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Acoustic Cloak
Objects coated in a new material would be "hidden" from noise
Engineers have designed a material that redirects sounds and could be used in buildings to shield them from noises. The sound-shielding material, if actually made, would be the first acoustic cloaking device.
Acoustic cloaking materials, which direct sound waves around an object so that they re-form on the other side with no distortion, do not exist in nature. But engineers at the Polytechnic University of Valencia, in Spain, have created a plan for making them, using alternating layers of two different materials. These materials would comprise arrays of sonic crystals – patterns of small rods made of aluminium or other materials that allow some sound waves to pass while blocking the passage of others.
For about 10 years, engineers in various Universities around the world have been designing metamaterials to manipulate light in the hope of creating new display technologies, microscope lenses, and computer chips dense with transistors. According to latest knowledge, these metamaterials can be used to manipulate sound waves as well as light waves.
In order for a material to work as an acoustic cloak, the speed of sound passing through it must be direction dependent. That is, sound waves travelling through the shielding material from one direction must move at a different speed than waves travelling in a perpendicular direction. These differences create scattering effects that should direct sound waves to flow over a shielded object like water flowing around a rock. Because the waves return to their original conformation after passing such a shielded object, a listener inside such a shield wouldn't hear the sounds flowing around.
Bourzac, Katherine MIT Technology Review June 17, 2008 http://www.technologyreview.com/computing/20912/?a=f
Opportunity: Would make areas that suffer from noise pollution habitable
Threat: Not all sounds are harmful, this technology would probably filter all noise
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