Structural manipulation of electromagnetic absorption properties of subwavelength metallic elements

Abstract

We present a design of metamaterial absorber and analyze mechanism of the proposed structures. Metamaterials can achieve the exotic relative electric permittivity and magnetic permeability which does not exist in nature. Thus, we focus on tuning the permittivity and permeability of metamaterials by varying the geometrical parameters and materials consisting the unit cell. High loss terms and impedance matching condition determined by permittivity and permeability of metamaterials should be attained for high absorption. For simultaneously satisfying the high loss terms such as imaginary part of permittivity and permeability and impedance matching condition, two kinds of the metamaterials were studied in microwave regime for increasing both permittivity and permeability. First, overlap capacitor structures for enhancement of permittivity by dipole enhancement. Second, 3-dimensional LC resonator structures for enhancement of permeability by magnetic resonances and this is determined by the equivalent circuit model. Transmission and reflection of these meteamaterials were calculated by the finite difference time domain (FDTD) method and the effective properties of the proposed structure were retrieved from the results by the transfer matrix method. Additionally, we also studied about absorption properties in visible regime through the metallic nano ring structure. In this structure, absorption at specific wavelength explained by plasmon response was observed. Here, absorption properties of the proposed structures were analyzed by the hybridization modes of plasmon responses calculated from FDTD method.