Synthesis and Characterization of Calcium Titanate-Filled Butyl Rubber Composites for Flexible Microwave Substrate Applications

Calcium titanate (CaTiO3)-filled butyl rubber (BR) composites were fabricated by mixing and hot pressing. The filler volume fraction was varied from 0 to 50%, and its effects on properties such as density, moisture absorption, dielectrics, coefficient of thermal expansion (CTE), thermal conductivity and thermal stability were studied. The phase purity of the powder was confirmed by x-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS), while scanning electron microscopy (SEM) was used to analyze the dispersion, morphology and microstructure of the samples. Optimal dielectric and thermal properties were obtained for the sample having 45% filler volume fraction. Relative permittivity (epsilon(r)) of 11.7, along with a low loss tangent (tan delta) of 0.0053, was achieved at the optimal filler content in the X-band (8.2-12.4 GHz) regime. A low CTE of 33.7 ppm/degrees C and low moisture absorption of 0.0798%, along with good thermal stability and acceptable thermal conductivity (0.6303 W/m K), were also obtained for the optimum filled sample. Moreover, an elongation of 31.9% was observed without any permanent deformation. The developed highly flexible dielectric substrate material can be effectively used for miniaturized flexible microwave circuit applications.

Automated summary

Calcium titanate (CaTiO3)-filled butyl rubber (BR) composites with different filler volume fractions were prepared and their properties were studied. The optimal sample with 45% filler volume fraction exhibited excellent dielectric and thermal properties, making it suitable for miniaturized flexible microwave circuit applications.