Research On Multifunctional Metasurface Beam Control Based On Digital Coding

A metamaterial is an artificial material that is usually composed of periodic arrangements of subwavelength unit structures with specific geometries.A metasurface refers to an artificial layered material with a thickness smaller than a wavelength.Metasurfaces can be thought of as metamaterials in two-dimensional form.Metasurfaces can realize flexible and effective regulation of electromagnetic wave polarization,amplitude,phase,polarization mode,propagation mode and other characteristics.Coding metasurfaces are the bridge between the physical unit structure and the world of digital information.This paper utilizes generalized Snell’s law,farfield scattering theory,Fourier convolution principle and Pancharatnam-Berry(PB)phase to realize the free regulation of digitally encoded metasurface electromagnetic beams.The main contents of the paper are as follows:(1)In order to reduce the ohmic loss of metal materials,this paper adopts an alldielectric material unit structure to construct a 2-bit encoding metasurface.First,based on the generalized Snell’s law,a basic sequence of digitally encoded metasurfaces is designed to realize anomalous deflection properties of transmitted beams.Due to the limitation of the number of cycles,the abnormal deflection angle can only be controlled discretely.In order to improve this defect,based on the Fourier convolution principle in digital signal processing,this paper performs Fourier addition and subtraction operations on the digital coding unit structure to obtain a new class of coding sequences.Make the transmitted beam realize continuous multi-angle deflection.In this paper,the all-dielectric unit structure is further utilized to construct a digital coding sequence in the form of checkerboard coding and mixed gradient form,and combined with the principle of Fourier convolution,the multi-functional beam splitting regulation of transmitted waves is realized.(2)Based on the Pancharatnam-Berry(PB)geometric phase principle,an alldielectric 3-bit coding unit structure is designed.Using the optimally designed coding unit,a digital coding metasurface is constructed.In this paper,the principle of digital code addition is introduced into the metasurface encoding sequence,and a multifunctional digital addition code metasurface sequence is constructed.For example,a metasurface sequence that undergoes digitally coded addition operations produces beam superposition properties in two independent directions.(3)In order to realize the independent regulation of the amplitude and phase of the incident beam,an all-dielectric double-sided encoding unit structure is proposed in this paper.By independently adjusting the geometric parameters of the bifacial structure,the amplitude and phase of the incident beam can be independently regulated.The optimally designed coding structural units are regularly arranged to construct a double-sided coding metasurface.By independently controlling the amplitude and phase of the incident beam,the scattering angle and amplitude of the beam can be precisely controlled.The independent modulation of amplitude and phase provides a higher degree of freedom for the design of multifunctional encoded metasurface devices.(4)This paper further proposes a C-type bilayer cell structure to construct an encoding metasurface.By adjusting the opening angle and rotation angle,the amplitude and phase of the incident beam can be independently regulated.Using classical photolithography techniques,micron-scale metasurface samples were prepared.The transmittance of the samples was tested using a terahertz time-domain spectrometer built in the laboratory.The theoretical simulation results are basically consistent with the experimental test results,which verifies the accuracy of the theoretical design.