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An invisibility cloak that hides ships from sonar



A sci-fi staple and perennial fantasy fashion choice, the invisibility cloak has been one of science’s holy grails for years. But while complete literal invisibility still eludes researchers, three Duke engineers — Bogdan-Ioan Popa, Lucian Zigoneanu and Steven Cummer — recently cracked the code to auditory invisibility, constructing a plastic material that can effectively hide objects, like ships, from sound waves, like sonar. It may not allow you to sneak through the halls of Hogwarts undetected, but hey, it’s a start. Here’s how it works.

1Sonar systems work by sending out sound waves and waiting for them to bounce back with information about objects in the area. So to hide a ship from sonar, you need a way to fake that the sound wave passed straight through it, hit the surface of the water, and returned without bumping into anything.

2The cloak is made up of nine layers of plastic punched full of equally sized, equidistant holes. For a sound wave, it’s like hitting a thicket of vines. Passing through it on the way to the ship (and again on the way back) makes the waves take so long to rebound that the receiver thinks they made it all the way to the surface. Bingo, no ship.

3Just as with a truck’s rearview mirrors, if sound waves can’t see you, you can’t see them. Or hear them, rather: The area under the cloak is effectively silent. Scientists think the material could be used to mute parts of concert halls or to protect workers’ ears. We think it could put a damper on our neighbor’s late-night trumpet recitals. (Finally.)

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