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Experimental Determination of Porous Media Properties for
Predicting Absorption of Bulk-Reacting Surfaces
Porous materials (open-cell foams) are commonly used and located
along enclosure boundaries for the purpose of sound attenuation. An
example of such an application is an anechoic chamber having the
porous material distributed along the chamber walls. Accurate
representation of the boundary condition is needed for the analytical
modeling of these enclosures. The proper characterization of porous
materials requires the determination of the effective complex phase
speed and effective complex density of the fluid during propagation
through the porous material. This seminar presents a two-step process in
which these characteristic properties are determined experimentally using
an acoustic standing wave tube device. The normal incidence acoustic
impedance of the porous material is obtained using the standing wave
tube for two cases: a zero velocity condition (hard wall), and zero
pressure condition behind the porous material. The effective phase speed
and density are then obtained from formulas containing the normal
incidence acoustic impedances measurements for both cases. For
verification, standing waves are predicted theoretically using the
previously obtained phase speed and density as inputs for the case of a
two-dimensional slender duct with the porous material lining a side wall.
These predictions are compared to experimental measurements of sound
pressure in the two-dimensional duct and good agreement is observed for
the open-cell foams considered.