A review of experimental investigations into the acoustic black hole effect and its applications for reduction of flexural vibrations and structure-borne sound

In this paper, a review of experimental investigations into the damping of flexural vibrations and the reduction of radiated sound power using the acoustic black hole effect are presented. The acoustic black hole effect damps flexural vibrations by reducing edge reflections from structures’ free edges via the use of wedges or tapered circular indentations of power-law profile. Wedges of power-law profile materialise one-dimensional acoustic black holes for flexural waves that can absorb a large proportion of the incident flexural wave energy. Tapered circular indentations of power-law profile act as two-dimensional acoustic black holes for flexural waves. The results of experimental investigations into the damping of flexural vibrations in turbofan blades incorporating a power-law profile are described along with the incorporation of two-dimensional acoustic black holes into smooth surfaced composite panels, and composite honeycomb sandwich panels. Finally, the results for multiple indentations (arrays) of two dimensional acoustic black holes and the associated reduction in structure-borne sound are given. The reported results demonstrate that the acoustic black hole effect can provide an effective damping of flexural vibrations in the aforementioned blades and panels, as well as an effective reduction of sound radiation from structures