Three-dimensional broadband omnidirectional acoustic ground cloak

Abstract

In addition to controlling the propagation of light, metamaterials have also received attention for controlling sound. Now, a device that can act as a broadband and omnidirectional acoustic cloak is experimentally demonstrated. The control of sound propagation and reflection has always been the goal of engineers involved in the design of acoustic systems. A recent design approach based on coordinate transformations, which is applicable to many physical systems1,2,3,4,5,6,7,8,9,10,11,12,13,14, together with the development of a new class of engineered materials called metamaterials, has opened the road to the unconstrained control of sound. However, the ideal material parameters prescribed by this methodology are complex and challenging to obtain experimentally, even using metamaterial design approaches. Not surprisingly, experimental demonstration of devices obtained using transformation acoustics is difficult, and has been implemented only in two-dimensional configurations10,15. Here, we demonstrate the design and experimental characterization of an almost perfect three-dimensional, broadband, and, most importantly, omnidirectional acoustic device that renders a region of space three wavelengths in diameter invisible to sound.