| In recent years,research on metamaterials has emerged in an endless stream.With the increase of working frequency and improvement of preparation process,infrared metamaterials can be studied and verified through simulation and experiment.Flexible structural design and adjustable electromagnetic parameters make it a promising application in the fields of thermal radiation control,sensors and detection.The electromagnetic resonance modes such as magnetic polariton,standing wave and ENZ mode existing in micro-nano structure are analyzed systematically and the coupling between different modes is studied.Based on this,the design of infrared broadband absorbers is guided.The main research work and innovations of this paper are as follows:（1）An infrared square grating structure capable of simultaneously exciting the magnetic polariton mode,the standing wave mode and its symmetric standing wave mode is designed based on the Si-TiN standing wave structure.The reflection phase difference in the standing wave formula in the reflection phase shift phenomenon at the Si/Metal interface is corrected by the Fresnel reflection coefficient formula.The MgF2film is introduced into the structure to control the magnetic polariton mode and the standing wave mode.The final simulation and experimental results show that the designed infrared square grating structure has quasi-continuous broadband absorbing effect in 58μm.The experimental results show that the bandwidth of 80%absorptivity is 2.19μm,and the absorptivity can be reached 99%at 6μm.（2）The effect of the surface grating pattern on the standing wave mode is studied.The grating not only affects the spatial distribution of the standing wave mode electric field,but also results in a symmetric standing wave mode,and the resonant frequency of the symmetric standing wave mode can be controlled by the grating size.Based on this,a gradual grating structure based on symmetric standing wave mode is designed and verified by simulation.The results show that the designed structure has broadband absorbing in 58μm,the bandwidth of 70%absorptivity can reach 2.51μm,and the highest absorptivity at 6.428μm is 90%.（3）The electromagnetic properties and excitation methods of the ENZ（epsilon near zero）mode in the SiO2-Al multilayer structure are studied in depth The results show that the existence of the electric field component perpendicular to the SiO2 film is the key to exciting the ENZ mode,and the excited ENZ mode has significant sub-wavelength binding effect and field localization effect.Based on the above analysis,an infrared square grating structure was designed.The magnetic polariton mode in the structure was used to excite the ENZ mode of SiO2 film.The ENZ mode was excited by the normal incident electromagnetic wave.（4）The effects of different structural parameters on the coupling phenomenon of ENZ mode and magnetic polariton mode are studied by simulation.It is found that the field strength of magnetic polariton can be effectively enhanced by ENZ mode and the best absorption can be obtained only when the two electromagnetic resonance modes are at the edge of the strong and weak coupling state.The coupling effect of the magnetic polariton mode and the ENZ mode is adjusted by introducing double-layer ENZ material into the square grating structure.The final simulation results show that the structure has continuous ultra-wideband absorption in the 716μm,the bandwidth greater than 80%absorptivity is as high as 6.13μm,and the highest absorption at 9.1μm is over 99%. |
