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Now, make objects invisible to sound

india Updated: Jun 25, 2011 13:25 IST

ANI
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Scientists have developed an acoustic 'cloaking device' that shields objects, making them invisible to sound waves.

Dr Steven Cummer of Duke University and his colleagues have come up with the technique that works in air, for audible frequencies between one and four kilohertz - corresponding to two octaves on the higher half of a piano.

The device works by using stacked sheets of plastic with array of holes through them. The exact size and placement of the holes on each sheet and the spacing between the sheets has a predictable effect on incoming sound waves.

The scientists revealed that the technique could be used in making ships invisible to sonar or in acoustic design of concert halls.

They explained that when placed on a flat surface, the stack redirects the waves in such a way that reflected waves are exactly as they would be if the stack were not there at all.

This means that an object under the stack – (in the experiment, a block of wood about 10cm long) would not ‘hear’ the sound, and any attempts to locate the object using sound waves would not find it.

“Fundamentally, in terms of hiding objects, it's the same - how anything is sensed is with some kind of wave and you either hear or see the effect of it,” the BBC quoted Cummer as saying.

“But when it comes to building the materials, things are very different between acoustics and electromagnetics,” he added.

The study appears in the Physical Review Letters.