Fig. 7: Influence of the thickness and airflow resistivity of the porous layer on the absorption coefficient.
From: Sierpiński carpet-inspired hierarchical patterning of porous materials for sound absorption
Maps of the difference of the absorption coefficients of successive hierarchical levels a α3 − α2, b α2 − α1, and c α1 − α0 as a function of the thickness H of the porous layer and of the frequency. The threshold of increased (regions of the plots in red) / decreased (regions of the plots in blue) performance can be easily identified by the 0-marked isolines (equal absorption performance between two successive hierarchical levels). d–f Maps of the difference of the absorption coefficients of successive hierarchical levels as a function of the airflow resistivity σ of the porous layer and of the frequency when the thickness of the porous cylinder is fixed at H = 80 mm. Similar to the previous case, most combinations of (σ, f) indicate that introducing hierarchical structures enhances absorption.
