May 26, 2006— Building a cloak of invisibility, Harry Potter-style, just got a little easier.
Two methods now precisely describe how a new class of engineered materials could be used to guide waves of electromagnetic radiation — including light — around objects, bestowing invisibility.
In the near future, the technique could shield stealth aircraft from radar detectors and protect equipment from unwanted radiation. But in the long term, the optical illusion could offer new ways to hide things in broad daylight.
"To turn this into something practical is not easy. But there is hope that this could be done because of new developments in optic materials," said Ulf Leonhardt of the University of St. Andrews in the U.K.
Leonhardt and John Pendry of the Imperial College London independently reported their work in this week's issue of Science.
Specially-designed "metamaterials" built on semiconductor chips, they report, can be tuned to divert approaching electromagnetic radiation in another direction.
Other researchers have been investigating how to use these materials to produce invisibility devices.
But Leonhardt and Pendry are the first to precisely calculate how a sphere or cylinder made from metamaterial could be designed to redirect the flow of oncoming waves of radiation around it. An object inside such a sphere would be rendered invisible.
To manipulate the waves, the researchers capitalize on light's proclivity to move along the path of least resistance.
That phenomenon produces familiar optical illusions, such as the way light bends when passing between air and water. A fish beneath the surface appears to be in one place, but try to grab him and you quickly realize his location was a trick of light.
Scientists describe how light behaves in a given material with a number known as the refractive index.
Leonhardt and Pendry have shown that if a material's refractive index could be changed from point to point, light rays might avoid it entirely.
How a cloaking device might actually look remains unclear. But it would employ the metamaterials built onto semiconductor chips and move radiation or light waves at specific speeds along a path of least resistance—that path being the edge of the sphere. The waves would flow around the sphere like a fluid and return to their original path undisturbed.
To the observer, the item in the center of the sphere would go unseen.
But there are still big hurdles to overcome before an invisibility cloak can be made real. So far, the calculations only account for one wavelength of light at the same time. And while that might work for radar applications, it wouldn't work for the entire spectrum of wavelengths in visible light at once, said Mark Dennis, a research fellow at the University of Southampton in the U.K.
"The real ingenuity to making a cloaking device is yet to come," Dennis said.
