Some Peculiarities of Intense Acoustic Beam Diffraction on a Semiscreen Obstacle

Some results of a physical experiment on studying the evolution of an intense acoustic beam on a semiscreen obstacle are reported. The beam is formed by using a plane piezoceramic transducer with a center frequency of 2 MHz. The semiscreen obstacle is installed beyond the last diffraction maximum of the linear distribution of an acoustic field from the used transducer along the acoustic axis The transverse distribution of the nonlinear acoustic field is studied for different distances from the semiscreen obstacle. Initial acoustic beam intensities correspond to acoustic Reynolds numbers from 5 to 30. It is shown that evolution of the beam behind the obstacle is governed by cumulative diffraction and nonlinear effects. It is demonstrated that the transverse distribution of the acoustic field behind the obstacle strongly depends on the intensity of the beam incident on the obstacle. In particular, a strong dependence on the intensity of the incident beam is observed for the position of diffraction maxima in the transverse distribution of the acoustic beam behind the semiscreen obstacle. The effect related with the appearance of additional extrema in the transverse field distribution at different harmonics is revealed. Numerical simulation based on the Khokhlov–Zabolotskaya–Kuznetsov equation is carried out with results confirmed by experimental data.