Metals: The Secret Behind Invisibility Cloaks

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The first time I saw a Harry Potter movie, I wasn’t able to finish it. A “scary, scary troll” basically chased me and my kindergarten accomplice from the theater. Seriously, if we hadn’t left right then, he probably would have leapt from the screen and made scary, scary troll noises as he followed us home. That’s what trolls do.

However, that troll kept me from analyzing Harry’s invisibility cloak during the film, which is a shame, since it was recently announced that his cloak could become a reality. Scientists have created metamaterial that can redirect light to make objects invisible through the microwave wavelength, “bending visible light the wrong way in three dimensional tests,” according to an article from LiveScience. Essentially, light would bend in another direction when hitting objects covered with this material, much like the way a pencil seems to disappear when half-submerged in water. Or the way Romulan spaceships disappear in Star Trek. Or the way Harry Potter sneaks into the library late at night, covered in his light-reflecting shield.

One promising cloaking device comes from plasmons. These are the “tiny electronic excitations” that are found on the surfaces of certain metals. Loops or coils of gold or silver are the best bet for finding plasmons. Through plasmons, scientists believe that they can cancel the visible light or other radiation from an object.

“Plasmons are created when electrons on the surface of a metallic material move in rhythm. They have other odd properties,” LiveScience reports. “Back in 1998, researchers … shone light on a sheet of gold foil that contained millions of tiny holes. The holes were smaller than the wavelength of the light. Amazingly, more light came out the other side than what hit the holes. Follow-up research found that plasmons — jittery little waves on the surface of the metal — were snagging light and stuffing it through the holes.”

If these cloaking devices are made possible, the uses are endless, and not just for teenage wizards. Scientists hope that these studies could help advance military stealth technologies.

–Amy Edwards

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