Modulating and tuning relative permittivity of dielectric composites at metamaterial unit cell level for microwave applications

•PP/TiO2 nanocomposites with εr in the range of 2–7 and low loss were fabricated.•Further tuning of εr was achieved by drilling holes based on metamaterial concept.•The resultant εr on 5×5×5mm3 unit cells conformed well to the simulation results.•A scheme to implement a dielectric GRIN lens with varying εr is presented.