Propagation Of Acoustic Waves In Crystals Research Articles

Bulk and surface acoustic wave phenomena in crystals: Observation and interpretation

Crystal acoustics is a field that has engaged the attention of theoreticians and experimentalists alike for decades and more. Many striking effects have been revealed, and elegant analytical techniques applied to their interpretation. This article is oriented towards the experimental aspects of the field and the interpretation of the phenomena that have been observed. Particular attention is given to reviewing the techniques that have probed the intricacy of acoustic wave propagation in crystals, including phonon imaging, laser- and capillary-fracture-generated ultrasound, transmission acoustic microscopy and surface Brillouin scattering, and a selection of results obtained with these techniques is presented. Some of these studies pertain to bulk waves and others to surface acoustic waves. The interpretation of far-field observations is carried out within the ray approximation, and elastodynamic Green’s functions are invoked in the interpretation of near-field results. Extensive use is made of the acoustic-slowness and wave surfaces, in particular features such as acoustic axes, with their attendant polarization singularities, and folds in the wave surface.

Nonlinear acoustics of solids: History and modern trends

The author had the pleasure to be involved in the pioneering experiments on the nonlinear acoustic wave propagation in crystals and metals (1960). It was found that even for small wave amplitudes acoustic harmonics generation took place for longitudinal waves. The results obtained were interpreted from the point of view of Hooke’s law nonlinearity due to nonparabolic interaction potential taking into account accumulation effects in nondispersive media. Besides that, transversal acoustic waves under some external effects like pressure, heating, etc., also demonstrated nonlinear behavior despite that it was forbidden in a framework of crystal lattice theory. It was accounted for by the development of structural disturbations in a material and seemed to be the first attempt to demonstrate the importance of acoustic nonlinear nondestructive testing of different materials. It was shown later that some construction materials and rocks have much higher nonlinear parameter values than those for crystals and metals. The paper will also present an historical review of recent developments in other areas of nonlinear acoustics in solids: measurements of nonlinear acoustic parameters, surface acoustic waves nonlinearity, ‘‘clapping’’ nonlinearity, defective solids and rocks, etc.

Elasticity of some high-density crystals

The adiabatic elastic constants of two garnets (spessartite-almandite and almandite), spinel (synthetic), rutile (synthetic), and olivine are reported. The stiffness constants Cpq were determined from the velocities of acoustic wave propagation in crystals. The velocities of wave propagation were measured by McSkimin's method. A frequency range of 6 to 12 Mc/s was used.