Experimental study of diffraction of shock acoustic waves at the edge of the screen

The paper presents the results of an experimental study of the diffraction of shock acoustic waves at the edge of the screen. Laboratory experiments were carried out in degassed distilled water under normal climatic conditions at a facility that provided positioning of the receiving-emitting system in three linear coordinates with an accuracy of no worse than 6 μm. Piston transducers with operating frequencies of 1 and 2 MHz, with various diameters of apertures from 1 cm to 4 cm were used as emitters. The maximum amplitude of acoustic pressure at the aperture of the emitters was 1 MPa. The acoustic wave profile was recorded using a membrane hydrophone with an almost uniform sensitivity characteristic in the frequency band up to 40 MHz. As a result of the experiments, some features of the diffraction of intense acoustic beams were discovered. In particular, profiles of acoustic waves having a spectral characteristic with the law of harmonic decay substantially different from the case of unlimited space are recorded near the acoustic axis of the emitter. An additional extremum was observed in the transverse distributions of the amplitudes of harmonics with numbers higher than 7, related both to the diffraction of individual harmonics and to the ongoing nonlinear generation of multiple harmonics pump frequencies.