Abstract :
Modal acoustic radiation impedance load on a spherical source vibrating with an arbitrary,
axisymmetric, time harmonic velocity distribution, while positioned concentrically within a
fluid sphere which is embedded in an infinite fluid-saturated poroelastic medium, is computed. This
configuration, which is a realistic idealization of sound projector (transducer) freely suspended in a
fluid-filled spherical cavity within a permeable surrounding formation, is of practical importance
with a multitude of possible applications in seismo-acoustics and noise control engineering. The
formulation utilizes Biot theory of sound propagation in elastic porous media along with the
appropriate wave field expansions and the pertinent boundary conditions to determine the resistive
and reactive components of model radiation impedances. Numerical example for spherical surface
excited in vibrational modes of various order (i.e., monopole, dipole, quadrupole, and multipole like
radiators) immersed in a water-filled cavity which is embedded within a water-saturated sandstone
surrounding formation is presented. Several limiting cases are discussed. Effects of porosity, frame
stiffness, source size and interface permeability condition on the impedance values are presented
and discussed. The presented formulation is equally adequate for situations in which the surrounding
formation consists of fibrous materials, as in noise control engineering applications. © 1997 Elsevier
Science Ltd.
