Terahertz multiband ultrahigh index metamaterials by bilayer metallic grating structure

One-dimensional metallic grating structure was proposed to realize high refractive index metamaterial in the terahertz region. By drastically increasing the effective permittivity by means of intense capacitive coupling and reducing the diamagnetic effect using a thin metallic thickness, a peak refractive index of 15.81 at the resonant frequency in embedded metallic grating can be obtained. Multiband high refractive index metamaterial can be realized by double symmetric metallic grating and asymmetric grating structure. For asymmetric grating metamaterial structure, two separate transmission peaks appear and result in two separate high refractive index. Interestingly, a near zero refractive index metamaterial can be obtained by the introduction of double asymmetric design. It was found that our designed ultrahigh refractive index metamaterials depend on the electric field coupling effect and the magnetic field diamagnetic response.