Modeling effects of material properties and composition on ultrasound propagation

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2017
Özkök, Okan
Ultrasonic methods for material characterization have increasingly been used for the last decades thanks to advances in electronics and digital technologies since conventional methods accommodate several disadvantages like being time consuming. Advanced technology has brought highly accurate measurements with reasonable confidence level, and flexible ultrasonic testing parameters. The aim of this work is to carry out material characterization by combining modeling study and outputs of the ultrasonic device. This study, being both theoretical and experimental, is divided into three subsections; characterization of non-linear viscoelastic parameters, concentration measurement of solutions and particle size measurement by ultrasonic methods. Viscoelastic parameters can be determined by the use of ultrasonic methods. In order to evaluate the output of the ultrasonic measurements properly, these outputs should be related to the material properties. Hence, a proper modeling of sound propagation in viscoelastic medium is necessary for adequate ultrasonic characterization of viscoelastic properties. The earlier studies on this subject essentially dealt with material characterization by the continuous wave propagation in viscoelastic mediums on the basis of base frequency of ultrasound. Nevertheless, material characterization by discrete wave propagation based on pulse repetition frequency has not been investigated apparently, so far. In our M.Sc. study, characterization of linear viscoelastic properties based on pulse repetition frequency is done. Therefore, in this study a mathematical model is developed for investigating the discrete sound propagation in non-linear viscoelastic medium for determination of non-linear viscoelastic parameters. As the viscoelastic model, Oldroyd-B model is applied. Viscoelastic parameters of CMC/water solutions are determined by the evaluation of the ultrasonic outputs in the model developed. Sound velocity is also a tool for the determination of concentration. However, compressibilities of liquid mixtures tend to show important deviations from the ideal behavior. It is strongly dependent on the interactions between molecules and provides valuable information on the structure of liquids. Hence, to interpret the concentration from the sound speed, a thermodynamical approach is followed. For this purpose, volume-translated Peng-Robinson equation of state is used to predict the concentrations of solutions from sound speed. In addition, experiments are done to verify the modeling outputs. The particle size distribution of colloidal dispersions can be determined by measuring its ultrasonic velocity and/or sound attenuation coefficient as a function of frequency. Once they are measured a suitable mathematical model should be used to interpret the spectra. Ultrasonic spectroscopy can be used to analyze particle sizes between about 10 nm and 1000 μm, and is suitable for application to concentrated systems (often up to 50 wt. %). This technique has considerable advantages over many alternative technologies because it can be applied to optically opaque systems without the need of any sample preparation. Nevertheless, modeling studies done so far use natural frequency of ultrasound, as in viscoelasticity. Hence, in this work mathematical model depending on pulse repetition frequency is developed for particle size measurement. 

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Citation Formats
O. Özkök, “Modeling effects of material properties and composition on ultrasound propagation,” Ph.D. - Doctoral Program, Middle East Technical University, 2017.