| Frequency selective surface(FSS)radome is the core equipment of highspeed aircraft communication and navigation with the characteristics of wave penetration within the working frequency band and stealth outside the working frequency band,which can effectively enhance the stealth penetration capability of the aircraft in complex electromagnetic environments.Traditional resin-based FSS has the disadvantages of low-temperature resistance(< 300 ℃),poor adhesion with the radome,and complex forming process,which is difficult to meet the requirements of the new ultra-high-speed aircraft(> 500 ℃),thus heavily restricting the development of strategic weapons and equipment.The rapid and efficient preparation of the FSS radome,the improvement of high-temperature resistance,and the shortening of the equipment production cycle are the keys to improve the comprehensive performance of the new generation of high-speed aircraft.With the advantages of convenient molding and high precision,3D printing technology is particularly suitable for the molding of high precision and cross-scale complex FSS structures,making the realization of high temperatureresistant ceramic-based FSS possible.Based on the application of high-speed missile stealth radome,a new type of high-temperature-resistant ceramic-based FSS was prepared through direct ink writing(DIW)3D printing technology in this paper.The required conductivity of FSS conductive ink and the effects of unit modeling characteristics on the electromagnetic transmission characteristics of FSS were calculated by electromagnetic simulation.The conductive ink was prepared based on the calculated results,and their rheological properties,mechanism of modeling structural control and microstructural control,the interfacial characterization with the ceramic basement were studied so that the optimization of conductive ink and the accurate 3D printing of FSS was realized.Finally,the high-temperature resistance FSS was 3D printed using the optimized ink,and the designed electromagnetic performance and high-temperature characteristics were verified.The results show that FSS composed of symmetrical Jerusalem cross-slot unit still has good filtering characteristics for obliquely incident electromagnetic waves.the dielectric properties of the material and the unit gap size are closely related to the resonant frequency,passband bandwidth,and transmittance of FSS.The higher the unit conductivity,the higher the passband transmittance of the FSS electromagnetic wave.The modeling error will lead to the fluctuation of the resonant frequency.The size of dipole width at both ends of the FSS unit is the most sensitive to the passband frequency of the FSS: a size error of 1 mm will bring about a resonant frequency offset of 35.9 GHz.The sensitivity of each structural feature of FSS to the size error of resonant frequency is as follows: slot width L3(35.9 GHz/mm)> cross width L2(23 GHz/mm)> dipole length L4(12.83GHz/mm)> unit thickness h(10 GHz/mm)>cross length L1(5.8 GHz/mm)> unit perimeter d(0.64 GHz/mm).The static viscosity and the modulus of GO water base slurry can be improved by decreasing the space between each nano GO flake and increasing their interaction force.Due to the differences in surface functional groups ratio,the GO with a large diameter can increase interaction force between GO flake and improve the static viscosity and the printing accuracy of the ink without increasing the solid content.The employment of constraints can improve the microstructure of printed GO by controlling the capillary force,and realize its high orientation distribution.The higher the orientation degree is,the higher the conductivity of GO after reduction is.The contact resistance between layers can be reduced by large-size GO,increasing the conductivity of graphene to 9053.32 S/m.For the graphene-silver ink,the addition of graphene avoids the free movement of solid particles,and improves the static viscosity of the ink.The 5.5wt.% graphenes can form a connected 3D network and modified the fluid characteristic from fit the Carreau-Yasudo model to fit the Cross model,and based on which,the high-precision 3D printing was realized.In the sintering process,the addition of graphene powder will decrease the interlayer bonding between conductive ink and ceramic,and increase the structural shrinkage consistency.And the addition of glass powder can increase the interlayer bonding,to avoid the separation between conductive ink and ceramic.According to the regulatio of graphene,glass,and the temperature higher than 800 ℃,the electromagnetic performance matching between the designed model and the printed physical FSS device was perfectly achieved.Based on the well control of molding structure and the microstructure of conductive ink.the 3D printed ceramic-based FSS structure has typical characteristics of in-band transparency and out-band stealth,and the design electromagnetic property and high-temperature characteristics are highly matched with the measured FSS.The electromagnetic transmittance of the 3D printed FSS was higher than 90% when the frequency is from14.4 GHz to 15.4 GHz,while it was less than 30% when the frequency is under 13.6 GHz,and its working temperature was higher than 800 ℃.With 3 wt.% glass powders,the thermal straining of FSS was negative,thus effectivity decreasing the deformation of FSS,the thermal stress between layers,and the deviation of electromagnetic wave transmittance and bandwidth of FSS at high temperatures,and increase the working temperature of FSS from 400 ℃ to above 800 ℃. |
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