Investigation of the formation and propagation of longitudinal and shear acoustic waves in solids based upon the ultrasonic transmission through a plane parallel plate at different angles of incidence
Unlike in gases and liquids, in solids both shear and longitudinal waves can be excited due to their elastic material properties. During passage through a plane parallel plate longitudinal and/or shear waves are excited depending on the incidence angle. The angles of total reflection for the longitudinal and shear wave and the angle at which the shear wave shows its maximum here correspond with the respective sound velocity. By recording the amplitudes of the longitudinal and transversal transmission signals over a corresponding range of the angle of incidence, these angles can be ascertained and the respective sound velocities determined. From the sound velocities, the elastic material factors of the plate materials used can be calculated, such as the modulus of elasticity and shear and the Poisson’s ratio.
The graphic shows the amplitude-angle curves for the determining of the angles for total reflection (longitudinal and transversal) and the maximum amplitude (transversal). Independent of the material, but for different angles, the amplitude-angle dependence of the transmission can always be described by three categories: longitudinal signal only (1), a mixed mode of longitudinal and transversal signal and transversal signal only (2).