Acoustic modelling of 3D-printed hybrid materials: a preliminary study

Analytical and finite element (FE) models are developed to predict the sound absorption coefficient of hybrid materials obtained through assembly of folded quarter-length resonators and periodic porous material. The analytical model uses the sum of the acoustic admittances. The acoustic admittance of resonators is simulated with Stinson's model. Johnson-Champoux-Allard-Lafarge (JCAL) model and transfer matrix method (TMM) are used to calculate the acoustic admittance of 1, 2 and 4-layers of porous materials with different geometric parameters. The FE model is implemented using the COMSOL Multiphysics. The helical tubes are simulated using the visco-thermal acoustic module while the porous layers are simulated with JCAL poro-acoustic module. 30-mm thick samples of hybrid materials are produced via additive manufacturing (AM). Normal incident sound absorption coefficient of the hybrid materials is measured using an impedance tube. The experimental and simulated sound absorption coefficients are compared. The impact of the structure parameters (resonator diameter and length as well as number of porous layers) on the sound absorption is assessed. The hybrid materials present low frequency and broadband sound absorption. Higher broadband sound absorption is obtained with 4-layers of porous material. Low frequency absorption ( 1000 Hz) is achieved with long folded resonators (L 100 mm).