After coating with nano-SiO2, the amplitudes of the real and imaginary parts of the complex dielectric constant of the carbonyl iron powder are significantly reduced; before and after coating with nano-SiO2, the amplitudes of the real and imaginary parts of the complex permeability of the carbonyl iron powder are basically No change (the average value of the amplitude change range is about ± 3%). Carbonyl iron powder mainly produces electron displacement polarization in an alternating electric field, and its microwave loss mechanism is the conductivity loss and tunneling effect of a conductive grid formed by intermittently connecting carbonyl iron powder particles. SiO2 has good electrical insulating properties, and after being coated with nano-SiO2, a nano-SiO2 insulating layer is formed on the surface of the carbonyl iron powder particles, which hinders the electron displacement polarization of carbonyl iron, so the real part of its dielectric constant ε′2 is greatly reduced. At the same time, the coating of SiO2 also reduces the conductivity of the mixed carbonyl iron powder, thereby weakening the conductivity loss ability of the mixed carbonyl iron powder, so that the imaginary part ε ″ 2 of the dielectric constant is also reduced.
The size and internal structure of carbonyl iron powder particles have a great influence on the movement of magnetic domain boundaries and eddy current conduction, which largely determines the magnetic permeability and magnetic loss performance of carbonyl iron powder. On the one hand, because the thickness of the nano-SiO2 coating layer is very thin (nano-level), the silica coating has little effect on the size of the carbonyl iron powder particles (micron level). On the other hand, the internal structure of carbonyl iron powder particles depends on the presence of carbon, nitrogen, and oxygen compounds, and the coating of nano-SiO2 does not affect the existence and content of these compounds inside carbonyl iron powder, so it cannot be changed. The internal structure of carbonyl iron powder particles. After coating, the electrical loss angle of carbonyl iron powder is significantly reduced; while the magnetic loss angle is basically unchanged in the 213GHz frequency band, and there is only a small fluctuation in the 1318GHz frequency band. Because the electrical loss tangent tan δe and the magnetic loss tangent tan δm characterize the electrical loss and magnetic loss capability of the material, respectively, the electrical loss capability of the carbonyl iron powder after nano-SiO2 coating is weakened, while the magnetic loss capability is basically unchanged. Therefore, considering the reflection and impedance matching of electromagnetic waves on the surface of the material, the closer the values ​​of the dielectric constant and permeability of the absorbing material are, the better the impedance matching of the material is, and the smaller the reflection is.
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