Acoustic ‘cloaking device’ shields objects from sound

June 28, 2011 | Source: BBC News
Acoustic Cloak

Reflections of sound off a surface (top), off an object on it (middle) and off a cloaked object (bottom) (credit: Physical Review of Letters)

Scientists at Duke University have developed a cloaking device using metamaterials that makes objects invisible to sound waves.

The device uses stacked sheets of plastic with regular arrays 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.

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

The researchers have demonstrated that their acoustic cloaking technique works in air, for audible frequencies between one and four kHz (roughly the first two octaves on the higher half of a piano).

With enhancements, the design could eventually be put to use in making ships invisible to sonar or in acoustic design of concert halls, the researchers said.