Vibration damping of sandwich panels using the Acoustic Black Hole effect

Among the existing passive vibration control techniques, the use of the acoustic black hole (ABH) is a solution that has the advantage of not increasing the mass of the structure in which it is integrated. In this paper, the benefits of inserting an ABH into a three-layer sandwich panel (fibreglass skins and honeycomb core) are investigated. It is known that an ABH effect can be achieved in a panel by locally reducing its stiffness (using a reduction in plate thickness according to a power law profile) and increasing local damping (using a coating of viscoelastic material). A sandwich panel induces a shear effect that strongly affect the wave propagation and lead to specific properties to the ABH effect. The equations of motion of a thick, symmetrical sandwich panel with non-uniform characteristics are obtained within the framework of zig-zag theory by applying Hamilton's principle. These equations lead to a semi-analytical model of order 6, from which an effective bending stiffness, dependent on both frequency and space can be derived. Using this model, it is demonstrated that the sandwich effective bending stiffness favours the ABH effect. This interesting property is also validated by experimental tests on sandwich panels using laser vibrometry.