| With the rapid development of the new generation of 5G technology,non-communication,industrial production and daily life are inseparable from the application of electromagnetic wave.In many important places,it does not interfere with the normal operation of other equipment,while preventing the external electromagnetic field from having uncontrollable adverse effects on the core equipment and causing huge economic losses,which cannot be separated from the protection of electromagnetic shielding materials.Compared with the shields made of highly conductive and high-density metal materials,conductive polymer electromagnetic shielding materials have become the research focus of incoming magnetic protection technology in recent years because of their comprehensive advantages such as light weight,easy processing and adjustable performance.Carbon fiber,a carbon material,is widely used as electromagnetic shielding composites because of its light weight,high strength,strong thermal conductivity and adjustable resistance.The high conductivity of carbon fiber causes a serious impedance mismatch between the fiber surface and the environment,and electromagnetic waves are reflected when passing through the fiber surface,resulting in secondary pollution of electromagnetic waves.At present,most researches on the structure control of carbon fiber ensure that electromagnetic shielding composites have high efficiency and reliability and meet the requirements of low reflection characteristics.The electromagnetic shielding material based on the gradient conductive structure is essentially a dual-function structure composed of adding an impedance matching absorption layer on the surface of the conductive reflective layer.The two synergies improve the impedance mismatch between carbon fiber and the environment and regulate the reflection characteristics.Compared with other complex simulation models,using numerical calculation method to simulate the electromagnetic shielding performance of multi-layer structures can save a lot of manpower and material resources,and provide a basis for shortening the test period and guiding the experimental results.This paper mainly focuses on the efficient simplified numerical model of the multi-layer heterogeneous structure to reduce the secondary reflection of electromagnetic wave on the surface of carbon fiber as the starting point.In view of the current means to optimize the reflectance of the surface of composite materials,further study the calculation method of the electromagnetic shielding performance of multi-layer fiber epoxy resin composite materials.A simplified calculation model for the electromagnetic shielding performance of multilayer structures is proposed based on the basic electromagnetic parameters of single-layer materials,and the rationality and effectiveness of the model are discussed,which provides a research basis for guiding the experimental design of the electromagnetic shielding performance of composite materials.Relevant research contents are as follows.(1)The SE_Avalue and RL value are obtained by combining the empirical calculation formula of electromagnetic shielding performance and the normalized input impedance equation.The simplified method of electromagnetic power parameters of single-layer composite materials and the calculation method of electromagnetic shielding performance of three-layer and 12-layer composite materials by using the electromagnetic parameters of single-layer materials are described.The electromagnetic parameters(surface conductor layer)of fibers with different properties were designed and the anisotropic fiber reinforced epoxy electromagnetic shielding composites were prepared by the mixed layering method.A,R and T of three kinds of fibers were simplified,and a method for calculating electromagnetic shielding properties of three-layer fiber reinforced epoxy resin composites was proposed based on the electromagnetic wave propagation model of multilayer structure.When the number of material layers is 4,some adjustments are made according to the simplification of A,R and T of 4CF/EP,4AF/EP,4r GO@AF/EP,and a simplified model is summarized to calculate the electromagnetic shielding performance of 12 layers of composite materials with different arrangements.(2)The preparation process of the progressive conductive gradient structure of"wave-absorption-reflection"is described,and its basic electromagnetic parameters,power parameters and electromagnetic shielding performance are discussed in depth.At the same time,the electromagnetic power parameters and electromagnetic shielding performance of multilayer composite materials are calculated by using the simplified method in the previous work,and the rationality and reliability of the structure are verified.r GO@AF/EP was prepared by multiple soaking method,and it was used as the absorbing layer and AF(wave penetration layer)and CF(reflection layer)were hot-pressed according to different layering sequences.Single layer,three layer and twelve layer fiber reinforced epoxy composite materials were prepared,and their electromagnetic shielding properties and basic electromagnetic parameters were tested.By introducing progressive conductive gradient structure,the surface reflectance of carbon fiber can be controlled preliminarily.Increasing the thickness of the transmittance layer and the dielectric layer has a more obvious regulating effect on reducing the surface reflection of carbon fiber and prolongs the transmission path of electromagnetic wave.In addition,A,R and T of single-layer AF,r GO@AF and CF were extracted and optimized by limiting certain conditions.The electromagnetic shielding properties of three-layer and twelve-layer fiber reinforced epoxy resin composites were calculated,and the error rates of the simplified model were all small.The simplified model can accurately calculate the electromagnetic shielding properties of multi-layer progressive conductive infrastructure composites.(3)The possibility and applicability of the simplified model in Chapter 2 to calculate the electromagnetic shielding performance of special structures are further discussed from the perspective of cell stacking and layering.Through the combination of AF and CF or r GO@AF and CF,based on the structure of arar,raar and arra,and using the experimental method in Chapter 3,composite materials with symmetrical stacked structure of units are prepared.By comparing the electromagnetic shielding characteristics of different structures,the influences of different stacked structure of units and different angles on EMI SE are discussed in depth.The special structure of arar,raar and arra and the difference of Angle change in the process of electromagnetic wave loss are expounded.At the same time,the electromagnetic shielding performance of several structures is calculated by using the simplified model,and the applicability of the simplified model to the stacked structures is discussed by comparing with the experimental results. |
PDF Full Text Request