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

Abstract

Dielectric materials with desirable relative permittivity (εr) may not be readily available in nature and are usually difficult to be tailored precisely. We hereby predict and experimentally achieve the flexible tuning of εr for dielectric materials at the unit cell level in microwave range, as inspired by the recent developments in metamaterials. A series of composite dielectric stock sheets with εr in the range of 3–7 and low loss tangent (tanδ<0.01) were successfully fabricated by dispersing different volume fractions of TiO2 nanoparticles into polypropylene polymer matrix. To further enable the flexible tuning of εr, sub-wavelength holes with different diameters were drilled on the composite dielectric sheets based on 5×5×5mm3 metamaterial unit cells. The resultant effective εr of the metamaterials conformed well to the simulation results by CST STUDIO SUITE® software. By utilizing the drilled-hole PP/TiO2 composite metamaterials, a potential scheme to implement a dielectric gradient index lens with discretized shells of varying εr is presented. This drilling-hole approach to modulate and tune the effective εr at the metamaterial unit cell level can be generalized to produce a variety of desirable permittivity values with great flexibility. The applications of these materials can be easily extended to other microwave or optical devices including cloaks, lenses, and beam shifters.