Generally, conductive fibers, resins, and lossy media are mixed uniformly and directly hot-pressed or sprayed. In a single-layer coating structure, the fiber content and arrangement direction have an impact on the dielectric properties of the composite laminate: the fiber and the direction of the applied electric field are sandwiched. The greater the angle, the higher the electrical breakdown strength of the laminate; the increase in fiber content, the lower the dielectric properties of the unidirectional fiber composite laminate. The single-layer wave-absorbing coating made of ferrite (sintered body), phenolic resin, and steel wire has been put into research and development. After mixing ferrite powder, polyethylene resin powder and short steel wire, it is mixed in organic solvent xylene. Medium dispersion, wave absorbing materials made by pressure, etc. However, the single-layer coating has a narrow absorption band, which cannot meet the requirements of stealth for light weight and broadband. The development of double-layer and multi-layer coating structures can meet the above requirements.
The first absorbing material RAM is a single layer. Absorbing materials are not only used in penetration technology, but developed countries are required to be coated with absorbing materials on high-rise buildings, bridges, iron towers, ships, etc. in order to eliminate clutter interference. For example, ferrite (sintered body) 10%~80%, phenolic resin 5%~80%, steel wire diameter 10~100m, length 1~5mm, form a single-layer absorbing coating, the characteristics of this absorbing material are The requirements for steel wire are given.
Using ferrite powder 56% (mass fraction), polyethylene resin powder 24% (mass fraction), short steel wire 20% (mass fraction), after mixing, dispersed in organic solvent xylene, made into a width of 200mm thick The 3mm blank board is heated on a roller at 250°C with a pressure of 1.96MPa, which can be made into a wave absorbing material of 200mm200mm×2.8mm. Domestic scholars have carried out research on the influence of fiber content and arrangement direction in composite materials on the dielectric properties of unidirectional glass fiber/epoxy composite laminates. The results show that the change of the direction of the fiber and the applied electric field will result in a great change in the electrical breakdown strength of the composite laminate. The larger the angle, the higher the electrical breakdown strength of the laminate; the increase in fiber content, the unidirectional fiber composite laminate The dielectric performance is reduced.
Radio wave absorbers have the same importance as heat insulation materials and stealth materials for emerging buildings. Some patents report that ferrite powder, synthetic resin and fiber are mixed in a certain proportion and become a paste. Painted on the spring metal mesh placed on the base material, its absorbing reflection attenuation is 14dB, and the bandwidth is It is 813GH1z. Ferrite powder is mixed with carbon black and then bonded with synthetic resin. There is a special molding machine that can be mass-produced. The wave-absorbing performance becomes worse above 8GHz, and the general reflection coefficient is 0.1.
Using neoprene "concrete" manufacturing method, it can absorb radar waves at 7.5GHz. This "concrete" includes 150 parts of neoprene, 3 parts of phenyl-}naphthylamine, 7.5 parts of zinc oxide, 6 parts of calcined magnesium oxide, 0.75 parts of stearic acid, 84 parts of semi-reinforced carbon black, and 494 parts of xylene. First mix phenyl B naphthylamine, magnesium oxide, zinc oxide and carbon black in a closed mixer (Banbury mixer) at 43°C for 3 minutes, then cool to 35°C and add neoprene . After that, the temperature was raised to 88°C within 7 minutes and mixed at 88-93°C. Put the obtained mixture into a roller and add zinc oxide at room temperature. Put the mixture in a paddle stirrer and add 1/2 xylene to continuously stir for more than 5.5 hours. The obtained mixture will contain 33.7% (mass fraction) of solids. The "concrete" is filtered to remove insoluble clots. Mix 171 parts (mass) of this "concrete" containing 33.7% solids with 12.6 parts of graphite and 42 parts of toluene (the mixture is dried in a closed container for 16 hours), and then the mixture is coated on a glass plate or rubber plate (pre-covered) There is a polyethylene film of 0.025mm), dried at room temperature for 30 minutes. Use the same method to apply another 9 layers, then remove the glass plate or rubber plate, and finally let the solvent volatilize at 70°C for 24h, and vacuum at 140°C for 1h. By pressing three layers of this 0.5mm thick film containing 119% (volume fraction) graphite and 22.7% (volume fraction) carbon black, a film with good absorption of 7.5GHz microwaves is obtained.