Analysis of the Complex Dielectric Permittivity Behavior of Porous Al$_{2}$O$_{3}$-SiC Composites in the 1 MHz -- 18GHz Frequency Range

The complex dielectric permittivity of electrically lossy, porous Al$_{2}$O$_{3}$-SiC composites was measured as a function of frequency over the range of 0.001-18 GHz (broadband). These composites were fabricated by an infusion method of incorporating SiC polymer precursor into porous alumina discs. Repeat polymer infusions and pyrolysis steps to 1000$^{o}$C were carried out, with some samples undergoing an additional air-fire prior to each subsequent step. Generally, it was found that for non-air-fired samples, moderate, controllable losses were attainable over a broad frequency range with $\log \varepsilon ''$ being inversely proportional to $\log f$. By contrast, the dielectric loss attainable for air-fired samples was generally very low. For all samples, various aspects of the variation of permittivity components $\varepsilon '$ and $\varepsilon ''$ with frequency were analyzed, with a view to determine the various factors contributing to dielectric response. In addition, the ramifications of this behavior on the properties of the material as a lossy composite were addressed.