Lattice density effect on the negative refractive index of a uniaxial metamaterial
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1223-EE02-05
Lattice density effect on the negative refractive index of a uniaxial metamaterial Claudio Amabile1 and Enrico Prati1 1 Laboratorio Nazionale Materiali e Dispositivi per la Microelettronica, Istituto Nazionale per la Fisica della Materia, Via Olivetti 2, I-20041 Agrate Brianza, Italy ABSTRACT Negative refractive index materials tuned at n = -1 are believed to realize perfect lensing of real and evanescent modes. Metamaterials are the natural candidates to realize negative refractive index by the inversion of the effective dielectric permittiviy and magnetic permeability. The effect of the density on the tuning in the proximity of n = -1 is studied in order to find viable solutions to the issue of discretization of the lattice which correspondingly produces steps in the electromagnetic parameters of metamaterials. We study the microwave frequency negative refractive index of a metamaterial as a function of the density of the lattice period. The negative refractive index is realized by means of a waveguide filled with a split ring resonator lattice, exploited below the cut off frequency of the waveguide. We discuss the passband behaviour and the collective effects on the negative refractive index. INTRODUCTION The lattice density effect on the negative refractive index of a metamaterial is experimentally investigated in the proximity of n = -1, in a range where perfect lenses which include evanescent modes are predicted. Such a value permits it to realize superlensing, for which resolution is not restricted by the diffraction limit.[1-4] The negative refractive index has been realized by means of a uniaxial metamaterial. Classical dielectrics theory predicts that macroscopic constitutive constants depend on both the features of the elementary cell - the single resonator in the case of a metamaterial - and their density. The dependence on the lattice density of negative refractive index materials has been only partially investigated in metamaterials.[5-9] The split ring resonator (SRR) based metamaterials have been solved analytically by some authors.[11-12] The effects of density on the effective refractive index are carried in a SRR based metamaterials. The negative permeability is realized by means of split ring resonators while the negative effective permittivity is provided by a sub cut-off square waveguide. A sub cut-off band is realized in the range where both the effective constitutive constants relevant for the propagation are negative.[13] The resonance frequency of the effective medium depends only on the single resonator properties, while the bandwidth depends on the density. We provide the dependence of the negative refractive index of the effective medium on the lattice density, as a function of the microwave frequency. We find a threshold density below which the pass band behavior disappears. The paper is organized in three sections: in the first short section the theoretical framework of uniaxial metamaterial rectangular waveguides is recalled; in the second the experimental results are sh
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