Research On Filtering Principle Of Infrared Dual-bandpass Frequency Selective Surface

Electromagnetic interference shielding on the optical windows is an important technique in fields such as Precision photoelectric detection equipment,space detection equipment and wireless communication equipment use.Electromagnetic interference and microwave weapons in space can make the aircraft "blind" and make it ineffective.Microwaves generated during the operation of certain microwave devices can also cause harm to the human body.Frequency selection surface technology is the best way to solve this problem.But the frequency selection surface currently used in the infrared band cannot meet the shielding requirements in multiband infrared photodetector.Therefore,a new type of dual-infrared bandpass frequency selective surface with strong electromagnetic shielding efficiency is of great significance to China's national defense and other fields.Therefore,this paper presents a new type of frequency selective surface structure based on the research of the bandpass frequency selective surface filtering mechanism and the design method of multi-period mixing,and carries out in-depth theory of its infrared filtering characteristics and electromagnetic shielding characteristics,and the main investigation work and achievements are described as follows:1.The effects of various size parameters on the infrared transmission characteristics of circular aperture and annular aperture frequency selection surface were analyzed.Based on the requirements of the research on the infrared transmission characteristics of the frequency selective surface,a theoretical analysis model was established using the finite-difference time-domain method.The influence of the size parameters of the circular aperture frequency selection surface and the circular aperture frequency selection surface on the infrared transmission characteristics is studied in depth using a frequency selective surface analysis model.2.A novel frequency selective surface structure was designed and verified to have dual-bandpass frequency selective characteristics in the infrared band.In order to solve the problem that the frequency selective surface has both dual-bandpass frequency selective characteristics in the infrared band and strong electromagnetic shielding characteristics,a new type of frequency selective surface structure is proposed,and the dual-bandpass frequency selective characteristics in the infrared band of the structure are analyzed by finite-difference time-domain method.3.An equivalent circuit model of a dual-bandpass frequency selective surface was established.The model was used to analyze the electromagnetic shielding effectiveness of the design frequency selection surface at the Ku band.The Langley equivalent circuit model is improved.Based on the improved Langley equivalent circuit model and the Parisa equivalent circuit model,an equivalent circuit model of the dual-infrared bandpass frequency selective surface is established.The frequency of this design is calculated by the model.The electromagnetic shielding efficiency curve of the surface is selected in Ku band,and the influence of dimensional parameters such as the outer diameter of the ring and the inner diameter of the ring on the surface structure of the frequency selected in this paper is analyzed in depth at the Ku band.4.The dual-band infrared bandpass frequency selective surface samples were processed,and verify its strong electromagnetic shielding characteristics and dualbandpass frequency selective characteristics.Using the vector network analyzer and Fourier spectrum analyzer to test the electromagnetic shielding characteristics and infrared transmission characteristics of the sample,the test results show that the Kuband electromagnetic shielding performance of the sample is better than 38 dB,and there are two passbands in the infrared band.The resonant wavelengths are 2.66?m and 17.82?m,and the transmittances are 67.07% and 64.67%.In conclusion,the dual-infrared bandpass frequency selection surface designed in this paper has both strong electromagnetic shielding efficiency and dual infrared bandpass filtering.