Absorption coefficient

Absorption coefficient

The absorption coefficient "α" is a property of a material. It defines the extent to which a material absorbs energy, for example that of sound waves or electromagnetic radiation. Wallace Sabine was a pioneer of this concept in acoustics and defined the unit of the "Sabin". A Sabin is defined as the absorption by a 1m square slab of perfectly-absorptive material (the same amount of sound loss as if there were a 1m square open window). [ [http://www.acoustics-engineering.com/sabin/wcsabine.htm] ]

In SI units, absorption coefficient is measured in inverse metres, and is represented by the Greek letter "α".


In chemistry, biological sciences and physics, the absorption coefficient is a measure of the how strongly a specific molecule will absorb energy and describes the propagation of sound or light through a specific material. It is very closely related to the absorption cross section.

Absorption coefficient is sufficient for describing energy propagation through a homogeneous system only. Propagation through a heterogeneous system is affected by scattering, [ Bohren,C. F. and Huffman, D.R. "Absorption and Scattering of Light by Small Particles", Wiley, (1983), isbn= 0-471-29340-7 ] . There is more general term attenuation that takes into account both absorption and scattering. It is widely used in acoustics as attenuation coefficient for characterizing particle size distribution. [Dukhin, A.S. and Goetz, P.J. "Ultrasound for characterizing colloids", Elsevier, 2002] , [ ISO 20998-1:2006 "Measurement and characterization of particles by acoustic methods"] .

See also

* Beer-Lambert law
* Scattering theory

External links

* [http://www.sengpielaudio.com/calculator-RT60Coeff.htm Absorption Coefficients α of Building Materials and Finishes]
* [http://www.engineeringtoolbox.com/accoustic-sound-absorption-d_68.html Sound Absorption Coefficients for Some Common Materials]


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