U.S. and British scientists said on Thursday they had found a way to hide an object from microwave radiation in a first step toward making a what they hope will be an invisibility cloak.
Such a device could be used to elude radar, but the researchers, like many scientists, are not working with any particular goal in mind but hope its uses will become apparent later.
“It’s not quite Harry Potter,” said David Smith of Duke University in North Carolina, referring to the child’s fictional character who can conceal himself in a magical cloak.
“It’s not exactly perfect — we can do better — but it demonstrates the mechanism, the way the waves swirl around the center region where you want to conceal things,” he said.
The cloaking device relies on new, laboratory-made materials called metamaterials, which can decrease both the scattering caused by a solid object and the shadow it casts.
Every solid object scatters radiation that hits it, from microwaves through to visible light. It is this scattering that allows objects to be seen, whether with the eye or using radar or ultrasound.
In this case the cloak is quite thick, Smith said — twice as big as the 6-inch copper tube it obscures. The materials are arranged in concentric rings.
In May the same team of researchers reported on their theory, and it took them just a few months to demonstrate it. The key is the metamaterials, which resemble a circuit board, Smith said.
“The material ends up being very complicated and not something you can make using materials that are lying around, like plastics or ceramics,” Smith said in a telephone interview.
Their device is small, with an outer diameter of about 12 inches.
The first cloak was a two-dimensional version and researchers have already started work on a three-dimensional version. They also want to broaden the range of wavelengths that it can block, although making something invisible to the human eye would present a much greater challenge.
“It is very unlikely that we could do it with this technology in the visible (spectrum),” Smith said. It would have to be scaled down to nanotechnology levels, but the metals involved behave differently on that scale, he said.
Microwave cloaks might be useful for eluding radar, said Costas Soukoulis, a theorist the U.S. Department of Energy’s Ames Laboratory in Iowa. “This is very, very important that experiments have produced what theorists had predicted,” Soukoulis told Science, which published the findings.
The researchers are funded by the Defense Advanced Research Projects Agency or DARPA and the design is based on a theory proposed by Sir John Pendry of Imperial College London. The metamaterials bend the electromagnetic waves, in this case microwaves.
“The waves’ movement is similar to river water flowing around a smooth rock,” said David Schurig, also of Duke.