Flow and Noise Control Using Graded-Porosity Porous Materials

The growth of industrial activity, transportation, and urban development has increased the demand for effective noise-reduction solutions. Porous materials are widely used for this purpose due to their ability to dissipate acoustic energy through viscous and thermal losses within interconnected pore structures, enabling efficient broadband absorption, particularly at mid- to high frequencies. Recent studies have focused on improving acoustic performance by tailoring microstructural parameters such as porosity, pore size, and density. In this study, triply periodic minimal surface (TPMS) and lattice structures with graded porosity were experimentally investigated using the Grazing Flow Impedance Tube Facility at the University of Bristol. The acoustic response was characterised in terms of reflection, absorption, and transmission loss for different density ratios (50–50, 80–20, and 20–80). The results show that while the balanced configuration exhibits geometry-independent behaviour, topology becomes increasingly important as the density ratio deviates from this condition. The solid-dominated case increases reflection and transmission loss, whereas the void-dominated configuration enhances broadband absorption. Among the tested geometries, the Fischer–Koch structure consistently achieves the highest transmission loss in non-balanced cases. These findings highlight the importance of jointly optimising porosity and topology to design lightweight, high-performance acoustic materials.