| Electromagnetic super-surfaces are planar artificial electromagnetic materials consisting of periodic or non-periodic arrangements of unitary structures of a specific geometry,which allow flexible modulation of electromagnetic waves through abrupt phase changes,equivalent reactance.The coding super-surfaces are “digital super-surfaces” based on binary digital logic,which can regulate electromagnetic waves through digital coding sequences,greatly simplifying the design process of the super-surface and improving the flexibility of regulating electromagnetic waves.In this theis,taking the coding super-surface as the research object and study its regulation of electromagnetic waves from theoretical analysis and numerical simulation as follows:(1)Reflective coding super-surface.A reflective coding unit based on a double-layer sector metal structure is designed,and eight coding units are obtained by controlling the angle and direction of the sector opening,which can achieve 360° phase coverage at 45° interval at1.5 THz frequency with high reflectivity at the same time.By arranging the coding units in different sequences,the desired beam separation or radar scattering cross section reduction can be achieved.In addition,this theis introduces graphene into the coding unit design and uses its variable conductivity property to achieve a 90° phase difference by changing the voltage,which is an attempt to the tunable coding unit design.(2)Dual-frequency point coding super-surface.A double-layer U-shaped open metal2-bit coding unit is designed.By adjusting the size and opening direction of the U-shaped open metal,the same unit structure has independent digital coding at two frequency points,and when different sequences of coding units are arranged,both can realize the independent regulation of electromagnetic waves at two frequency points by the coding super-surface,which expands the function of the coding super-surface.(3)Double-sided frequency-convertible point coding super-surface.In order to improve the freedom of beam modulation,a double-sided 3-bit dual-frequency coding super-surface is designed by changing the size and orientation of the U-shaped metal as the basic unit and using both positive and negative structures,and the effects of different coding sequences on the direction and number of electromagnetic waves at the two frequency points are discussed by numerical simulation combined with theoretical analysis. |
