A boundary that sustains a negligible specular reflection coefficient over a wide frequency band

In a previous paper the authors analyzed and discussed the specular reflection coefficient of a plane boundary comprised of a plate, a compliant layer, and a fluid. The analysis showed that a negligible specular reflection coefficient may be derived provided specific resonance conditions are met. The resonance of concern is that between the surface mass of the plate and the surface stiffness of the compliant layer. The conditions of resonance included the value that must be assigned to the loss factor in the compliant layer. In the present paper, an attempt is made to determine the conditions that must be placed on the surface stiffness of the compliant layer in order to increase the frequency range over which a negligible specular reflection coefficient may be maintained. The tolerances in these conditions are also estimated.