Research On Terahertz Near-zero Refractive Index Metamaterials

Metamaterial is a kind of artificial composite material with periodic unit structure.Through designing the structural unit's size and shape,it has singular electromagnetic properties and hence has a wide range of applications in the fields of electromagnetics,optics and materials science.The research of early metamaterials mainly focuses on the negative value of the intrinsic parameters like the refractive index,permittivity and permeability.With scientific explorations into depth,the research on the metamaterials with near-zero parameters gradually attracts scientists' attention.According to the relationship between refractive index,permittivity and permeability,it can be seen that the near-zero refractive index can be achieved by near-zero permittivity or permeability.In this paper,we focus on the research and design of near-zero permeability metamaterials and near-zero refractive index metamaterials in the terahertz band.The main contents are as follows:(1)We proposed a metal-dielectric composite structure with near-zero permeability at terahertz frequency.The terahertz wave is incident perpendicular to the surface of the metamaterial.When the electric field is TM polarization,the optimal value of ?-near-zero is 0 near the resonance frequency of 1.44 THz,and the bandwidth(|?|<0.05)is about 0.2 THz.When the electric field is TE polarization,the optimal value of ?-near-zero is 0 near the resonance frequency of 0.978 THz,and the bandwidth(|?|<0.05)is about 0.1 THz.It can be concluded that the metamaterial with geometric parameters fixed,the ?-near-zero effect can be achieved in different frequency bands by changing the polarization direction.The effect of the thickness d of the polyimide,the layers of metal and the angle of incidence was numerically analyzed.Furthermore,the tolerance error of the structure was also discussed and the performance was compared with the previous studies.The proposed ?-near-zero metamaterial has a wide range of applications in terahertz devices such as sensors,modulators and filters.(2)We proposed a kind of near-zero refractive index terahertz metamaterial based on a standing SRR structure.The terahertz wave is incident perpendicular to the surface of the metamaterial.The electric field is in the TM polarization.The near-zero(n<0.15)bandwidth is approximately 0.125 THz,and the minimum refractive index is 0.13.The influence of substrate thickness,height of SRR ring,length of metal arm of SRR and angle of incidence on the near-zero refractive index was analyzed.The tolerance error range of this structure was discussed and the performance was compared with the previous studies.The near-zero refractive index metamaterials with a vertical structure have a wide range of applications in the sensor.