Introduction

Guided wave dispersion curve calculations are based on the assumption of an infinite continuous plane wave excitation producing a set of particular phase velocity values at specific frequencies. However, in real applications, the excitation sources are of a finite size over a finite frequency spectrum. This chapter establishes the guidelines for evaluating the effects of excitation sources on wave excitation. In particular, we address the problem of guided wave excitation and propagation in a traction-free plate.

Many excitation mechanisms can be used to generate ultrasonic waves in a solid medium. The commonly used sources for guided wave excitation are piezoelectric transducers, electromagnetic acoustic transducers (EMAT), magnetostrictive devices, physical impact, and laser ultrasonics. The piezoelectric transducer can be used in a normal incident or oblique incidence situation with an angle wedge. Instead of propagating the waves from the transducer to the structure, the EMAT and laser, for example, generates ultrasound within the structure either as a surface loading or a body loading. Most recently, for purposes of structural health monitoring (SHM), piezoelectric wafer transducers are attached directly to the structure to generate specific kinds of ultrasonic guided waves in the structure.