Here’s how to make an invisibility cloak

[Troll]

Here’s how to make an invisibility cloak
Theoretical cloaking device could soon become reality (sort of)

Researchers say they are rapidly closing in on new types of materials that can throw a cloak of invisibility around objects, fulfilling a fantasy that is as old as ancient myths and as young as "Star Trek" and the Harry Potter novels.

Unlike those tales of fictional invisibility, the real-life technologies usually have a catch. Nevertheless, limited forms of invisibility might be available to the military sooner than you think.

"We're very confident that at radar frequencies, these materials can be implemented on a time scale of 18 months or so," John Pendry of Imperial College London told MSNBC.com.

Pendry's research team is one of two groups whose results were posted Thursday on the journal Science's Web site in advance of print publication. The two papers lay out different theoretical methods for creating invisibility, not only for radar but potentially for optical wavelengths as well.

Still more teams are out there with ideas to make things invisible — using methods ranging from superlenses that cancel out the light from nearby objects to actual cloaks onto which video can be projected as a moving camouflage. The most exotic technologies involve "metamaterials," blends of polymers and tiny coils or wires that twist the paths of electromagnetic radiation.

"There are recipes for controlling metamaterials," explained University of Pennsylvania electrical engineer Nader Engheta, who published his own invisibility recipe last year. "Metamaterials are very interesting products."

The latest research papers describe how metamaterial could be fabricated to bend light in carefully curved paths around the object to be hidden, so that an observer would see right through it — or more accurately, right around it — to the other side.

The cloak would act like you've opened up a hole in space," Duke University's David Smith, one of Pendry's co-authors, explained in a news release. "All light or other electromagnetic waves are swept around the area, guided by the metamaterial to emerge on the other side as if they had passed through an empty volume of space."

Pendry told MSNBC.com that the cloak wouldn't reflect any light, and wouldn't cast a shadow either. "It would be like Peter Pan had lost his shadow," he said, referring to the fictional character who had to have his shadow stitched back on.

Dreams come true, with a few catches
Theoretically at least, the metamaterial could work like the helmet of invisibility celebrated in Greek myth, or the cloaking device that hid Romulan and Klingon vessels in the "Star Trek" series, or the invisibility cloak that came in so handy for Harry Potter in J.K. Rowlings' novels.

"Fiction has predicted the course of science for some time. ... Maybe these Harry Potter novels were ahead of their time," Pendry said, half-jokingly.

Of course, there are some scientific catches that the tale-tellers never had to worry about:

For a total invisibility effect, the waves passing closest to the cloaked object would have to be bent in such a way that they would appear to exceed relativity's light speed limit. Fortunately, there's a loophole in Albert Einstein's rules of the road that allows smooth pulses of light to undergo just such a phase shift.
The invisibility effect would work only for a specific range of wavelengths. "There is a price to be paid if you want a thin cloak, in that it operates only over a narrow range of frequencies," Pendry said.
The cloak could be made to cover a volume of any shape, but "you can't flap your cloak," Pendry said. Moving the material around would spoil the effect.
The tiny structures embedded in the metamaterial would have to be smaller than the wavelength of the electromagnetic rays you wanted to bend. That's a tall order for optical invisibility, because the structures would have to be on the scale of nanometers, or billionths of a meter. It's far easier to create radar invisibility, Pendry said: "You're talking millimeters" — that is, thousandths of a meter.
The radar application is of great interest to military outfits such as the Defense Advanced Research Projects Agency, which funded Pendry's team. "Radar is a defense technology, and if you wish to hide from it, this sort of cloak would be a good way of doing it," he said. Such a technology would be "far superior to stealth," he said.

If optical cloaks could be designed, that would be of interest to the military as well. "One obvious thing would be that you could construct a hutch in which you could hide a tank, and the hutch would make it appear as though the tank wasn't there. ... You could also think of weightier things, like submarines or battleships, where you might want to put some of this stuff," Pendry said.

Civilian applications, too
There'd be plenty of applications in the civilian world as well, even for rudimentary cloaking devices. For example, you could create receptacles to shield sensitive medical devices from disruption by MRI scanners, or build cloaks to route cellphone signals around obstacles. "You may wish to put a cloak over the refinery that is blocking your view of the bay," Duke University's David Schurig, another of Pendry's co-authors, was quoted as saying.

While Pendry's team proposed constructing all-over cloaking devices, the other research paper published Thursday describes a simpler method that would involve shaping the metamaterials into cylindrical cloaking devices. The method could also work to block sound waves — like the cone of silence on the "Get Smart" TV show, but not as silly.

The catch here is that the invisibility effect would work only if you were on the same plane as the hidden object. "You could look on top of it, and look inside the cloak," said the paper's author, Ulf Leonhardt of the University of St. Andrews in Scotland.

Leonhardt told MSNBC.com that "potentially a mixture of the two schemes will lead to a practical design." He said the paper from Pendry's team gave him some additional ideas to work with.

"I read it for the first time just last Friday, and I've come up already with something new," he said.

© 2006 MSNBC Interactive

http://msnbc.msn.com/id/12961080/

[canoilers]

That should help peeping toms out alot, that could be kinda scarey if used in certain ways.

[Alex]

That's an interesting story; I could understand almost everything and It has really interestings things... The invisible cloak.. :D

[Troll]

That should help peeping toms out alot, that could be kinda scarey if used in certain ways.

It would be kinda scarey.

[Troll]

A real invisibility cloak is in our grasp: scientists

CHICAGO (AFP) - Harry Potter fans take note: scientists have finally come up with a workable design for an invisibility cloak.

Physicists figured out the complex mathematical equations for making objects invisible by bending light around them last year.

A group of engineers at Purdue University in Indiana have now used those calculations to design a relatively simple device that ought to be able to - one day soon - make objects as big as an airplane simply disappear.

The design calls for tiny metal needles to be fitted into a hairbrush-shaped cone at angles and lengths that would force light to pass around the cloak. This would make everything inside the cone appear to vanish because the light would no longer reflect off it.

"It looks pretty much like fiction, I do realize, but it's completely in agreement with the laws of physics," said lead researcher Vladimir Shalaev, a professor of electrical and computer engineering at Purdue.

"Ideally, if we make it real it would work exactly like Harry Potter's invisibility cloak," he said. "It's not going to be heavy because there's going to be very little metal in it."

The still-theoretical design will be published this month in the journal Nature Photonics.

Shaleav said he needs to secure funding to build the device and expects it would take two to three years to come up with a working prototype.

The major limitation is that the current design can only bend the light of a single wave-length at a time, and does not work with the entire frequency range of the visible spectrum.

"How to create a design that works for all colors of visible light at the same time will be a big technical challenge, but we believe it's possible," Shalaev said. "In principal it's doable."

Even blocking a single frequency can lead to useful applications, Shaleav said.

The cloak could shield soldiers from night-vision goggles which use only one wavelength of light. It could also be used to hide objects from "laser designators" used by the military to illuminate a target, he said.

Other researchers have managed to clock objects from the microwave range of the spectrum, which are much larger than the wavelengths of visible light.

This new design is the first for cloaking objects of any size in the range of light visible to humans.

It works by using tiny needles to alter the "index of refraction" around the cone.

Every material has its own refractive index which determines how light bends and slows down as it passes from that material into another. It's commonly described as the bent-stick-in-water effect, which occurs when a stick placed in a glass of water looks bent when seen from outside the glass.

Natural materials typically have a refractive index greater than one. But the tiny metal needles layered inside the cone work to gradually alter the index from zero at the inner surface of the cloak, to one at the outer surface of the cloak. This guides, or bends, light around the cloaked object.

The technology for making the tiny needles is already used to make nanotech devices. The needles in the theoretical design are about as wide as 10 nanometers, or billionths of a meter, and as long as hundreds of nanometers.

A single nanometer is roughly the size of 20 hydrogen atoms strung together.

http://news.yahoo.com/s/afp/20070406/sc_afp/ussciencephysicsinvisibility;_ylt=ArnTGaSRvQ_otMSz qY_kL8jMWM0F

[ELEANOR MAW]

Thanks for the info, I sometimes feel like I would like to be invisible at times, like when I get a council tax bill.

[Troll]

Invisibility Cloak: From Hogwarts to Reality

The only way to see anything is for our eyes to intercept visible radiation—light waves—bouncing off it. That makes the recipe for invisibility obvious: just make the object absorb all the light that falls on it. Last year, for instance, scientists at Duke University manufactured a cloak made out of metamaterials, which are artificial composites that interact with electromagnetic radiation in a certain way. In that case, copper rings and wires on sheets of fiberglass deflected microwaves, causing the cloak to be invisible to any being whose eyes are sensitive to microwaves rather than visible waves. Okay, not exactly what J.K. Rowling had in mind, but definitely a step in the right direction.

Now Muggle physicists have taken one more step toward reproducing Harry Potter’s invisibility cloak, this time with visible light waves. In an upcoming issue of the journal Physical Review Letters, physicists Zhichao Ruan, Min Yan, Curtis W. Neff and Min Qiu of Sweden’s Royal Institute of Technology and China’s Zhejiang University show that a cloak made of metamaterials and shaped into a column could make the Muggle, witch or or wizard inside completely invisible.

The key is that the metamaterials force light to follow a particular path. (That’s also the reason your hair looks darker when wet: the water molecules make light bounce around within the hair, with the result that fewer escape to reach your eye; less light equals darker object.) “When electromagnetic waves pass through the invisibility cloak, the cloak will deflect the waves, guide them around the object, and return them to the original propagation direction without perturbing the exterior field,” the physicists write. Done right, the column (for complicated reasons, a cylindrical shape is better for invisibility than, say, a flat rectangle) would guide light around the inner chamber, preventing it from ever reaching anything—including an eye or camera—beyond. But light scattered from objects behind the cloak might also be guided around it, meaning that when you looked at the cloak you would see whatever was behind it, just as with Harry Potter’s. As the authors say, “a cloak with the ideal material parameters is a perfect invisibility cloak.”

There are a few hurdles to manufacturing what would surely be first on every child’s (and criminal’s) wish list. The most daunting is that if the metamaterials had even the slightest flaw, light would scatter off the cloak, rendering it visible. The cloak would be invisible from the inside, too—that is, you would be unable to see anything outside the cloak.

The metamaterials would be layered, and if the hidden wizard removed one layer he would appear as a thin line, the physicists calculate, and the background would be slightly distorted. As more inner layers were removed, the wizard would become more visible and the background more distorted, until with the final step in this odd strip-tease he would be fully visible again.

http://blog.newsweek.com/blogs/labnotes/archive/2007/08/31/invisibility-cloak-from-hogwarts-to-reality.aspx

[mcjessica]

hahaha what a wierd thing to spend time and resources creating. That's pretty cool though.

[Troll]

Invisibility cloak one step closer, scientists say

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."


http://news.yahoo.com/s/nm/20080810/sc_nm/cloaking_dc

[tonyme]

Wow! Isn't that interesting:p

Thanks Andrew

[Paul]

There's already an easier way to do this involving cameras. :p