The Research Of Terahertz Quarter Wave Plate Based On Metamaterials

Terahertz(THz)waves are electromagnetic waves between 0.1 and 10 THz.THz technology has become a hot spot in global scientific research.Terahertz quarter wave plate is a polarization conversion device that can achieve the mutual conversion of linearly polarized waves and circularly polarized waves at terahertz band.Metamaterial is a subwavelength periodic artificial composite structure with extraordinary physical properties which are not found in natural materials.Metamaterials can achieve special functions such as electromagnetic induced transparency(EIT),slow light effect,and electromagnetic absorption,and have important development potential in the fields of medicine and health,aerospace and defense and military.The research,design and analysis of terahertz quarter wave plates based on metamaterials have important theoretical research value and practical significance.Firstly,this dissertation expounds the research background of terahertz quarter wave plates and the current research status at home and abroad,and analyzes and discusses the existing problems of existing terahertz quarter wave plates.Secondly,using the equivalent medium theory,equivalent circuit theory,and symmetry analysis theory to study the electromagnetic properties of metamaterials.The working principle of quarter wave plate is analyzed by electromagnetic wave polarization theory,and the design method of transmission quarter wave plate based on metamaterials structure is proposed.Then,according to the proposed design method,a terahertz quarter wave plate based on a single split ring resonator is presented,and its relative operating bandwidth(axial ratio is less than 3d B and polarization conversion efficiency is greater than 50%)is 16.8%;Based on the split ring resonator structure,three improved terahertz quarter wave plates were proposed,including a double split ring resonator structure,an "split ring resonator meanderline " structure,and "split ring resonator cross shape" structure,its relative operating bandwidth is 28.6%,42.4%,and 28.0%,and its maximum(minimum)polarization conversion efficiency is 88.7%(64.2%),82.8%(50.0%),and 86.6%(50.0%).The effects of the change of the main geometric parameters of the metamaterial structure on the device performance are discussed.Finally,two terahertz quarter wave plates with better simulation performance were processed and tested,and then the test results of the samples were compared with the simulation design results to analyze the reasons for the errors.The terahertz quarter wave plate designed in this work has the advantages of large axial ratio bandwidth and high polarization conversion efficiency.It has important potential application value in the fields of terahertz communication and terahertz sensing.