INFLUENCE OF ADDITIVE MANUFACTURING ON ACOUSTIC METAMATERIALS PERFORMANCE: A CASE STUDY

Research on metamaterials relies on the rapid prototyping of samples implementing all geometrical details suggested by analytical or numerical studies. Therefore, precision in the realization of this geometry is vital for obtaining an acoustic result coherent with the analytical and numerical design. Additive manufacturing (AM) is the main technique in acoustic metamaterials (AMMs) prototyping, and so far, it has displayed interesting properties for quickly reproducing the geometries addressing specific resonance frequencies. However, AM parameters are generally not intended precisely for acoustic purposes, which may lead to a mismatch between the expected analytical or numerical results. In this study, AM parameters have been investigated to define the optimal printing configuration of a coiled-up resonator (as an example of AMM). Three printing techniques - Fused deposition modelling (FDM), Stereolithography (SLA), and Selective Laser Melting (SLM) - and four materials - PLA, PETGg, Resin, and Steel - have been investigated, due to their popularity among academic and private researchers. The sound absorption coefficient of each sample has been measured experimentally in two Italian research laboratories (INRIM Turin and University of Bologna). Next, the experimental results were compared to the analytical and numerical ones considering the impact of five specific parameters: Printing velocity, Printing layer height, Filling density, Internal surface Roughness, and Internal surface porosity. The SLA/Resin combination performed better overall; however, properly set FDM and PETGg can achieve nearly the same acoustic precision in a cheaper and faster way. It is expected that these findings could be replicated for other AMMs.