Pyramidal absorber having multiple backing layers providing improved low frequency response

摘要

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. Optimization is achieved by mathematically sampling the wall's wave reflection at wave frequencies and wave incident angles that are defined by the designer. The output of the optimization method provides a wall design which minimizes wave reflection therefrom by defining the number of backing layers to be used, the thickness of each backing layer, the electrical conductivity of each backing layer, and the permittivity or dielectric constant of each backing layer.