Seeing through invisibility
Posted: Wednesday, September 03, 2008 6:25 PM by Alan Boyle
Duke
This demonstration shows how a cylindrical "invisibility cloak" bends microwaves
moving from left to right around a interior space, concealing the space from view.
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First, scientists developed a real-life invisibility cloak. Now Chinese researchers are working on an anti-invisibility device to see through the cloak.
This may sound like a development that would concern the Romulans in a "Star Trek" episode rather than real people. But the research, published online today on the Optics Express Web site, addresses real-world concerns about the cloaking devices that are being built in labs today.
Such devices can make whatever is inside invisible to particular wavelengths, by bending light around the sheath of the "cloak." They've been compared to the magical invisibility cloak in the Harry Potter novels as well as the Romulan cloaking device on the classic "Star Trek" TV series.
The real thing, however, is much more limited than the fictional items. The cloaking device developed a couple of years ago at Duke University, for example, looks more like a slide-projector carousel and can make something seem relatively "invisible" only to a narrow band of microwaves.
Nevertheless, the work that scientists are doing with plastic-and-metal metamaterials could eventually lead to radar-evading ships, planes or submarines.
"Cloaking is an important problem, since invisibility can help survival in a hostile environment," Huanyang Chen of Shanghai Jiao Tong University said in the American Institute of Physics' report on the research.
The theoretical anti-cloak that Chen and his colleagues describe would cancel out the effect of a cloaking device by coming into contact with the inner surface of the cloaking device's refractive material.
To some extent, it's a matter of scientific one-upsmanship. The researchers say they've shown that even the best cloaking device would not be a perfectly stealthy shield, "as there exist some objects that it cannot hide." But the anti-cloak would also address a problem even Harry Potter could understand.
Any device shielded in an invisibility cloak would not be able to sense the waves being bent around it. For example, suppose you had a remote-controlled sensor sitting at the bottom of the ocean, shielded from radar or sonar by a cloak of metamaterials. Occasionally you might want to pick up on the signals in the "invisible" wavelengths, just to see what's in the area, but the cloak would block your sensor from seeing (or hearing) those signals.
That's when you would press your anti-cloak against the cloak and take a peek - just as Harry Potter might lift a corner of his invisibility cloak to look out at Lord Voldemort's minions (and hope they don't look in while he's doing it).
"With the anti-cloak, Potter can see outside if he wants to," Chen said.
Chen's colleagues in the anti-cloaking research include Xudong Luo and Hongru Ma of Shanghai Jiao Tong Univeristy as well as C.T. Chan of the Hong Kong University of Science and Technology.
