Sound absorption in uniform and layered gyroid and diamond triply periodic minimal surface porous absorbers

Abstract

We investigate the acoustical properties of additively manufactured porous absorbers with gyroid and diamond triply periodic minimal surface pore geometries. Porous samples with different relative densities are fabricated using vat photopolymerization and tested using acoustic impedance and airflow resistivity measurement setups. Optical microscopy shows that the increased wall thicknesses due to polymer expansion causes the actual relative densities of the fabricated samples to exceed the intended designs. The two-microphone tests demonstrate that higher relative densities enhance sound absorption effectiveness, with the diamond geometry outperforming the gyroid at equivalent relative densities. The airflow resistivity tests indicate that the superior performance of the diamond samples stems from their increased airflow resistance, attributable to the absence of through-holes in their structure. We use the inverse characterization approach to model the absorbers using the Johnson-Champoux-Allard rigid formulation, uncovering additional variations in bulk transport properties that are linked to the differing geometries. The validated numerical models are then used to predict the sound absorption performance of sound package designs with various series and parallel relative density gradients using a transfer matrix method. Our results show that such layered configurations of additively manufactured TPMS-based absorbers can enable the design of sound packages with application-specific absorption performance.