Underwater sound absorption characteristics of compliant acoustic coatings with adjustable stiffness

Abstract A type of compliant acoustic coating with adjustable stiffness is proposed by a combination of a multilayer adjustable stiffness element and a compliant skin. By adjusting its deformation, the stiffness of the acoustic coating switches between different steady levels, thus tuning its underwater sound absorption performance. Based on the series spring model and the effective medium theory, theoretical models are established for describing the adjustable stiffness of the multilayer element and the sound absorption characteristics of the acoustic coating cells. A conceptual coating model is designed, in which the multilayer adjustable stiffness element is composed of three layers of cells with different structural parameters, corresponding to three different stiffness. Theoretical analysis and numerical simulation are carried out to explore the adjustable stiffness characteristics and sound absorption characteristics of the concept model, with the numerical results of the adjustable stiffness and sound absorption characteristics validated experimentally. The influence of structural parameters is investigated, where the limb thickness t is found to present a dominant influence on the stiffness of the multilayer adjustable stiffness element and the increase in stiffness can improve sound absorption performance in the low and middle frequency bands. The conceptual model shows how the idealized conditions considered in this work could turn into functional prototypes of compliant acoustic coatings with adjustable stiffness.