National Geographic News
An &#x27;&#x27;invisibility cloak&#x27;&#x27; device.

A pink object seems to vanish behind a chunk of calcite, underwater and illuminated by green light.

Photograph courtesy George Barbastathis

Rachel Kaufman

for National Geographic News

Published January 28, 2011

Harry Potter and Bilbo Baggins, take note: Scientists are a step closer to conquering the "magic" of invisibility.

Many earlier cloaking systems turned objects "invisible" only under wavelengths of light that the human eye can't see. Others could conceal only microscopic objects. (See "Two New Cloaking Devices Close In on True Invisibility.")

But the new system, developed at Massachusetts Institute of Technology and the Singapore-MIT Alliance for Research and Technology (SMART) Centre, works in visible light and can hide objects big enough to see with the naked eye.

The "cloak" is made from two pieces of calcite crystal—a cheap, easily obtained mineral—stuck together in a certain configuration.

Calcite is highly anisotropic, which means that light coming from one side will exit at a different angle than light entering from another side. By using two different pieces of calcite, the researchers were able to bend light around a solid object placed between the crystals.

"Under the assembly there is a wedge-shaped gap," said MIT's George Barbastathis, who helped develop the new system. "The idea is that whatever you put under this gap, it looks from the outside like it is not there."

Invisibility Cloak a Boon for Drivers?

The new invisibility cloak still has its drawbacks: For one, it works best under green light. The researchers designed the cloak this way because the calcite can only be configured for a very narrow wavelength of light, and human eyes are most sensitive to green, Barbastathis said.

(Related: "'Electromagnetic Wormhole' Could Make Objects Invisible.")

In addition, the cloaking effect works only if you look at the hidden object from a certain direction. Viewing the object from another angle will make it "reappear."

Also, the system can only cloak objects that fit under the mineral wedge, which in this case is just two millimeters tall. Still, a larger piece of calcite should be able to hide larger objects.

Barbastathis is confident that his team or another group will come up with a true, three-dimensional invisibility cloak soon. In the meantime, he can think of at least one practical application from the system as it stands. (Also see "Acoustic 'Invisibility' Cloaks Possible, Study Says.")

"I live in Boston, and in Boston a lot of streets converge at very sharp angles, so when you look at the traffic light, it's confusing whether you're seeing the traffic light for you or the light that is for the other street," he said.

With the current cloak, "you could hide certain lights from drivers so they do not get confused."

The new invisibility cloak is described in a paper published last week in the journal Physical Review Letters.



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