Scattering effects induced by imperfections on an acoustic black hole placed at a structural waveguide termination

Abstract

International audienceThe so-called " acoustic black hole " effect (ABH) is a passive vibration control technique based on the flexural waves properties in thin structure of varying thickness. A usual implementation consists in using a plate with tapered extremity with a power-law profile, covered with a thin damping layer. The inhomogeneity of the structure leads to a decrease of flexural wave speed and an increase of their amplitude, therefore resulting in an efficient energy dissipation if damping layer is placed where the thickness is minimal. The manufacture of an efficient extremity is difficult because of the small thickness, and often generates imperfections and tearing. Moreover , previous works suggest multiple that flexural modes are propagating across the width of the ABH tip. A model of an ABH multimodal waveguide taking into account an imperfect termination is developed. It shows that an elementary imperfection can affect the reflection coefficient of the extremity and reduce it. Scattering and propagation properties of the extremity are also studied. An incident mode excites several modes that are localised in the tapered region and local resonances explain the drops in the reflection coefficient. Experimental evidence of the influence of the imperfection on the reflection coefficient is provided. A key result of the paper is that manufacturing imperfections are not detrimental to the ABH effect

Enhanced Acoustic Black Hole effect in beams with a modified thickness profile and extended platform

“…To maximize the ABH effect, however, the ultimate pursuit of extremely thin wedge tip is of high cost and harsh demand for the precision machining and would also lead to tip damage of tearing and irregularities. Although Bowyer et al [14] experimentally showed that the damage on the wedge tip does not notably affect the ABH effect; 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 Denis et al [15] reported that the imperfect wedge tip would reduce the reflection because of the resultant scattering effects; structures with ultra-thin or damaged tips however can hardly be applied in industry due to the structural strength problems. Therefore, on the premise of the minimum achievable truncation thickness by currently available manufacturing technology, ways maximize the ABH effect need to be explored.…”

Damping control for improvement of acoustic black hole effect

“…This theoretical behaviour is however difficult to obtain because of manufacturing constraints which impose a non-zero thickness at the border, inducing some reflections of flexural waves. Using a damping layer [4] may be a solution to damp the waves in the black hole, even if this is not mandatory since local imperfections at the edge may induce dissipation through nonlinear effects [5].…”

Acoustic Black Holes in Structural Design for Vibration and Noise Control

“…Chong also indicates that the smooth and stepped ABH beams are slightly different [22]. Denis et al also find that the controlled imperfection of the tip of the 1D ABH causes a decrease of the reflection coefficient, which indicates that imperfect extremities are not detrimental to the performance of the ABH effect [65]. These two studies lower the stringent requirement of the ideal power-law thickness variation of ABH.…”