At the Meeting of the Acoustical Society of America taking place this week in Minnesota, Penn State University researchers described a design they've developed that allowed a 3-foot-tall pyramid made from perforated steel plates to deflect sound waves in a way that could make it invisible to instruments like sonar.The team engineered a metamaterial -- a synthetic material that typically features properties that don't occur naturally -- that could bend sound waves in a particular way. So far, most of these sorts of materials have been developed in order to deflect sound waves in the air, but the researchers, led by research associate Amanda Hanford, designed their material to be used underwater -- a much more difficult task since water is denser than air. In their experiments, the researchers showed that their material effectively cloaked itself when submerged.

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