Numerical and Experimental Study of Sound Power Reduction Performance of Acoustic Black Holes in Rectangular Plates

Global attenuation of structural velocities is one of the most effective approaches in order to reduce noise emitted by shell structures such as a car roof or aircraft fuselage panels. This global reduction can be achieved by the application of passive damping treatments like constraint layer damping on large fractions of the vibrating surface. The main disadvantage of this approach arises from the fact that it leads to increasing total cost and weight of the structure. To overcome this problem, acoustic black holes can be used to create locations with high vibration amplitudes and low bending waves velocity in order to dissipate the energy of structure borne sound by very limited application of damping treatments. Acoustic black holes are funnel shaped thickness reductions that attract sound radiating bending waves and allow a global vibration reduction by an acceptable use of additional damping. This paper presents the results of a numerical and experimental study of acoustic black holes located on a rectangular plate. The presented work is focused on the influence of size, position and number of acoustic black holes on the acoustic performance. A large number of different configurations of these parameters is studied by finite-element-analysis and evaluated in terms of vibration amplitude and sound power level. In order to confirm simulation results the most efficient configuration is implemented in laboratory setup and characterized in terms of vibrational and acoustic performance.