Abstract: Wall coverings for anechoic chambers are disclosed having an array of lossy pyramid cone material mounted on multiple backing layers of absorbing material. The number of backing layers to be used, their physical dimension (thickness) and their material properties (conductivity and permittivity) are selected so as not to modify the high frequency (UHF) behavior of the pyramid structure, while at the same time providing a greatly reduced low frequency (VHF) reflection coefficient for the composite absorbing wall. The physical dimension and the material properties of each of the multiple backing layers are selected by a constrained nonlinear optimization data processing procedure or method. The optimization method utilizes known S parameters of the pyramid array, and either known properties of the backing layers, or constrained backing layer properties that are defined by the wall designer.

Abstract: A pyramidal cone absorber structure is equated to an effective absorbing layer model having effective permittivity and permeability properties. A Riccati equation, governing the coefficient of reflection of the effective absorbing layer is derived. A computer program solves the Ricatti equation for the coefficient of reflection using initial values of complex permittivity. Iterative solutions are then obtained using increasing values of complex permittivity until no further reduction in the maximum coefficient of reflection over a specified frequency range is obtained, thus indicating optimum performance of the pyramidal cone absorber structure for a given set of cone dimensions. Optimization of the pyramidal cone absorber structure may also be optimized for a fixed set of complex permittivity values by varying the cone length and backing layer dimensions while maintaining the sum of those two dimensions constant.