The Preparation And Electromagnetic Performance Study Of Barium Ferrite Composites

The research of absorbing material is very significant for electromagnetic protect, and develops in the direction of broadband, thin thickness, light weight and strong absorbing performance. The absorbing material with single loss mechanism has the disadvantage of low absorption efficiency and narrow absorbing band. Thus, this thesis studies composite absorbers with different loss mechanisms. The effects of multiphase composite microstructure change on macroscopic physical properties are investigsted, with barium ferrite(Ba Fe12O19) as the main absorbing agent, poly(vinylidene fluoride)(PVDF) as the matrix, and introducing different content of Ba Ti O3 or graphene, in order to obtain a kind of absorbing materials with excellent properties.The hexagonal flake Ba Fe12O19 powder was prepared by chemical precipitation method, then was mixed with different ratio of Ba Ti O3 nano powder. The solvent dimethyl formamide(DMF) dissolved PVDF and then mixed with Ba Fe12O19/Ba Ti O3 powder. After the PVDF/Ba Fe12O19/Ba Ti O3(PBT) composite materials were prepared, the measurement of electromagnetic properties was carried out by a vector network analyzer in 2-18 GHz. When the mass ratio of m(Ba Fe12O19) : m(Ba Ti O3) was 1:3, the reflection loss(RL) of the composite materials reached 6.34 in 11.7 GHz, which was not an ideal absorption performance.Then the PVDF/Ba Fe12O19/Graphene composite materials were also studied to obtain better absorbing materials. During the reduction process of graphite oxide, Ba Fe12O19 powder was added, and the core-shell Ba Fe12O19/graphene(BR) composites were prepared. Then the composites were combined with PVDF to form PVDF/Ba Fe12O19/graphene(PBR) composite materials. When mass ratio of m(graphite oxide) : m(Ba Fe12O19) and m(PVDF) : m(BR) were 1:25 and 1:4, respectively, the wave absorption performance of materials reached the best. The addition of graphene greatly improved the dielectric loss of materials, the reflection loss reached 17 d B in 13.1GHz, and the band width of 10 d B was 3.3 GHz, the materials presented certain ability of microwave absorption. With the increasing of graphene content, the absorbing performance decreased, and absorption peaks moved to low frequency. We also found that the optimum thickness of the absorbing materials is about 2 mm, and with the increasing of the thickness, the absorption peaks moved to low frequency. In addition, the effect of size of barium ferrite particles on the electromagnetic performance of PBR composites was investigated, and the absorption performance and bandwidth of materials increased, and the absorption peaks moved to the higher mid-frequency, with the particles size decreasing of the Ba Fe12O19.