A novel compact volumetric metamaterial structure with asymmetric transmission and polarization conversion

Abstract

The novel folded ring resonator (FRR) is uniaxial bi-anisotropic and possesses a strong resonant magnetic bandgap. Within the bandgap at 4.75 GHz, the cubic FRR is significantly subwavelength because it is $\lambda$/13 along any coordinate axis and $\lambda$/7 along the body diagonal. The bulk behavior of a cubic lattice of the novel structure demonstrates backward mode behavior centered near the frequency 4.5 GHz with a bandwidth of 12.2% as derived from the dispersion curve. Parametric sweeps of the critical dimensions are presented showing the tunability of the structure. The field nature of the backward mode is explained in terms of the realized simultaneous electric and magnetic dipole reponses. For finite thickness layers of the novel FRR, the transmitted phase is shown to indicate the presence of a backward mode in agreement with the bulk response. The novel structure also functions as a linear to circular polarizer for a single layer. Due to the asymmetry of the structure, asymmetric transmission occurs within the backward mode in the form of circular cross-polarization dichroism and direction dependent transmission. Although the backward mode occurs for any incident angle it is shown to be anisotropic in nature. A backward mode bandwidth as wide as 23.3% is achieved along the body diagonal of the cubic unit cell, which is the principal axis.