Effects of carbon black (CB) and alumina oxide on the electromagnetic- and microwave-absorption properties of SiC fiber/aluminum phosphate matrix composites

A single-layer radar-absorbing structure in the X-band (8.2 GHz to 12.4 GHz) was designed and fabricated by blending conductive carbon black (CB) with the binder matrix of SiC fiber/aluminum phosphate matrix composites. The slurry comprising Al(H₂PO₄)₃ solution, CB, and Al₂O₃ filler was used as matrix precursor. The complex permittivities of the composites were measured in the X-band. The reflection loss characteristics were calculated using the theory of transmission and reflection. Experimental results showed that the real and imaginary parts of the composites were proportional to the filler concentrations, and the increase rates of the real and imaginary parts were different in terms of filler concentrations. The microwave absorbing ability of the composites was further evaluated, and the addition of 4 wt% CB to the composites was found to noticeably improve the absorption property of the 2.8-3.2 mm-thick composites with the assistance of 5-15 wt% Al₂O₃.