Sound absorption performance of three-dimensional Hilbert fractal acoustic metamaterials

To verify the feasibility of applying the Hilbert fractal curve to the design of three-dimensional sound-absorbing structures, a design and fabrication process for a three-dimensional Hilbert fractal acoustic metamaterial (3D-HFAM) structure was proposed. The 3D-HFAM structure is made of a resin shell, folded into a maze-like channel with a rectangular tube opening. A simulation analysis was carried out on the influencing factors of the sound absorption coefficient of 3D-HFAM at different orders. The actual data confirm the effects of channel width, channel spacing, and crystal edge length on the sound absorption coefficient. Compared with a single structure, the multi-unit parallel structure expanded the sound absorption bandwidth. Various 3D-HFAM samples were prepared, and the sound absorption coefficients of single 3D-HFAM samples as well as parallel multiple units with different geometric parameters were tested using an impedance tube system. The experimental tests agreed with the simulation results, confirming the successful design and preparation of the metamaterials as described in the text, as well as verifying the multi-unit coupling effect. The study also found that 3D-HFAM exhibits multiple sound absorption peaks in the low-frequency range with high peaks, providing an efficient path for the design of sound-absorbing structures with potential application prospects.