The propagation of sound above and within a hardbacked rigid porous layer

Abstract

The present paper examines, theoretically and experimentally, the sound field in the vicinity of a non-locally medium due to an airborne source. The non-locally reacting medium is characterized by a porous layer of finite thickness which is placed on a perfectly reflecting plane. According to an asymptotic analysis, the total sound field within the rigid porous medium consists of two components. Each of these two components can be represented by an integral expression. They can then be evaluated by a standard saddle path method to obtain a uniform asymptotic solution. Numerical validation with wave-based numerical schemes demonstrates the accuracy and computational efficiency of the derived asymptotic formula. Additional validation is provided through indoor experimental data obtained by using a layer of glass beads for modeling the rigid porous medium. When the receiver is situated within the porous layer near the perfectly reflecting plane, experimental measurements and theoretical predictions suggest that the interaction of the refracted wave with the perfectly reflecting plane has a significant impact on the total sound field. Experimental data and numerical simulations also indicate that it is rather difficult to distinguish the results between a thin rigid porous layer and a semi-infinite rigid porous medium for an airborne receiver.