ABSTRACT
This chapter discusses topologically more complex scatterers. The first is a thin spherical shell with two circular holes: topologically this object is doubly connected. The second scatterer is the complementary surface, a spherical shell with an equatorial slot. The regularised systems obtained is used for analytic and numerical studies of the scattering of acoustic plane waves by the class of scatterers described. When a plane acoustic wave strikes an acoustically soft spherical barrel or an acoustically hard spherical shell with an equatorial slot, the scattered field may be determined from the solution of a set of symmetrical triple series equations related. Integration over the shell, of the component of acoustic pressure at each point on the shell in the direction of plane wave propagation, necessarily gives a zero value for the mechanical force factor η.
