Omnidirectional graded index sound absorber

Olga Umnova , Branko Zajamsek

It has been shown recently that a circular cylindrical layer with dielectric constant, altering as with radius r can capture incident light irrespective of the incidence angle and direct it towards the absorbing core hence achieving the “black hole” effect. If effective and compact acoustical analogues of such structures are developed, they will act as omnidirectional broadband absorbers of sound. Following the approach previously used to design flat gradient acoustic lens and electromagnetic “black holes”, a graded index metamaterial layer has been built using an array of small scatterers with their concentration varying along the structure radius. In an array of small rigid circular cylinders the effective density (which is the acoustical analogue of the dielectric constant) varies with filling fraction. This means that by varying this parameter the desired dependence of effective density on radius can be achieved. A porous fibrous material has been used as an absorbing core. The device has been tested and is shown to provide a nearly total absorption of sound with wavelengths shorter than its diameter.

Mots clés: metameterials; graded index structure; sound absorption

Domaines: Acoustique [physics.class-ph]

Olga Umnova, Branko Zajamsek. Omnidirectional graded index sound absorber. Acoustics 2012, Apr 2012, Nantes, France. ⟨hal-00811033⟩