Researchers in the US have built the first practical device that can cloak an object from being detected by sound waves. The cloak, which is made from a cylindrical array of acoustic cavities, has been shown to operate in water at ultrasonic frequencies. The technology could in principle be adapted to cloak underwater objects from sonar.
Several research groups have already managed to build “invisibility cloaks” that hide objects from electromagnetic waves. Such cloaks are made from “metamaterials” – artificial structures with special optical properties such as negative indices of refraction. These structures are arranged such that incoming light waves flow smoothly around the cloak, joining up on the other side as if the cloak and object were not there.
The same principles can be applied to sound and in 2008 Nicholas Fang and colleagues at the University of Illinois at Urbana-Champaign in the US created an acoustic “superlens” using acoustic metamaterials. Now Fang and team claim to have built the first practical broadband and low-loss acoustic cloak