We describe a MGB approach for ultrasonic beam propagation
shown in Fig. 1, where a single Gaussian beam is radiated from a
circular source and travels in solid media composed of two
anisotropic solids and an interface. We assume the beam
propagation along symmetry directions of anisotropic solids and
a normal interface with respect to the beam path. Thus, the x1–x3
plane in Fig. 1 constitutes a symmetry plane and the x3-axis
represents one of the symmetry directions. For the geometry of
Fig. 1, a Gaussian velocity profile for either a P-, SV- or SH-wave is
present at the source and propagates as a Gaussian beam into the
solid 1. In Fig. 1, V1(0) and M1(0) are the known starting amplitude
and phase values in the Gaussian at the source location ð x˜3 Þ.
The propagation distance x˜3 is measured along the central axis of
the Gaussian beam, x3. (x1,x2) are coordinates perpendicular to x3
with x1 in the plane of incidence and x2 normal to that plane.
The velocity amplitude and phase of a propagating Gaussian
beam in the solid can be completely described by solving the
paraxial wave equation (Huang, 2005). For the geometry of Fig. 1,
the particle velocity in the Gaussian beam at a distance x3 ¼ x˜3