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Butyl rubber-micron barium titanate (BR/BT) and butyl rubber-nano barium titanate (BR/nBT) composites were prepared by sigma mixing followed by hot pressing. The tensile tests show that both the composites were mechanically flexible. The microwave dielectric properties of both BR/BT and BR/nBT composites were investigated as a function of ceramic loading and were found to be improved with filler content. The butyl rubber has a relative permittivity (e r ) of 2.4 and loss tangent (tan d) of 0.0017 at 5 GHz. At a filler loading of 0.24 volume fraction (v f ) of micron sized barium titanate (BaTiO 3 ) powder loading, the composite attained a e r of 7 and tan d of 0.014 and for the same filler content of nano BaTiO 3 the composite have e r of 8.9 and tan d of 0.019 at 5 GHz. The thermal and mechanical properties of both the composites were investigated. The experimental values of e r of both BR/BT and BR/nBT composites for different volume fractions were compared with theoretical models.

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Mechanically flexible butyl rubber–SrTiO3 composites were prepared through sigma mixing followed by hot pressing. Tensile tests established the mechanical flexibility of the composites. Swelling tests revealed the degree of matrix–filler interactions. The effect of SrTiO3 ceramic filler on the dielectric properties of the composites was studied at 1 MHz and 5 GHz using an LCR meter and a Split Post Dielectric Resonator, respectively. The relative permittivity of the composites increased with filler loading while maintaining low dielectric loss. For the maximum filler content of 0.42 volume fraction, the composite showed a relative permittivity of 13.2 and a loss tangent of 2.8 × 10−3 at 5 GHz. Theoretical modeling of effective relative permittivity of the composites was performed and the results were correlated with the experimental data. Effect of repeated bending on the microwave dielectric properties of the composite was also studied. The coefficient of thermal expansion of the composites was observed to decrease with the increased ceramic filler dispersion and reached a minimum value of 26.2 ppm/°C.