High Circular Dichroism in Extrinsic Chiral Metamaterials Based on Sawtooth and Zigzag Arrangements With Experimental Validation

Abstract

This study analyzes the extrinsic chirality of metamaterials based on printed circuit board (PCB). Inspired by extrinsic planar metamaterials, two novel 3-D chiral metamaterials (CMMs) have been proposed and analyzed. In these structures, called sawtooth and zigzag arrangements, each unit cell and not the entire metamaterial is tilted with respect to the incident field. In both cases, the same single-layer metallic pattern, that is, a split-ring resonator (SRR), was used. In comparison with the traditional planar extrinsic chiral structures, it is shown, by numerical and experimental characterization, that these new types of arrangements exhibit a larger circular dichroism (CD), approximately 0.90, in the X-band, with a significant wideband response. The analysis of the extrinsic chirality shows that it is originated by the dipole moments excited on the unit cells. With circular polarization, the constructive/destructive interference between these dipoles produces CD. However, owing to the broadside coupling between adjacent unit cells, the proposed nonplanar arrangements provide higher CD values than the planar structure.