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Active enhancement of the absorbent properties of a porous material

Denis Thenail, Marie-Annick Galland and Michel Sunyach

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We present in this paper an active anechoidal termination composed of a porous material, whose absorbent properties are improved by a secondary source. A simple model of acoustic propagation in a porous medium leads to optimal absorption criteria, which are verified by absorption coefficient measurements under normal incidence at the end of a Kundt duct. A secondary source is placed at the backward interface of the material, and imposes zero pressure by destructive interferences, which is a necessary condition for the maximum absorption. Several control set-ups are tested and provide the anechoism for broadband excitations.


PACS

81.05.Rm Porous materials; granular materials

43.20.+g General linear acoustics

62.65.+k Acoustical properties of solids

Subjects

Condensed matter: structural, mechanical & thermal

Dates

Issue 1 (March 1994)



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