David Kirkpatrick

November 16, 2010

Metamaterials and artificial black holes

Yeah, I know I’m way off the blogging pace these days — just very busy. But, I couldn’t let this release go past.

The release, warm from the inbox:

Artificial Black Holes Made with Metamaterials

Design for Manmade Light Trapping Device Could Help Harvest Light for Solar Cells.

WASHINGTON, Nov. 16, 2010 /PRNewswire-USNewswire/ — While our direct knowledge of black holes in the universe is limited to what we can observe from thousands or millions of light years away, a team of Chinese physicists has proposed a simple way to design an artificial electromagnetic (EM) black hole in the laboratory.

(Logo: http://www.newscom.com/cgi-bin/prnh/20100714/AIPLOGO)

(Logo: http://photos.prnewswire.com/prnh/20100714/AIPLOGO)

In the Journal of Applied Physics, Huanyang Chen at Soochow University and colleagues have presented a design of an artificial EM black hole designed using five types of composite isotropic materials, layered so that their transverse magnetic modes capture EM waves to which the object is subjected. The artificial EM black hole does not let EM waves escape, analogous to a black hole trapping light. In this case, the trapped EM waves are in the microwave region of the spectrum.

The so-called metamaterials used in the experiment are artificially engineered materials designed to have unusual properties not seen in nature. Metamaterials have also been used in studies of invisibility cloaking and negative-refraction superlenses. The group suggests the same method might be adaptable to higher frequencies, even those of visible light.

“Development of artificial black holes would enable us to measure how incident light is absorbed when passing through them,” says Chen. “They can also be applied to harvesting light in a solar-cell system.”

The article, “A simple design of an artificial electromagnetic black hole” by Wanli Lu, JunFeng Jin, Zhifang Lin, and Huanyang Chen appears in the Journal of Applied Physics. See: http://link.aip.org/link/japiau/v108/i6/p064517/s1

ABOUT Journal of Applied Physics

Journal of Applied Physics is the American Institute of Physics’ (AIP) archival journal for significant new results in applied physics; content is published online daily, collected into two online and printed issues per month (24 issues per year). The journal publishes articles that emphasize understanding of the physics underlying modern technology, but distinguished from technology on the one side and pure physics on the other. See: http://jap.aip.org/

ABOUT AIP

The American Institute of Physics is a federation of 10 physical science societies representing more than 135,000 scientists, engineers, and educators and is one of the world’s largest publishers of scientific information in the physical sciences. Offering partnership solutions for scientific societies and for similar organizations in science and engineering, AIP is a leader in the field of electronic publishing of scholarly journals. AIP publishes 12 journals (some of which are the most highly cited in their respective fields), two magazines, including its flagship publication Physics Today; and the AIP Conference Proceedings series. Its online publishing platform Scitation hosts nearly two million articles from more than 185 scholarly journals and other publications of 28 learned society publishers.

SOURCE  American Institute of Physics

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http://photoarchive.ap.org/
Photo:http://photos.prnewswire.com/prnh/20100714/AIPLOGO
http://photoarchive.ap.org/
American Institute of Physics

Web Site: http://www.aip.org

September 30, 2010

Metamaterials and warp drives

Filed under: et.al., Science — Tags: , , , , , — David Kirkpatrick @ 2:20 pm

It’s almost time to call metamaterials simply that science fiction stuff. Usually you hear about metamaterials around these parts in posts about actual invisibility cloaking technology, and here’s one about metamaterials and warp drives. Metamaterials — turning science fiction into science fact …

From the link:

That means physicists can use metamaterials to simulate the universe itself and all the weird phenomenon of general relativity. We’ve looked at various attempts to recreate black holes, the Big Bang and even multiverses.

But there’s another thing that general relativity appears to allow: faster than light travel. In 1994, the Mexican physicist, Michael Alcubierre, realised that while relativity prevents faster-than-light travel relative to the fabric of spacetime, it places no restriction on the speed at which regions of spacetime can move relative to each other.

That suggests a way of building a warp drive. Alcubierre imagined a small volume of flat spacetime in which a spacecraft sits, surrounded by a bubble of spacetime that shrinks in the direction of travel, bringing your destination nearer, and stretches behind you. He showed that this shrinking and stretching could enable the bubble–and the spaceship it contained–to move at superluminal speeds.

Today, Igor Smolyaninov at the University of Maryland, points out that if these kinds of bubbles are possible in spacetime, then it ought to be possible to simulate them inside a metamaterial.

April 22, 2010

New negative-index metamaterial for invisibility cloaks and more

Here’s news on a new artificial optical material with applications for invisibility cloaking tech and more.

From the first link:

Caltech-led team designs novel negative-index metamaterial that responds to visible light

Uniquely versatile material could be used for more efficient light collection in solar cells

IMAGE: Arrays of coupled plasmonic coaxial waveguides offer a new approach by which to realize negative-index metamaterials that are remarkably insensitive to angle of incidence and polarization in the visible range….

Click here for more information.

PASADENA, Calif.—A group of scientists led by researchers from the California Institute of Technology (Caltech) has engineered a type of artificial optical material—a metamaterial—with a particular three-dimensional structure such that light exhibits a negative index of refraction upon entering the material. In other words, this material bends light in the “wrong” direction from what normally would be expected, irrespective of the angle of the approaching light.

This new type of negative-index metamaterial (NIM), described in an advance online publication in the journal Nature Materials, is simpler than previous NIMs—requiring only a single functional layer—and yet more versatile, in that it can handle light with any polarization over a broad range of incident angles. And it can do all of this in the blue part of the visible spectrum, making it “the first negative index metamaterial to operate at visible frequencies,” says graduate student Stanley Burgos, a researcher at the Light-Material Interactions in Energy Conversion Energy Frontier Research Center at Caltech and the paper’s first author.

“By engineering a metamaterial with such properties, we are opening the door to such unusual—but potentially useful—phenomena as superlensing (high-resolution imaging past the diffraction limit), invisibility cloaking, and the synthesis of materials index-matched to air, for potential enhancement of light collection in solar cells,” says Harry Atwater, Howard Hughes Professor and professor of applied physics and materials science, director of Caltech’s Resnick Institute, founding member of the Kavli Nanoscience Institute, and leader of the research team

What makes this NIM unique, says Burgos, is its engineering. “The source of the negative-index response is fundamentally different from that of previous NIM designs,” he explains. Those previous efforts used multiple layers of “resonant elements” to refract the light in this unusual way, while this version is composed of a single layer of silver permeated with “coupled plasmonic waveguide elements.”

Surface plasmons are light waves coupled to waves of electrons at the interface between a metal and a dielectric (a non-conducting material like air). Plasmonic waveguide elements route these coupled waves through the material. Not only is this material more feasible to fabricate than those previously used, Burgos says, it also allows for simple “tuning” of the negative-index response; by changing the materials used, or the geometry of the waveguide, the NIM can be tuned to respond to a different wavelength of light coming from nearly any angle with any polarization. “By carefully engineering the coupling between such waveguide elements, it was possible to develop a material with a nearly isotopic refractive index tuned to operate at visible frequencies.”

This sort of functional flexibility is critical if the material is to be used in a wide variety of ways, says Atwater. “For practical applications, it is very important for a material’s response to be insensitive to both incidence angle and polarization,” he says. “Take eyeglasses, for example. In order for them to properly focus light reflected off an object on the back of your eye, they must be able to accept and focus light coming from a broad range of angles, independent of polarization. Said another way, their response must be nearly isotropic. Our metamaterial has the same capabilities in terms of its response to incident light.”

This means the new metamaterial is particularly well suited to use in solar cells, Atwater adds. “The fact that our NIM design is tunable means we could potentially tune its index response to better match the solar spectrum, allowing for the development of broadband wide-angle metamaterials that could enhance light collection in solar cells,” he explains. “And the fact that the metamaterial has a wide-angle response is important because it means that it can ‘accept’ light from a broad range of angles. In the case of solar cells, this means more light collection and less reflected or ‘wasted’ light.”

“This work stands out because, through careful engineering, greater simplicity has been achieved,” says Ares Rosakis, chair of the Division of Engineering and Applied Science at Caltech and Theodore von Kármán Professor of Aeronautics and Mechanical Engineering.

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In addition to Burgos and Atwater, the other authors on the Nature Materials paper, “A single-layer wide-angle negative index metamaterial at visible frequencies,” are Rene de Waele and Albert Polman from the Foundation for Fundamental Research on Matter Institute for Atomic and Molecular Physics in Amsterdam. Their work was supported by the Energy Frontier Research Centers program of the Office of Science of the Department of Energy, the National Science Foundation, the Nederlandse Organisatie voor Wetenschappelijk Onderzoek, and “NanoNed,” a nanotechnology program funded by the Dutch Ministry of Economic Affairs.

Visit the Caltech Media Relations website at http://media.caltech.edu.

August 4, 2010

Invisibility cloak update

It’s been several months since I’ve come across any news on invisibility cloak technology, something of a pet subject around here, but here’s the very latest — findings on transformation optics.

From the second link, the release:

New findings promising for ‘transformation optics,’ cloaking

WEST LAFAYETTE, Ind. — Researchers have overcome a fundamental obstacle in using new “metamaterials” for radical advances in optical technologies, including ultra-powerful microscopes and computers and a possible invisibility cloak.

The metamaterials have been plagued by a major limitation: too much light is “lost,” or absorbed by metals such as silver and gold contained in the metamaterials, making them impractical for optical devices.

However, a Purdue University team has solved this hurdle, culminating three years of research based at the Birck Nanotechnology Center at the university’s Discovery Park.

“This finding is fundamental to the whole field of metamaterials,” said Vladimir M. Shalaev, Purdue’s Robert and Anne Burnett Professor of Electrical and Computer Engineering. “We showed that, in principle, it’s feasible to conquer losses and develop these materials for many applications.”

Research findings are detailed in a paper appearing on Aug. 5 in the journal Nature.

The material developed by Purdue researchers is made of a fishnet-like film containing holes about 100 nanometers in diameter and repeating layers of silver and aluminum oxide. The researchers etched away a portion of the aluminum oxide between silver layers and replaced it with a “gain medium” formed by a colored dye that can amplify light.

Other researchers have applied various gain media to the top of the fishnet film, but that approach does not produce sufficient amplification to overcome losses, Shalaev said.

Instead, the Purdue team found a way to place the dye between the two fishnet layers of silver, where the “local field” of light is far stronger than on the surface of the film, causing the gain medium to work 50 times more efficiently.

The approach was first developed by former Purdue doctoral student Hsiao-Kuan Yuan, now at Intel Corp., and it was further developed and applied by doctoral student Shumin Xiao.

Unlike natural materials, metamaterials are able to reduce the “index of refraction” to less than one or less than zero. Refraction occurs as electromagnetic waves, including light, bend when passing from one material into another. It causes the bent-stick-in-water effect, which occurs when a stick placed in a glass of water appears bent when viewed from the outside.

Being able to create materials with an index of refraction that’s negative or between one and zero promises a range of potential breakthroughs in a new field called transformation optics. Possible applications include a “planar hyperlens” that could make optical microscopes 10 times more powerful and able to see objects as small as DNA; advanced sensors; new types of “light concentrators” for more efficient solar collectors; computers and consumer electronics that use light instead of electronic signals to process information; and a cloak of invisibility.

Excitement about metamaterials has been tempered by the fact that too much light is absorbed by the materials. However, the new approach can dramatically reduce the “absorption coefficient,” or how much light and energy is lost, and might amplify the incident light so that the metamaterial becomes “active,” Shalaev said.

“What’s really important is that the absorption coefficient can be as small as only one-millionth of what it was before using our approach,” Shalaev said. “We can even have amplification of light instead of its absorption. Here, for the first time, we showed that metamaterials can have a negative refractive index and amplify light.”

The Nature paper was written by Xiao, senior research scientist Vladimir P. Drachev, principal research scientist Alexander V. Kildishev, doctoral student Xingjie Ni, postdoctoral fellow Uday K. Chettiar, Yuan, and Shalaev.

Fabricating the material was a major challenge, Shalaev said.

First, the researchers had to learn how to precisely remove as much as possible of the aluminum oxide layer in order to vacate space for dye without causing a collapse of the structure.

“You remove it almost completely but leave a little bit to act as pillars to support the structure, and then you spin coat the dye-doped polymer inside the structure,” he said.

The researchers also had to devise a way to deposit just the right amount of dye mixed with an epoxy between the silver layers of the perforated film.

“You can’t deposit too much dye and epoxy, which have a positive refractive index, but only a thin layer about 50 nanometers thick, or you lose the negative refraction,” Shalaev said.

Future work may involve creating a technology that uses an electrical source instead of a light source, like semiconductor lasers now in use, which would make them more practical for computer and electronics applications.

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The work was funded by the U.S. Army Research Office and the National Science Foundation.

Hit this link for the related image (it’s just too big for this blog and I didn’t feel like doing any resizing), and here’s the accompanying caption for the image:

This illustration shows the structure of a new device created by Purdue researchers to overcome a fundamental obstacle in using new “metamaterials” for radical advances in optical technologies, including ultrapowerful microscopes and computers and a possible invisibility cloak. The material developed by the researchers is a perforated, fishnet-like film made of repeating layers of silver and aluminum oxide. The researchers etched away a portion of the aluminum oxide between silver layers and replaced it with a “gain medium” to amplify light. (Birck Nanotechnology Center, Purdue University)

May 27, 2010

Nanotech and optics

Very cool findings about light-activated nanoshells.

The release:

Optical Legos: Building nanoshell structures

Self-assembly method yields materials with unique optical properties

IMAGE: Heptamers containing seven nanoshells have unique optical properties.

Click here for more information.

HOUSTON — (May 27, 2010) — Scientists from four U.S. universities have created a way to use Rice University’s light-activated nanoshells as building blocks for 2-D and 3-D structures that could find use in chemical sensors, nanolasers and bizarre light-absorbing metamaterials. Much as a child might use Lego blocks to build 3-D models of complex buildings or vehicles, the scientists are using the new chemical self-assembly method to build complex structures that can trap, store and bend light.

The research appears in this week’s issue of the journal Science.

“We used the method to make a seven-nanoshell structure that creates a particular type of interference pattern called a Fano resonance,” said study co-author Peter Nordlander, professor of physics and astronomy at Rice. “These resonances arise from peculiar light wave interference effects, and they occur only in man-made materials. Because these heptamers are self-assembled, they are relatively easy to make, so this could have significant commercial implications.”

Because of the unique nature of Fano resonances, the new materials can trap light, store energy and bend light in bizarre ways that no natural material can. Nordlander said the new materials are ideally suited for making ultrasensitive biological and chemical sensors. He said they may also be useful in nanolasers and potentially in integrated photonic circuits that run off of light rather than electricity.

The research team was led by Harvard University applied physicist Federico Capasso and also included nanoshell inventor Naomi Halas, Rice’s Stanley C. Moore Professor in Electrical and Computer Engineering and professor of physics, chemistry and biomedical engineering.

Nordlander, the world’s leading theorist on nanoparticle plasmonics, had predicted in 2008 that a heptamer of nanoshells would produce Fano resonances. That paper spurred Capasso’s efforts to fabricate the structure, Nordlander said.

The new self-assembly method developed by Capasso’s team was also used to make magnetic three-nanoshell “trimers.” The optical properties of these are described in the Science paper, which also discusses how the self-assembly method could be used to build even more complex 3-D structures.

Nanoshells, the building blocks that were used in the new study, are about 20 times smaller than red blood cells. In form, they resemble malted milk balls, but they are coated with gold instead of chocolate, and their center is a sphere of glass. By varying the size of the glass center and the thickness of the gold shell, Halas can create nanoshells that interact with specific wavelengths of light.

“Nanoshells were already among the most versatile of all plasmonic nanoparticles, and this new self-assembly method for complex 2-D and 3-D structures simply adds to that,” said Halas, who has helped develop a number of biological applications for nanoshells, including diagnostic applications and a minimally invasive procedure for treating cancer.

###

Additional co-authors of the new study include Rice graduate students Kui Bao and Rizia Bardhan; Jonathan Fan and Vinothan Manoharan, both of Harvard; Chihhui Wu and Gennady Shvets, both of the University of Texas at Austin; and Jiming Bao of the University of Houston. The research was supported by the National Science Foundation, the Air Force Office of Scientific Research, the Department of Defense, the Robert A. Welch Foundation, the Department of Energy and Harvard University.

PhysOrg covers this story here.

April 3, 2010

Invisibility cloak-plus

Filed under: Science — Tags: , , , — David Kirkpatrick @ 1:47 am

An interesting spin on the burgeoning invisibility cloak tech.

From the link:

In a twist on the concept of an invisibility cloak, researchers have designed a material that not only makes an object invisible, but also generates one or more virtual images in its place. Because it doesn’t simply display the background environment to a viewer, this kind of optical device could have applications that go beyond a normal invisibility cloak. Plus, unlike previously proposed illusion devices, the design proposed here could be realized with artificial metamaterials.

The team of engineers, Wei Xiang Jiang, Hui Feng Ma, Qiang Cheng, and Tie Jun Cui from Southeast University in Nanjing, China, describes the recently developed class of optical transformation media as “illusion media.” As they explain in a new study, any object enclosed by such an illusion medium layer appears to be one or more other objects. The researchers’ proposed device is designed to operate at microwave frequencies.

“The illusion media make an enclosed object appear like another object or multiple virtual objects,” Cui told PhysOrg.com. “Hence it can be applied to confuse the detectors or the viewers, and the detectors or the viewers can’t perceive the real object. As a result, the enclosed object will be protected.”

Invisibility cloak that generates virtual images gets closer to realization

Illusion media can transform a real image into a virtual image. For example, a golden apple (the actual object) enclosed within the illusion medium layer appears as two green apples (the illusion) to any viewer outside the virtual boundary (dashed curves). Image credit: Jiang, et al.

August 16, 2009

More cloaking news

Filed under: Science — Tags: , , , , — David Kirkpatrick @ 11:03 pm

This isn’t really on my typical topic of invisibility cloaks, but it is a very interesting cloaking technology.

The release:

A new cloaking method

This is not a ‘Star Trek’ or ‘Harry Potter’ story

IMAGE: Graeme Milton, a distinguished professor of mathematics at the University of Utah, is the senior author of two newly published studies outlining the numerical and theoretical basis for a new…

Click here for more information. 

SALT LAKE CITY, Aug. 17, 2009 – University of Utah mathematicians developed a new cloaking method, and it’s unlikely to lead to invisibility cloaks like those used by Harry Potter or Romulan spaceships in “Star Trek.” Instead, the new method someday might shield submarines from sonar, planes from radar, buildings from earthquakes, and oil rigs and coastal structures from tsunamis.

“We have shown that it is numerically possible to cloak objects of any shape that lie outside the cloaking devices, not just from single-frequency waves, but from actual pulses generated by a multi-frequency source,” says Graeme Milton, senior author of the research and a distinguished professor of mathematics at the University of Utah.

“It’s a brand new method of cloaking,” Milton adds. “It is two-dimensional, but we believe it can be extended easily to three dimensions, meaning real objects could be cloaked. It’s called active cloaking, which means it uses devices that actively generate electromagnetic fields rather than being composed of ‘metamaterials’ [exotic metallic substances] that passively shield objects from passing electromagnetic waves.”

Milton says his previous research involved “just cloaking clusters of small particles, but now we are able to cloak larger objects.”

IMAGE: These images are from animated computer simulations of a new method — developed by University of Utah mathematicians — for cloaking objects from waves of all sorts. While the new…

Click here for more information. 

For example, radar microwaves have wavelengths of about four inches, so Milton says the study shows it is possible to use the method to cloak from radar something 10 times wider, or 40 inches. That raises hope for cloaking larger objects. So far, the largest object cloaked from microwaves in actual experiments was an inch-wide copper cylinder.

A study demonstrating the mathematical feasibility of the new cloaking technique – active, broadband, exterior cloaking – was published online today in the journal Optics Express. A related paper was published online Aug. 14 in Physical Review Letters.

Milton conducted the studies with Fernando Guevara Vasquez and Daniel Onofrei, both of whom are assistant professors-lecturers in mathematics. The research was funded by the National Science Foundation and the University of Utah.

Cloaking: From Science Fiction to Science

Cloaking involves making an object partly or completely invisible to incoming waves – sound waves, sea waves, and seismic waves, but usually electromagnetic waves such as visible light, microwaves, infrared light, radio and TV waves.

Cloaking things from visible light long has been a staple of science fiction, from invisible Romulan Bird of Prey warships in “Star Trek” to cloaking devices in books, games, films and shows like “Harry Potter,” “Halo,” “Predator,” and “Stargate.”

In recent years, scientists devised and tested various cloaking schemes. They acknowledge practical optical cloaking for invisibility is many years away. Experiments so far have been limited to certain wavelengths such as microwaves and infrared light, and every method tried so far has limitations.

Compared with passive cloaking by metamaterials, the new method – which involves generating waves to protect or cloak an object from other waves – can cloak from a broader band of wavelengths, Milton says.

“The problem with metamaterials is that their behavior depends strongly on the frequency you are trying to cloak from,” he adds. “So it is difficult to obtain broadband cloaking. Maybe you’d be invisible to red light, but people would see you in blue light.”

Most previous research used interior cloaking, where the cloaking device envelops the cloaked object. Milton says the new method “is the first active, exterior cloaking” technique: cloaking devices emit signals and sit outside the cloaked object.

Videos Simulate How Cloaking Method Works

The new studies are numerical and theoretical, and show how the cloaking method can work. “The research simulates on a computer what you should see in an experiment,” Milton says. “We just do the math and hope other people do the experiments.”

The Physical Review Letters study demonstrates the new cloaking method at a single frequency of electromagnetic waves, while the Optics Express paper demonstrates how it can work broadband, or at a wide range of frequencies.

In Optics Express, the mathematicians demonstrate that three cloaking devices together create a “quiet zone” so that “objects placed within this region are virtually invisible” to incoming waves. Guevara Vasquez created short videos of mathematical simulations showing a pulse of electromagnetic or sound waves rolling past an object:

 

     

  • In one video, with the kite-shaped object uncloaked, the wave clearly interacts with the object, creating expanding, circular ripples like when a rock is thrown in a pond. 

     

  • In the second video, the object is surrounded by three point-like cloaking devices, each of which emits waves that only propagate a short distance. Those points and their emissions resemble purple sea urchins. As the passing waves roll by the cloaking devices, waves emitted by those devices interfere with the passing waves. As a result, the passing waves do not hit the cloaked object and there are no ripples.

 

Milton says the cloaking devices cause “destructive interference,” which occurs when two pebbles are thrown in a pond. In places where wave crests meet, the waves add up and the crests are taller. Where troughs meet, the troughs are deeper. But where crests cross troughs, the water is still because they cancel each other out.

The principle, applied to sound waves, is “sort of like noise cancelation devices you get with headphones in airplanes if you travel first class,” Milton says.

Protecting from Destructive Seismic and Tsunami Waves

“We proved mathematically that this method works when the wavelength of incoming electromagnetic radiation is large compared with the objects being cloaked, meaning it can cloak very small objects,” Milton says. “It also can cloak larger objects.”

Because visible light has tiny wavelengths, only microscopic objects could be made invisible by the new method.

“The cloaking device would have to generate fields that have very small wavelengths,” Milton says. “It is very difficult to build antennas the size of light waves. We’re so far from cloaking real-sized objects to visible light that it’s incredible.”

But imagine incoming waves as water waves, and envision breakwater cloaking devices that would generate waves to create a quiet zone that would protect oil rigs or specific coastal structures against incoming tsunami waves. Or imagine cloaking devices around buildings to generate vibrations to neutralize incoming seismic waves.

“Our method may have application to water waves, sound and microwaves [radar],” including shielding submarines and planes from sonar and radar, respectively, and protecting structures from seismic waves during earthquakes and water waves during tsunamis, Milton says. All those waves have wavelengths much larger than those of visible light, so the possible applications should be easier to develop.

“It would be wonderful if you could cloak buildings against earthquakes,” Milton says. “That’s on the borderline of what’s possible.”

The new method’s main disadvantage “is that it appears you must know in advance everything about the incoming wave,” including when the pulse begins, and the frequencies and amplitudes of the waves within the pulse, Milton says. That might require placement of numerous sensors to detect incoming seismic waves or tsunamis.

“Even though cloaking from light is probably impossible, it’s a fascinating subject, and there is beautiful mathematics behind it,” Milton says. “The whole area has exploded. So even if it’s not going to result in a ‘Harry Potter’ cloak, it will have spinoffs in other directions,” not only in protecting objects from waves of various sorts, but “for building new types of antennas, being able to see things on a molecular scale. It’s sort of a renaissance in classical science, with new ideas popping up all the time.”

 

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A video showing an object uncloaked and cloaked as a wave passes may be seen and downloaded from http://vimeo.com/6092319 or as separate videos from http://vimeo.com/5406253 (no cloaking) and http://vimeo.com/5406236 (with cloaking).

University of Utah Public Relations

August 14, 2009

Invisibility cloak tech creates fake portal

Via KurzweilAI.net — Here’s the latest news on invisibility cloaktechnology, a longtime favorite subject for this blog.

A lot of this stuff is really getting deeper and deeper into the world of science fiction as science fact. Of course, I’m still waiting to see a convincing real-world demonstration of the basic cloaking technology touted the last few years, so maybe all this news remains in the world of fiction. Either way, it’s a fun topic.

Beyond the looking glass…
PhysOrg.com, Aug. 13, 2009

A “hidden portal” invisibility cloak may be possible using exotic new single-crystal yttrium-iron-garnet ferrite metamaterials that force light and other forms of electromagnetic radiation in complicated directions, researchers from the Hong Kong University of Science and Technologyand Fudan University have found.

People standing outside the portal would see something like a mirror.

 
Read Original Article>>

July 7, 2009

Invisibility cloak plus

Filed under: Science, Technology — Tags: , , , — David Kirkpatrick @ 3:10 pm

Via KurzweilAI.net — I’ve done plenty of blogging on invisibility cloaking technology, and here’s the lastest. I think this tech is very cool and I hate to throw any cold water on the latest news, but I’d be more impressed with seeing an actual effective working model of a simple cloaking device before getting to wild with advanced varients like those described below.

Modified invisibility cloak could make the ultimate illusion
New Scientist Tech, July 7, 2009

An illusion device using metamaterials that makes one object look like another could one day be used to camouflage military planes or create “holes” in solid walls.

To make a cup look like a spoon, for example, light first strikes the cup and is distorted. It then passes through a complementary metamaterial which cancels out the distortions to make the cup seem invisible. The light then moves into a region of the metamaterial that creates a distortion as if a spoon were present. The result is that an observer looking at the cup through the metamaterial would see a spoon.

 
Read Original Article>>

May 22, 2009

The latest in cloaking tech

I’ve done plenty of blogging on invisibility cloaking technology. Here’s a release from yesterday on the very latest news. It does seem we’re getting pretty close to an actual invisibility cloak. Science fiction becomes science fact once again.

The release:

New ‘broadband’ cloaking technology simple to manufacture

IMAGE: This image shows the design of a new type of invisibility cloak that is simpler than previous designs and works for all colors of the visible spectrum, making it possible…

Click here for more information. 

WEST LAFAYETTE, Ind. – Researchers have created a new type of invisibility cloak that is simpler than previous designs and works for all colors of the visible spectrum, making it possible to cloak larger objects than before and possibly leading to practical applications in “transformation optics.”

Whereas previous cloaking designs have used exotic “metamaterials,” which require complex nanofabrication, the new design is a far simpler device based on a “tapered optical waveguide,” said Vladimir Shalaev, Purdue University’s Robert and Anne Burnett Professor of Electrical and Computer Engineering.

Waveguides represent established technology – including fiber optics – used in communications and other commercial applications.

The research team used their specially tapered waveguide to cloak an area 100 times larger than the wavelengths of light shined by a laser into the device, an unprecedented achievement. Previous experiments with metamaterials have been limited to cloaking regions only a few times larger than the wavelengths of visible light.

Because the new method enabled the researchers to dramatically increase the cloaked area, the technology offers hope of cloaking larger objects, Shalaev said.

Findings are detailed in a research paper appearing May 29 in the journal Physical Review Letters. The paper was written by Igor I. Smolyaninov, a principal electronic engineer at BAE Systems in Washington, D.C.; Vera N. Smolyaninova, an assistant professor of physics at Towson University in Maryland; Alexander Kildishev, a principal research scientist at Purdue’s Birck Nanotechnology Center; and Shalaev.

“All previous attempts at optical cloaking have involved very complicated nanofabrication of metamaterials containing many elements, which makes it very difficult to cloak large objects,” Shalaev said. “Here, we showed that if a waveguide is tapered properly it acts like a sophisticated nanostructured material.”

The waveguide is inherently broadband, meaning it could be used to cloak the full range of the visible light spectrum. Unlike metamaterials, which contain many light-absorbing metal components, only a small portion of the new design contains metal.

Theoretical work for the design was led by Purdue, with BAE Systems leading work to fabricate the device, which is formed by two gold-coated surfaces, one a curved lens and the other a flat sheet. The researchers cloaked an object about 50 microns in diameter, or roughly the width of a human hair, in the center of the waveguide.

“Instead of being reflected as normally would happen, the light flows around the object and shows up on the other side, like water flowing around a stone,” Shalaev said.

The research falls within a new field called transformation optics, which may usher in a host of radical advances, including cloaking; powerful “hyperlenses” resulting in microscopes 10 times more powerful than today’s and able to see objects as small as DNA; computers and consumer electronics that use light instead of electronic signals to process information; advanced sensors; and more efficient solar collectors.

Unlike natural materials, metamaterials are able to reduce the “index of refraction” to less than one or less than zero. Refraction occurs as electromagnetic waves, including light, bend when passing from one material into another. It causes the bent-stick-in-water effect, which occurs when a stick placed in a glass of water appears bent when viewed from the outside. Each material has its own refraction index, which describes how much light will bend in that particular material and defines how much the speed of light slows down while passing through a material.

Natural materials typically have refractive indices greater than one. Metamaterials, however, can be designed to make the index of refraction vary from zero to one, which is needed for cloaking.

The precisely tapered shape of the new waveguide alters the refractive index in the same way as metamaterials, gradually increasing the index from zero to 1 along the curved surface of the lens, Shalaev said.

Previous cloaking devices have been able to cloak only a single frequency of light, meaning many nested devices would be needed to render an object invisible.

Kildishev reasoned that the same nesting effect might be mimicked with the waveguide design. Subsequent experiments and theoretical modeling proved the concept correct.

Researchers do not know of any fundamental limit to the size of objects that could be cloaked, but additional work will be needed to further develop the technique.

Recent cloaking findings reported by researchers at other institutions have concentrated on a technique that camouflages features against a background. This work, which uses metamaterials, is akin to rendering bumps on a carpet invisible by allowing them to blend in with the carpet, whereas the Purdue-based work concentrates on enabling light to flow around an object.

 

###

 

Related Web site:

Vladimir Shalaev:
https://engineering.purdue.edu/ECE/People/profile?resource_id=3322

IMAGE CAPTION:

This image shows the design of a new type of invisibility cloak that is simpler than previous designs and works for all colors of the visible spectrum, making it possible to cloak larger objects than before and possibly leading to practical applications in “transformation optics.” (Purdue University)

A publication-quality image is available at http://news.uns.purdue.edu/images/+2009/shalaev-cloaking.jpg

Abstract on the research in this release is available at: http://news.uns.purdue.edu/x/2009a/090520ShalaevCloaking.html

May 14, 2009

Invisibility cloak, plus

Yep, news on invisibility cloaks  returns once again. This time with a twist — metamaterials that can go beyond a simple cloak of invisibility and actually create the illusion of a totally different object in place of the one being cloaked.

Via KurzweilAI.net:

Illusion Cloak Makes One Object Look like Another
The physics arXiv blog, May 13, 2009

Metamaterials could be used for an even more exotic effect than invisibility cloaks: to create the illusion that a different objectis present, Hong Kong University of Science and Technology researchers say.

 
Read Original Article>>

March 18, 2009

Optical communications expo set for March 22-26

Here’s the details:

OFC/NFOEC features breakthroughs in next-generation ethernet, metamaterials, networks

Major research conference to be held in San Diego, March 22-26

WASHINGTON, March 17—The world’s largest international conference on optical communications begins next week and continues from March 22-26 at the San Diego Convention Center in San Diego. The Optical Fiber Communication Conference and Exposition/National Fiber Optic Engineers Conference (OFC/NFOEC) is the premier meeting where experts from industry and academia intersect and share their results, experiences, and insights on the future of electronic and wireless communication and the optical technologies that will enable it.

Journalists are invited to attend the meeting, where more than 15,000 attendees are expected. This year’s lineup will have many engaging talks and panels, including:

 

     

  • MARKET WATCH, a three-day series of presentations and panel discussions featuring esteemed guest speakers from the industrial, research, and investment communities on the applications and business of optical communications. See: http://www.ofcnfoec.org/conference_program/Market_Watch.aspx

     

  • PLENARY PRESENTATIONS: “The Changing Landscape in Optical Communications,” Philippe Morin, president, Metro Ethernet Networks; “Getting the Network the World Needs,” Lawrence Lessig, professor, Stanford Law School; “The Growth of Fiber Networks in India,” Shri Kuldeep Goyal, chairman and managing director, Bharat Sanchar Nigam Ltd. To access speaker bios and talk abstracts, see: http://www.ofcnfoec.org/conference_program/Plenary.aspx

     

  • SERVICE PROVIDER SUMMIT, a dynamic program with topics and speakers of interest to CTOs, network architects, network designers and technologists within the service provider and carrier sector. See: http://www.ofcnfoec.org/conference_program/Service_Provider_Summit.aspx

 

The OFC/NFOEC Web site is http://www.ofcnfoec.org. Also on the site is information on the trade show and exposition, where the latest in optical technology from more than 550 of the industry’s key companies will be on display.

Head below the fold for some conference highlights. (more…)

March 14, 2009

Nanocups to improve optics

I’ve already bloggedon this nanotech breakthrough from Rice University before, and here’s the latest news straight from the source.

The release:

Nanocups brim with potential
Light-bending metamaterial could lead to superlenses, invisibility cloaks

Researchers at Rice University have created a metamaterial that could light the way toward high-powered optics, ultra-efficient solar cells and even cloaking devices.

Naomi Halas, an award-winning pioneer in nanophotonics, and graduate student Nikolay Mirin created a material that collects light from any direction and emits it in a single direction. The material uses very tiny, cup-shaped particles called nanocups.

In a paper in the February issue of the journal Nano Letters, co-authors Halas and Mirin explain how they isolated nanocups to create light-bending nanoparticles.

In earlier research, Mirin had been trying to make a thin gold film with nano-sized holes when it occurred to him the knocked-out bits were worth investigating. Previous work on gold nanocups gave researchers a sense of their properties, but until Mirin’s revelation, nobody had found a way to lock ensembles of isolated nanocups to preserve their matching orientation.

“The truth is a lot of exciting science actually does fall in your lap by accident,” said Halas, Rice’s Stanley C. Moore Professor in Electrical and Computer Engineering and professor of chemistry and biomedical engineering. “The big breakthrough here was being able to lift the nanocups off of a structure and preserve their orientation. Then we could look specifically at the properties of these oriented nanostructures.”

Mirin’s solution involved thin layers of gold deposited from various angles onto polystyrene or latex nanoparticles that had been distributed randomly on a glass substrate. The cups that formed around the particles – and the dielectric particles themselves – were locked into an elastomer and lifted off of the substrate. “You end up with this transparent thing with structures all oriented the same way,” he said.

In other words, he had a metamaterial, a substance that gets its properties from its structure and not its composition. Halas and Mirin found their new material particularly adept at capturing light from any direction and focusing it in a single direction.

Redirecting scattered light means none of it bounces off the metamaterial back into the eye of an observer. That essentially makes the material invisible. “Ideally, one should see exactly what is behind an object,” said Mirin.

“The material should not only retransmit the color and brightness of what is behind, like squid or chameleons do, but also bend the light around, preserving the original phase information of the signal.”

Halas said the embedded nanocups are the first true three-dimensional nanoantennas, and their light-bending properties are made possible by plasmons. Electrons inside plasmonic nanoparticles resonate with input from an outside electromagnetic source in the same way a drop of water will make ripples in a pool. The particles act the same way radio antennas do, with the ability to absorb and emit electromagnetic waves that, in this case, includes visible wavelengths.

Because nanocup ensembles can focus light in a specific direction no matter where the incident light is coming, they make pretty good candidates for, say, thermal solar power. A solar panel that doesn’t have to track the sun yet focuses light into a beam that’s always on target would save a lot of money on machinery.

Solar-generated power of all kinds would benefit, said Halas. “In solar cells, about 80 percent of the light passes right through the device. And there’s a huge amount of interest in making cells as thin as possible for many reasons.”

Halas said the thinner a cell gets, the more transparent it becomes. “So ways in which you can divert light into the active region of the device can be very useful. That’s a direction that needs to be pursued,” she said.

Using nanocup metamaterial to transmit optical signals between computer chips has potential, she said, and enhanced spectroscopy and superlenses are also viable possibilities.

“We’d like to implement these into some sort of useful device,” said Halas of her team’s next steps. “We would also like to make several variations. We’re looking at the fundamental aspects of the geometry, how we can manipulate it, and how we can control it better.

“Probably the most interesting application is something we not only haven’t thought of yet, but might not be able to conceive for quite some time.”

The paper can be found at http://pubs.acs.org/doi/abs/10.1021/nl900208z?prevSearch=mirin&searchHistoryKey.

March 5, 2009

Invisibility cloak, part six

Filed under: Science, Technology — Tags: , , , — David Kirkpatrick @ 7:53 pm

I’ve done plenty of blogging on cloak of invisibility tech, and here’s the latest news from PhysOrg.

From the second link:

A paper published in the March 2009 issue of SIAM Review, “Cloaking Devices, Electromagnetic Wormholes, and Transformation Optics,” presents an overview of the theoretical developments in cloaking from a mathematical perspective.

One method involves light waves bending around a region or object and emerging on the other side as if the waves had passed through empty space, creating an “invisible” region which is cloaked. For this to happen, however, the object or region has to be concealed using a cloaking device, which must be undetectable to electromagnetic waves. Manmade devices called metamaterials use structures having cellular architectures designed to create combinations of material parameters not available in nature.

Mathematics is essential in designing the parameters needed to create metamaterials and to show that the material ensures invisibility. The mathematics comes primarily from the field of partial differential equations, in particular from the study of equations for electromagnetic waves described by the Scottish mathematician and physicist James Maxwell in the 1860s.

One of the “wrinkles” in the mathematical model of cloaking is that the transformations that define the required material parameters have singularities, that is, points at which the transformations fail to exist or fail to have properties such as smoothness or boundness that are required to demonstrate cloaking. However, the singularities are removable; that is, the transformations can be redefined over the singularities to obtain the desired results.

January 16, 2009

The latest in cloaking tech

Haven’t blogged on this subject in a while. It’s always fun to cover, though.

The release:

Next generation cloaking device demonstrated

IMAGE: Pictured is the new cloak with bump, left, and the prototype, right.

Click here for more information. 

DURHAM, N.C. – A device that can bestow invisibility to an object by “cloaking” it from visual light is closer to reality. After being the first to demonstrate the feasibility of such a device by constructing a prototype in 2006, a team of Duke University engineers has produced a new type of cloaking device, which is significantly more sophisticated at cloaking in a broad range of frequencies.

The latest advance was made possible by the development of a new series of complex mathematical commands, known as algorithms, to guide the design and fabrication of exotic composite materials known as metamaterials. These materials can be engineered to have properties not easily found in natural materials, and can be used to form a variety of “cloaking” structures. These structures can guide electromagnetic waves around an object, only to have them emerge on the other side as if they had passed through an empty volume of space.

IMAGE: This is David R. Smith with the new cloak device.

Click here for more information. 

The results of the latest Duke experiments were published Jan. 16 in the journal Science. First authors of the paper were Duke’s Ruopeng Liu, who developed the algorithm, and Chunlin Li. David R. Smith, William Bevan Professor of electrical and computer engineering at Duke, is the senior member of the research team.

Once the algorithm was developed, the latest cloaking device was completed from conception to fabrication in nine days, compared to the four months required to create the original, and more rudimentary, device. This powerful new algorithm will make it possible to custom-design unique metamaterials with specific cloaking characteristics, the researchers said.

“The difference between the original device and the latest model is like night and day,” Smith said. “The new device can cloak a much wider spectrum of waves — nearly limitless — and will scale far more easily to infrared and visible light. The approach we used should help us expand and improve our abilities to cloak different types of waves.”

Cloaking devices bend electromagnetic waves, such as light, in such a way that it appears as if the cloaked object is not there. In the latest laboratory experiments, a beam of microwaves aimed through the cloaking device at a “bump” on a flat mirror surface bounced off the surface at the same angle as if the bump were not present. Additionally, the device prevented the formation of scattered beams that would normally be expected from such a perturbation.

The underlying cloaking phenomenon is similar to the mirages seen ahead at a distance on a road on a hot day.

“You see what looks like water hovering over the road, but it is in reality a reflection from the sky,” Smith explained. “In that example, the mirage you see is cloaking the road below. In effect, we are creating an engineered mirage with this latest cloak design.”

Smith believes that cloaks should find numerous applications as the technology is perfected. By eliminating the effects of obstructions, cloaking devices could improve wireless communications, or acoustic cloaks could serve as protective shields, preventing the penetration of vibrations, sound or seismic waves.

“The ability of the cloak to hide the bump is compelling, and offers a path towards the realization of forms of cloaking abilities approaching the optical,” Liu said. “Though the designs of such metamaterials are extremely complex, especially when traditional approaches are used, we believe that we now have a way to rapidly and efficiently produce such materials.”

With appropriately fine-tuned metamaterials, electromagnetic radiation at frequencies ranging from visible light to radio could be redirected at will for virtually any application, Smith said. This approach could also lead to the development of metamaterials that focus light to provide more powerful lenses.

The newest cloak, which measures 20 inches by 4 inches and less than an inch high, is actually made up of more than 10,000 individual pieces arranged in parallel rows. Of those pieces, more than 6,000 are unique. Each piece is made of the same fiberglass material used in circuit boards and etched with copper.

The algorithm determined the shape and placement of each piece. Without the algorithm, properly designing and aligning the pieces would have been extremely difficult, Smith said.

 

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The research was supported by Raytheon Missile Systems, the Air Force Office of Scientific Research, InnovateHan Technology, the National Science Foundation of China, the National Basic Research Program of China, and National Science Foundation of Jiangsu Province, China.

Others members of the research team were Duke’s Jack Mock, as well as Jessie Y. Chin and Tie Jun Cui from Southeast University, Nanjing, China.

October 17, 2008

Transformation optics promise big payoff

It’s been quite a while since I’ve blogged on the possibility of a “cloak of invisibility,” so this PhysOrg article caught my eye. It covers a research field known as transformation optics, and the promise there is great. We’re talking the aforementioned cloak, plusultra-powerful microscopes and computers. All this is done by harnessing nanotechnology and “metamaterials.”

From the second link:

The field, which applies mathematical principles similar to those in Einstein’s theory of general relativity, will be described in an article to be published Friday (Oct. 17) in the journal Science. The article will appear in the magazine’s Perspectives section and was written by Vladimir Shalaev, Purdue’s Robert and Anne Burnett Professor of Electrical and Computer Engineering.

The list of possible breakthroughs includes a cloak of invisibility; computers and consumer electronics that use light instead of electronic signals to process information; a “planar hyperlens” that could make optical microscopes 10 times more powerful and able to see objects as small as DNA; advanced sensors; and more efficient solar collectors.

“Transformation optics is a new way of manipulating and controlling light at all distances, from the macro- to the nanoscale, and it represents a new paradigm for the science of light,” Shalaev said. “Although there were early works that helped to develop the basis for transformation optics, the field was only recently established thanks in part to papers by Sir John Pendry at the Imperial College, London, and Ulf Leonhardt at the University of St. Andrews in Scotland and their co-workers.”

August 11, 2008

Cloaking device becoming feasible?

From KurzweilAI.net — I’ve blogged on 3D cloaking devices before, very likely the previous KurzweilAI.net linked blog post from mid-May is an earlier report of this project. Both stories originate from UC Berkeley.

At any rate, here’s 3D cloaking part two:

Practical Cloaking Devices On The Horizon?
PhysOrg.com, Aug. 10, 2008University of California, Berkeley scientists have created a multilayered, “fishnet” metamaterial that unambiguously exhibits negative refractive index, allowing for invisibility in three dimensions for the first time, Nature magazine plans to report this week.

 
Read Original Article>>

 

Update — Here’s another take on this story, once again from PhysOrg. This time with pictures!

From the link:

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.

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

And here’s the image:

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
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

June 30, 2008

Quantum stickiness, Hawking and teh funny

From KurzweilAI.net, micromachine stiction, Stephen Hawking tackles the universe’s inflation and defining humor.

How a quantum effect is gumming up nanomachines
New Scientist news service, June 28, 2008

Researchers are making progress in overcoming static friction, or or “stiction,” which sticks together the parts of micromachines on scales of between 10 and 300 nanometers and limits progress in reducing their size, affecting computer hard drives and other devices with small moving parts.

Stiction is due to the Casimir effect, a quantum-mechanics phenomenon that causes surfaces to be attracted. Methods to reduce its effect include use of patterned surfaces, suspending the components in a liquid, and use of metamaterials.

 
Read Original Article>>

Hawking ‘close’ to explaining universe’s inflation
New Scientist (article preview), June 28, 2008

Starting with current observations of the universe and working back to narrow down the initial set of possibilities and by treating the early cosmos as a quantum object with a multitude of alternative universes that gradually blend into ours, Stephen Hawking and colleagues think they are close to perfecting an answer to explain why the infant universe expanded so rapidly.

(Subscription required)

 
Read Original Article>>

Mechanism and function of humor identified by new evolutionary theory
PhysOrg.com, June 27, 2008

Humor occurs when the brain recognizes a pattern that surprises it, suggests Alastair Clarke in the forthcoming book, Humour.

“Now that we understand the mechanism of humour, the possibility of creating an artificial intelligence being that could develop its own sense of humour becomes very real,” he says. “This would, for the first time, create an AI capable of exhibiting one of the defining characteristics that make us human, making it seem significantly less robotic as a result.”

 
Read Original Article>>

May 14, 2008

More science fiction turning into science fact

From KurzweilAI.net, taking steps toward an invisibility cloak

New material may be step towards 3D invisibility cloak
New Scientist, May 13, 2008

A researcher at the University of California at Berkeley claims to have made a 3D metamaterial with a negative refractive index, the first 3D material of this kind.

Physicists have in recent years made it possible to bend, or refract, light in the opposite direction to any natural materials. These metamaterials make it possible to create invisibility cloaks that hide an object by steering light around it. The materials and “invisibility cloaks” built so far have all been flat, working only in two dimensions.

The negative refraction index will have to be confirmed by measuring the speed of light in the material.

See Also Physicists draw up plans for real ‘cloaking device’

 
Read Original Article>>

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