Butyl rubber–Ba0.7Sr0.3TiO3 composites for flexible microwave electronic applications

Butyl rubber–Ba0.7Sr0.3TiO3 composites (BR–BST) were prepared by sigma mixing followed by hot pressing. The stress–strain studies show the good flexibility of the composite. The dielectric properties of the composites were investigated at both radio and microwave frequencies. The relative permittivity (εr) and loss tangent (tan δ) improved with filler loading at both the frequencies. The relative permittivity and loss tangent of the BR–BST composites at a maximum filler loading of 0.39 volume fraction (vf) are 13.1 and 0.009 respectively at 5 GHz measured by Split Post Dielectric Resonator (SPDR). The effective relative permittivity of the BR–BST composites is compared with theoretical models. The variation of εr with temperature was also investigated in the range 22–80 °C at 1 MHz. The microwave dielectric properties of the composites are also studied after repeated bending. The coefficient of thermal expansion (CTE) of the butyl rubber–BST composites decreased with the addition of the BST ceramic.