Invisibility cloak 'step closer'

For now, the invisibility cloak remains a thing of science fiction

Scientists in the US say they are a step closer to developing materials that could render people invisible.

Researchers at the University of California in Berkeley have developed a material that can bend light around 3D objects making them "disappear".

The materials do not occur naturally but have been created on a nano scale, measured in billionths of a metre.

The team says the principles could one day be scaled up to make invisibility cloaks large enough to hide people.

Stealth operations

The findings, by scientists led by Xiang Zhang, were published in the journals Nature and Science.

The light-bending effect relies on reversing refraction, the effect that makes a straw placed in water appear bent.

Previous efforts have shown this negative refraction effect using microwaves—a wavelength far longer than humans can see.

In order to have the 'Harry Potter' effect, you just need to find the right materials for the visible wavelengths Ortwin Hess

The new materials instead work at wavelengths around those used in the telecommunications industry—much nearer to the visible part of the spectrum.

Two different teams led by Zhang made objects made of so-called metamaterials—artificial structures with features smaller than the wavelength of light that give the materials their unusual properties.

One approach used nanometre-scale stacks of silver and magnesium fluoride in a "fishnet" structure, while another made use of nanowires made of silver.

Light is neither absorbed nor reflected by the objects, passing "like water flowing around a rock," according to the researchers. As a result, only the light from behind the objects can be seen.

Cloak and shadow

The fine structure of the material gives it light-bending abilities

"This is a huge step forward, a tremendous achievement," says Professor Ortwin Hess of the Advanced Technology Institute at the University of Surrey.

"It's a careful choice of the right materials and the right structuring to get this effect for the first time at these wavelengths."

There could be more immediate applications for the devices in telecommunications, Prof Hess says.

What's more, they could be used to make better microscopes, allowing images of far smaller objects than conventional microscopes can see.

And a genuine cloaking effect isn't far around the corner.

"In order to have the 'Harry Potter' effect, you just need to find the right materials for the visible wavelengths," says Prof Hess, "and it's absolutely thrilling to see we're on the right track."