Impedance tube sound absorption measurements of additively manufactured metamaterials: A systematic study of design parameter influences

Acoustic metamaterials offer enhanced control over sound waves, enabling the design of innovative structures for diverse applications. In this work, we investigate the impact of measurement uncertainties on the sound absorption performance of three-dimensionally printed acoustic metamaterials in an impedance tube. Two representative types, the Helmholtz resonator and coiled-up space structure, are fabricated in multiple variations and characterized experimentally and numerically. The influence of factors such as printing-induced surface texture/roughness, infill density, assembly errors, and air gaps between the tube inner wall and the sample is systematically analyzed. Rather than providing a quantitative evaluation, the work characterizes observed sources and effects of uncertainty and examines how design parameters influence measurement outcomes. The results reveal that surface roughness, assembly, and tube-sample air gap can significantly distort the measured response. Notably, layer height and assembly-induced gaps can be treated as design parameters to optimize absorption, while infill density can optimize manufacturing efficiency. While uncertainties in impedance tube measurements of porous materials have been extensively evaluated, metamaterial structures have received limited investigation. The findings of this work not only clarify the effects and sources of uncertainty in impedance tube measurements of metamaterials but also expand previous research analysis and provide a guideline to address ambiguities.