Freely Manipulated Broadband Terahertz Electromagnetic Wave Scattering Properties Based On Encoding Metasurfaces

Metamaterials are artificial structures composed of periodic or nonperiodic subwavelength unit cells,which are a kind of equivalent material that is made by replacing elementary particles such as molecules and atoms of natural materials with ordered artificial "particles".This paper proposes a coded metasurfaces based on the concept of metamaterial that a new structure consisting of ultra-material structural elements based on Snell's law ultra-thin two-dimensional array plane,electromagnetic/optical by controlling wavefront phase,amplitude and polarization.The concept of encoding metasurfaces makes the connection between the physical metamaterial particles and the digital code,so the digital coding can be performed on the coding surface for signal processing to achieve unusual physical phenomena.In this paper,a complete 2? transmission phase with high efficiency at the target frequency can be manipulated by a multi-layer super-surface structure.By combining with Snell's theorem,far-field scattering principle,Fourier convolution principle and Pancharatnam-Berry(PB)theory,the omnidirectional control of the terahertz beam can be realized,and the preset deflection angle can be realized.First,flexible control of the deflection angle of the line polarization abnormality is realized.The 2-bit is used for X-direction coding,and different periodic sequences are designed to obtain the deflection angle.A new sequence is obtained by a four-bit operation according to the Fourier convolution principle.Different deflections of the transmitted beam are achieved.In addition,this paper also verifies the feasibility of circular polarization.Next,1-bit coding is used to encode the chessboard in the X direction,the Y direction and the square matrix,and at the same time control the azimuth and elevation of the transmitted beam and realize the separation of the main lobe,and combine the 2-bit sequence to perform the checkerboard coding in the general matrix form.Control the azimuth and elevation of the transmitted beam and control the number of main lobes.According to the PB theory,the coded metasurfaces is designed,and the unit structure is rotated and coded to realize the first-order and second-order vortex phase plates,and different order vortex beams are generated.This study shows that the 1-bit different coding modes can effectively control the transmission direction and effectively reduce the side lobes.In 2-bit coding,Fourier convolution provides an efficient method of optimizing the coding to achieve a predesigned transmit beam.This method is superior to previous solutions in its ability to generate anomalous beam transmissions with flexibility and continuous control in any direction.In addition,the rotational coding of the unit structure can produce a vortex beam.