Vrednotenje akustičnih lastnosti granuliranih materialov za razvoj metamaterialov z izboljšano zvočno izolacijo in absorpcijo

Acoustic characterization of granular materials is crucial for developing advanced acoustic metamaterials capable of enhanced sound insulation and absorption. Current methods of characterizing such materials often produce ambiguous or misleading results due to their sensitivity to boundary conditions and the complex internal structures of granular media. This thesis introduces a novel experimental methodology based on the time-domain wave decomposition of impulse responses measured in an impedance tube, specifically developed to overcome these limitations. The method improves measurement accuracy of transmission losses and explicitly accounts for viscous dissipation within granular materials independent of boundary effects. Detailed experiments reveal significant relationships between particle size distributions, granule contact densities, and acoustic properties. Smaller granules increased airflow resistivity, enhancing low-frequency sound insulation by up to 30 dB per 10 mm, while larger particles demonstrated clear Helmholtz resonances and standing wave phenomena at 1000 Hz. Medium-sized particles exhibited optimal dissipation characteristics, balancing viscous losses and reactive acoustic phenomena effectively. These findings offer critical insights into the underlying acoustic mechanisms within granular metamaterials, facilitating their tailored use in noise control solutions in both industrial and architectural contexts. The newly established methodology and resulting models significantly contribute to the acoustic materials science literature, providing robust guidelines for future acoustic metamaterial designs.