Absolute acoustic band gap in coupled multilayer structures

We show theoretically that by combining two or more finite superlattices, it is possible to realize an omnidirectional acoustic mirror that prevents propagation of acoustic waves over a wide range of frequencies. An appropriate choice of the elastic parameters in the superlattices enables us to propose a structure in which any incident wave launched from any type of substrate (or vacuum) falls inside a minigap of the coupled SLs and therefore undergoes a total reflection.