An Acoustic Cloak
17 June 2008, 16:35
Categories: nanocomposites optics--photonics
A number of researchers around the world have been working on invisibility cloaks that can render objects invisible. In 2007, Duke University researchers advanced the early theoretical work of John Pendry, at Imperial College in London, by creating a shield that makes objects invisible to a particular frequency of microwave light. Four months ago, researchers at the University of Maryland used plasmon technology to create the world’s first invisibility cloak for visible light. These researchers have commonly used metamaterials to create their cloaks, which are artificially structured composites designed to have properties unmatched by natural materials. The metamaterials enable light waves to pass around objects, without distortion, so that they effectively disappear.
Now, a group of Spanish engineers at the Polytechnic University of Valencia have designed a material that can serve as an acoustic shield. In a manner akin to the invisibility cloak, the sound-shielding material would direct sound waves around an object so that they re-form on the other side without distortion. Using 200 alternating layers of two different substances, the composite material would be comprised of arrays of sonic crystals that allow some sound waves to pass while blocking the passage of others.
Because the waves return to their original conformation after passing around a shielded object, the object effectively becomes invisible to sonar, and a listener inside such a shield wouldn’t hear the sounds flowing around. The sound-shielding material, if actually made, would be the first acoustic cloaking device and could also be useful in hiding military ships and other vessels from sonar. Additionally, some think that the material could be used to redirect sounds around buildings to shield them from noises.
Posted by: The Editors
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