The microstructure and electromagnetic (EM) properties of four kinds of SiC fibers have been studied. These fibers are composed of amorphous SiC_xO_y, SiC nanocrystallines, free carbon, and nanopores, whose volume fractions are analyzed quantitatively. The content of free carbon notably affects the fiber's conductivity: the logarithm of conductivity increases linearly with the increase in the free carbon content when the volume fraction sum of free carbon and SiC exceed the percolation threshold. The EM loss mechanism is mainly composed of the conduction loss caused by free carbon and the polarization loss caused by SiC nanocrystallines. The content of free carbon is the decisive factor for the type of EM loss mechanism: the proportion of conduction loss increases linearly with the increase in free carbon content. Conduction loss is necessary for good EM absorption property, and polarization loss favors broadband absorption. For SiC fibers dominated by polarization loss, excellent absorption properties can be obtained in composites with higher fiber volume fraction (>20 vol%), which is crucial for structural absorbing materials.

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SiC纤维的组织与电磁性能的关系

研究了四种SiC纤维的微观结构和电磁（EM）性能。这些纤维由无定形SiC _x O _y组成，SiC纳米晶体，游离碳和纳米孔，对其体积分数进行了定量分析。游离碳含量显着影响纤维的导电性：当游离碳和SiC的体积分数之和超过渗滤阈值时，导电率的对数随游离碳含量的增加而线性增加。EM损耗机理主要由自由碳引起的传导损耗和SiC纳米晶体引起的极化损耗组成。游离碳含量是EM损耗机理类型的决定性因素：传导损耗的比例随游离碳含量的增加而线性增加。为了获得良好的EM吸收性能，传导损耗是必需的，而极化损耗则有利于宽带吸收。对于以极化损耗为主的SiC纤维，