MODAL RESONANCES OF THE FRANZ WAVES

An approach is presented to find the modal resonances of the Franz wav es. The results are given from the resonance computation for problems of a plane acoustic wave scattered by acoustically rigid and soft sphe res and cylinders (for oblique and normal incidence), The results obta ined are compared with the Franz wave asymptotics. The successive n mo dal resonances are strongly overlapping in frequency and are superimpo sed almost in antiphase, thus the modulus of the superposition is smal ler than that of every single modal resonance. Therefore the influence of the Franz waves on the form function can be observed only at low f requency. The widths of the modal resonances in scattering by a rigid sphere or cylinder is smaller than in scattering by soft ones and thus the contribution of the Franz waves to the total form function is mor e pronounced for scattering by a rigid sphere or cylinder.