Single-layer microwave absorbers: influence of dielectric and magnetic losses on the layer thickness

We propose a convenient graphical method for the determination of the optimal thickness for single-layer absorbers under normal wave incidence. Matching condition demands coincidence of thicknesses of equal amplitudes and phases for reflection and transmission coefficients of the wave reflected from the first-boundary air-absorber and the wave transmitted and reflected from second-boundary absorber-metal, respectively. Reflection loss maps are constructed as functions of layer thickness and one of the material parameters tgepsilon or tgmu for constant ratio epsilon(r)/mu(r) and another parameter tgmu or tgepsilon (epsilon(r) and mu(r) are the real parts of complex relative permittivity and permeability and tgepsilon and tgmu are the dielectric and magnetic loss tangents of the material). It is shown that smaller optimal thicknesses as well as higher absorption at smaller layer thickness can be achieved for the absorbers that have mainly magnetic losses in comparison with those that have mainly dielectric losses for the same values of the ratio epsilon(r)/mu(r). The results are achieved for 10 GHz. They can be transformed to any microwave frequency through the use of the relative frequency coefficient. (C) 2003 Elsevier Science B.V. All rights reserved.