Designing a negligible specular reflection coefficient for a panel with a compliant layer

Abstract

The specular reflection coefficient of a basic boundary that possesses surface impedance that is mass controlled can be rendered negligible by cladding it with a compliant layer. In this rendering the surface stiffness of the compliant layer and the surface mass of the basic boundary form a resonant dynamic system. The negligible specular reflection coefficient is obtained when the ratio of the surface impedance of the basic boundary and that of the fluid bears, at the resonance frequency and at a specific incidence angle, a direct relationship to the sum of the loss factors in the basic boundary and the compliant layer. A relationship is then derived between the surface stiffness of the compliant layer and its loss factor. This relationship must be necessarily satisfied if a vanishing specular reflection coefficient is to be achieved. The relationship is exemplified by a primitive boundary that is composed of a panel and a compliant layer. Examples relating to this primitive boundary are computed and displayed.