ABSTRACT
Before we draw conclusions for the propagation of elastic waves from the elastodynamic governing equations augmented by constitutive relations, we will refer to the governing equations of acoustics and electromagnetics (Chapter 6) complemented by plane waves as well as source field and scattered field representations. On one hand, US-NDT likes to think in the terminology of (scalar) acoustics, and on the other hand, coupling mechanisms between elastic and electromagnetic phenomena-electromagnetic-acoustic transducers, piezoelectric transducers, and laser excitation of ultrasound-are of fundamental importance. In addition, microwave methods gain more and more attention-e.g., the application of ground probing radars for NDT of concrete (Krieger et al. 1998; Mayer et al. 2003)—suggesting a comparison of the theoretical foundations of electromagnetic and elastic waves. Yet, as already mentioned, we will only cite and not derive facts, eventually providing plausible arguments.
