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Title: The development of an acoustic technique for the study of the viscoelastic properties of liquids at microwave frequencies
Author: Richter, John
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 1966
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The development of an experimental electronic and acoustic system is described for viscoelastic investigations in the frequency range 300Mc/s to 2000Nc/s., The viscoelastic properties of liquids are evaluated from measured values of the reflection coefficient when a plane shear wave is incident normally on a solid-liquid interface. Because of the high acoustic losses in isotropic materials at the frequencies of present interest it is necessary to use a low loss crystalline solid as the propagating medium. Theoretical investigations are carried out to assess the adequacy of the classical elasticity theory in describing microwave acoustic waves in anisotropic media. The dependence upon crystallographic orientation of all the important propagation and excitation properties for the three acoustic modes is fully determined in crystal Quartz. A phenomenological theory, involving a viscosity tensor, is developed for the calculation of acoustic attenuation in an anisotropic viscoelastic medium. The anisotropic viscosity tensor of crystal quartz at room temperature is determined from precise attenuation measurements. The experimental acoustic system employs a single crystal quartz rod. One end of the quartz is inside an electromagnetic cavity resonator and it acts as the electromechanical transducer operating by non-resonant surface excitation. A new theory of surface excitation is developed enabling the design and construction of a novel type of cavity resonator. The acoustic performance of the transducer system is determined by the piezoelectric field probe technique, developed for this purpose in the course of the present work. The thesis also gives full description of the electronic system which has been developed. Owing to the high accuracy of the experimental system, it is possible to obtain excellent measurements of the real part of - the mechanical impedance for liquids of any viscosity. As an example of the application of this technique to the measurement of the viscoelastic properties on liquids, the temperature dependence of the limiting high frequency rigidity modulus of certain aromatic hydrocarbons is determined. To interpret these measurements a new theory is presented, relating the shear rigidity to free volume in a liquid.
Supervisor: Lamb, J. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available