Way out: Theoretical blueprint for invisibility


Invisibility cloaks and starship cloaking devices may not only belong in the worlds of Harry Potter and Star Trek, according to researchers at Duke University’s Pratt School of Engineering and at Imperial College London. Using a new design theory, a blueprint was developed for an invisibility cloak with many uses, they suggest, such as hiding a refinery, electrical or other transmission towers, or manufacturing facilities in the way of a beautiful view. It could also clear an electromagnetic pathway, researchers say, for improved wireless communications.

A cloak like this could hide an object so well that observers would be completely unaware of its presence. The researchers’ invisibility cloak could be realized with artificial composite materials called metamaterials.

“The cloak would act like you've opened up a hole in space,” said David R. Smith, Augustine Scholar and professor of electrical and computer engineering at Duke's Pratt School. “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.”

Electromagnetic waves would flow around an object hidden inside the metamaterial cloak just as water in a river flows virtually undisturbed around a smooth rock, they say. First demonstrated by Smith and his colleagues in 2000, metamaterials can be made to interact with light or other electromagnetic waves in very precise ways. The cloak has not actually been created, but the researchers claim to have begun to produce metamaterials with suitable properties.

“There are several possible goals one may have for cloaking an object,” said David Schurig, a research associate in electrical and computer engineering. “One goal would be to allow electromagnetic fields to essentially pass through a potentially obstructing object. For example, you may wish to put a cloak over the refinery that is blocking your view of the bay.”

By eliminating the effects of obstructions, cloaking also could improve wireless communications, researchers said. Along the same principles, an acoustic cloak could serve as a protective shield, preventing the penetration of vibrations, sound, or seismic waves, they say.

Cloaking would only be the first among a variety of uses for the design method, the researchers suggest. With fine-tuned metamaterials, electromagnetic radiation at frequencies ranging from visible light to electricity could be redirected at will for virtually any application. One example could be the development of metamaterials that focus light to provide a more perfect lens through optimization of its shape.

“To exploit electromagnetism, engineers use materials to control and direct the field: a glass lens in a camera, a metal cage to screen sensitive equipment,‘black bodies’ of various forms to prevent unwanted reflections,” the researchers said in their article.

The design theory provides the precise mathematical function describing a metamaterial with structural details that would allow its interaction with electromagnetic radiation in the manner desired, they said, to guide fabrication of metamaterials with those precise characteristics.

The theory is simple, Smith said. “It's nothing that couldn't have been done 50 or even 100 years ago,” he said. “However, natural materials display only a limited palette of possible electromagnetic properties. The theory has only now become relevant because we can make metamaterials with the properties we are looking for.”

The team's next major goal is an experimental verification of invisibility to electromagnetic waves at microwave frequencies. Such a cloak, the scientists said, would have utility for wireless communications, among other applications.

For more information from Duke University’s Pratt School of Engineering, click here .

For more from Imperial College, click here .

—Edited by Lisa Sutor , Control Engineering contributing editor

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