טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentMan Natalya
SubjectWaves in Multilayered Media
DepartmentDepartment of Quality Assurance and Reliability
Supervisor Dr. Phineas Dickstein


Abstract

Multilayered structures and compartments are widely used in many industries, such as the aeronautical industry. Non-destructive acoustic techniques are applied to verify the structural integrity of the multilayered compartments and to assess their serviceability.

Modeling the propagation of ultrasonic waves in laminated materials is a complicated task. In general, such materials are both inhomogeneous and anisotropic; therefore, there exist a number of modes of wave propagation associated with different directions of propagation. A complexity arises also from the many reflections from the interfaces between the layers.

Existing models in the time domain do not provide an easy way to describe the propagation of the ultrasonic waves in the multilayered compartments. In this work a model in the frequency domain is developed for an arbitrary number of layers. The motivation to develop the model in the frequency domain is that in many applications the frequency response and features are those of interest, and that some mathematical operations are more convenient in the frequency domain.

In this study recursive equations were developed and introduced, based on the Scott and Gordon approach that enable to calculate the frequency features of ultrasonic waves propagating in multilayered compartments composed of any arbitrary number of layers. The equations are compact, and the calculations are carried out through an iterative process.

To verify and validate the model, numerous experiments were carried out, in which many compartments composed of different layers were tested ultrasonically.

The experimental results and the theoretical simulations turned out to be in good agreement. The model has proven to accurately provide detailed features of the ultrasonic spectra of layered structures.