Laurent ALLIES (1999) ETUDE DES PHENOMENES DE NON-LINEARITES ULTRASONORES: Analyse théorique et expérimentale de systèmes de mesure du paramètre B/A par la méthode d'amplitude finie Université Henri Poincaré Nancy: Abstract: The objective of this thesis is the theoretical and experimental study comparative methods used for measurement of the ultrasonic parameter of nonlinearity B/A of liquid media and biological. These principles of measurement, pertaining to the family known as finite amplitude methods, rest on the harmonic analysis of the ultrasonic wave detected after its crossing in the medium to characterize. In a first part, after a presentation of the theoretical bases of nonlinear acoustics, we develop the various analytical solutions connecting parameter B/A to the harmonic components of the detected wave, then we propose new solutions for the second harmonic, simpler and exploitable in experiments. These solutions integrate the phenomena of diffraction, absorption, and nonlinearity.
After a review of the various methods of measurement described in the literature, we devote the fourth chapter to the theoretical and experimental analysis of the comparative methods using two transducers, for the emission and the detection of the ultrasonic wave. The originality of this work rests on the taking into account of the sensitivities of the transducers in the various expressions of parameter B/A. We thus develop a function of sensitivity of the system of measurement allowing to define the experimental situations most adapted to the comparative method. The principal interest of this method is to free itself from the calibration of the transducers, which is possible if the function of sensitivity is close to the unit. Experiments validate then the various theoretical developments.
In the last chapter we propose a method of original measurement of parameter B/A in pulse-echo mode using one transducer in emission-reception. This process is then supplemented by a device of filtering improving detection of the second harmonic of the echo. The experiments confirm the theoretical predictions and show the possibility of exploiting this system in quantitative medical imagery, by the additional knowledge of parameter B/A of the analyzed biological environment.
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