Papers by Keyword: Electromagnetic Parameter

Abstract: Magnetic nanocrystalline alloy Fe_0.2(Co_0.2Ni_0.8)_0.8 microfibers and nanocomposite SrFe₁₂O₁₉/Ni_0.5Zn_0.5Fe₂O₄ microfibers are used as the absorbents in the double-layer structure for microwave absorption. The double-layer absorbers with a total thickness of 2 mm consisting of Fe_0.2(Co_0.2Ni_0.8)_0.8 and nanocomposite SrFe₁₂O₁₉/Ni_0.5Zn_0.5Fe₂O₄ microfibers are designed, and their microwave absorption properties are predicted based on the electromagnetic parameter measurements. The results show that the double-layer absorber with the absorption layer of SrFe₁₂O₁₉/Ni_0.5Zn_0.5Fe₂O₄ microfibers and the thickness of 0.6 mm has the best microwave absorption properties, with the bandwidth ( the reflection loss less than −10 dB) of 7.3 GHz ranging from 10.7 GHz to 18 GHz, and the maximum reflection loss of −71.4 dB at 12.1 GHz.

Abstract: In this paper, the prepared nanocomposite BaFe₁₂O₁₉/α-Fe microfibers and nanocrystalline magnetic alloy Fe_0.2(Co_0.2Ni_0.8)_0.8 microfibers are used as absorbents in the double layer structure for microwave absorption. The double layer absorbers with a total thickness of 2.0 mm, in which various matching and absorbing layers are designed, and their absorption properties are estimated. The results show that the absorbers with the matching layer of nanocomposite BaFe₁₂O₁₉/α-Fe microfibers have a very high microwave absorption performance. The absorption bandwidth (the reflection loss (RL) less than-20 dB) reaches 5.8 GHz ranging from 12.2 to 18 GHz, and the minimum RL value is-61.2 dB at about 15.2 GHz with 0.9 mm matching layer and 1.1mm absorbing layer respectively.

Abstract: This paper studies electromagnetic parameters' impact of λ/4 type dielectric absorber on absorbing properties. Calculation shows that the maximum absorption amount is corresponding to specific values of K and R when absorber's permittivity is stable, when the thickness of material is determined and the real part permittivity is increased, the absorption peaks move to lower frequency and reduce the distance between adjacent peaks, while the imaginary part of permittivity and resistance of membrane resistance only affect absorption peaks' amount but have no effect on the peaks' position. Accordingly, it is reasonable to adjust the material's electromagnetic parameters according to the above rule when the high-performance λ/4 dielectric-type absorber is prepared.

Abstract: In this paper, an electromagnetic parameters measuring system based on a concave cylindrical cavity is presented. The concave cylindrical cavity resonator mode is with separated electric field and magnetic field distribution region, which is not observed in other cavities. It is shown that permittivity and permeability can be tested by placing samples in the strongest electric field region and magnetic field region, respectively. Therefore, by using this measurement system, the electromagnetic parameters of microwave absorbing materials can be accurately characterized.

Abstract: Using the dielectric loss property of carbon black , cement-based composites were prepared by introducing carbon black into cement. The reflection losses were studied using arched testing method in the frequency range of 2~18 GHz. The results showed that the absorption properties were improved in high frequency. The filling ratio of carbon black as well as the thickness of samples had influence on the absorption properties. The lowest reflection loss of-10.6 dB was obtained at 18 GHz of 5wt.% carbon black filled cement with thickness of 20mm. The new material can be used for building indoor electromagnetic radiation protection.

Abstract: Honeycomb absorbing materials were measured using the method of free space in this paper. The reflectance of honeycomb absorbing materials was calculated and simulated, and it was verified based on the measured results. It was demonstrated that this test method was feasible. Through studying on absorbing properties of honeycomb, the results have showed that the radar absorbing properties of honeycomb are related to electromagnetic parameters, as well as thickness of the dip-coatings. With the increase of thickness of the dipping layer, the radar absorbing capability of high frequency and low frequency wave are significantly increased. It is worth noting that the resonance peak moved to the low frequency with the increase of dipping layer thickness. These results are useful for design of honeycomb absorbing materials.

Abstract: In this paper, the polyaniline (PANI) coated multi-walled carbon nanotubes (MWNTs) was prepared in situ polymerization. Adding PANI/MWNTs into epoxy resin（EP）, we got PANI / MWNTs / EP composite microwave absorbing materials. Through testing permittivity 、permeability and reflection loss of materials, the paper showed the effect of PANI/MWNTS to the dielectrical and microwave absorbing properties of materials.The results showed： PANI/MWNTs had great effect on dielectrical and microwave absorbing properties of materials. But the imaginary permeability was close to 0. That indicated that it mainly consumed electromagnetic wave by dielectric loss. In 200-1000MHZ, materials had better absorbing property and lower reflection loss (-13.6).

Abstract: Urchinlike Ni particles with different spines were synthesized. The microstructures and morphologies of the resulting materials were investigated by X-ray diffraction and scanning electron microscopy. And the electromagnetic parameters of these urchinlike Ni were measured with vector network analyzer at 2-18 GHz frequency. The results indicate that the electromagnetic parameters are affected by morphologies of materials. The long urchin spines will lead to larger permittivity.

Abstract: A power system on hybrid electric vehicle (HEV) was chosen for research. On the basis of analysis of characteristic parameters of motor on system, the hybrid system’ dynamics characteristic under electro-mechanical coupling was completely studied. The vibration of hybrid power system was qualitatively studied on theory and experiments when motor were under two different kinds of mode from electricity to push, and two results were consistent with each other well.

Abstract: La _0.7 Sr _0.3 MnO ₃ powders have been synthesized at different temperatures by the traditional solid state method. The crystal structures have been characterized by X-ray diffraction (XRD). The electromagnetic parameters were measured by vector network analyzer (VNA) within the frequency range of 5.85-18GHz. It’s found that the pure perovskite structure has been obtained at the temperature of 1000°C. The bandwidth for R<-6dB became thinner with the sintering temperature’s increase from 1000°C to 1150°C, and the absorbing peak moves to the higher frequency first and low frequency then, the absorbing peak is enhanced first and weakened then.