Acoustic material able to open up a hole in space

Contrary to earlier predictions, Duke University engineers have found that a three-dimensional sound cloak is possible, at least in theory.
Such an acoustic veil would do for sound what the "invisibility cloak" previously demonstrated by the research team does for microwaves--allowing sound waves to travel seamlessly around it and emerge on the other side without distortion.

"We've devised a recipe for an acoustic material that would essentially open up a hole in space and make something inside that hole disappear from sound waves," said Steven Cummer, Jeffrey N. Vinik Associate Professor of Electrical and Computer Engineering at Duke's Pratt School of Engineering. Such a cloak might hide submarines in the ocean from detection by sonar, he said, or improve the acoustics of a concert hall by effectively flattening a structural beam.

As in the case of the microwave cloak, the properties required for a sound cloak are not found among materials in nature and would require the development of artificial, composite metamaterials.

The engineering of acoustic metamaterials lags behind those that interact with electromagnetic waves (i.e. microwaves or light), but "the same ideas should apply," Cummer said.

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