Effects of SiC fibers on microwave absorption and electromagnetic interference shielding properties of SiCf/SiCN composites

SiC fibers have key effects on designing and optimizing electromagnetic wave absorption (EMA) and electromagnetic interference shielding (EMI) properties of SiC fiber reinforced ceramic matrix composites. In this paper, ZMI-SiC fibers and Amosic-SiC fibers were used to fabricate SiCf/SiCN composites with good EMA or EMI properties. Both ZMI-SiC and Amosic-SiC fibers are composed of interpenetrating superfine SiC nano crystals, graphene-like free carbons and amorphous SiOC phase. Amosic-SiC fibers exhibit better crystallizations and higher free carbon contents than ZMI-SiC fibers. Therefore, Amosic-SiCf/SiCN composite possesses higher electrical conductivity, dielectric and EMI properties than ZMI-SiCf/SiCN composite. The total shielding effectiveness of Amosic-SiCf/SiCN composite reaches 25 dB in the whole X band. ZMI-SiCf/SiCN composite possesses relatively low dielectric constant and high loss tangent, rendering composite good EMA properties. The reflectivity of ZMI-SiCf/SiCN composite is smaller than 7 dB in the whole X band. The mechanisms of dielectric loss, EMI and EMA for composites are discussed.