Research On Preparation And Microwave Properties Of Low Frequency Iron-based Composite Absorbing Material

Radar absorbing material had been widely used in civilian communication and military stealth areas. The application of stealth and anti-stealth in low-frequency S-band（1.5³.5GHz） radar was currently got more and more attention and civil 3G, 4G communications also fell in this band. However, its application technology was still a bottleneck. So it was necessary and urgent to do research on absorbing materials which had good absorbing properties in low-frequency S-band radar.Carbonyl iron had high permeability, good temperature stability and its industrial production technology was mature. It was one of the absorbing material which had been got the most research. Howeve, its absorbing properties in low-frequency S-band radar was still to be improved.In this study, composite absorbing materials of carbonyl iron / SiO₂ and carbonyl iron / MnZn ferrite had been prepared by two methods. One was coating and the other was by adding a non-magnetic insulator or magnetic insulator to the carbonyl iron.These two ways could get the regulate electromagnetic parameters of the composite absorbing materials and thereby improved its absorbing properties. The SEM, XRD and vector network analyzers had been used to characterize the morphology, phase structure, microwave electromagnetic parameters and other characteristics. Research the absorbing properties of the obtained samples in low-frequency S-band radar had been done by the analyzed results. Finally, the reflection loss were been analyzed through the transmission line theory.High-performanced SiO₂ / flaked carbonyl iron composite absorbing materials was prepared by sol-gel.Firstly, flaked carbonyl iron absorbing material was obtained by ball milling process.Secondly, SiO₂ / flaked carbonyl iron composite absorbing material was obtained by adding different amounts of TEOS（silicon 28）. The results showed that the structure of the SiO₂ / flaked carbonyl iron powdesr were all showed the morphology of flat loose structure. The thickness of the powder increased. However, XRD showed that the composite particles was still body-centered a-Fe phase structure. With the increasing content of silicon 28, the intensity of the diffraction peak of the particles had been reduced and the electromagnetic parameters changes significantly. The movement of the reflection loss peak to low-frequency was closely related to the increasing of the dielectric loss value. So the increasing of the silicon 28 would help to improve the properties of the composite absorbing materials in low-frequency. The maximum reflection loss peak all appeared in low-frequency with different amounts of silicon 28. The composite absorbing materials showed good absorbing properties in low-frequency. When the coating thickness was 1mm and the amount of silicon 28 was 6ml, the reflection loss peak of the SiO₂ / flaked carbonyl iron reached to the lowest. When the frequency was 4GHz its RL reached to-7.5dB.Composite absorbing materials carbonyl iron / SiO₂ were prepared by ball milling. Different amounts of SiO₂（1%, 2%, 3%, 4%） was added to the carbonyl iron. Then milled 30 h. The results showed that SiO₂/ carbonyl iron powder showed the morphology of flat loose structure after high energy ball milling. The phenomenon of the agglomeration of the carbonyl iron had improved with the increasing of the SiO₂. Highly dispersed particles increased the dispersion properties of carbonyl iron, which reduced the dielectric constant of the composite. XRD showed that the composite particles was still body-centered a-Fe phase structure; The permittivity increased and the permeability declined. When the thickness of SiO₂/carbonyl iron composite particles was 2.5mm, the reflection loss peak appeared in 2 4GHz in each amount of SiO₂. The absorption loss peak of the composite particles move to high frequency and the minimal absorption loss peak reduced with the increasing of SiO₂. When the mass fraction of SiO₂ was added to 4%, the sample had the best reflection loss. When the reflection loss was 3.72 GHz, it reached to-22.32 dB.Finally, carbonyl iron/ MnZn ferrite composite absorbing materials were prepared by ball milling process.Doing research on the absorbing properties of the sample powders in low-frequency by adding different amounts（2%, 4%, 6%, 8%） of MnZn ferrite. Since compared to carbonyl iron the MnZn ferrite had a low dielectric constant（insulator） but had a certain magnetic. The two materials could not only learn from each other but also could not reduce the permeability too much. Balancing the electromagnetic parameters of these two absorbing materials could obtaine a dielectric constant higher permeability and the appropriate size of permittivity in low-frequency S-band radar. The results show that the agglomeration had improved after coating with the increasing amount of the MnZn ferrite. XRD phase showed the composite absorbing materials were still a-Fe phase. The permittivity increased and then decreased and the permeability showed the same changes. The reflection loss peak first moved to low frequency and then moved to high frequency.When the thickness of the coating material was 2.5mm and MnZn ferrite mass fraction was 6%, Mn Zn ferrite / carbonyl iron composite particles had the lowest loss peak. When the frequency was 1.65 GHz, its RL reached to-10.25 dB.