Karl's Weird News

Drug smugglers, terrorists and nuclear players rejoice!  Practical underwater invisibility is almost here!

Acoustic superlens could cloak objects from sonar:

Researchers have been messing about with optical metamaterials and invisibility cloaks for a few years now. And while progress has been rapid, nobody’s going to be fooling Voldemort any time soon. But the same exotic tricks that apply to light can equally be applied to sound. And potentially more easily too because sound has a longer wavelength. The business parts of acoustic metamaterials should therefore be significantly easier to build than their optical counterparts. And that’s just what Nicholas Fang and buddies from the University of Illinois at Urbana- Champaign have done: create a flat slab of acoustic metamaterial that focuses sound with a negative refractive index. They’ve even fashioned a design that works as a “superlens” that focuses the so-called evanescent sound waves that form within a single wavelength of the source– a world first apparently. Fang and co have created an acoustic metamaterial by carving an array of holes into an aluminium sheet and filling the holes with water. The holes then resonate when water moves over them, like wind over the mouth of a bottle.