Scattering of Plane Waves from a Compliant Tube Grating in a Linear Viscoelastic Layer.

摘要

The nature of plane wave scattering from a grating in a viscoelastic medium is shown to be fundamentally different from that in a fluid or elastic medium. The solution to the generalized Helmholtz equation is determined in terms of inhomogeneous plane dilatational or shear (P or S) waves. Angles between the propagating and attenuating wave vectors are determined by the boundary conditions. The evanescent waves that arise from the grating equations cannot propagate parallel to the grating as is the case for an elastic-like or fluid medium. Measured transmission loss of plane waves incident on a compliant tube layer in a fluid are compared with predictions of an analytical model. The effects of the elastic stiffness and the mechanical loss factors of a layer of linear viscoelastic material on the performance of the compliant tube arrays are investigated for two different elastomeric encapsulants. Values of the complex shear modulus used as input to the model were determined by use of viscoelastic temperature-frequency relationships. (Author)