Study On Terahertz Wave Lens Based On Gradient Phase Metasurface

Achieving control of electromagnetic waves has always been a hot research topic in the field of electromagnetism.Generally,phase accumulation on the propagation path is the main method.However,this method is complicated and inefficient to manipulate of electromagnetic waves due to the bulkiness volume and high loss of the material.The metasurface is a two-dimensional deriving from metamaterial.When the electromagnetic wave passes through the metasurface,a phase mutation is introduced to control the wavefront phase of the electromagnetic wave.The metasurface structure of sub-wavelength size enables electromagnetic wave reflection and refraction in a small size and a very thin thickness,breaking through the limitation of the volume of conventional materials.According to the different structures of the design,it is possible to control any electromagnetic wave.In this paper,the metasurface of several types of transmissive sub-wavelength periodic structures are designed according to the gradient phase theory to control the wavefront phase of terahertz waves to realize the artificial control of terahertz wave propagation.First,we obtained an array of v-shaped metal antenna structural units that can respond in the terahertz band by simulation.These elements have a torsional ability to the polarization of the incident terahertz wave.The cross-polarized transmitted wave and the incident terahertz wave have a geometric phase abrupt change(also called P-B phase).By artificial control,a discontinuous gradient phase can be formed,and the phase range can cover 0 to 2?.Secondly,according to Fermat's principle and gradient phase theory,three kinds of metalenses are designed by using a set of v-shaped metal antenna structural units designed above.The metal antenna structural units are placed according to different positional distributions to form different metasurface according to different functions.These three metasurface can be used to achieve lens functions such as abnormal refraction,line focus,and point focus.The super-surface of the sub-wavelengthperiodic structure designed in this paper can effectively control the propagation mode of terahertz waves and enrich the artificial control devices in the terahertz band.