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Posted Aug 15, 2008, 5:17 AM
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Registered User
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Join Date: Jun 2006
Posts: 1,071
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If only we already had the ability to deal more easily with the shadow problem over open spaces from buildings like the Transbay Tower at over 1000 feet in San Francisco, but there still is hope. If not in time for Transbay, maybe other even taller buildings will be less of a problem in San Francisco someday. If would also be nice if the cloaking effect can be turned on or off during certain times for such buildings.
From: http://www.comcast.net/articles/news...ibility.Cloak/
Quote:
Scientists closer to developing invisibility cloak
Mon Aug 11, 8:03 PM EDT
WASHINGTON — Scientists say they are a step closer to developing materials that could render people and objects invisible. Researchers have demonstrated for the first time they were able to cloak three-dimensional objects using artificially engineered materials that redirect light around the objects.
Previously, they only have been able to cloak very thin two-dimensional objects.
The findings, by scientists at the University of California, Berkeley, led by Xiang Zhang, are to be released later this week in the journals Nature and Science.
The new work moves scientists a step closer to hiding people and objects from visible light, which could have broad applications, including military ones.
People can see objects because they scatter the light that strikes them, reflecting some of it back to the eye. Cloaking uses materials, known as metamaterials, to deflect radar, light or other waves around an object, like water flowing around a smooth rock in a stream.
Metamaterials are mixtures of metal and circuit board materials such as ceramic, Teflon or fiber composite. They are designed to bend visible light in a way that ordinary materials don't. Scientists are trying to use them to bend light around objects so they don't create reflections or shadows.
It differs from stealth technology, which does not make an aircraft invisible but reduces the cross-section available to radar, making it hard to track.
The research was funded in part by the U.S. Army Research Office and the National Science Foundation's Nano-Scale Science and Engineering Center.
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From: http://news.nationalgeographic.com/n...ity-cloak.html
Quote:
Invisibility-Cloak Materials Bend Light "Backward"
Brian Handwerk
for National Geographic News
August 12, 2008
Invisibility cloaks may be a bit closer to reality, researchers say, thanks to the development of two new materials that are the first to bend visible light the "wrong" way in three dimensions.
The so-called metamaterials are artificial composites designed to manipulate light in ways that natural materials can't—in these cases by refracting it backward. (Related: "The Power of Light" in National Geographic magazine.)
If their cloaking capabilities are fully realized, metamaterials could make an object invisible by bending light waves so that they curve around the object and then reconnect, seemingly unaltered, on the other side—similar to the way water flows around a boulder.
"Of course cloaking captures everybody's attention, but these papers aren't [just] about cloaking," said Xiang Zhang, a professor at the University of California, Berkeley, and head of the research teams publishing related papers in two different journals this week.
"[The studies] are about the ability to engineer these material properties that never exist in nature. With that ability one can do many things, and cloaking is only one of them."
Such materials could also boost the power of microchips and antennas and allow the creation of "superlenses" that could image objects smaller than the wavelength of light, the study authors report.
Negative Refraction One new metamaterial, described in Science, is a microscopic arrangement of silver wires—each about 20 times thinner than a human hair—embedded in aluminum oxide.
The other metamaterial, detailed online in Nature, is a layer cake of alternating nanoscale strips of silver and magnesium fluoride that were cut into a fishnet pattern.
Both materials exhibit negative refraction—bending visible light in a different direction than expected in nature.
A pencil sticking out a glass of water, for example, normally appears slightly bent at the point where it meets the water's surface but is still seen submerged. With negative refraction, the pencil would appear to stick back out of the water.
Previous metamaterials have been able to achieve a cloaking effect only in two dimensions in larger microwave wavelengths that are not visible to humans.
In addition to having 3-D negative refraction for a broader visible light spectrum, the new advances help overcome the sticky problem of energy loss.
Previous metamaterials actually absorbed most of the light, rather than bending it away, reducing the "invisible" properties. The new materials were designed to keep energy away from the most absorbent materials.
"It's like when you try to cross a river and keep your feet dry. You may jump across stones and cross without getting your feet wet," study leader Zhang said.
"That's exactly what we did. We tried to engineer these materials such that energy passing through is hopping through [other materials] and not the metal—because in the metal you have a big energy loss."
Scaling Up
David Schurig, a physicist and metamaterial expert at North Carolina State University in Raleigh, called the types of materials discussed by both papers "probably the most exciting metamaterials in existence today."
"Even in their current state, or maybe a few generations [later], they could have applications in optical communications or imaging," added Schurig, who was not involved with the research.
But, he noted, efforts to cloak anything above microscopic size are likely quite a ways off.
"You want to cloak things that are big, otherwise they are already essentially invisible, because they are [microscopic]," Schurig said.
"To cloak a person, you need metamaterial that's on that length scale, and that's much, much bigger than what [these papers] have demonstrated."
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From: http://www.msnbc.msn.com/id/12961080/
Quote:
Here’s how to make an invisibility cloak
Theoretical cloaking device could soon become reality (sort of)
By Alan Boyle
Science editor
MSNBC
updated 11:03 a.m. PT, Thurs., May. 25, 2006
The black lines in this drawing show the path that light rays would take through a theoretical cloaking device. The device's metamaterial would be patterned in such a way to route the rays around the cloaked sphere.
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.
This diagram shows how light rays could theoretically be bent around a concealed object, making it seem as if an observer were looking straight through the object.
"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.
© 2008 MSNBC Interactive
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It's reassuring to hear that it is likely that hines will keep the pelli design! I actually really like the tower! It is very classy in my view.
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