Practical Invisibility.

[Aren Jay]

+ (http://www.mercurymarauder.net/forums/l)
Practical Cloaking Devices On The Horizon?
Physics (http://physics.physorg.com/) / Physics (http://physics.physorg.com/sub_Physics/)
(PhysOrg.com) -- Invisibility cloaks get a step closer to realization, with the demonstration of a new material that can bend (visible) light the 'wrong' way for the first time in three dimensions.
In Nature this week, researchers report a metamaterial that produces negative refraction of visible light, and show that it can be can be easily probed from free space, paving the way for practical optical device applications.

Metamaterials are artificially engineered structures that have properties, such as negative refractive index, not attainable with naturally occurring materials. Only thin, effectively two-dimensional materials have been demonstrated until now, limiting practical applications.

Jason Valentine, Xiang Zhang and colleagues at the University of California, Berkeley create a multilayered, ‘fishnet’ structure which unambiguously exhibits negative refractive index. This straightforward and elegant demonstration enhances our ability to mould and harness light at will.

Read a follow-up story: Invisibility cloak now within sight: scientists (http://www.physorg.com/news137649366.html)

This paper will be published electronically on Nature's website soon. It will not appear in print on 14 August, but at a later date. (DOI: 10.1038/nature07247)



Published: 10 hours ago, 04:56 EST, August 11, 2008 (http://archive.physorg.com/11/08/2008)
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Put this on your Marauder and see if you can find your car in the parking lot.

[Aren Jay]

Invisibility cloak now within sight: scientists (Update 2)


<!-- Google TOP Adsense block -->Physics (http://physics.physorg.com/) / Physics (http://physics.physorg.com/sub_Physics/)
<!-- ====IMAGE====== --><!-- ENLARGE -->http://www.physorg.com/newman/gfx/news/nanowiremeta.jpg Shown is a schematic and two scanning electron microscope images with top and side views of a metamaterial developed by UC Berkeley researchers. The material is composed of parallel nanowires embedded inside porous aluminum oxide. As visible light passes through the material, it is bent backwards in a phenomenon known as negative refraction. Credit: Image by Jie Yao, UC Berkeley
Click here to enlarge image (http://www.physorg.com/newman/gfx/news/hires/nanowiremeta.jpg)


(PhysOrg.com) -- Scientists at the University of California, Berkeley, have for the first time engineered 3-D materials that can reverse the natural direction of visible and near-infrared light, a development that could help form the basis for higher resolution optical imaging, nanocircuits for high-powered computers, and, to the delight of science-fiction and fantasy buffs, cloaking devices that could render objects invisible to the human eye.


<!-- Google FISRT Adsense block -->
<!-- ads for no java browsers --><NOSCRIPT></NOSCRIPT>Two breakthroughs in the development of metamaterials - composite materials with extraordinary capabilities to bend electromagnetic waves - are reported separately this week in the Aug. 13 advanced online issue of Nature, and in the Aug. 15 issue of Science.


<!-- ENLARGE -->http://www.physorg.com/newman/gfx/news/fishnetmetam.jpg

On the left is a schematic of the first 3-D "fishnet" metamaterial that can achieve a negative index of refraction at optical frequencies. On the right is a scanning electron microscope image of the fabricated structure, developed by UC Berkeley researchers. The alternating layers form small circuits that can bend light backwards. Image by Jason Valentine, UC Berkeley
Click here to enlarge image (http://www.physorg.com/newman/gfx/news/hires/fishnetmetam.jpg)


Applications for a metamaterial entail altering how light normally behaves. In the case of invisibility cloaks or shields, the material would need to curve light waves completely around the object like a river flowing around a rock. For optical microscopes to discern individual, living viruses or DNA molecules, the resolution of the microscope must be smaller than the wavelength of light.

The common thread in such metamaterials is negative refraction. In contrast, all materials found in nature have a positive refractive index, a measure of how much electromagnetic waves are bent when moving from one medium to another.

In a classic illustration of how refraction works, the submerged part of a pole inserted into water will appear as if it is bent up towards the water's surface. If water exhibited negative refraction, the submerged portion of the pole would instead appear to jut out from the water's surface. Or, to give another example, a fish swimming underwater would instead appear to be moving in the air above the water's surface.




More invisibility that you can see.

[Aren Jay]

Other research teams have previously developed metamaterials that function at optical frequencies, but those 2-D materials have been limited to a single monolayer of artificial atoms whose light-bending properties cannot be defined. Thicker, 3-D metamaterials with negative refraction have only been reported at longer microwave wavelengths.

"What we have done is take two very different approaches to the challenge of creating bulk metamaterials that can exhibit negative refraction in optical frequencies," said Xiang Zhang, professor at UC Berkeley's Nanoscale Science and Engineering Center, funded by the National Science Foundation (NSF), and head of the research teams that developed the two new metamaterials. "Both bring us a major step closer to the development of practical applications for metamaterials."

Zhang is also a faculty scientist in the Material Sciences Division at the Lawrence Berkeley National Laboratory.

Humans view the world through the narrow band of electromagnetic radiation known as visible light, with wavelengths ranging from 400 nanometers (violet and purple light), to 700 nanometers (deep red light). Infrared light wavelengths are longer, measuring from about 750 nanometers to 1 millimeter. (A human hair is about 100,000 nanometers in diameter.)

For a metamaterial to achieve negative refraction, its structural array must be smaller than the electromagnetic wavelength being used. Not surprisingly, there has been more success in manipulating wavelengths in the longer microwave band, which can measure 1 millimeter up to 30 centimeters long.

In the Nature paper, the UC Berkeley researchers stacked together alternating layers of silver and non-conducting magnesium fluoride, and cut nanoscale-sized fishnet patterns into the layers to create a bulk optical metamaterial. At wavelengths as short as 1500 nanometers, the near-infrared light range, researchers measured a negative index of refraction.
Jason Valentine, UC Berkeley graduate student and co-lead author of the Nature paper, explained that each pair of conducting and non-conducting layers forms a circuit, or current loop. Stacking the alternating layers together creates a series of circuits that respond together in opposition to that of the magnetic field from the incoming light.

Valentine also noted that both materials achieve negative refraction while minimizing the amount of energy that is absorbed or "lost" as light passes through them. In the case of the "fishnet" material described in Nature, the strongly interacting nanocircuits allow the light to pass through the material and expend less energy moving through the metal layers.

"Natural materials do not respond to the magnetic field of light, but the metamaterial we created here does," said Valentine. "It is the first bulk material that can be described as having optical magnetism, so both the electrical and magnetic fields in a light wave move backward in the material."

The metamaterial described in the Science paper takes another approach to the goal of bending light backwards. It is composed of silver nanowires grown inside porous aluminum oxide. Although the structure is about 10 times thinner than a piece of paper - a wayward sneeze could blow it away - it is considered a bulk metamaterial because it is more than 10 times the size of a wavelength of light.

The authors of the Science paper observed negative refraction from red light wavelengths as short as 660 nanometers. It is the first demonstration of bulk media bending visible light backwards.



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"The geometry of the vertical nanowires, which were equidistant and parallel to each other, were designed to only respond to the electrical field in light waves," said Jie Yao, a student in UC Berkeley's Graduate Program in Applied Science and Technology and co-lead author of the study in Science. "The magnetic field, which oscillates at a perpendicular angle to the electrical field in a light wave, is essentially blind to the upright nanowires, a feature which significantly reduces energy loss."


The innovation of this nanowire material, researchers said, is that it finds a new way to bend light backwards without technically achieving a negative index of refraction. For there to be a negative index of refraction in a metamaterial, its values for permittivity - the ability to transmit an electric field - and permeability - how it responds to a magnetic field - must both be negative.


The benefits of having a true negative index of refraction, such as the one achieved by the fishnet metamaterial in the Nature paper, is that it can dramatically improve the performance of antennas by reducing interference. Negative index materials are also able to reverse the Doppler effect - the phenomenon used in police radar guns to monitor the speed of passing vehicles - so that the frequency of waves decreases instead of increases upon approach.


But for most of the applications touted for metamaterials, such as nanoscale optical imaging or cloaking devices, both the nanowire and fishnet metamaterials can potentially play a key role, the researchers said.


"What makes both these materials stand out is that they are able to function in a broad spectrum of optical wavelengths with lower energy loss," said Zhang. "We've also opened up a new approach to developing metamaterials by moving away from previous designs that were based upon the physics of resonance. Previous metamaterials in the optical range would need to vibrate at certain frequencies to achieve negative refraction, leading to strong energy absorption. Resonance is not a factor in both the nanowire and fishnet metamaterials."


While the researchers welcome these new developments in metamaterials at optical wavelengths, they also caution that they are still far off from invisibility cloaks and other applications that may capture the imagination. For instance, unlike the cloak made famous in the Harry Potter novels, the metamaterials described here are made of metal and are fragile. Developing a way to manufacture these materials on a large scale will also be a challenge, they said.


Nevertheless, the researchers said achieving negative refraction in an optical wavelength with bulk metamaterials is an important milestone in the quest for such devices



Article is too many words.

[TAKEDOWN]

Wow is all I can say.

[Eric-Blk2004]

Man imagine if that feel into the wrong hands...

O wait it might have already

[Dr Caleb]

Trouble with good invisibilty - if all the light is refracted around you, then none enters your eyes.

You be invisible, and blind.

[Spectragod]

Will this help with speeding tickets??

[Marauder386]

Will this help with speeding tickets??

My radar will still ping off you ... but go ahead and try ... :lol:


:cool4:

[Windsor58]

If anybody on this site can afford that stuff, let me know. I can suggest more practical philonthropic exercises for you (I need a new nav/stereo system for my MM, plus I have several credit cards that are accepting donations)... :^)

[finster101]

Zhang definately sounds Klingon. I would wait until Spock finishes his computations and go with his opinion. :D

[Aren Jay]

My radar will still ping off you ... but go ahead and try ... :lol:


:cool4:


That is just it, your radar won't.


The F-37X or whatever it will be called will be both radar invisible and visually invisible. Add in Morris Wards "Starlight plastic" paint and it will be heat invisible too.

[Marauder386]

That is just it, your radar won't.


The F-37X or whatever it will be called will be both radar invisible and visually invisible. Add in Morris Wards "Starlight plastic" paint and it will be heat invisible too.



:lol: ... I have a couple of different types of "radar" ... Keep trying ... :lol:


:cool4:

[Aren Jay]

Tuesday, August 12, 2008
Bringing Invisibility Cloaks Closer
The fabrication of two new materials for manipulating light is a key step toward realizing cloaking.
By Katherine Bourzac (http://my.technologyreview.com/mytr/social/profile.aspx?wuid=7477)

Invisible net: A new material that can bend near-infrared light in a unique way has a fishnet structure. These images of a prism made from the material were taken with a scanning electron microscope. The holes in the net enable the material to interact with the magnetic component of the light, which enables the unusual bending and demonstrates its promise for use in future invisibility cloaks. In the inset, the layers of metal and insulating material that make up the metamaterial are visible.
Credit: Jason Valentine et al.




another too long to post at one time message.

[Aren Jay]

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 (http://www.technologyreview.com/Infotech/16930/?a=f). 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 (http://sciencemag.org/) and Nature (http://www.nature.com/nature/index.html) 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 (http://www.me.berkeley.edu/faculty/zhang/), could show the way toward invisibility cloaks that shield objects from visible light. But Steven Cummer (http://www.ee.duke.edu/~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 (http://xlab.me.berkeley.edu/members.htm), a graduate student


and a little bit more.

[Aren Jay]

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.


See, how will your radar work with this?

[Aren Jay]

Sounding better and better the more I read about it.



WASHINGTON (Reuters) - Scientists have created two new types of materials that can bend light the wrong way, creating the first step toward an invisibility cloaking device.

One approach uses a type of fishnet of metal layers to reverse the direction of light, while another uses tiny silver wires, both at the nanoscale level.

Both are so-called metamaterials -- artificially engineered structures that have properties not seen in nature, such as negative refractive index.

The two teams were working separately under the direction of Xiang Zhang of the Nanoscale Science and Engineering Center at the University of California, Berkeley with U.S. government funding. One team reported its findings in the journal Science and the other in the journal Nature.

Each new material works to reverse light in limited wavelengths, so no one will be using them to hide buildings from satellites, said Jason Valentine, who worked on one of the projects.

"We are not actually cloaking anything," Valentine said in a telephone interview. "I don't think we have to worry about invisible people walking around any time soon. To be honest, we are just at the beginning of doing anything like that."

Valentine's team made a material that affects light near the visible spectrum, in a region used in fiber optics.

"In naturally occurring material, the index of refraction, a measure of how light bends in a medium, is positive," he said.

"When you see a fish in the water, the fish will appear to be in front of the position it really is. Or if you put a stick in the water, the stick seems to bend away from you."

These are illusions caused by the light bending when it moves between water and air.

NEGATIVE REFRACTION

The negative refraction achieved by the teams at Berkeley would be different.

"Instead of the fish appearing to be slightly ahead of where it is in the water, it would actually appear to be above the water's surface," Valentine said. "It's kind of weird."

For a metamaterial to produce negative refraction, it must have a structural array smaller than the wavelength of the electromagnetic radiation being used. This was done using microwaves in 2006 by David Smith of Duke University in North Carolina and John Pendry of Imperial College London.

Visible light is harder. Some groups managed it with very thin layers, virtually only one atom thick, but these materials were not practical to work with and absorbed a great deal of the light directed at it.

"What we have done is taken that material and made it much thicker," Valentine said.

His team, whose work is reported in Nature, used stacked silver and metal dielectric layers stacked on top of each other and then punched through with holes. "We call it a fishnet," Valentine said.
The other team, reporting in Science, used an oxide template and grew silver nanowires inside porous aluminum oxide at tiny distances apart, smaller than the wavelength of visible light. This material refracts visible light.
Immediate applications might be superior optical devices, Valentine said -- perhaps a microscope that could see a living virus.
"However, cloaking may be something that this material could be used for in the future," he said. "You'd have to wrap whatever you wanted to cloak in the material. It would just send light around. By sending light around the object that is to be cloaked, you don't see it."