Jianqiang Wei

Reflection loss mechanism of single layer absorber for flake-shaped carbonyl-iron particle composite

The reflection loss (RL) properties including the frequency, intensity, and bandwidth of absorption peaks for the flake-shaped carbonyl-iron particle/paraffin composite were investigated in detail. By measuring the reflection coefficient of the composite without (S11-OPEN) and with (S11-SHORT) a backed metal plate, the origin of the RL peak was directly verified. The separated electromagnetic wave energy reflected at the air-absorber interface and the absorber-metal plate interface was achieved from S11-OPEN and S11-SHORT parameters, and they were used to explain the intensity variation of the RL peak. The bandwidth of the RL peak was also deduced from viewpoint of interface reflection waves. The calculated bandwidth from the derived formula agreed well with the experimental data.

Microwave permeability spectra of flake-shaped FeCuNbSiB particle composites

The effective permeability of flake-shaped FeCuNbSiB particles/nonmagnetic matrix composition in high frequency was measured and calculated. In contrast to the relatively larger size and irregular shape particles, the flake particles have higher permeability. The results are attributed to the different magnetic loss mechanisms. According to the skin-effect criterion, we find that the magnetic loss in flake particles is mainly caused by the natural resonance, compared with the eddy current effect in the larger size and irregular shape particles. Using the shape anisotropy, the flake soft magnetic particles overcome the difficulty of the relatively small intrinsic anisotropies and increase the natural resonant frequencies to the gigahertz range, leading to the higher real part and imaginary part of the permeability. The resonance peak of flake particles was simulated using the combination of the Landau–Lifshitz–Gilbert equation and Bruggeman’s effective medium theory considering a random spatial distributio...

Microwave reflection characteristics of surface-modified Fe50Ni50 fine particle composites

Surface-modified planar-anisotropy Fe50Ni50 particle-resin composites have been studied in the microwave frequency range. After surface modification, the eddy current effect is suppressed effectively while the permeability is almost unchanged. High permeability and appropriate permittivity are obtained at the meantime. Simulated microwave reflection result shows that the matching thickness, corresponding frequency, μ and e is coincident with the quarter wavelength matching condition. The surface-modified Fe50Ni50/resin composites can be attractive candidates for thinner microwave absorbers in L-band (1–2 GHz).

Microwave permeability of flake-shaped FeCuNbSiB particle composite with rotational orientation

Flake-shaped FeCuNbSiB particles were fabricated by ball milling the annealed ribbons. The composites of flake particles/paraffin wax were prepared with and without rotational orientation in an applied magnetic field. The complex permeability of the composites was measured in the frequency range of 0.1–18 GHz. The oriented composite showed higher permeability and resonance frequency compared with the unoriented one, while its value of (μ0−1)fr reached 128.9 GHz and exceeded the Snoek’s limit. Considering random and uniform distribution of the flake planes of the particles in the unoriented and oriented composites, respectively, the real part and imaginary part of the complex permeability of the composites were calculated using the Landau–Lifshitz–Gilbert equation and Bruggeman’s effective medium theory. The calculated results were basically in agreement with the experimental data.

Enhanced microwave absorption properties of Fe3Al/Al2O3 fine particle composites

Fe3Al/Al2O3 composites were prepared by mechanochemical synthesis using a mixture of Fe2O3, Al and Fe as the starting material. Microwave characteristics were measured in the range 0.1–18 GHz. A reflection loss (RL) exceeding −20 dB in the frequency range 7.2–17.4 GHz was achieved for an absorber of 1.5–2.5 mm. An optimal RL of −45 dB was obtained at 8.9 GHz for an absorber thickness of 2.2 mm. The good microwave absorption properties resulted from a proper impedance match as a consequence of the insulator Al2O3 around Fe3Al.

Growth of highly textured manganese zinc ferrite films on glass substrates

Highly textured manganese zinc ferrite (Mn0.7Zn0.3Fe2O4) films have been successfully fabricated on glass substrates by pulse laser deposition at relatively low temperatures. Investigations indicated that the strain, which is induced by high deposition rate and the difference of thermal coefficient between the film and glass substrate, is attributed to the growth of textured structure. Growth of highly textured cobalt ferrite film was also achieved using the same method. This work provided a possible technique for fabricating high quality ferrite films on glass substrates.

Microwave reflection properties of planar anisotropy Fe50Ni50 powder/paraffin composites

The reflection properties of planar anisotropy Fe50Ni50 powder/paraffin composites have been studied in the microwave frequency range. The permeability of Fe50Ni50 powder/paraffin composites is greatly enhanced by introducing the planar anisotropy, and can be further enhanced by using a rotational orientation method. The complex permeability can be considered as the superposition of two types of magnetic resonance. The resonance peak at high frequency is attributed to the natural resonance, while the peak at low frequency is attributed to the domain-wall resonance. The simulated results of the microwave reflectivity show that the matching thickness, peak frequency, permeability, and permittivity are closely related to the quarter wavelength matching condition. The Fe50Ni50 powder/paraffin composites can be attractive candidates for thinner microwave absorbers in the L-band (1–2 GHz).