The Design Of Smart Hyperbolic Metamaterials And Electrically Tunable Abnormal Optical Behavior

Metamaterials are artificial subwavelength-structured media that exhibit unusual electromagnetic, optical, acoustic properties. Hyperbolic metamaterial is one of the most unique metamaterials. One of the principal components of hyperbolic metamaterials' permittivity or permeability is opposite in sigh to the other two principal components, which results in hyperbolic equifrequency surface. This feature make hyperbolic metamaterials have many unique properties. In this paper, new type of hyperbolic metamaterials with electric field tenability is designed. We investigate the electric field tunable abnormal optical behavior. The main work and results in this paper are summarized as follows:1. We theoretically investigate optical refraction behavior in a fluid system which contains silica-coated gold nanorods dispersed in silicone oil under an external electricfield. Because of the formation of a chain-like or lattice-like structure of dispersed nanorods along the electric field, the fluid shows a hyperbolic equifrequency contour characteristic and, as a result, all-angle broadband optical negative refraction for transverse magnetic wave propagation can be realized. We calculate the effective permittivity tensor of the fluid and verify the analysis using finite element simulations. Investigate the relation of optical property of the fluid system and applied external electric field. The dependence of focus position of the fluid system on the external field strength has been studied. Similarly, the negative refractive index can vary with the electric field strength and external field distribution. Under a non-uniform external field, the gradient refraction behavior can be realized.2. We design an ultra-thin terahertz metamaterial absorber based on graphene/MgF2 multilayer stacking unit cells arrayed on an Au film plane and theoretically demonstrate a dual-band total absorption effect. Due to strong anisotropic permittivity, the graphene/MgF2 multilayer unit cells possess a hyperbolic dispersion. The strong electric and magnetic dipole resonances between unit cells make the impedance of the absorber match to that of the free space, which induces two total absorption peaks in terahertz range. These absorption peaks are insensitive to the polarization and nearly omnidirectional for the incident angle. But the absorption intensity and frequency depend on material and geometric parameters of the multilayer structure. The absorbed electromagnetic waves are finally converted into heat and, as a result, the absorber shows a good nanosecond photothermal effect.