This Disc Makes Objects Invisible to Sonar [Sonar]

Source: http://gizmodo.com/5729554/this-device-makes-objects-invisible-to-sonar

How do you make an underwater invisibility cloak? You start by creating a device that can manipulate sonar waves. This small cylinder, developed by researchers at the University of Illinois, does just that.

Nicholas Fang, a mechanical science and engineering professor at the University of Illinois, lead the development of the device, which is made of 16 concentric rings of acoustic circuits. Sound waves find their way into the channels between the circuits, moving faster toward the innermost rings. But as this speeding up requires energy, the waves instead gather on the outer rim of the cloak, essentially bending the sound waves around itself and hiding anything inside it.

In testing, the cloak made objects of various shapes and sizes acoustically invisible to sound waves from 40 to 80 KHz, though further refinements need to be made for faster moving objects. Still, Fang is pleased with his progress. "This is certainly not some trick Harry Potter is playing with," he explained. Oh? Bummer. [Paper via Daily Tech and Phys Org]