Compact acoustic black hole with vortex-shaped configuration for low- and broadband-frequency vibration damping

Acoustic black holes (ABHs) have attracted significant research interest due to their ability to absorb flexural waves over a broadband frequency range above the cut-on frequency. However, achieving a lower cut-on frequency requires a substantial increase in size, which limits their applicability to low-frequency vibration damping. To address this limitation, this study proposes a novel two-dimensional (2-D) ABH design for low- and broadband-frequency vibration damping in plate structures. The proposed ABH is designed by coiling multiple concave-shaped ABHs and arranging them rotationally along a circumference, forming a vortex-shaped configuration. This configuration allows accommodation of longer ABHs without enlarging an installation space, thereby lowering the cut-on frequency. The proposed ABH achieves a significantly lower cut-on frequency and enhanced vibration damping performance compared to a conventional 2-D ABH occupying the same installation space. These advantages are validated through both numerical simulations and experiments. Furthermore, the damping performance is further improved at specific frequencies by breaking rotational symmetry of the vortex-shaped configuration.