ABSTRACTPiezoelectric materials have gained wide acceptance in the world and have been successfully used in a myriad of applications (industrial, engineering, etc.) thanks to their potential and ability of electromechanical conversion. The research in this thesis focuses on exploring the capabilities of surface-mounted piezoelectric (PZT) patches in exciting and detecting lamb waves in order to assess the integrity of a sample of aluminum plates. Therefore, numerical and analytical formulations of the impedance of an unbonded PZT patch were conducted and two different S.H.M techniques: the ultrasonic nondestructive technique of pitch-catch and the traditional technique of phased arrays were studied. First, a free PZT patch was modeled both analytically and numerically in order to see how its impedance varies depending on its mechanical parameters. The modeling can help understanding the electromechanical behavior of the patch and control its quality before using it in SHM tasks. Second, the technique of pitch catch was used in order to study the effect of crack depth on the propagation of lamb waves. For this reason, experiments on aluminum plates with defects of variable depths were conducted and results show significant variations of the energy of the wave as function of the crack depth. Finally, the technique of phased arrays, using a linear array of piezoelectric patches, was investigated in order to focus the lamb waves in specific directions and enhance the detection of small notches manufactured in the aluminum plates. Results showed that the simple phased array made of six simple piezoelectric transducers was able to detect the notches predefined on the aluminum plates.
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