Similar to invsibility cloaks in a mathematical sense, "cloaks of silence" or 3D acoustic cloaks are theoretically possible, according to two independent research teams in the U.S. and Hong Kong. Based on the mathematics of how sound scatters from materials, a spherical shell — with properties that change to accommodate sound waves from all directions — would have to be constructed from a "metamaterial" that incorporates manmade structures because no natural material has such a property profile. Meanwhile, researchers in Spain are searching for a suitable rod material to form the matrix of a cylindrical cloak that could function over a broad range of acoustical frequencies. One potential application is cloaking submarines from sonar detectors.
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Re: Let There Be Silence!
