ANOMALOUS ABSORPTION OF LONGITUDINAL ACOUSTIC-WAVES BY A THIN-LAYER OF VISCOUS-FLUID

The existence of anomalous absorption of longitudinal acoustic waves passing obliquely through a narrow slit with viscous fluid is demonstrated. In the frictional contact approximation two cases are treated analytically, viz, when the fluid layer is placed between two identical elastic media and when one medium can be considered as infinitely rigid. Typical layer thickness values corresponding to the absorption maximum are determined. The absorptivity maximum value (up to dozens of percents) is shown to depend only on the wave incidence angle and the ratio of Lame factors of the elastic media. In the case of an infinitely rigid medium the ratio of the transformation factor at the absorptivity maximum to that in the absence of a layer is found to be a universal constant equal to 0.25.