SIMPLE, RELAXATIONAL MODELS FOR THE ACOUSTICAL PROPERTIES OF POROUS-MEDIA

By viewing thermal and viscous diffusion in porous media as relaxation al processes, a particularly simple, phenomenological model for sound propagation in these materials is developed. The relaxation model para meters (characteristic times) are chosen by comparison to three existi ng models. Delany and Bazley's empirical equations; the Biot-Allard mi crostructural model; and Champoux and Stinson's generalized, microstru ctural model. It is shown that the relaxation model can effectively mi mic the Delany-Bazley equations in their valid frequency range; yet, u nlike the Delany-Bazley equations, the relaxation model has the advant age providing of realistic predictions at a broad range frequencies. I n more exacting applications the characteristic times can be selected in a manner that makes the relaxation model predictions practically in distinguishable from the two microstructural models. The advantage of the relaxation model in these applications is its simple equations.