Research On New Type Of Broadband Wave-transparent Material Technology

Radome is a multifunctional component with the characteristics of wave transmission,load bearing,heat insulation etc.With the rapid development of high speed flight vehicle,the demand of high temperature broadband transparent-wave radome materials is increasing day by day,the bandwidth of the wave transmission can be broaden by reducing material dielectric constant,low density porous silicon nitride ceramics broaden the bandwidth of the wave transmission by reducing density to get low dielectric constant,but the brittle problem of the ceramic material limits its application in engineering.To achieve research goal of the bandwidth of the wave transmission,solve the problem of porous ceramic brittleness,in this paper,from the two different way of thinking,broadband transparent-wave material is designed,preparated and researched:(1)with silicon nitride short fiber as main raw material,adopts the suction filter to suppress forming the preparation of porous silicon nitride short fiber material,study the dielectric properties and compression strength,obtains has good thermal shock resistance of low dielectric porous silicon nitride staple fiber materials.(2)the design and verification of electromagnetic microstructure are carried out for wideband wave transmission.The influence rules of the structure,size and matching relationship of the electromagnetic microstructure unit with the substrate on the wideband transmission performance are systematically studied.Two kinds of wideband transmission electromagnetic metamaterials are prepared with resin as the substrate,and their wideband transmission properties are theoretically verified.Porous silicon nitride short fibers are prepared by boron nitride as sintering additives at high temperature.The density of silicon nitride short fiber porous materials with a density of0.35~0.85 g/cm~3 is prepared by controlling the molding pressure,and the dielectric constant is within the range of 1.4~2.3,meeting the low dielectric constant requirements for wideband wave transmission design.The content of boron nitride additives,heat treatment system and body density to the influence law of the dielectric properties and compression strength of silicon nitride short fiber porous material are studied.With the increase of the content of boron nitride additives gradually forms a good connection between silicon nitride fiber each other,when the content of boron nitride more than 4 wt%,boron nitride distribution in silicon nitride fiber pore,unable to play a role of sintering additives.When the sintering temperature at1100℃~1500℃,the boron nitride sintering additives oxidation degree increasing,high temperature to form liquid phase to promote the connection between the silicon nitride fiber,but the silicon nitride fiber mechanical properties begin to decline at 1400℃,the silicon nitride fiber start crystallization at 1500℃.Therefore,1300℃is the best heat treatment temperature.When boron nitride additives content to 2 wt%,the sintering temperature is 1300℃,silicon nitride fiber form good combination.Density of 0.55 g/cm~3 material dielectric constant is 1.78,1200℃compression strength is 5.16 MPa,1400℃compression strength is 2.16 MPa.Short fiber porous silicon nitride material main failure mechanism is fiber fracture,macroscopic materials structure is not damage 5 times of thermal shock test after 1400℃.To the density of0.55 g/cm~3 material of broadband potter permeability and heat insulation performance theory predicts that in order to give attention to both heat insulation performance,using six order 51mm wall thickness design,under the condition of the design,material surface under the condition of temperature 1200℃,time of 1000 s back temperature is 71℃,meanwhile frequency bandwidth of the transmittance more than 70%is 5.5 GHz under the conditions of different angle of in 0~60°incidence.Quartz fiber/cyanate resin composite material(dielectric constant 3.3)is used as the base material to design a 5-layer structural metamaterial containing hexagonal gap electromagnetic element.The layer spacing of the electromagnetic element is 6.5mm and the total thickness of the material is 13.1mm.Calculation results show that:when the incident angle from 0°to 45°,the bandwidth of the transmittance more than 70%is 9.76 GHz,it has wide bandwidth and high broadband transmittance.The broadband transparent-wave electromagnetic metamaterial with400 mm*400 mm*13.1 mm is prepared,broadband transparent-wave properties are verified.The measured results show that when the incident angle from 0°to 45°,the bandwidth of the transmittance more than 70%is 7.99 GHz,which is consistent with the theoretical calculation results.