Dual-scale porosity effects in the acoustic response of mesh-reinforced resistive screens

This study explores the acoustic behavior of glass fiber-reinforced composite materials made by resistive screens backed by structural support meshes. These systems are characterized by a double porosity: a micro-porosity (φm) associated with the screen's perforations and a macro-porosity (φr) resulting from the mesh-induced partial occlusion. The micro- and macro-porosity, along with other transport parameters, are assessed through optical image processing. The measured values of φm range between 0.015 and 0.028, while φr varies from 0.31 to 0.39. The corresponding airflow resistivity spans 1.09×106 to 1.92×106 Pa s/m2. Based on the obtained transport parameters, an equivalent fluid model is applied to predict the acoustic response, introducing a correction to account for the dual-porosity nature of the system. Theoretical predictions are compared with experimental data in terms of the normal-incidence sound absorption coefficient, measured via the two-microphone technique inside a 100 mm diameter impedance tube with a fixed 56 mm air cavity behind the samples. Results demonstrate that both the mesh configuration and the pore shape strongly influence the airflow resistivity, the viscous characteristic length, and the absorption peak frequency. The tested samples achieve a maximum sound absorption coefficient of about 0.90 around 1100 Hz. These dual-scale systems not only enhance low-frequency absorption and tunability through the interplay between micro- and macro-porosity, but also improve structural rigidity while enabling lightweight and potentially more sustainable acoustic solutions suitable for transportation and building applications.