Invisibility 'cloak' moves closer to reality

The development of an invisibility 'cloak' could be just months away because of new research into the manipulation of electromagnetic waves, says a Duke University scientist.
The cloak is shown lying over a bump on a flat surface. Both the bump and surface are covered by a reflective coating. ((Image courtesy of Jack Mock))
The development of an invisibility "cloak" could be just months away because of new research into the manipulation of microwaves, says a Duke University scientist.

Researchers at Duke University in Durham, N.C., and Southeastern University in Nanjing, China, created a piece of material that can conceal an object under it from microwave detection.

Dubbed a "broadband ground-plane cloak," the material can't yet be used for visible wavelengths. But it soon could, said David Smith, one of the researchers responsible for its development.

"For this particular structure there's very little standing in the way," Smith told CBC News when asked about obstacles to creating a cloak that renders objects visually undetectable. "I think it will be demonstrated in the not-too-distant future."

When pressed, Smith said it could happen in a matter of "perhaps months."

The 50 centimetre by 10 centimetre cloak is made of metamaterials — tiny pieces of uniquely structured artificial circuits that manipulate electromagnetic waves. The research team developed the material in nine months, tested it, and published their findings in the latest edition of the journal Science.

In their study, the researchers placed a 2.5 centimetre bump covered with a reflective coating atop another reflective layer. They then placed the cloak on top of the bump and bounced microwaves off it.

When a beam of incoming microwaves hits the flat, mirror-like surface, it is reflected (top left), but when it hits a bump on the surface, the radiation scatters (top middle). Placing the cloaking material on top of the bump restores the mirror, so that the beam is reflected as if it had hit a flat surface (top right). The bottom panels show the same cloaking effect with different wavelengths. ((Image courtesy of AAAS/Science))
Ordinarily, when microwaves hit a bump, they scatter in different directions. In this case the microwaves were manipulated by the material to make it appear as though it was resting on a flat surface, effectively hiding the object from microwave detection.

Advance in technology 'night and day'

In 2006, Smith and another team of researchers developed a smaller cloak that concealed a free-standing copper cylinder from microwave detection. But the newer, more complex material, works for a much broader band of waves, boosting the possibility that the technology could be adapted for visible light.

"In terms of bandwidth, it's night and day," Smith said. "This one by comparison is almost infinite."

While the previous cloak only worked for free-standing objects, the new material "makes something vanish from the surface of the mirror instead." It is also more effective in deflecting the microwaves than the previous cloak, he said.

While the system works solely for objects placed on top of flat, mirrored surfaces, there are numerous practical applications, particularly for radar and radio communication.

But Smith conceded that the practical applications of rendering objects invisible on a flat surface may not be as significant as its radio- or microwave applications. Free-space cloaking — the type employed by fictional teen wizard Harry Potter — is a long-term prospect that requires a lot more research, Smith said.