Three-layer microwave absorber using cement-based composites

Based on electromagnetic wave propagation laws, a three-layered cement-based microwave absorber that exhibits an impedance-graded structure was designed and fabricated. The surface layer, composed of mortar with 10% rubber powder replacing sand, easily achieves matching to free space. The final-layer mortar, which comprises 30%wt spinel ferrite and 0·5% carbon fibre by volume, has significant absorbing effects. The middle-layer mortar, with ferrite, forms the impedance-graded structure from the surface to the final layer. The results show that the reflectivity of the three-layer cement-based absorber is below −10 dB in the frequency range 8–18 GHz. This kind of cementitious composite could be used for protecting buildings from electromagnetic interference.