Studies On Microwave Absorption Properties Of Co Based Oxide Composite

With the rapid development of modern science and technology, different frequency electromagnetic radiation is filled with our living space and increasingly threaten people's health, protecting our body from electromagnetic radiation becomes an important task. As an important functional material, microwave absorbing materials, which may solve electromagnetic radiation pollution, has become wide interesting in the military, civil, medical, information, and environmental science. The research trend of microwave absorbing materials is towards to high absorption, broad band-width, well compatibility, thin coating, light weight, high-temperature durability and corrosion-resistant. Considering the Bi2Sr2Co2Oy compound is typical of layered materials, and also has strongly anisotropy, which make it may be the potential microwave absorbing material, the electromagnetic properties in RF and microwave frequencies of Bi2Sr2Co2Oy compound based composites was studied in this paper. The main research results are as follows:1. The composite coating mixed with certain ratio Bi2Sr2Co2Oy and graphite using latex as binder was prepared, and the RF dielectric constant and microwave absorbing properties were measured. It was found in graphite coating shows relaxation phenomenon when frequency higher than 1300 MHz, contrast to Bi2Sr2Co2Oy coating with a frequency-independent dielectric constant. In the composite coatings, the dielectric constant increases, and relaxation phenomenon becomes more obvious with increase of graphite content. Microwave absorbing properties of the composites reveal that the microwave absorbing band-width becomes narrow and concentrates in high frequency range with increase of graphite content in the composites. The composite coating shows strong absorbing properties with effective broad bandwidth when the graphite content in the composite was 40 wt%.2. The composite coating mixed with certain ratio Bi2Sr2Co2Oy and Ba-ferrite using latex as binder was prepared, and the RF dielectric constant and microwave absorbing properties were measured. It was found that dielectric constant drops and relaxation phenomenon becomes less obvious when the ferrite content increase in the composites coating. Microwave absorbing properties of composite coating indicates that the absorbing band width becomes narrow material with increase of ferrite content, however, composite coating shows a strong when ferrite content is 40 wt% in composites, and the absorbing band shifts to relatively low-frequency range.3. C-axis oriented Bi-layered cobaltites polycrystalline samples were prepared by three-step solid-state reaction method, and the dielectric constant of samples was measured in radio frequency. The experimental results have shown that the relative dielectric constant of oriented samples was about 80, comparing to more than 150 of non-oriented samples. Loss angle tangent of oriented samples was less than half of that of non-oriented samples. These results can be explained that the interfacial polarization has important contribution to the dielectric constant in non-oriented materials, whereas it has hardly any contribution to that in c-axis oriented materials.To sum up, it is found that the composite coatings show strong correlation between material contents and the electromagnetic properties in RF and microwave frequency, and show strong microwave absorbing properties in certain microwave band. However, comparing with the requirement of practical application, the composite electromagnetic properties should be further improved.