Influence of the interface reflections on the microwave reflection loss for carbonyl iron/paraffin composite backed by a perfect conduction plate

In this work, the influence of interface reflections on the microwave reflection loss (RL) for carbonyl iron/paraffin composite backed by a perfect conduction plate with 30 vol% concentration at various thicknesses was investigated in the 0.1-18 GHz. Using a vector network analyzer, the scattering parameters (S-11 and S-21) were measured in two different ways. Based on the quarter-wavelength matching model, the results of measurement were analyzed. The experiment shows that there are many minimum values (dips) in RL at various thicknesses when the reflective wave, which is reflected from the absorbing layer and the emerging wave, which is reflected from the backed metal plate are out of phase by 180 degrees, and the peak intensity of the RL is directly affected by the intensity of the reflective wave and the emerging wave. Furthermore, the experiment and numerical calculation demonstrates that the modulus of the normalized input impedance vertical bar Z(in)/Z(0)vertical bar equals approximately 1, but the ratio between the modulus of permittivity and permeability vertical bar epsilon/mu vertical bar is far from unity at the minimal reflection point. (C) 2011 Elsevier B.V. All rights reserved.