Distortion of the focused finite amplitude ultrasound beam behind the random phase layer

The field of spectral components of a focused finite-amplitude ultrasound beam in water behind the layer that introduces a constant shift randomly distributed over its plane is studied experimentally and numerically. Based on the focal field distributions obtained and the criterion proposed, the degree of maintenance of the focusing condition for the first six harmonics of the beam radiated at 1.1 MHz is evaluated. Several layer positions at a distance from the radiator are considered. It is shown that focusing of the higher-order harmonics may be less subjected to destruction by the phase layer than that of the wave at the fundamental frequency. The theory and experiment are compared for the 90° and 180° phase layers. For the latter case, selective destruction of focusing of the odd harmonics is demonstrated.