Using a new design theory, researchers at Duke Universitys Pratt School of Engineering and Imperial College London have developed the blueprint for an invisibility cloak. Once devised, the cloak could have numerous uses, from defense applications to wireless communications, the researchers said.
Such a cloak could hide any object so well that observers would be totally unaware of its presence, according to the researchers. In principle, their invisibility cloak could be realized with exotic artificial composite materials called "metamaterials," they said.
"The cloak would act like youve opened up a hole in space," said David R. Smith, Augustine Scholar and professor of electrical and computer engineering at Dukes 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, Smith said.
The research team, which also includes David Schurig of Dukes Pratt School and John Pendry of Imperial College London, reported its findings on May 25, 2006, in Science Express, the online advance publication of the journal Science. The work was supported by the Defense Advanced Research Projects Agency.
"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. "Using the previous generation of materials, design is largely a matter of choosing the interface between two materials." In the case of a camera, for example, this means optimizing the shape of the lens.
The recent advent of metamaterials opens up a new range of possibilities by providing electromagnetic properties that are "impossible to find in nature," the researchers said.
Their 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. That function could then guide the fabrication of metamaterials with those precise characteristics, Smith explained.
The theory itself is simple, Smith said. "Its nothing that couldnt have been done 50 or even 100 years ago," he said.
"However, natural materials display only a limited palette of possible electromagnetic properties," he added. "The theory has only now become relevant because we can make metamaterials with the properties we are looking for."
"This new design paradigm, which can provide a recipe to fit virtually any electromagnetic application, leads to material specifications that could be implemented only with metamaterials," Schurig added.
The teams next major goal is an experimental verification of invisibility to electromagnetic waves at microwave frequencies, the scientists said. Such a cloak, they said, would have utility for wireless communications, among other applications.
