Preparation And Microwave Absorbing Properties Of Ferrite Matrix Composites

In recent years,with the increasing usage of electronic devices and communication facilities in industry,electromagnetic interference has become a pollution problem,which not only has influence on the operation of electronic devices,but may also be harmful to the health of human beings.To date,the ideal electromagnetic absorbers are requested to have not only strong absorption and wide absorption frequency range,but also low density and good thermal stability.In recent years,ferrites have attracted significant attention due to their interesting magnetic,magneto-resistive,and magneto-optical properties.The high magnetic loss makes it ideal for microwave absorption materials.However,pure ferrites the microwave absorption is mostly dependent on the magnetic loss and the bad impedance matching characteristic makes the microwave absorption properties extremely weak,which is not an ideal for microwave absorbing materials.One of the effective ways to solve the problem is to couple magnetic with other types of composite absorbing material or added other in ferrite absorbing composite absorbent medium composition,can effectively improve the electromagnetic parameters to the impedance matching.Ternary composite was built using ferrite absorbing materials and other types of compound.Besides,binary composite material was formed by adding other phase ferrite absorbing medium to the ferrite.And this paper studied the wave absorption performance of above mentioned composites.The main research contents and results are as follows:?1?PANI/CoFe₂O₄/PVDF composite was synthesized by an in-situ polymerization method.The electromagnetic data demonstrate that the PANI/CoFe₂O₄/PVDF composite exhibit an excellent microwave absorption in the range of 2.0-18.0 GHz.The maximum reflection loss value can reach-57.7 d B at 7.6 GHz with the thickness of 4 mm and the absorption bandwidth with the RL below-10 dB is up to 3.4 GHz?from 6.5 to 9.9 GHz?,which indicates that the microwave absorbing properties of the PANI/CoFe₂O₄ composite can be enhanced by the introduction of PVDF and the PANI/CoFe₂O₄/PVDF composite has potential applications for high-efficient microwave absorbers.?2?PANI/CoFe₂O₄/Ba_0.4Sr_0.6TiO₃ composites were prepared by an in-situ polymerization method.Measurements of the reflection loss show that the maximum RL value of the PANI/0.1CoFe₂O₄/0.9 Ba_0.4Sr_0.6TiO₃ composite is 30.2 dB at 5.6 GHz with the thickness of 3 mm and the bandwidth below 10 dB is 2.6 GHz?from 4.2 to 7.8 GHz?.The results indicate that CoFe₂O₄ and Ba_0.4Sr_0.6TiO₃ particles are efficiently coated by PANI so that the PANI/CoFe₂O₄/Ba_0.4Sr_0.6TiO₃ composites exhibit an enhanced impedance matching between the dielectric and magnetic loss.?3?PANI/CoFe₂O₄/Ba₃Co₂Fe₂₄O₄₁ composite was prepared by an in-situ polymerization method.The microwave absorption properties of the composite were investigated by usingthe network analyzer HP-8720 ES in the 2-18 GHz frequency range.The results show that the maximum reflection loss value of the PANI/CoFe₂O₄/Ba₃Co₂Fe₂₄O₄₁ composite reaches-30.5 dB at 10.5 GHz with a thickness of 3 mm and the bandwidth of reflection loss below-10 dB reaches up to 1.2 GHz.The excellent microwave absorption properties of the as-prepared PANI/CoFe₂O₄/Ba₃Co₂Fe₂₄O₄₁ composite due to enhanced impedance match between the dielectric loss and magnetic loss.?4?Zn O/BaFe₁₂O₁₉ thick films with four different ZnO/BaFe₁₂O₁₉ mass fractions were synthesized by a tape casting in the presence of plate-like BaFe₁₂O₁₉ and ZnO sphere.The microwave absorption properties were also investigated in the 2-18 GHz frequency range,and the results showed that Zn O/BaFe₁₂O₁₉ thick films have multiple reflection attenuation peaks and the microwave absorption properties can be tuned easily by varying the Zn O/BaFe₁₂O₁₉ ratio.When the mass ratio of BaFe₁₂O₁₉ to ZnO is 15:85,the thick films exhibit a minimum RL of-48.6 dB at 17.2 GHz with a thickness of 4.5 mm.The excellent electromagnetic performance Zn O/BaFe₁₂O₁₉ thick films could be attributed to the effective complementarities between the dielectric loss and the magnetic loss.?5?The two-layer BaFe₁₂O₁₉/reduced graphene oxide?RGO?thick film was prepared by a tape casting method,Which as-prepared BaFe₁₂O₁₉ particles consist of random grain and oriented grain.The SEM results indicate that layered RGO and random BaFe₁₂O₁₉ and oriented BaFe₁₂O₁₉ particles are well distributed in polyvinyl butyral and polyethylene glycol/diethyl-ophthalate.The oriented oriented grain BaFe₁₂O₁₉/RGO thick film exhibits a saturation magnetization of 30 emu/g.A minimum reflection loss is-34.6 dB at 15 GHz with a thickness of 3.5 mm and the absorption bandwidth with RL below-10 dB is up to 5.6 GHz.This good microwave absorption property is ascribed to the combination of excellent electrical conductivity of RGO and outstanding magnetic properties of the mixture of oriented BaFe₁₂O₁₉.?6?Novel BaFe₁₂O₁₉@Fe₃O₄ composites were successfully synthesized by a hydrothermal method.The minimum RL of BaFe₁₂O₁₉@Fe₃O₄ composites at the thickness of 2.0 mm reached-29.2 dB,and the effective absorption bandwidth was 4.4 GHz.The absorbing performance of the BaFe₁₂O₁₉@Fe₃O₄ composite was better than Fe₃O₄ and they exhibited a promising prospect as microwave absorbing materials.