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Cloaking devices -- it's not just 'Star Trek' anymore
During the 175th Meeting of the Acoustical Society of America, being held May 7-11, 2018, in Minneapolis, Minnesota, [Amanda D.] Hanford will describe the physics behind an underwater acoustic shield designed in her lab.
Hanford and her team set out to engineer a metamaterial that can allow the sound waves to bend around the object as if it were not there. Metamaterials commonly exhibit extraordinary properties not found in nature, like negative density. To work, the unit cell -- the smallest component of the metamaterial -- must be smaller than the acoustic wavelength in the study.
[...] To date, most acoustic metamaterials have been designed to deflect sound waves in air. Hanford decided to take this work one step further and accept the scientific challenge of trying the same feat underwater. Acoustic cloaking underwater is more complicated because water is denser and less compressible than air. These factors limit engineering options.
(Score: 3, Insightful) by mhajicek on Friday May 11 2018, @04:20AM
There would be distortion, like the sonar equivalent of predator camo. It may be possible for advanced processing to pick up the outline.
The spacelike surfaces of time foliations can have a cusp at the surface of discontinuity. - P. Hajicek