DURHAM, USA, 26 May 2006 - In theory, an invisibility cloak could be built using available technology, according to an international team of scientists.

The scientists, from Duke University's Pratt School of Engineering in the U.S. 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, they said.

In principle, their invisibility cloak could be realised with exotic artificial composite materials called "metamaterials", they said.

"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, he said.

"There are several possible goals one may have for cloaking an object," said David Schurig a research associate in electrical and computer engineering at Duke. "One goal would be to conceal an object from discovery by agents using probing or environmental radiation."

"Another would be to allow electromagnetic fields to essentially pass through a potentially obstructing object," he said. "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, such cloaking also could improve wireless communications, Schurig said. Along the same principles, an acoustic cloak could serve as a protective shield, preventing the penetration of vibrations, sound or seismic waves.

Although the theoretical cloak now reported has yet to be created, the Duke researchers are on their way to producing metamaterials with suitable properties, Smith said.

Their design theory provides the precise mathematical function describing a metamaterial with structural properties that would allow it to become invisible. That function could then guide the fabrication of metamaterials with those precise characteristics, Smith explained.

The theory itself 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," he added. "The theory has only now become relevant because we can make metamaterials with the properties we are looking for."

The team reported its findings yesterday in Science Express, the online advance publication of the journal Science.