Asymmetric transmission of sound wave in cavitating liquids

Two modes of the asymmetric sound transmission are observed experimentally in a one-dimensional system composed of coupled two layers of liquids. Their cavitation thresholds are different from each other. When the sound wave propagates from the high-threshold liquid to the low-threshold liquid, the two liquids can avoid the cavitation for a medium driving pressure. When it propagates from the low-threshold liquid to the high-threshold liquid, however, the low-threshold liquid can be cavitated by the same driving pressure, though the high-threshold liquid remains uncavitated. Therefore, there is a sound transmission asymmetry, or sound rectification in this double-layer liquid. Furthermore, when the system is driven by a high pressure, cavitation can take place in both high- and low-threshold liquids in the sound transmission from the high-threshold liquid to the low-threshold liquid, but only the low-threshold liquid can be cavitated in the opposite transmission. This mechanism gives an asymmetry with reversed rectifying direction. The efficiency of rectification is related to the driving sound pressure and the cavitation thresholds of the two liquids based on experimental results. Finally, the experimental observations are reproduced by the numerical simulation based on the modified two-phase fluid mechanics.