A ray technique to calculate the multiple reflected and transmitted waves in layered media.

摘要

In this thesis we consider the problem of calculating the propagation of acoustic waves within an ideal solid isotropic multilayer plate structure. In such a situation the process of mode conversion as the wave interacts with each interface of the plate creating an increasing number of waves to track, and to perform calculations on as the wave propagates within the layered media. We choose to explore this problem by examining the ray paths of the multiple reflections within the plate structure, and show that upon careful consideration many of these paths will travel equivalent distances in time and space becoming coincident. The principle of superposition can then be used to combine these coincident paths; this reduces the number of waves to track, and simplifies the problem so that the necessary calculations can be performed in a time efficient manner. In addition the use of the a ray model gives initial results which are independent of properties of the incident acoustic waves.; In the first part of this thesis the theoretical basis of the ray technique will be overviewed, and the existence of equivalent and coincident paths in the single and multilayer plate structure is examined. Next it will be described how a second set of calculations can be used to consider the attenuation of the media, recalculate the time of flight and horizontal distances of the rays due to altering the thickness of the layers of the plate, and extend the ray based results to more realistic acoustic waves. By including these factors as a separate set of calculations creates a more flexible technique, as the attenuation, thickness of the plate, or acoustic wave's space-time domain properties can be changed without recalculating the initial amplitude results, as long as the other features of the theoretical sample remain constant. Finally, the results of this thesis will examine various cases for validation, comparison to experimental results, and the examination of options for the detection of bonding or disbonding within a typical bonded plate sample.