Impedance of pistons on a two-layer medium in a planar infinite rigid baffle

Abstract

An integral transform technique is used to develop a general solution for the impedance of rigid pistons acting on a two-layer medium. The medium consists of a semi-infinite acoustic fluid on a viscoelastic thick plate in a rigid infinite baffle. The stresses acting on the planar baffle, as a result of piston motion, are determined using theory of linear elasticity and are therefore unrestricted in terms of applicable frequency range. The special case of a circular piston is considered and expressions for the self-and mutual impedances are developed and evaluated numerically. Numerical results are compared with classical piston impedance functions and finite-element model results. At low frequencies (k(0)a<1), the self-impedances vary significantly from the classical piston impedance functions due to the shear properties of the viscoelastic medium. In the midfrequency range (1<k(0)a<pi) the self-impedances vary from the classical piston impedance functions for moderate viscoelastic layer thicknesses (0.5<ha<2). The mutual impedances associated with pistons on a two-layer medium generally exhibit an increased decay, as a function of separation distance, over the classical results.