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Invisibility undone
September 03, 2008Harry Potter beware! A team of Chinese scientists has developed a way to unmask your invisibility cloak. According to a new paper in the latest issue of Optics Express, the Optical Society's (OSA) open-access journal, certain materials underneath an invisibility cloak would allow invisible objects be seen again.
"Cloaking is an important problem since invisibility can help survival in hostile environment," says Huanyang Chen of Shanghai Jiao Tong University in China. He and his colleagues have proposed a theoretical "anti-cloak" that would partially cancel the effect of the invisibility cloak, which is another important problem as it turns out.
If this sounds like more movie magic, it's no accident. From the 1933 classic The Invisible Man to the more recent installment in the Harry Potter series, devices that achieve invisibility have long been the stuff of film fantasy. In recent years, however, scientists using special types of "meta" materials have shown that these Hollywood fantasies could one day become reality after all.
These materials are effectively invisible because of the way they interact with light. All materials scatter, bounce, absorb, reflect and otherwise alter light rays that strike them. We perceive color, for instance, because different materials and coatings interact with light differently. Transformation media cloaks are special materials that can bend light so much that it actually passes around the object completely. In 2006, scientists at Duke University demonstrated in the laboratory that an object made of metamaterial is partially invisible when viewed using microwaves.
Sounds cool? Not so fast. Invisibility as it has been achieved so far in the laboratory is very limited. It works, but only for a narrow band of light wavelengths. Nobody has found a way yet to make an object invisible to the broad range of wavelengths our eyes are attuned to seeing, says Chen, and doing so would be a challenge.
An even greater problem for anyone who has aspirations to be concealed in public one day is that invisibility achieved through transformation media is a two-way street. With no light penetrating a perfect invisibility cloak, there would be no way for an invisible person to see outside. In other words, invisible people would also be blind-not exactly what Harry Potter had in mind.
But now, Chen and his colleagues have developed way to partially cancel the invisibility cloak's cloaking effect. Their "anti-cloak" would be a material with optical properties perfectly matched to those of an invisibility cloak. (In technical jargon, an anti-cloak would be anisotropic negative refractive index material that is impedance matched to the positive refractive index of the invisibility cloak).
While an invisibility cloak would bend light around an object, any region that came into contact with the anti-cloak would guide some light back so that it became visible. This would allow an invisible observer to see the outside by pressing a layer of anti-cloak material in contact with an invisibility cloak.
"With the anti-cloak, Potter can see outside if he wants to," says Chen, who conducted the research together with his colleagues at Shanghai Jiao Tong University and The Hong Kong University of Science and Technology.
American Institute of Physics
These materials are effectively invisible because of the way they interact with light. All materials scatter, bounce, absorb, reflect and otherwise alter light rays that strike them. We perceive color, for instance, because different materials and coatings interact with light differently. Transformation media cloaks are special materials that can bend light so much that it actually passes around the object completely. In 2006, scientists at Duke University demonstrated in the laboratory that an object made of metamaterial is partially invisible when viewed using microwaves.
Sounds cool? Not so fast. Invisibility as it has been achieved so far in the laboratory is very limited. It works, but only for a narrow band of light wavelengths. Nobody has found a way yet to make an object invisible to the broad range of wavelengths our eyes are attuned to seeing, says Chen, and doing so would be a challenge.
An even greater problem for anyone who has aspirations to be concealed in public one day is that invisibility achieved through transformation media is a two-way street. With no light penetrating a perfect invisibility cloak, there would be no way for an invisible person to see outside. In other words, invisible people would also be blind-not exactly what Harry Potter had in mind.
But now, Chen and his colleagues have developed way to partially cancel the invisibility cloak's cloaking effect. Their "anti-cloak" would be a material with optical properties perfectly matched to those of an invisibility cloak. (In technical jargon, an anti-cloak would be anisotropic negative refractive index material that is impedance matched to the positive refractive index of the invisibility cloak).
While an invisibility cloak would bend light around an object, any region that came into contact with the anti-cloak would guide some light back so that it became visible. This would allow an invisible observer to see the outside by pressing a layer of anti-cloak material in contact with an invisibility cloak.
"With the anti-cloak, Potter can see outside if he wants to," says Chen, who conducted the research together with his colleagues at Shanghai Jiao Tong University and The Hong Kong University of Science and Technology.
American Institute of Physics
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Scientists and curiosity seekers who want to know what a partially or completely cloaked object would look like in real life can now get their wish -- virtually.
COES professor's 'metamaterials' research lands cover of international journal
Dr. Dentcho Genov, an assistant professor of physics and electrical engineering at Louisiana Tech University and a Louisiana Optical Network Initiative (LONI) Institute fellow, is featured on the cover of the most recent issue of Nature Physics, one of the most respected and prestigious physics journals in the world.
Beyond the looking glass
While the researchers can't promise delivery to a parallel universe or a school for wizards, books like Pullman's Dark Materials and JK Rowling's Harry Potter are steps closer to reality now that researchers in China have created the first tunable electromagnetic gateway.
The guiding of light: A new metamaterial device steers beams along complex pathways
Using a composite metamaterial to deliver a complex set of instructions to a beam of light, Boston College physicists have created a device to guide electromagnetic waves around objects such as the corner of a building or the profile of the eastern seaboard.
Stripping leukemia-initiating cells of their 'invisibility cloak'
Two new studies reveal a way to increase the body's appetite for gobbling up the cancer stem cells responsible for acute myeloid leukemia (AML), a form of cancer with a particularly poor survival rate.
'Invisibility cloak' could protect against earthquakes
Research at the University of Liverpool has shown it is possible to develop an 'invisibility cloak' to protect buildings from earthquakes.
Discovery at UAB brings us nearer to making the dream of invisibility true
A group of researchers from the Department of Physics at UAB have designed a device, called a dc metamaterial, which makes objects invisible under certain light - very low frequency electromagnetic waves - by making the inside of the magnetic field zero but not altering the exterior field.
New 'broadband' cloaking technology simple to manufacture
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."
Blurring the Line Between Magic and Science: Berkeley Researchers Create an 'Invisibility Cloak'
The great science fiction writer Arthur C. Clarke famously noted the similarities between advanced technology and magic. This summer on the big screen, the young wizard Harry Potter will once again don his magic invisibility cloak and disappear.
Scientists closer to making invisibility cloak a reality
J.K. Rowling may not have realized just how close Harry Potter's invisibility cloak was to becoming a reality when she introduced it in the first book of her best-selling fictional series in 1998. Scientists, however, have made huge strides in the past few years in the rapidly developing field of cloaking. Ranked the number five breakthrough of the year by Science magazine in 2006, cloaking involves making an object invisible or undetectable to electromagnetic waves.
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Closer to vanishing: bending light as a step toward invisibility cloaks.(visible light): An article from: Science News by D. Castelvecchi (Author) This digital document is an article from Science News, published by Thomson Gale on March 24, 2007. The length of the article is 482 words. The page length shown above is based on a typical 300-word page. The article is delivered in HTML format and is available in your Amazon.com Digital Locker immediately after purchase. You can view it with any web browser. Citation Details Title: Closer to vanishing: bending light as a step toward invisibility cloaks.(visible light) Author: D. Castelvecchi Publication: Science News (Magazine/Journal) Date: March 24, 2007 Publisher: Thomson Gale Volume: 171 Issue: 12 Page: 180(1) Distributed by Thomson... | |
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