Study On Active Control Technology Of FSS Using Photoconductive Thin Film

As an important component in the field of electromagnetic shielding,FSS has higher requirements for its accuracy and function.Considering the practicality,using photoconductive film in FSS is proposed in this thesis,which realizes the optical active control of FSS,the designs and fabrications of its unit structure,that it can be applied to not only the situations of radomes and aircraft skins,etc.,but also the optical window with higher requirements for light transmittance.According to the theoretical knowledge,the relationship between unit structure and electromagnetic properties of FSS is analyzed in the thesis.Applying the photoconductive film to the metal FSS is proposed by comparing the advantages and disadvantages of several active FSSs such as loading electronic control components,coupling type and loading electromagnetic variable media.In addition,the feasibility of the technical scheme is discussed from the aspects of theory and structure.The CST electromagnetic simulation software is used to design and simulate FSSs’structures in different shapes,such as"cross dipole","tripole",and"circle",etc..The results of electromagnetic simulation are caused by the variance of the feature size:（1）"cross dipole":With the length as variable,the central resonance frequency is changed from 25GHz to 29GHz.（2）"tripole":With the length as variable,the central resonance frequency is changed from 17GHz to 18GHz/21GHz.（3）"circle":With the radius as variable,the central resonance frequency is changed from 36GHz to 39.5GHz/41GHz.In the experiment,by analyzing and selecting the photoconductive thin film materials and doping elements,CdS and CdSe are determined as the main materials of thin film,and CdCl₂,InCl₃,CuCl₂ are the mixed materials.Through a large number of experiments,it demonstrates that the best effect is when the ratio between CdS and CdSe is 1:1 to 5:1,and for CdCl₂,InCl₃,and CuCl₂ is 3.6:2.6:1.3.Electron beam evaporation technology and ion infiltration method are used to complete the preparation and doping of photoconductive thin films.Combining with photolithography and etching technology,the optically controlled FSS of"cross dipole","tripole"and"circle"samples are fabricated.By testing the contour size,illumination frequency,illumination power,and shielding effect respectively,it shows that with the condition of the best illumination power in 200mW/cm² and illumination frequency in 0.6μm,the central resonance frequency of"cross dipole"type changes from24.5GHz to 28.5GHz,the"tripole"changes from 16.8GHz to 20.9GHz,and the"circle"changes from 35GHz to 42GHz.It is basically consistent with the results of simulation,which verifies the feasibility of the photoconductive thin film for active control of the FSS.