Design And Performance Analysis Of Terahertz Metasurface Absorber And Filter

In recent years,with the development of various optoelectronic technologies,such as photoconductive antenna,optical rectification,electro-optical sampling and other new technologies,especially the rapid development of ultrafast technology,it has provided great convenience for terahertz radiation and detection,making the research of terahertz(THz)technology and related devices gradually make remarkable progress.With the development of micro nano fabrication technology and integrated optical technology,the development direction of various photon devices will gradually move towards miniaturization and integration.Metasurface is a kind of artificial electromagnetic structure composed of subwavelength metal unit structure.Compared with natural materials,it has excellent features such as tunability,frequency selection,etc.,and it can realize functions that natural materials cannot achieve,such as negative refraction,electromagnetic invisibility,etc.More and more terahertz functional devices are designed for absorption,filtering,sensing,polarization and other aspects,which greatly promote the development of terahertz technology.Based on the theory of metasurface design,three kinds of metasurface functional devices,which can realize absorption,filtering and polarization filtering in terahertz band,are designed,and their performances are analyzed.Firstly,the theoretical basis and design method of metasurface design are studied.It includes the theoretical derivation of negative refractive index and negative permeability of the metasurface,and the absorption principle of the metasurface structure for terahertz electromagnetic wave.By analyzing its impedance matching,the condition that the absorption structure can achieve the absorption of electromagnetic wave intensity is obtained.Similarly,the principle of electromagnetically induced transparency(EIT)effect in atomic system is introduced,which can also be applied to the design of metasurface structure,and its principle is analyzed in the way of equivalent circuit.In this paper,the simulation design is based on CST Microwave Studio software,and its principle and operation are briefly introduced.Secondly,the design and analysis of terahertz metasurface broadband absorber are carried out.First of all,the design of resonant absorber based on a single square ring resonant.In order to increase its absorption spectrum segment,the concentric stack is used to design,not only the spectrum segment is widened,but also the absorption peak is increased.In the further optimization design,multiple structures of different sizes are spliced into "meta-element" form for design,and finally the design results of high efficiency absorption,low side lobe and simple structure in a wide range of spectrum are obtained.In addition,in the design process,the performance of each structure is analyzed,and its absorption principle and performance are described in detail.Thirdly,the terahertz metasurface narrowband filter is designed and analyzed.When designing the filter,we still start with the resonant absorber of a single square ring.In order to get a better filtering effect,we use EIT effect to destroy its rotationally symmetric structure,and introduce a long metal strip to form the bright dark mode resonance.On this basis,we optimize the design,and finally get the design results with good filtering effect in the narrow band.In addition,when the structure is immersed in a liquid with different refractive index,the change of resonance peak frequency is approximately linear with the refractive index of the materials to be measured,which shows that the structure has certain application ability in the sensor.Finally,the design and analysis of terahertz metasurface grid polarization filter are carried out.When designing the structure of the linear grid polarization filter,the first step is to start with the single-layer grid polarization filter,and focus on the influence of the change of the duty cycle of the grid on the polarization extinction ability.Considering the transmission performance and the processing difficulty,the next step is to use the duty cycle of 50%.In order to improve the polarization extinction ability of the grid polarization filter,another layer of metal grid is placed in parallel under the dielectric layer.The influence of the horizontal distance between the upper and lower layers of metal grid on the polarization extinction ability is mainly studied.Finally,a double-layer grid polarization filter with high polarization extinction ratio and high TM wave transmissivity is obtained.