A type of negative-index metamaterial composed of periodic arrays of SRRs is proposed and numerically investigated in the visible frequencies. Employing the high order magnetic resonance to induce negative permeability, negative refractive index is obtained between 395 THz and 430 THz with the maximum FOM=4.59. The effective permeability exhibits a rapid convergence with increasing number of metamaterial layers. Different responses from the electric and magnetic resonances to the changing geometric parameters are compared and analyzed in terms of the field distribution. Simulation results show that the high order magnetic resonance can be greatly enhanced at visible frequencies as well as effectively tuned over a wide spectral range without notably altering the coupling between unit cells.
[Show abstract][Hide abstract] ABSTRACT: The influence of symmetry breaking in a planar metamaterial on transparency effect is numerically investigated. The planar metamaterial's cell is formed by three parallel metal wires. From numerical simulation results, we can see that the transparency effect results from the asymmetric coupling between the cut wires. The excited mechanism of the transparency effect is further analyzed by using the hybridization concept. It is found that the coupling fields between the cut wires play key roles and lead to the spectral splitting of the resonance, i.e., the classical electromagnetically induced transparency effect. The metamaterial sensor based on the refractive index variation of the surrounding material is also numerically demonstrated and yields a sensitivity of 9.47 mm/RIU and a figure of merit of 13.5. In addition, the spectral response of the metamaterial is quantitatively described via the "three-particle" model. The analytically calculated results of the model show a good agreement with the simulation results.
[Show abstract][Hide abstract] ABSTRACT: By introducing the frequency tuning sensitivity, an analytical model based on equivalent LC circuit is developed for the relative frequency tuning range of THz semiconductor split-ring resonator (SRR). And the model reveals that the relative tuning range is determined by the ratio of the kinetic inductance to the geometric inductance (RKG). The results show that under the same carrier density variation, a larger RKG results in a larger relative tuning range. Based on this model, a stacked SRR-dimer structure with larger RKG compared to the single SRR due to the inductive coupling is proposed, which improves the relative tuning range effectively. And the results obtained by the simple analytical model agree well with the numerical FDTD results. The presented analytical model is robust and can be used to analyze the relative frequency tuning of other tunable THz devices.
[Show abstract][Hide abstract] ABSTRACT: The couplings between single/dual split ring resonators (SRRs) and their mirror images in a rectangular waveguide are systematically investigated through theoretical analysis and experimental measurements. Such couplings can be manipulated mechanically by rotating the SRRs along a dielectric rod and/or shifting the SRRs up/down along the sidewall of the rectangular waveguide, resulting in shifts of the resonant frequencies and modulations of the resonant magnitudes. These controllable properties of SRRs pave the routers toward designing tunable band notch filters. In particular, it is experimentally demonstrated that the designed filters possess 7.5% tuning range in the X-band.
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