Acoustic surface evanescent wave and its dominant contribution to extraordinary acoustic transmission and collimation of sound.

We demonstrate both theoretically and experimentally the physical mechanism that underlies extraordinary acoustic transmission and collimation of sound through a one-dimensional decorated plate. A microscopic theory considers the total field as the sum of the scattered waves by every periodically aligned groove on the plate, which divides the total field into far-field radiative cylindrical waves and acoustic surface evanescent waves (ASEWs). Different from the well-known acoustic surface waves like Rayleigh waves and Lamb waves, ASEW is closely analogous to a surface plasmon polariton in the optical case. By mapping the total field, the experiments well confirm the theoretical calculations with ASEWs excited. The establishment of the concept of ASEW provides a new route for the integration of subwavelength acoustic devices with a structured solid surface.