Underwater anechoic layer with parallel metallic plate insertions: Theoretical modelling

A novel underwater composite anechoic layer is proposed by inserting periodically placed longitudinal parallel steel plates into a viscoelastic rubber matrix. Built upon the complex viscosity model of viscoelastic materials, a theoretical model is established to evaluate the sound absorption performance of the proposed anechoic layer. For validation, finite element simulations are carried out, and good agreements are achieved between theory and simulation. Compared with the reference structure purely made of rubber, the new anechoic layer exhibits greatly improved sound absorption performance. It is demonstrated that the steel plate insertions significantly enlarge the shear deformation of rubber at plate-rubber interfaces, causing greatly improved viscous dissipation of acoustic energy. Systematic variations of material properties and geometrical parameters reveal the dominant roles of rubber viscosity and plate spacing. Further, a theoretical model is developed to study the effect of non-tight connection at rubber-plate interfaces. This study broadens the application scope of the complex viscosity model and provides useful guidance for designing novel anechoic layers with tailored underwater acoustic performances.