Over the past few decades, structural health monitoring (SHM) has been extensively used to identify, locate, and quantify structural damages. Great advancements in sensor technology and application of piezoceramic materials have resulted in novel methods for SHM. The coupled electro-mechanical properties of piezoelectric materials enable scientists to generate and capture waves that can be effectively employed for damage detection. Among piezo-based SHM techniques, Lamb waves are widely used since they can propagate long distances without much attenuation. Lamb waves are guided waves which propagate in plate-like mediums bounded by two surfaces and arise as a result of superposition of multiple reflections of longitudinal waves and shear vertical waves from bounding surfaces. Apart from the lamb waves, an independent set of waves called shear horizontal waves (SH-waves) also exists in plates with in-plane particle motions parallel to the plate's surface. Since the first symmetric shear horizontal mode (SH0) is non-dispersive and travels with constant velocity, scientists have been encouraged to use transducers which purely excite SH waves for SHM of plates. In present study, existing modes of the compressive and shear piezoelectric actuator/sensor used for excitation of lamb and SH waves are described and compared. Then, the effect of piezoelectric coefficients on the characteristics of generated waves are investigated numerically by actuating and sensing compressive (S0), flexural (A0), and shear wave modes in metallic plates using both compressive and shear PZT transducers.
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