Acoustic performance analysis of perforated metamaterials: comparative study of bio-composites and synthetic conductive materials

Perforated metamaterials are developed for innovative sound control within this research. This study investigates the effects of varying infill patterns (50 % and 100 %) of perforation on conductive TPU (Thermoplastic Polyurethane) and PLA (Polylactic Acid) circular samples (30 mm diameter, with 3 mm wall thickness), which were produced via FDM (Fused Deposition Modelling) 3D printing and tested using an impedance tube setup. The acoustic performance of 3D-printed perforated metamaterials made from bio-composite materials (ProtoPasta Conductive PLA) and synthetic conductive materials (Nylforce and Ninjatek) is explored, emphasising the potential for reducing the environmental impact through the use of bio-composites. Acoustic testing covered a frequency range of 160 Hz to 5 kHz, with adjustable back cavity depths of 8.5 mm, 23.5 mm, and 43.5 mm to assess a wide range of frequency absorption capabilities. The results indicate that thicker samples (50 mm) with 100 % infill show superior absorption, particularly at mid-to-high frequencies (2000–5000 Hz), while lower infill densities reduce absorption efficiency. Statistical analysis confirmed that conductive TPU showed slightly higher mean absorption than conductive PLA, particularly in denser configurations, but the difference was not statistically significant (p > 0.05). Additionally, back cavity depth significantly influenced performance, with deeper cavities enhancing low-frequency absorption. Perforation density and infill geometry played a crucial role in absorption tuning. The comparative analysis underscores the feasibility of sustainable, multifunctional noise control solutions. The findings suggest that perforated metamaterials can be optimized for broad-spectrum and low-frequency noise mitigation, making them suitable for electromagnetic shielding applications.