ACOUSTO-ELASTIC MULTIPLE-SCATTERING - A COMPARISON OF ULTRASONIC EXPERIMENTS WITH MULTIPLE MULTIPOLE EXPANSIONS

Solid rods are submerged in a water tank and illuminated by an ultraso nic source transducer. Along the water surface, transducers are used t o measure the propagating wave fields. Even for only three rods, the s cattered wave field is very complex. Although the major events can be readily interpreted as direct reflections, the remaining wave field co nsists of complicated interactions of the wave fields with the scatter ers and the water surface. To aid the interpretation, the experiment i s modeled numerically using the multiple multipoles method which decom poses the wave fields by their respective origins. Hence, particular e vents can be correlated with particular scatterers as well as with par ticular paths of propagation. The numerical method has already been us ed as a versatile tool to model acoustic or elastic multiple-scatterin g problems where homogeneous scatterers were embedded in a homogeneous full space. In the present paper, the scheme is expanded to multiple scattering between solids submerged in a fluid. For each scatterer, th e waves induced in the fluid are expressed by sets of multipole soluti ons with different origins. Thus by construction, the scattered wave f ields are decomposed by scatterer. The numerical solutions match the u ltrasonic experiments very well. Furthermore, the different events can be identified as reflections, internal multiples, or diffractions thr ough the solid rods. (C) 1997 Acoustical Society of America.