Passive control of vibrations using Acoustic Black Holes

An Acoustic Black Hole embedded in a thin walled structure consists in a tapered indentation of power-law profile, covered by a thin visco-elastic layer. Such local variations of the bending stiffness and surface density leads to a gradually decreasing phase velocity and a gradually increasing local loss factor towards the ABH center. It is shown that such an Acoustic Black Hole is an efficient vibration damper. The number of papers studying this device is growing since the first works on this field in the 1980's. These papers show that several properties are usually observed in an ABH : Low reflection coefficient, localised vibration, trapped modes, cut-off frequeny. The aim of this paper is to provide a state of the art on these properties and to illustrate them by presenting modelling and experimental characterization of different classes of 1D (beam) and 2D (plate) configurations. For this purpose, investigations are performed on a collection of 1D and 2D ABH of various types; 1D ABH with varying thickness only, 1D ABH with varying thickness and width, non linear 1D ABH, 1D ABH with local defects, slots, circular 2D ABH with and without central hole, circular 2D ABH with and without central masses, periodic lattice of 2D ABH embedded on a flat panel. The capability of these different configurations to damp vibrations is discussed.