Acoustic black hole manufacturing for practical applications and the effect of geometrical and material imperfections

One of the main challenges in NVH engineering today is not only finding effective methods of reducing noise and vibration from structures, but also the integration of these new methods into a manufacturing process. Acoustic black holes reduce amplitudes of resonant flexural vibrations by reducing edge reflections from structures’ free edges via the use of wedges of power-law profile (one dimensional acoustic black holes) or tapered circular indentations of power-law profile (two-dimensional acoustic black holes). Such acoustic black holes can absorb a large proportion of the incident flexural wave energy. In this paper, the manufacturing of acoustic black holes for some practical applications is considered. The effect of geometrical and material imperfections associated with manufacturing on the performance of acoustic black holes is also investigated experimentally. These imperfections are: tip length and corrugations, edge truncations, etc. Also, the effects of commonly used joining techniques are considered. The reported results demonstrate that the effect of geometrical and material imperfections is not detrimental for the performance of the acoustic black holes. In spite of the presence of imperfections, they provide an effective damping of flexural vibrations, as well as an effective reduction of sound radiation from vibrating structures.