Ultrasonic propagation in solids

Abstract

This dissertation gives a critical survey of the present state of knowledge in the field of ultrasonic propagation in solids. Acoustic waves of high frequency suffer absorption during propagation and the analysis of this absorption has both theoretical and technical interest. The observed loss mechanisms in solids: thermal conductivity, thermoelastic relaxation, scattering, plastic flow, structural relaxation, anharmonic coupling and magnetic effects. Theoretical explanations of these various types of losses in single and polycrystalline solids and also in high polymers, such as in rubbers and plastics are given. For reliable measurements, suitable transducers and precision experimental techniques are essential. Ultrasonic generators such as magnetostrictive, piezo electric, and the recently developed multicrystalline ceramic transducers are described. The experimental procedures for the measurement of sound velocity and attenuation during propagation are broadly grouped into three classes, (a) Resonant methods, (b) Optical methods, and (c) Pulse techniques. Optical diffraction methods are extensively used for velocity measurement and for the determination of elastic and elasto-optic constants of solids, whereas the resonant and pulse methods are used for both velocity and absorption measurement. At megacycle frequencies, at present, the pulse technique is the only method for precision absorption measurement. The recent measurement of attenuation at low temperatures and the relation with 'dislocation' theory are discussed. Attenuation measurements lead to another practical application in the use of certain solids, as delay lines in radar systems and in devices for storing informations. A chapter on solid delay lines has been included. The equivalence of the theory of heat and high frequency sound transmission and the earlier theory of heat transmission by Debye, have been discussed.