The Design And Fabrication Of The Broadband High Refractive Index Metamaterials In The Terahertz Region

Metamaterials are a class of artificial composite materials which has subwavelength periodic structures.Due to they exhibit many unique properties that natural materials do not have,so they are of great research value and have attracted extensive research interests of many researchers.With the continuous improvement of terahertz sources and detectors in recent years,terahertz technology has developed unprecedentedly.In the past ten years,most of the researches on metamaterials concentrated on the negative refractive index materials(NIM),zero-refractive-index materials,and polarization converter etc.,but there are few studies about on high-refractive-index metamaterials.(1)One-dimensional metallic grating structure was proposed to realize high refractive index metamaterial in the terahertz region.By significantly increasing the effective permittivity of the material through strong capacitive coupling,and reduce the dimagnetic effect by using thin metal 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 broadband near zero refractive index metamaterial from 1.67 to 1.71 THz can be obtained by the introduction of double asymmetric design.(2)By drastically decreasing the diamagnetic effect with a thin window type structure in the unit cell and increasing the effective permittivity through strong capacitive coupling,we report a window-type broadband isotropic two-dimensional metamaterial with extremely high refractive index in the terahertz region.The effective electromagnetic parameters for the metamaterial were extracted by S-parameter extraction method.It is found that ultrahigh refractive index metamaterials depend on the electric field coupling effect,the magnetic field diamagnetic response,and the geometric parameters in the unit cell.The designedpeak index of refraction of near 18.22 at about 1.15 THz is predicted.From 1.09 THz to 1.29 THz,the refractive index exceeds 15 in the frequency band about 200 GHz.In addition,the window type broadband isotropic high refractive index metamaterial is also polarization-independent.(3)Combining the innovations of the structure which are designed in the previous two chapters,we designed a double-sided square broadband high refractive index metamaterial where form two resonance peaks,which the resonance at 1.12 THz is mainly caused by electrical response and magnetic response,high refractive index is as high as 38.68.And the bandwidth is 1.46 THz at the half width of the refractive index.Then the quality factor of the double-sided square metallic structure metamaterial was calculated,we found this high refractive index metamaterial maintain low loss characteristics in a wide frequency band.(4)To perform experimental verification we design a large-scale "window" type high refractive index metamaterial.We fabricated the "window" type high refractive index metamaterial device using laser exposure and wet etching.Then the terahertz time domain spectrometer was used to detect the performance of the processed samples,and we compared the simulation data with the results measured by spectrometer.These two results fit well.