Absorption Coefficient

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Absorption Coefficient

(symbol Missing Image:IMG SRC="equat/alphasm.gif" WIDTH=14 HEIGHT=11 alt="absorption coefficient symbol")

1. A measure of the amount of normally incident radiant energy absorbed through a unit distance or by a unit mass of absorbing medium. Compare transmission coefficient.
The absorption coefficient is frequently identified as follows:

Missing Image:IMG SRC="equat/2abco.gif" WIDTH=183 HEIGHT=45 ALT="I(<subLx )= I(L0) e (-k (L) x)"> where ILx is the flux density of radiation of wavelength L, initially of flux density IL0, after traversing a distance x in some absorbing medium. (Substitute L for lambda.)
2. In acoustics, the ratio of the sound energy absorbed by a surface of a medium (or material) exposed to a sound field or sound radiation to the sound energy incident on the surface. The stated values of this ratio are to hold for an infinite area of the surface. The conditions under which measurements of absorption coefficients are made are to be stated explicitly.
Three types of absorption coefficients associated with three methods of measurement are: chamber absorption coefficient, obtained in a certain reverberation chamber; free-wave absorption coefficient, obtained when a plane, progressive, sound wave is incident on the surface of the medium; sabine absorption coefficient, obtained when the sound is incident from all directions on the sample.


This article is based on NASA's Dictionary of Technical Terms for Aerospace Use