Effect of Ba(Zn1/3Ta2/3)O3 and SiO2 ceramic fillers on the microwave dielectric properties of butyl rubber composites

Butyl rubber-Ba(Zn1/3Ta2/3)O-3 (BR-BZT) composites and butyl rubber-silica (BRS) composites were prepared by sigma mixing. The dielectric properties at 1 MHz and 5 GHz of BR-BZT and BRS composites were investigated as a function of ceramic loading and were found to be improved with filler loading. For a optimum BZT loading of 0.26 v(f), the BR-BZT composite have epsilon(r) = 4.88, tan delta = 0.0022 (at 5 GHz), coefficient of thermal expansion (CTE) = 112 ppm/A degrees C, thermal conductivity (TC) = 0.30 Wm(-1) K-1 and water absorption = 0.047 vol%. The BRS composites attained epsilon(r) = 2.79, tan delta = 0.0039 (at 5 GHz), CTE = 102 ppm/A degrees C, TC = 0.40 Wm(-1) K-1 and water absorption = 0.078 vol% for the same loading of silica. The stress-strain curves of both composites showed good flexibility of the composite. The measured relative permittivity and TC of both composites were compared with different theoretical approaches.