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The acoustic 'invisiblity cloak' that makes ships undetectable
A new sonar-subverting device can shield objects from sound waves. Is this something straight out of Harry Potter?
Researchers have figured out a way to audibly disguise gigantic ships using layers of plastic that absorb and reflect sound waves.
Researchers have figured out a way to audibly disguise gigantic ships using layers of plastic that absorb and reflect sound waves.
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cientists at Duke University have created an acoustic "invisibility cloak" that shields objects — like ships — from sound waves, making them undetectable by sonar, and rendering them acoustically "invisible." Really? Here, a brief guide:

Is this really an "invisibility cloak"?
Sort of. The "cloak" is a series of plastic sheets that, when draped over an object, would make it invisible to sound waves.

How does it work?
The device uses man-made plastics called "metamaterials." Stacks of the plastic are "peppered with holes," which are arranged in a way to redirect, absorb, and reflect sound waves in a specific pattern, says Rebecca Boyle at Popular Science. The result is that anything underneath the sheet would not be able to hear sound, and sound waves would not be able to locate it. Instead of sounds waves bouncing off an object as they normally do, they'd just "keep on keeping' on, as if the device and the object under it were never there," says Nidhi Subbaraman at MSNBC. Something like sonar, which uses sound waves to detect the location of ships at sea, would be rendered useless.

Does it only work for sonar?
Nope. The cloak could also be used to contain sound within a space or room, says Jason Palmer at BBC News. Coating walls with the sheets would soundproof a studio or room better than ever before. "With some fine-tuning to the design," says Subbaraman, "the device could also be used to enhance the acoustics of concert halls."

Is it hard to make sound invisible?
Not really. If anything, this approach to "cloaking" sound is notable for its simplicity. "It's almost like someone could take a pencil and poke holes in a particular way in the plastic," says Dr. Steven Cummer, who worked on the device, as quoted by BBC News. The most complicated aspect of the device is the layering of the sheets so that the holes are properly aligned to block and contain the sound waves.

What about a real Harry Potter invisibility cloak?
A prototype for an invisibility cloak that would make an object visually undetectable to the naked eye — just like the boy wizard's in Harry Potter — has been in development since 2006. In fact, the science British researchers are using to create it served as the blueprint for the acoustic invisibility cloak. The principle is essentially the same: Metamaterials are used to bend light waves in a way that makes objects under them invisible. This new acoustic invisibility cloak, however, is the "first physical proof of that idea," says Subbaraman.

Sources: BBC News, MSNBC, Popular Science, Associated Press

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