Determining liquid properties by extraordinary acoustic transmission through phononic crystals

This contribution shows how a resonance-induced extraordinary acoustic transmission through a phononic crystal structure can be used as sensor for liquid properties. The phononic crystal consists of a metal plate with a periodic array of holes. Ultrasound propagates in a way that the incidence direction of sound is perpendicular to the plate. A characteristic transmission peak has been found to strongly depend on liquid sound velocity. The respective peak maximum frequency serves as measure for liquid composition. Numerical calculations based on FDTD and FEA reveal more insides to the propagation characteristics, in particular the presence of specific plate modes. Experimental investigations using a laser vibrometer and the Schlieren method support the theoretical findings.