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Acoustic Invisibility Cloak Makes Objects Unhearable

• Rebecca Boyle via PopSci.com

A new acoustic invisibility cloak made of a plastic metamaterial makes objects invisible to sound waves, researchers say. It could be used to shield ships from sonar, or build better soundproof walls for concert halls and other spaces. We’ve seen this idea before, but now Duke University researchers have actually built it.

Invisibility cloaks work by bending light waves in ways that would not normally be possible, through the use of man-made materials called metamaterials. This cloak uses many of the same principles to bend sound waves, so a ship made of this material would render sonar useless, because the sound waves would not bounce back.

This device consists of stacked sheets of plastic peppered with holes, whose arrangement and size redirects sound waves, BBC News reports. The device resonates at frequencies that either absorb or reflect sound waves, so it both blocks and contains them — anything underneath the stack would not hear sound, and sound waves could not be used to locate something coated with the stack. It works in air for audible frequencies between one and four kilohertz, which corresponds to two octaves on the higher half of a piano, BBC says.

 

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