Introduction

Before studying stress wave propagation in such waveguide structures as solid rods, bars, plates, hollow cylinders, or multiple layers, it is useful and interesting to review some applicable concepts taken from studies of dispersive wave propagation where wave velocity is a function of frequency. Wave propagation characteristics in waveguides are functions of frequency.

Let’s first, however, consider wave propagation in a taut string where some basic dispersive concepts can be studied. Models of a taut string, a string on an elastic base, a string on a viscoelastic foundation will be discussed.

Even though wave dispersion can be considered for anisotropic media (where wave velocity is a function of direction), the emphasis in this chapter is on dispersion due to structural geometry. Some basic terms are introduced, including wave velocity, wavenumber, wavelength, material and geometrical dispersion, phase velocity, group velocity, attenuation, cutoff frequency, frequency spectrum, and energy transmission, all of which will be useful in further studies. Graphical interpretations and analysis of phase and group velocity are also covered in this chapter. Additional details can be found in other texts including Graff (1991).