Muggle boffins try on first invisibility cloak

Forget Harry Potter. A team of US scientists claims to have demonstrated the world's first working "invisibility cloak".

However, the boffins from Duke University's Pratt School of Engineering in North Carolina explained that the cloak deflects microwave beams, rather than visible light, so it will not make objects invisible to the human eye.

But the cloak will deflect microwaves around the "hidden" object inside with little distortion, making it appear almost as if nothing were there at all.

Such coverings that can render objects effectively invisible to microwaves could have a variety of wireless communications or radar applications, according to the researchers.

The scientists manufactured the cloak using artificial composite "metamaterials" arranged in a series of concentric circles that confer specific electromagnetic properties.

The cloak represents "one of the most elaborate metamaterial structures yet designed and produced", the scientists said.

It also represents the most comprehensive approach to invisibility yet realised, with the potential to hide objects of any size or material property.

"By incorporating complex material properties, our cloak allows a concealed volume, plus the cloak, to appear to have properties similar to free space when viewed externally," said David Smith, Augustine Scholar and professor of electrical and computer engineering at Duke.

"The cloak reduces both an object's reflection and its shadow, either of which would enable its detection."

The team produced the cloak according to electromagnetic specifications determined by a new design theory proposed by Sir John Pendry of Imperial College London in collaboration with the Duke scientists.

The principles behind the cloaking design, although mathematically rigorous, can be applied in a relatively straightforward way using metamaterials, according to cloak designer David Schurig, a research associate in Duke's electrical and computer engineering department.

"One first imagines a distortion in space similar to what would occur when pushing a pointed object through a piece of cloth, distorting, but not breaking, any threads," said Schurig.

"In such a space light or other electromagnetic waves would be confined to the warped 'threads' and therefore could not interact with, or 'see', objects placed inside the resulting hole."

The scientists said it was currently "uncertain" whether it would be possible to use the same principles to produce cloaks that confer invisibility within the visible frequency range.

"It is not yet clear that we are going to get the invisibility that everyone thinks about with Harry Potter's cloak or the Star Trek cloaking device," said Professor Smith.