Wall
The Wall subnode defines the surface properties of the scattering object. Several Wall subfeatures can be added to represent different properties of the boundaries of the surface. Select the Type as Sound hard wall (the default), Reflection coefficient, Normal impedance, or Absorption coefficient.
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For Sound hard wall, there is perfect specular reflection with no absorption of energy at the boundary. The condition corresponds to a reflection coefficient R = 1.
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For Reflection coefficient, enter a value for R (SI unit 1). The reflection coefficient is a complex valued quantity that can depend on the angle of incidence θi. The angle is defined through the built-in variable paas.theta.
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For Normal impedance, enter a value for the normal impedance Zn (SI unit: Pas/m). The reflection coefficient of the surface is computed according to the classical plane wave reflection expression
where Z = ρc is the specific characteristic acoustic impedance of the medium and θi is the (local) angle of incidence. This corresponds to a locally reacting surface. The normal impedance is typically complex valued.
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For Absorption coefficient, enter a value for the (normal) absorption coefficient αn (SI unit: 1) and the phase (SI unit: rad). Both can depend on the angle of incidence in the same way as the reflection coefficient. The reflection coefficient of the surface is computed according to
Angle dependency of the absorption or reflection coefficient can be introduced using the angle if incidence variable paas.theta or the cosine to the angle of incidence paas.costheta.