Additively manufactured hybrid auxetic structures for enhanced low frequency acoustic performance through experiments and modelling.

Re-entrant auxetic designs, known for their superior mechanical properties, are increasingly explored in various industrial applications. This study aims to enhance the multifunctionality of such designs by preserving their mechanical characteristics while improving their acoustic performance. A multi-layer hybrid structure integrating microperforated panels with auxetic geometry was proposed. This design enabled each auxetic cavity to function as a Helmholtz resonator. Sample fabrication was performed with fused deposition modeling (FDM), an Additive Manufacturing technique, using PLA as build material. The perforations and minimum structural features were designed to maintain structural integrity and mechanical properties while facilitating ease of manufacturing. A computational modeling approach was verified and validated using numerical and experimental results from the literature. Impedance tube testing techniques were employed to validate the numerical model for sound transmission loss (STL) and sound absorption coefficient (SAC), ensuring precise measurement of acoustic properties and confirming the accuracy of the simulations. A total of 18 variants of proposed design were numerically examined in the low to mid-frequency range (50-1800 Hz). The effects of various geometric and material parameters on acoustic performance were recorded. Results indicate substantial enhancement in SAC as well as STL from baseline design of the same dimensions. SAC above 0.5 was achieved for a broad frequency range of 1180 Hz with an average STL of 55 dB. This research advances the development of multifunctional subwavelength metamaterials by presenting a structure that exhibits exceptional STL and SAC-a combination not previously documented in recent literature.