| The development of radar absorption materials strongly depends on the fabrication of high-absorption absorbers,magnetic alloy flakes have attracted more and more attention nowadays due to their excellent electromagnetic properties such as the high saturation magnetization and weak demagnetization effect which benefits to exceed the Snoek’s limit so that higher complex permeability could be obtained and so on. This dissertation is devoted to the preparation of magnetic alloy flakes using high energy ball milling method,and also demonstrates the influence of flat ratio,volume content, surface coating modification process and adding ferrite powder on the microwave electromagnetic properties, impedance matching performance and absorbing characteristics of the magnetic alloy powder.The analysis and simulation of the influence factors and rules of the intrinsic complex permeability in the frequency range of 1~18GHz for the alloy powder absorber had been carried out theoretically. A number of conclusions were obtained. Both of the real and imaginary parts of the complex permeability of the magnetic alloy powder increase with the saturation magnetization while decrease with the anisotropy field and the natural resonance frequency shifts to a higher value.The complex permeability of the alloy powder, which can be increased significantly by the orientation of the direction of magnetization for magnetic domain, also decrease with the damping coefficient with the natural resonance peak shifting to a lower frequency. The simulation work was also done for the effective complex permeability of ellipsoidal particles/wax composites using the effective medium theory and ellipsoidal particle model. The results show that the equivalent complex permeability of the composite components increases with the flat ratio of the flakes and can achieve larger values after the composites were oriented in an external magnetic field than that of randomly oriented distribution.The larger complex permeability has the benefit of the flattening and oriented distribution in insulation matrix for the alloy powder particles. It is found that one can also increase the complex permeability of the randomly oriented flakes/wax composites through an increase in the volume fraction of the magnetic particles.All of these conclusions can provide theoretical guidances for the design and application of excellent radar absorption materials.The experimental work was done on the effects of the mechanical ball milling process on the magnetic properties of the alloy powder. It is found that one can make the alloy particles flattening by ball milling treatment,which will result in an obviously increasement on the complex permeability.Hower, an excessive milling treatment may break the flakes,which would bring a decreasement of flat ratio and the complex permeability instead.The effect of the volume fraction of the flaky magnetic particles on the electromagnetic properties of the composites was also studied. It is found that a suitable volume content of the flakes can effectively improve the microwave absorption ability of the composite sample.The work was also performed on the electromagnetic properties of the Si O2-coated flaky alloy powder particles. The results show that a proper coating and modification process can substantially decrease the complex permittivity of the composites, and this permittivity decrease can in turn improve the electromagnetic match and enhance the absorption of the composites.The last work is on the electromagnetic properties of the magnetic alloy powder flakes/3Ba0.52Sr0.48O·2Co O·10.8Fe2O3(Co2Z) ferrite particle/wax composites. The results show that the addition of appropriate amount of Co2 Z powder can significantly reduce the complex permittivity of the composites, which will effectively improve the electromagnetic matching performance and absorbing properties. |
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