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Invisibility cloaks near?

May 25, 2006
Special to World Science

From Harry Potter to Star Trek, science fiction is rife with invisibility cloaks. But can they really exist? Two new studies suggest they could, at least in theory. 

The researchers offered hypothetical explanations for how they could work.

The devices could have a wide range of uses, from high-tech spying to far more innocent purposes, the scientists suggested. 

For example: “You may wish to put a cloak over the refinery that is blocking your view of the bay,” said David Schurig of Duke University in Durham, N.C., one of the researchers.

Light moves in waves called electromagnetic radiation. Physical objects obstruct these waves and scatter them in many directions. This scattering reveals the object’s presence. 

So the trick is to guide the waves of light around an object so that they proceed as if they hadn’t been scattered. 

What type of material is up to such a task? The scientists proposed using “metamaterials,” engineered combinations of materials whose properties can be tuned by design. This would involve manipulating their structure at nanoscales, or size scales nearly as small as that of individual atoms.

In this way, the researchers suggested, materials could be tuned so that when electromagnetic waves encountered a cloaking device they would produce neither a reflection nor a shadow. The studies are published in the May 25 advance online issue of the research journal Science.

One research team, at Duke and at Imperial College London, developed what they called a blueprint for an invisibility cloak.

“The cloak would act like you've opened up a hole in space," said Duke’s David R. Smith. “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.” 

Light would flow around an object hidden in the cloak just as water in a river flows virtually undisturbed around a smooth rock, Smith said. He claimed the Duke researchers are on their way to producing metamaterials with suitable properties. 

The group said their blueprint provides mathematical equations describing a metamaterial whose structural details would let it interact with light in the desired way. The equations could guide the fabrication of the appropriate metamaterials, Smith explained. 

The blueprint is “nothing that couldn’t have been done 50 or even 100 years ago,” Smith said. The difference is that today, it’s possible to actually make the materials. “Natural materials display only a limited palette of possible electromagnetic properties,” he noted. 

The design could theoretically work not only for light but other sorts of electromagnetic radiation, including microwaves. The Duke team said their next major goal is to make it work for microwaves, an achievement that would be useful for wireless communications and other purposes.
 

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