Steering the propagation direction of a non-linear acoustic wave in a solid material

In this research non-collinear wave mixing is used as a non-destructive testing method where the amplitude of the scattering wave contains information on the condition of a material. The practical implementation of non-collinear wave mixing as a non-destructive testing technique is limited by many factors such as the geometry and shape of the structure, the accessibility to the specimen's surfaces and the ultrasonic sensors available to perform measurements. A novel approach to steer the propagation direction of a generated wave from the mixing of two incident acoustic waves is proposed. The angle of the scattering wave is controlled by the frequencies of the two interaction waves, rather than by the angle between these waves. The scattering amplitude was analytically solved for the longitudinal plus shear interaction process. The analytical solution was validated with experiments. The model qualitatively agrees with the experiments. Furthermore, the possibility to use a wider range of excitation frequencies of the incident waves was found. This is a great advantage in applications where the space and access to the specimen under test is limited.