Research On Electromagnetic Beam Steering Based On Zero Refractive Index Metamaterials

Metamaterials are artificial composite media that are periodically arranged and can induce special electromagnetic responses.It can break through the bottleneck of many theoretical phenomena,and has potential application prospects in the fields of physics,chemistry,quantum mechanics and other disciplines.The unique extraordinary physical properties of metamaterials can provide new ideas for the regulation of electromagnetic wave optical fields.Most of the initial research on metamaterials focused on left-handed materials.With the extensive attention of more researchers,zero-refractive-index metamaterials with zero equivalent refractive index have gradually attracted everyone’s attention.Because of the infinite phase velocity and wavelength,zero-refractive-index metamaterials have the characteristics of almost no phase delay after light passes through,and have application prospects in optical devices such as directional antennas,curved waveguides,and invisibility cloaks.This paper mainly focuses on how to realize more convenient and practical zero-refractive-index metamaterials and electromagnetic beam control.(1)A metamaterial superunit model is proposed,which realizes the near-zero characteristic of double-broadband refractive index.In the terahertz band,insufficient bandwidth and high loss severely limit the wide application of zero-refractive-index metamaterials.Therefore,a superunit structure composed of four subunits is proposed in this paper to improve the degree of control freedom.The double-sided coupling effect of double zero refractive index metamaterials is obtained by inversion of subelement structural parameters and surface current distribution.The resonance principle and the near-zero refractive index generation mechanism of the superelement model are discussed in detail.The superunit metamaterial can not only achieve the characteristics of double broadband near zero refractive index,the near zero refractive index bandwidth can reach 30 GHz,and the optical loss of the metamaterial is low.(2)A rectangular-column two-dimensional square lattice photonic crystal is proposed to realize zero-refractive-index metamaterials.In order to further reduce optical loss and improve transmittance and other issues,this paper uses photonic crystals to control extremely low loss and ultra-high transmittance.By analyzing the energy band structure of the photonic crystal structure and optimizing the lattice constant and side length of the rectangular column,the Dirac cone dispersion can appear in the center of the Brillouin zone.The optimally designed zero-refractive-index metamaterial structures are arranged into a lens pattern,and the electromagnetic field distribution characteristics of the metamaterial structures are numerically analyzed to verify the zero-phase change and focusing properties of our designed zero-refractive-index metamaterial concave lens.In order to take full advantage of the low-loss properties of metamaterials,a transmissive invisibility cloak was designed based on the optimally designed zero-refractive-index metamaterials.In order to further control the stealth device,based on the principle of transformation optics,a reflective carpet stealth cloak is proposed in this paper.By analyzing the amplitude distribution and phase distribution characteristics of the electromagnetic field of the cloak,it is confirmed that the designed stealth device has a good stealth effect.(3)A multi-band near-zero refractive index metamaterial constructed by dielectric spheres is proposed.Considering the problems of ohmic loss and low coupling efficiency of metal materials,three-dimensional dielectric spheres are used in this chapter to further realize near-zero refractive index.It is worth noting that most of the previous studies have focused on the near-zero refractive index of single-band or dual-band metamaterials,while there are very few three-band near zero.This paper proposes that the refractive index of metamaterials is close to zero in the three bands of 17.96-19.46 GHz,22.36-23.16 GHz and 23.68-24.32 GHz.The zero-refractive-index characteristic is verified by numerical analysis of the electric field and phase distribution in the three frequency bands.On this basis,in order to further verify the tunneling effect of metamaterials,a three-dimensional polarization-insensitive stealth cloak is designed,which achieves remarkable stealth properties in three bands.(4)An easy-to-fabricate "I"-type zero-refractive-index metamaterial is proposed.Based on the realization of zero-refractive-index metamaterials in the previous chapters,in addition to obtaining zero equivalent refractive index of metamaterials in the range of 0.33THz-0.4THz,and at 0.255 THz,the equivalent refractive index is as high as 13.8,providing greater the degree of freedom of electromagnetic wave regulation.Using classical lithography technology,a single-sided metal structure was experimentally processed,and the transmission properties of metamaterials were measured using a terahertz time-domain spectroscopy system.The experimental results are in good agreement with the simulation results.