Acoustic scattering from a cylindrical shell bounded by hemispherical endcaps. Resonance interpretation with surface waves propagating in cylindrical and spherical shells

The studies of the acoustic scattering from infinite cylinders or spheres have shown the strong influence of the propagation of surface waves. Two types of surface waves are distinguished: the Rayleigh or Whispering Gallery waves and the Scholte–Stoneley wave. In this paper, theoretical and experimental results obtained on objects constituted by a cylindrical shell bounded by two hemispherical shells are presented, when these objects are insonified in the direction parallel to their main axis. To explain the experimental results, the stationary condition is written in the meridian plane of these objects. To apply this condition, the phase velocities of the waves propagating in the cylindrical and in the spherical parts must be known. First, the phase velocity of waves propagating along the length of cylindrical shells is theoretically and experimentally studied. Then an experimental study of the phase velocities of the waves propagating on spherical shells is carried out. Finally, the results of these two studies are used to explain the acoustic behavior of objects constituted by a cylindrical shell bounded by two hemispherical endcaps in the case of axial excitation.