Analysis of the complex dielectric permittivity behavior of porous Al₂O₃–SiC composites in the 1 MHz to 18 GHz frequency range

The complex dielectric permittivity of electrically lossy, porous Al₂O₃–SiC composites was measured as a function of frequency over the range of 0.001 to 18 GHz. These composites were fabricated by an infusion method of incorporating SiC polymer precursor into porous alumina disks. Repeat polymer infusions and pyrolysis steps to 1000 °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. 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 ϵ′ and ϵ″ with frequency were analyzed, with a view to determine the various factors contributing to dielectric response. Microstructure analysis using scanning electron microscopy was also performed.