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Enhancing rigid frame porous layer absorption with three-dimensional periodic irregularities
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10.1121/1.4773276
/content/asa/journal/jasa/133/2/10.1121/1.4773276
http://aip.metastore.ingenta.com/content/asa/journal/jasa/133/2/10.1121/1.4773276

Figures

Image of FIG. 1.
FIG. 1.

Example of a -periodic fluid-like porous sheet backed by a rigid wall that contains periodically arranged macroscopic cubic irregularities excited by a plane incident wave: (a) in plane dimensions in case of a one irregularity unit cell and (b) out of plane dimensions in case of a two irregularity unit cell.

Image of FIG. 2.
FIG. 2.

Real and imaginary parts of the dispersion relation roots in the absence of irregularities . Real part of the modified modes of the layer , for are shown by dots.

Image of FIG. 3.
FIG. 3.

Absorption coefficient of a porous layer of characteristic backed by a flat rigid backing (dashed line), of the same porous material but of thickness backed by a flat rigid backing (dash dotted line), of characteristic backed by a rigid flat backing with an air layer of thickness in between (dotted line), (a) backed by an irregular rigid backing of geometry (solid line) and (b) backed by an irregular rigid backing of geometry (solid line) at normal incidence. Finite-element results are also plotted and pointed out by squares.

Image of FIG. 4.
FIG. 4.

Configuration and —Transfer function on at , and its different contributions, when the configurations are excited at normal incidence: (solid line), (dashed line), (dash dotted line), and (dotted line).

Image of FIG. 5.
FIG. 5.

(a) Absorption coefficient of a porous layer of characteristic backed by an irregular rigid backing of geometry when the configurations are excited at (solid line), (dashed line), (dash dotted line), and (dotted line) for and (b) evolution of as a function of for .

Image of FIG. 6.
FIG. 6.

(Color online) Cross-sectional view of the experimental set-up and sample design (a), picture of the sample (b), and sample layer in the impedance tube (c).

Image of FIG. 7.
FIG. 7.

Comparison between the absorption coefficient of a porous layer of characteristic , backed by a flat rigid backing (dotted line), and backed by an irregular rigid backing of geometry as calculated with the present method (solid line), and measured experimentally (○)

Image of FIG. 8.
FIG. 8.

Absorption coefficient of a porous layer of characteristic backed by a flat rigid backing (dotted line), backed by an irregular rigid backing of geometry (solid line) and of geometry (dash dotted line) as calculated with the present method and as calculated by finite element method (squares).

Tables

Generic image for table
TABLE I.

Acoustical parameters of the porous material constituting the sheet of thickness .

Generic image for table
TABLE II.

Geometry of the configuration. All dimensions are in cm.

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/content/asa/journal/jasa/133/2/10.1121/1.4773276
2013-01-30
2014-04-21
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Enhancing rigid frame porous layer absorption with three-dimensional periodic irregularities
http://aip.metastore.ingenta.com/content/asa/journal/jasa/133/2/10.1121/1.4773276
10.1121/1.4773276
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