very small UFOs...

 

[Anonymous]

As far as radar goes... I remember being treated to reading declassified government documents in OAC physics class when I was 19 (I guess this would have been 1995, then). The papers dated from 1984. They dealt with stealth technology, specifically radar invisibility. We were studying waves at that point, I believe, and this was kind of a cool example for our professor to have brought.

Waves interfere with each other - two waves, for instance, of the same size but in opposite phases will cancel each other completely out. Two waves in the same phase and of the same size, added together, will equal one wave of the same length but of double amplitude (height).
Differing sizes or phase shifts will create different effects, but basically you "add" the waves together to produce the result.

The kind of cloaking in experimentation was deflection of radio waves in such a way that they would interfere with the source waves, making the position of the stealth craft invisible or difficult to detect. Nowadays stealth craft are built such that no/few surfaces will reflect the radio waves directly back at the transmission source, making them effectively "invisible" to radar.

 

[wembley8]

"Waves interfere with each other - two waves, for instance, of the same size but in opposite phases will cancel each other completely out."

One could in theory - and this of course has nothing to do with any actual system - have an aircraft with an adaptive skin the thickness of which could be adjusted to be exactly half the wavelength of the incident radar.

There are many aspects to stealth.

 

[Mighty_Emperor]

Another report:

Invisibility Shields Planned by Engineers

James Owen in London
for National Geographic News
February 28, 2005

In popular science fiction, the power of invisibility is readily apparent. Star Trek fans, for example, know that the devious Romulans could make their spaceships suddenly disappear.

But is the idea really so implausible? Not according to new findings by scientists who say they have come up with a way to create cloaking device.

Electronic engineers at the University of Pennsylvania in Philadelphia are researching a device they say could make objects "nearly invisible to an observer." The contrivance works by preventing light from bouncing off the surface of an object, causing the object to appear so small it all but disappears.

The concept was reported today by the science news Web site [email protected]. It says the proposed cloaking device would not require any peripheral attachments (such as antennas or computer networks) and would reduce visibility no matter what angle an object is viewed at.

Sir John Pendry, a physicist at Imperial College, London, said the concept potentially holds several important applications "in stealth technology and camouflage."

While types of invisibility shielding have been developed before, the phenomenon described by Andrea Alú and Nader Engheta sounds like something that might have been witnessed from the bridge of science fiction's starship Enterprise.

The concept is based on a "plasmonic cover," which is a means to prevent light from scattering. (It is light bouncing off an object that makes it visible to an observer).

The cover would stop light from scattering by resonating at the same frequency as the light striking it. If such a device could cope with different wavelengths of electromagnetic radiation (including visible light), in theory, the object would vanish into thin air.

Plasmonic Covers

Alú and Engheta investigated experimental plasmonic covers that incorporated metals, such as gold and silver, to hide visible light.

When light strikes a metallic material, waves of electrons, called plasmons, are generated. The engineers found that when the frequency of the light striking the material matched the frequency of the plasmons, the two frequencies act to cancel each other out.

Under such conditions, the metallic object scattered only negligible amounts of light.

The researchers' studies show that spherical and cylindrical objects coated with plasmonic shielding material produce very little light scattering. These objects, when hit by the right wavelength of light, were seen to become so small that they were almost invisible.

The study is supported by the U.S. Defense Advanced Research Projects Agency, which researches and develops cutting edge military technology.

Some experts note, however, that cloaking devices that could enable military vehicles and aircraft, let alone spaceships, to become completely invisible to the enemy are likely to remain elusive for the foreseeable future.

John Pendry, the Imperial College physicist, said that light-shielding covers would have to be customized to match the properties of each and every object they hide.

It would be still more difficult to devise shields that could cope with all wavelengths of the visible spectrum—from red to violet light—and not just a single color.

Types of invisibility shielding previously proposed by scientists depend on advanced camouflage systems, rather than objects being made to look undetectably tiny. Such systems involve light sensors that create a mirror image of the background scene on the concealed object.

Source

 

[sthomasb]

The researchers' studies show that spherical and cylindrical objects coated with plasmonic shielding material produce very little light scattering. These objects, when hit by the right wavelength of light, were seen to become so small that they were almost invisible.

I guess that was an unfamiliar sight!

The cover would stop light from scattering by resonating at the same frequency as the light striking it. If such a device could cope with different wavelengths of electromagnetic radiation (including visible light), in theory, the object would vanish into thin air.

Wouldn't the cloaked object still obscure that which it... obscures? For it to really "vanish into thin air", wouldn't it have to reflect whatever is in the background instead of not reflecting any light at all (because how could it be invisible if it's not also transparent)?

Well I think it´s great that there are some people out there with patience enough to attempt this kind of thing, trying to build these wonderful things out of ideas coming from wonderful fiction. :yeay:

says I.

 

[Mal_Adjusted]

Greets

re obscuring what's behind the cloaked object

i believe that it might be possible to bend the light around the stealth object so that it doesn't block what's behind it. (but whether you could do that 360 degs in 3 dimensions i dunno.)

mal

 

[Anonymous]

If we think about visible light, reducing scattering to near zero just makes the object black; so the object would still be visible.
There is already technology that reduces scattered visible light; it is called black paint.

But reducing scattering of radar waves to near zero would make the object effectively invisible- as radar relies on reflected waves.
This makes the object essentially invisible in reflected radiation.

 

[Stormkhan]

So that would be invisible to radar (stealth technology) rather than yer actual "Blimey! Where's that ship gone wot was in the harbour? I turn my back for a few minutes and some lubber nicks it! What's that big hole in the water there?" invisibility (which - correct me if I'm wrong - means not seen by the naked eye).

 

[wembley8]

"So that would be invisible to radar (stealth technology)"

Yes, if the ship was of a similar size to the radar wavelength, eg a few centimetres across.

Only good for hiding small ships.

With visible wavelengths, it can make things invisibly but only if they're .0007 mm or so across.

 

[Stormkhan]

So can we expect a new generation of ultra-stealth military vehicles which, while being utterly undetectable by radar, has a payload only large enough to carry a garden pea?

Still, the theory may be sound and while applications may be limited at present it shows it can be done ... which is the first step in the development of any weapon.

 

[Anonymous]

i suppose it allows a swarm,something which hast been used as yet in war or anywhere else.
why build one big battle ship/plane when you can have millions of small attacking robots lol
even if you kill some of them the rest ......................................

 

[wembley8]

"So can we expect a new generation of ultra-stealth military vehicles which, while being utterly undetectable by radar, has a payload only large enough to carry a garden pea? "

Er, no. If it's invisible to centimetric radar, it will still show up on both longer and shorter wavelength radar (as well as thermal imaging, visible light etc).

But I agree that military applications are likely to come first.

And yes, swarms of micro-UAVs have already been proposed...

 

[Rrose_Selavy]

'Cloaking device' idea proposed

So they are theoretically er...maybe able to cloak a speck of dust ? Its a start I suppose but not use wht peaceful use it could have if fully realised . Don' t trust those Romulans......

'Cloaking device' idea proposed
The cloaking devices that are used to render spacecraft invisible in Star Trek might just work in reality, two mathematicians have claimed.
They have outlined their concept in a research paper published in one of the UK Royal Society's scientific journals.

Nicolae Nicorovici and Graeme Milton propose that placing certain objects close to a material called a superlens could make them appear to vanish.

It would rely on an effect known as "anomalous localised resonance".


If the speck of dust is close enough it induces a very aggressive response in the cloaking material
Professor Sir John Pendry, Imperial College London

However, the authors have so far only done the maths to verify that the concept could work. Building such a device would undoubtedly pose a significant challenge.

Starting small

Cloaking devices are a form of stealth technology much favoured by Star Trek baddies such as the Romulans and Klingons.

The complex mathematical phenomenon outlined by Milton and Nicorovici closes the gap a little between science fiction and fact.

The phenomenon is analogous to a tuning fork (which rings with a single sound frequency) being placed next to a wine glass. The wine glass will start to ring with the same frequency; it resonates.

The cloaking effect would exploit a resonance with light waves rather than sound waves.

The concept is at such a primitive stage that the scientists talk only at the moment of being able to cloak particles of dust - not spaceships.

In this example, an illuminated speck of dust would scatter light at frequencies that induce a strong, finely tuned resonance in a cloaking material placed very close by.

The resonance effectively cancels out the light bouncing off the speck of dust, rendering the dust particle invisible.

One way to construct a cloaking device is to use a superlens, made of recently discovered materials that force light to behave in unusual ways.

Vanishing point

Professor Sir John Pendry, of Imperial College London, who helped pioneer superlenses, said: "If the speck of dust is close enough it induces a very aggressive response in the cloaking material which essentially acts back on the speck of dust and forces it to stop shining.

"Even though light is hitting the speck of dust, scattering of the light is prevented by the cloak which is in close proximity," he told the BBC News website.

The authors of the paper argue that the cloak needn't just work with a speck of dust, but could also apply to larger objects.

But they admit the cloaking effect works only at certain frequencies of light, so that some objects placed near the cloak might only partially disappear.

"I believe their claims about the speck of dust and a certain class of objects. In the paper, they do give an instance about a particular shape of material they can't cloak. So they can't cloak everything," said Professor Pendry.

"Nevertheless, it's a very neat idea to get this aggressive response from the material to stop tiny things emitting light."

The Imperial College physicist agreed this particular concept had potential military uses: "Providing the specks of dust are within the cloaked area, the effect will happen. A cloak that only fits one particular set of circumstances is very restrictive - you can't redesign the furniture without redesigning the cloak."

Details are published in Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences.

Story from BBC NEWS:
http://news.bbc.co.uk/go/pr/fr/-/1/hi/s ... 968338.stm

Published: 2006/05/03 16:34:49 GMT

© BBC MMVI

 

[Anonymous]

Yay! So we have the warp drive (another thread) and cloaking devices. Anybody got anything on phasers and teleporters?

 

[Pete Younger]

http://pr.caltech.edu/media/Press_Releases/PR11935.html

 

[Rrose_Selavy]

Plan for cloaking device unveiled
Researchers in the US and Britain have unveiled their blueprints for building a cloaking device.
So far, cloaking has been confined to science fiction; in Star Trek it is used to render spacecraft invisible.

Professor Sir John Pendry says a simple demonstration model that could work for radar might be possible within 18 months' time.

Two separate teams, including Professor Pendry's, have outlined ways to cloak objects in the journal Science.

These research papers present the maths required to verify that the concept could work. But developing an invisibility cloak is likely to pose significant challenges.

Both groups propose methods using the unusual properties of so-called "metamaterials" to build a cloak.

These metamaterials can be designed to induce a desired change in the direction of electromagnetic waves, such as light. This is done by tinkering with the nano-scale structure of the metamaterial, not by altering its chemistry.

Light flow

John Pendry's team suggest that by enveloping an object in a metamaterial cloak, light waves can be made to flow around the object in the same way that water would do so.

"Water behaves a little differently to light. If you put a pencil in water that's moving, the water naturally flows around the pencil. When it gets to the other side, the water closes up," Professor Pendry told the BBC.


"A little way downstream, you'd never know that you'd put a pencil in the water - it's flowing smoothly again.
"Light doesn't do that of course, it hits the pencil and scatters. So you want to put a coating around the pencil that allows light to flow around it like water, in a nice, curved way."

The work provides a mathematical "recipe" for bending light waves in such a way as to achieve a desired cloaking effect.

John Pendry, along with colleagues David Smith and David Schurig at Duke University in North Carolina, US, have been testing suitable metamaterials for the device they plan to build.

This, Sir John explained, would consist of a sphere or cylinder wrapped in a sheath of metamaterial which could cloak it from radio waves.

"It's not tremendously fancy, but that for us would be quite an achievement," he told the BBC News website.

Professor Ulf Leonhardt, author of another cloaking paper in Science, described the effect for light as a "mirage".

"What you're trying to do is guide light around an object, but the art is to bend it such that it leaves the object in precisely the same way that it initially hits it. You have the illusion that there is nothing there," he told the BBC's Science in Action programme.

The work could have uses in military stealth technology - but engineers have not yet created the materials that could be used to cloak an aircraft or a tank, John Pendry explains. Professor Pendry's research has been supported by the US Defense Advanced Research Projects Agency (Darpa).

Several other scientific teams have proposed ideas for cloaking devices. One theoretical paper proposed using a material known as a superlens to cancel out light being scattered from an object.

Story from BBC NEWS:
http://news.bbc.co.uk/go/pr/fr/-/1/hi/s ... 016068.stm

Published: 2006/05/25 18:00:43 GMT

© BBC MMVI

 

[ramonmercado]

[/quote]Optical materials

Cast no shadows
May 25th 2006
From The Economist print edition

How to weave a cloak that makes you invisible


IN NORSE mythology, a magic cloak granted invisibility to Sigurd, a demi-god and skilled warrior with superhuman strength. Millennia later, a similar garment bestowed invisibility on Harry Potter, a schoolboy wizard. In the mortal (or Muggle) realm, engineers have for years tried with varying degrees of success to build such a device. This week a team of physicists and materials scientists announced it had devised a pattern for a potentially perfect invisibility cloak.

Light is an electromagnetic wave, with a longer wavelength than X-rays and ultraviolet, and a shorter wavelength than infra-red, microwaves and radio waves. All these electromagnetic waves are governed by four mathematical expressions established almost 150 years ago by James Clerk Maxwell. These equations represent one of the most elegant and concise ways to state the behaviour of electric and magnetic fields and how they interact with matter. However, because they are so concise, they also embody a high level of mathematical sophistication.


The team—Sir John Pendry of Imperial College London with David Schurig and David Smith of Duke University in North Carolina—used the equations to devise a way to cloak an object with a material that would deflect the rays that would have struck it, guide them around it and return them to their original trajectory. Maxwell's equations conserve certain properties—the magnetic field intensity, the electric displacement field and the Poynting vector that describes the electric flux of an electromagnetic field. These properties remain the same when others are altered. The team showed how these fields could be manipulated to flow around objects like a fluid, returning undisturbed to their original paths. The findings were published online this week by Science.

The trick is to use metamaterials: materials that owe their characteristics to features of their structure that are smaller than the wavelength of the electromagnetic radiation. For light, this is on the scale of tens of thousandths of a millimetre. Metamaterials can and have been designed and made to possess certain properties, even counter-intuitive ones. Using metamaterials means the scheme should work for all objects, regardless of their shape. Moreover, unlike other proposed invisibility cloaks, it does not require knowledge of what is behind the wearer, nor are crude projections involved.

So far, so good: the theory is in place. Sadly, the implementation lags behind. Moreover, there are several other difficulties that may prevent a device conferring total invisibility from being built. The first is that the plan described by Sir John and his colleagues works only for a small range of wavelengths. A surgeon wearing metamaterial gloves tuned to make his hands invisible might benefit from being able to see exactly where the scalpel was cutting. However, an invisibility cloak designed to hide something from people who were looking for it would not work. An aeroplane shrouded in such kit might be invisible to the human eye but it would be picked up readily by radar, which operates at radio wavelengths.

Even if it ultimately proved possible to make an aeroplane completely invisible at all wavelengths, there would be a further problem. According to the laws of physics, an invisible person would necessarily be blind. In order to see light, the eye must absorb it, but in order for a person to be invisible, the body must not absorb any light. Thus, a spy plane could not be completely invisible if it were to be used for espionage or, indeed, flown at all, since its pilots would need to know its position relative to the ground.

http://www.economist.com/science/displa ... id=6971134

 

[eburacum]

I'll believe it when I don't see it.

 

[ramonmercado]

The First Invisibility Shield

JR Minkel

'View Photos'

WHAT: A way to make objects invisible. The trick is to use metamaterial, a complex hybrid structure of metal and insulator that makes light move around an object like air flowing over an airplane wing. In a process called refraction, these materials interact with light in such a way that it travels faster through the metamaterial than it does through a vacuum, the famed c in Einstein’s special theory of relativity. Properly tuned, the light emerges from the shield as if there were no object present. But unfortunately for would-be spies, it’s very difficult to make cloaking devices that work on more than one wavelength of light at a time.

WHY: Military stealth. A B-2 bomber isn’t truly invisible to radar. It just absorbs and redirects the radar waves, making the plane much harder to spot (its radar signature is the size of a pigeon rather than an aircraft). A bomber, tank or building covered in a radar-sensitive metamaterial shield would literally disappear from radar screens.

WHEN: For certain applications, commercial deploy- ment could be within a decade. The best-studied metamaterials work only on microwaves. Duke University physicist David R. Smith hopes to shield a toaster-size object from microwave frequencies within the next six months. Metamaterials that work on visible light—which isn’t a single frequency but a spectrum of frequencies—are at a more primi- tive state. A specific meta- material design would be required to redirect each frequency in the visible range, and integrating that many components into a device might take 10 years for the initial lab demonstration alone.

WHO: The mathematical models were developed independently by two groups, the first led by Ulf Leonhardt at the University of St. Andrews in Scotland and the second by Smith with John Pendry of Impe- rial College London. Smith could soon prove the concept experimentally.

FAQs

Has anyone made a metamaterial?
Yes. Scientists in the U.S. and the U.K. have made metamaterials with what’s called a negative index of refraction. Generally, these metamaterials are coiled metal wires surrounded by air or another insulator and affect only microwave radiation. Can the cloaking be perfect? Almost. Any metamaterial absorbs a little bit of light and therefore casts a slight shadow.

Could an actual cloak ever hide a person?
Yes, but current designs would work only if you painted yourself all one color. A cloak, which for comfort’s sake needs to be pretty thin, could bend radiation of just a single frequency, so it could only hide an object of one color. There’s a possibility, though, that a thick shell could include a wider variety of metamaterials and broaden the invisibility to multiple frequencies.

What would the inside of the cloak look like?
If a cloak worked over the entire spectrum, the lack of light would make the inside black, and you wouldn’t be able to see outside. No one knows exactly what would happen if you turned on a flashlight inside the cloak.

www.popsci.com/popsci/technology/b0b13d ... drcrd.html

 

[GNC]

One of those photos on that site includes a picture of the Predator from the film of the same name. How desperate were they for pictures? I see no "invisibility shield". Which, OK, might mean it works.

 

[OldTimeRadio]

One of those photos on that site includes a picture of the Predator from the film of the same name. How desperate were they for pictures?

I think the still from PREDATOR was included to illustrate the history of invisibility as a science fiction concept. Else why the photograph of H. G. Wells?

 

[lupinwick]

Invisible to microwaves anyway...

A US-British team of scientists has successfully tested a cloak of invisibility in the laboratory.

The device mostly hid a small copper cylinder from microwaves in tests at Duke University, North Carolina.

It works by deflecting the microwaves around the object and restoring them on the other side, as if they had passed through empty space.

But making an object vanish before a person's eyes is still the stuff of science fiction - for now.

http://news.bbc.co.uk/1/hi/sci/tech/6064620.stm

 

[misterwibble]

'Mostly hid'?

Is that like "mostly dead"?

 

[TinFinger]

no think stealth fighters
they are also mostly hid iirc

 

[Xanatico]

So besides making light flow around it, it also makes it move faster than it does in a vacuum? Yeah, I believe all that.

 

[ramonmercado]

OK, they know a bit more about the physics behind it but we're still no closer to a functioning shield. Pity, it would make pieing politicians easier. Theres a diagram at the link which makes things a bit easier to follow.

Scientists interpret physics behind invisibility cloaks



When a polarized plane wave is incident upon an ideal spherical cloak, the object behind the cloak is completely hidden, as shown in this figure (wave arrows from behind pass through the cloak to appear in front). Credit: Chen, et al. ©2007 PRL.


Is a perfect invisible cloak theoretically possible? Are there certain wavelengths—such as those in the visible spectrum—that can’t be made invisible? How will using imperfect materials affect the performance of a cloak? Scientists from Zhejiang University and MIT have recently analyzed the physics behind invisibility cloaks in an attempt to answer some of these questions.

Hongsheng Chen, Bae-Ian Wu, Baile Zhang, and Jin Au Kong have published their research on invisibility cloaks in a recent issue of Physical Review Letters. The group analytically demonstrated how electromagnetic waves interact with invisibility cloaks made of metamaterials, an interaction that is often different from conventional scattering with regular particles. Their findings will hopefully be useful for cloak design and applications, an exciting research area that is still in its early stages.

“When an electromagnetic wave is incident onto a conventional sphere, part of the radiation will be scattered in all directions; while for a metamaterial cloak, the incident wave will smoothly pass through the cloak undeflected,” Chen explained to PhysOrg.com. “It is very interesting that a perfect metamaterial cloak shows no reflection or absorption but rather allows the Poynting power to bypass the hidden object. Our research also shows that the Poynting power inside of the cloak is not uniform: when close to the inner boundary of the cloak, the power flow density is close to zero, while near the outer boundary of the cloak, the power flow density becomes large.”

The first invisible cloak made of metamaterials was created last year by Duke University researchers Shurig et al. Metamaterials, which are composed of a man-made matrix of tiny metal wires and loops that control electromagnetic waves, can create an area in space where no electromagnetic waves propagate. The light waves flow around the cloaked object like water in a creek flows around a rock, appearing on the other side in such a way that an observer can’t tell that the waves flowed around an obstacle.

In the first experimental trial, the cloak hid the concealed object from the electromagnetic microwaves in two dimensions. Chen and his colleagues wanted to know if perfect invisibility could be achieved under any wavelength. The scientists explained that perfect invisibility is achieved when the scattering cross section is zero, which indicates that the cloak exhibits zero scattering. The group found that the parameters for a perfect cloak are very difficult to realize, and that when some specific type of loss is included, the three dimensional spherical cloak wrapped around a hidden object exhibits zero backscattering while a two dimensional cylindrical cloak does not.

“The cloak is both anisotropic and inhomogeneous: all of the components in the permittivity and permeability tensor are functions of the radius, which implies that the perfect invisibility cloak is very difficult to design,” Chen explained. “If we introduce a specific type of loss both in a spherical cloak and a cylindrical cloak, only the spherical cloak exhibits a zero backscattering, which indicates only the spherical cloak can still be rendered invisible with a monostatic (transmitter and receiver in the same location) detection. This is because the impedance of the spherical cloak is still matched to the free space in this particular loss case.”

Because they have less stringent requirements, imperfect cloaks may offer a more realistic alternative for engineers. Although imperfect cloaks have non-zero scattering, the objects they cloak can still appear isolated from the outside field under certain specific conditions and the incident fields cannot penetrate into the hidden object. Besides, for an imperfect cloak with matched impedance, it can still be rendered invisible with monostatic detection, which is most widely used in current radar.

“For a monostatic detection, no reflection wave will be received by the detector if the imperfect cloak has a matched impedance with the free space,” Chen explained. “Therefore, the imperfect cloak, even with its parameters deviated far from the ideal parameters, still can be made completely invisible with the monostatic detection as long as it satisfied the impedance requirement.”

Since almost all current radars belong to the monostatic class, Chen explained that this research can offer a more realistic alternative for engineers. In the future, applications of invisible cloaks could include military uses such as making planes and weapons invisible to radar, enabling the possibility of looking out walls as if they were windows, and hiding ugly factories for aesthetic reasons.

“The effectiveness of the cloak based on the analytical solutions of the electromagnetic wave interactions with metamaterial cloaks (ideal or non-ideal) can be quantitatively provided,” Chen said. “Our research work therefore provides a new way for the cloak design and to qualify the effectiveness or performance of a non-ideal cloak.”

Citation: Chen, Hongsheng, Wu, Bae-Ian, Zhang, Baile, and Kong, Jin Au. “Electromagnetic Wave Interactions with a Metamaterial Cloak.” Physical Review Letters 99, 063903 (2007).

http://www.physorg.com/news107011336.html

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