Variation of the acoustic directivity pattern due to inhomogeneous objects in the region of nonlinear interaction

Abstract

The homogeneity of the physical medium can be investigated using nonlinear interaction of the acoustic waves. The proposed approach utilizes the fact that the secondary acoustic field is dependent on configuration of the region of nonlinear interaction (RNI), inhomogeneity of its physical properties and the transmitting signals of the primary acoustic field. Therefore, by studying a directivity pattern of the secondary acoustic field at combination frequencies it is possible to determine a number and location of the inhomogeneous objects in the RNI. The axial position and transverse dimensions of the objects affect the directivity pattern measured in the far field. In the case of the axially symmetric RNI, displacement of an object leads to the asymmetry of the directivity pattern and can be easily estimated. The model is proposed to account for the respective effect of the objects size, degree of asymmetry, and dynamics of the directivity pattern at the combination frequencies. The developed approach suggests that the methods of nonlinear acoustics can be effectively used for physical diagnostics and condition monitoring.