Enhanced bandgaps below the cut-on frequency of a novel acoustic black hole metabeam

Acoustic black holes (ABHs) are widely used for mid-to-high-frequency vibration suppression but are ineffective below a certain threshold, known as the cut-on frequency. ABH metamaterials, which integrate ABHs with metamaterials, have gained attention for improving low-frequency vibration attenuation. However, existing studies primarily focus on bandwidth broadening while overlooking attenuation enhancement. This paper proposes an ABH metabeam with added layers or holes to simultaneously increase the attenuation constant and expand the bandwidth below the cut-on frequency. A theoretical model based on the wave and Rayleigh-Ritz method is developed to compute the complex dispersion relations of the proposed metabeams, with results verified via finite element simulations. Compared to bare ABH metabeams, added layers enhance both the attenuation constant and bandwidth of the second to fourth bandgaps but weaken the first bandgap. In contrast, introducing appropriately sized holes strengthens the first bandgap without compromising the second to fourth bandgaps. Notably, combining added layers with holes enhances the second to fourth bandgaps without weakening the first. The proposed ABH metabeam presents a promising approach for improving low-frequency vibration attenuation in ABH-based structures.