Random Incidence Sound Absorption of Porous Materials With Periodic Holes of Decreasing Profile

This study investigates the acoustic performance of porous materials incorporating embedded periodic holes with a decreasing profile. Finite element simulations are used to assess the sound absorption coefficients and surface impedance under both oblique and random incidence (diffuse field) conditions for materials with low and high airflow resistivity. Acoustic field analysis reveals that while low-resistive materials support plane wave propagation, higher resistivity induces pressure diffusion, disrupting wavefront uniformity. For incidence angles up to 45 deg the diffuse field sound absorption coefficient is higher than 0.99 from 250 Hz to 3000 Hz and presents a peak of 0.98 at 110 Hz. As the incidence angle increases, the acoustic velocity through the material decreases and tends to zero as the incidence angle approaches 90° and the surface impedance increases and consequently the absorption coefficient decreases. The introduction of periodic holes significantly improves low-frequency diffuse field sound absorption compared to traditional porous materials, demonstrating the potential of this design for real-life acoustic applications.