Preparation and microwave absorbing properties of three-layered cement-based composites

Based on the electromagnetic wave propagation and attenuation laws, a three-layered cement-based microwave absorber was designed, which owns an impedance-graded structure. The surface layer is made of mortar with 10% crumb rubber replacing sand,easily realizes matching to the free space. The last layer mortar comprised of 30% wt spinel ferrite and 0.5% carbon fiber, has significant absorbing capability. The medium layer mortar with ferrite forms the impedance graded structure from the surface layer to the last layer. The results show that reflectivity of the three-layer cement-based absorber is below -10 dB in the frequency range from 8 GHz to 18 GHz. This kind of the cementitious composites could be used for buildings protecting from electromagnetic interference (EMI).