Want to be invisible? Theories see a possible way

WASHINGTON - New materials that can change the way light and other forms of radiation bend around an object may provide a way to make objects invisible, say researchers.

Two separate teams of researchers have come up with theories on ways to use experimental "metamaterials" to cloak an object and hide it from visible light, infrared light, microwaves and perhaps even sonar probes.

Their work suggests that science-fiction portrayals of invisibility, such as the cloaking devices used to hide space ships in Star Trek, might be truly possible.

Harry Potter's cloak or The Invisible Man of films and fiction might be a bit harder to emulate, however, because the materials must be used in a thick shell.

The concept begins with refraction - a quality of light in which the electromagnetic waves take the quickest, but not necessarily the shortest, route. This accounts for the illusion that a pencil immersed in a glass of water appears broken, for instance.

"Imagine a situation where a medium guides light around a hole in it," Physicist Ulf Leonhardt of Britain's University of St. Andrews, wrote in one of the reports, published in Friday's issue of the journal Science.

The light rays end up behind the object as if they had travelled in a straight line.

"Any object placed in the hole would be hidden from sight. The medium would create the ultimate optical illusion: invisibility, Leonhardt wrote.

"Such devices may be possible. The method developed here can be also applied to escape detection by other electromagnetic waves or sound." The theory is different from that used on modern "stealth" bombers, for example, which bounce radar off their surfaces so they cannot be seen.

Instead, an object would be encased in a shell of metamaterials and they would create an illusion akin to a mirage, said David Schurig of Duke University in North Carolina, who worked on the second report.

Metamaterials are composite structures that deliberately resemble nothing found in nature. They are engineered to have unusual properties, such as the ability to bend light in unique ways.

Like all physics, the invisibility idea requires a little imagination.

"Think of space as a woven cloth," Shurig said in a telephone interview. "Imagine making a hole in the cloth by inserting a pointed object between the threads without tearing them." The light, or microwaves, or radar would travel along the threads of the cloth, ending up behind the object without having touched it.

"You just need the right set of material properties and you can guide light," Shurig said.

The Duke lab started working on metamaterials with a grant from the Defence Advanced Research Projects Agency. Such materials could provide super-light electronics in aircraft or cars, or highly efficient lenses.

Working with John Pendry of Imperial College London, Shurig and David Smith at Duke came up with the idea of using these materials to bend light and other electromagnetic radiation.

"We are going to try to have an experimental demonstration of these effects. There are a few more steps to go. We are working on these steps," Smith said in a telephone interview.

Anyone making such a cloak would have to choose what form of radiation one wanted invisibility from, Shurig said. The invisibility would work both ways - a person hidden from the visible light spectrum would have to use infrared or sonar or microwaves to see out, he said.

"If want to cover the whole visible spectrum that would a tall order," Shurig said.

- REUTERS