In recent years, there have been more researches on absorbing materials composed of ferrite and other materials. On the basis of the good absorbing performance of ferrite, the problem of narrow absorption band of a single absorber has been solved. The absorbing material with ferrite as the absorbent also has certain defects. For example, the surface density is large. In order to reduce its density and improve its dispersibility, barium ferrite is wrapped on the ceramic hollow sphere by the sol-gel method. The particle size is 80nm, the maximum absorption is 31dB, the absorption bandwidth is 4GHz greater than 10dB, and the density of the material is only 1.8g/cm3. The citrate sol-gel method was used to form a hexagonal magnetoplumbite barium ferrite BaFe12O19 layer with a thickness of less than 1 pm on the surface of the porous glass beads, and a 1.8mm thick coating was prepared by polymer emulsion and composite powder. The microwave reflection loss of the coating is greater than -8dB in 5-18GHz, and the maximum absorption is 15dB at 6GHz.
With epoxy resin as the matrix, polyaniline and nano-barium ferrite particles as the main additives, high-performance composite anti-interference materials are prepared. Through analysis, it is known that the dielectric loss factor of the composite absorbing material ranges from 0.87 to 1.79, and the hysteresis loss factor ranges from 0.159 to 0.402. The dielectric loss has a greater influence in the frequency range of 2.6 to 4.0 GHz. Therefore, the absorbing properties of composite materials gradually increase with the increase of frequency in the frequency range of 2.6~4.0GHz. The in-situ doping polymerization method was used to coat M-type barium ferrite particles (BaFe2O19) with a particle size of 60 to 80 nm with polyaniline to obtain a composite material with a rod-like structure. The material was found through the absorption performance test: The reflectivity drops rapidly as the frequency increases, reaching a minimum of 64.2dB at 4.87GHz; as the frequency further increases (4.87~9.0GHz), the reflectivity quickly rises to 26.34dB, forming a peak . After that, the frequency increases again, and the reflectivity remains almost constant, about 25dB, and the absorption bandwidth below -20dB is 15.07GHz (2.68~17.75GHz), which has a very good broadband absorption function.
The nano-nickel ferrite was prepared by the polymer gel method, and then the nickel ferrite/polystyrene composite was prepared by the hot pressing method. In the X-band, the complex permittivity and complex permeability of the composite material increase with the increase of the calcination temperature of nickel ferrite, and the minimum reflectance coefficient value decreases with the increase of temperature. The minimum reflectivity of the nickel ferrite/polystyrene composite prepared by the nickel ferrite calcined at 1000℃ is -12.67dB at -11.47GHz, and the bandwidth greater than 10dB is 2.63GHz. La, Ce, and Zn doped strontium ferrite Sro.7 lao0.15Ce0.15Fe11.7.Zn3O19 nanocrystalline powder was prepared by the sol-gel method, and then the doped strontium ferrite was prepared by the in-situ polymerization method. Polyaniline composite material, the research results show that polyaniline is coated on the surface of doped strontium ferrite particles, and its microwave absorption performance is excellent, and it has a synergistic effect of magnetic loss and electrical loss; when the thickness of the composite sample is 2.6mm; the absorption peak is close to- 40dB, the peak frequency is higher than 12.4GHz, and the absorption bandwidth greater than 10dB is expected to reach 5.5GHz. Ways to further improve the wave-absorbing properties of ferrite: ①Ultra-fine ferrite particles and make them porous; ②Using magnetic material coating technology; ③Developing composite ferrite coatings. Japan is a world leader in the development of ferrite absorbing materials. The ferrite/chloroprene rubber or ferrite/chlorosulfonated polyene and other absorbing coatings developed by Japan when the coating thickness is 1.7~2.5mm , The attenuation of radar wave reflection at 5~10GHz reaches 30dB.
Japan has also developed a double-layer structure broadband high-efficiency absorbing coating consisting of "impedance conversion layer ten low impedance resonance layers", in which the conversion layer is composed of a mixture of ferrite and resin, and the resonance layer is composed of ferrite conductive short fibers and It is composed of resin, which can absorb 1~2GHz radar wave. The absorption rate is 20dB. This is the best absorbing coating so far. The United States has developed a series of ferrite absorbing coatings. The main components are lithium cadmium, nickel cadmium and lithium zinc ferrite. Body, it can make the radar wave reflection attenuation up to 20dB in the centimeter wave band to the decimeter wave band. For example, magnetic loss dielectric radar absorbing coatings include ferrite series coatings from Condiction, USA, which are 1mm thick, have attenuation of 10~12dB within 2~10GH2, and heat resistance up to 500℃; Emerson's Eccosorb Coating268E has a thickness of 1.27mm, The mass per unit area is 4.9kg/m2, and it has good attenuation performance in the common radar frequency band 1-16GHz, with an attenuation of 10dB. However, the actual mass of the magnetic loss type coating is usually 8-16kg/m2, so reducing the quality is an important problem to be solved urgently. According to reports, the level of domestic ferrite absorbing materials is in the 88GHz frequency range, the reflectivity of the whole frequency range reaches -10dB, the surface density is about 5kg/m2, and the thickness is about 2mm.