Investigation on Microwave Absorbing Properties of Double-Layer Cementitious Composites

Double-layer cementitious plates with absorbing microwave properties were designed, based on the impedance matching theory and electromagnetic wave propagation laws. The reflectivity of cementitious composites was measured in the frequency ranges from 8 GHz to 18GHz, and the influence of silica fume on the impedance of the composites surface was studied. Meanwhile, absorbing properties of cementitious plates, which used ferrite and carbon fiber composited ferrite as microwave absorbers, were also investigated respectively. It is shown that the addition of silica fume can improve the impedance matching between the cementitious composites and free space. Compared with the single-layer structure, the reflectivity of the double-layer cementitious plates decreased around 6 dB ~ 8 dB. The maximum reflection loss of double-layer cementitious plate employing carbon fiber and ferrite reached -16.2dB, while the absorption bandwidth under – 10 dB was from 9.6 to 18 GHz.