通过有机泡沫浸渍/高温炭化和热压固化/高温炭化两种工艺分别制备了具有宏观三维连通网络结构的SiC/C泡沫和显微三维连通多孔结构的SiC/C泡沫同质压制块.使用谐振腔微扰法对比测试了2 450 MHz频率下两种材料的电磁参数随电导率的变化.结果表明:随着电导率的增加,SiC/C泡沫及其同质压制块的介电常数实部ε_(r)'均逐渐增加;电损耗tgδ_e均先增加,达到最大值后逐渐减小;SiC/C泡沫的磁损耗tgδ_m不断增加,而其同质压制块的tgδ_m值则先快速增加,达到最大值后缓慢下降.当二者具有相同有效电导率时,SiC/C泡沫的ε_(r)'值比其同质压制块约小1/2,tgδ_e值至少大2倍,而压制块的tgδ_m值超过SiC/C泡沫4倍多.SiC/C泡沫及其同质压制块是非磁性的,它们的磁损耗均由其特殊结构与电磁场相互作用产生的,是一种非本征磁损耗.
SiC/C foams and their monoliths of the same compositions,with various electrical conductivities were prepared by polymer sponge replication/carbonization and hot-press solidification/carbonization respectively.Both materials have a three-dimensionally connected pore structure with the former on a macroscopic scale and the latter a microscopic scale.The electromagnetic parameters of the SiC/C foams and the monoliths versus their electric conductivities were measured at a frequency of 2 450 MHz by the TE_(10) resonant cavity perturbation method.Results show that when the electrical conductivities of the SiC/C foams and the monoliths increase gradually,their dielectric constants ε_(r') increase gradually and their dielectric losses tg δ_e exhibit a maximum.The magnetic loss tg δ_m of the SiC/C foams increases continually while that of the monoliths first increases quickly then decreases slowly with increasing electric conductivities.When the effective electric conductivities of the SiC/C foams and the monoliths are the same,the ε_(r') values of the SiC/C foams are about a half and the tg δ_e values are at least 2 times larger than those of the monoliths,while the tg δ_m values of the monoliths are more than 4 times those of the SiC/C foams.The SiC/C foams and the monoliths are both non-magnetic,and their magnetic losses are found to be caused by their special structures interacting with the incident electromagnetic waves.Thus it is apparent that this kind of magnetic loss is extrinsic.
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