Acousto-elastic multiple scattering: A comparison of ultrasonic experiments with multiple multipole expansions

Abstract

Solid rods are submerged in a water tank and illuminated by an ultrasonic source transducer. Along the water surface, transducers are used to measure the propagating wave fields. Even for only three rods, the scattered wave field is very complex. Although the major events can be readily interpreted as direct reflections, the remaining wave field consists of complicated interactions of the wave fields with the scatterers and the water surface. To aid the interpretation, the experiment is modeled numerically using the multiple multipoles method which decomposes the wave fields by their respective origins. Hence, particular events can be correlated with particular scatterers as well as with particular paths of propagation. The numerical method has already been used as a versatile tool to model acoustic or elastic multiple-scattering 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, the waves induced in the fluid are expressed by sets of multipole solutions with different origins. Thus by construction, the scattered wave fields are decomposed by scatterer. The numerical solutions match the ultrasonic experiments very well. Furthermore, the different events can be identified as reflections, internal multiples, or diffractions through the solid rods.