Microwave Absorbing Properties Of Iron-basedmicro Powder/binder Composite Materials

Magnetic composites possess high resistance, outstanding chemical stability and mechanical performance, besides, they are in low density. Because of these advantages, magnetic composites are valuable for many applications. Among microwave applications of magnetic materials, electromagnetic wave absorbers are more and more important in recent years. As to obtain a good absorbing performance, the material is needed with high microwave permeability, high magnetic loss, and a matching permittivity as well. a-Fe is an excellent electromagnetic wave absorber, it is widely used as traditional microwave absorber materials. This thesis designs a variety of ways in order to increase microwave absorption properties of iron-based composite materials.The first part refers the way to improve magnetic loss. By a hydrothermal synthesis and hydrogen reduction method, high magnetic permeability of the sheet a-Fe particles was prepared. In order to get enhanced microwave absorption by increase the permeability of the material to increase the magnetic loss. The results of the experiments show that only by increasing the permeability of the material without impedance matching problem is difficult to make waves into the absorber, and the material with high magnetic permeability will not increase the microwave absorption properties. Surface treatment then was carried out to get better impedance matching composite material. This shows that for absorption of electromagnetic waves into the body should first solve the internal problem is the material permeability is secondary to the size of the problem.The second part refers to the surface treatments of iron-flakes by mechanical milling as the base in order to improve the electromagnetic characteristics of the material. SiO2 and ZnO were coated on the carbonyl iron surface. The results of experiments show that not only SiO2 as good wave-transparent materials but also ZnO as a dielectric material, their exits on the surface of iron can improve the impedance matching; as a result, the composite materials will be excellent microwave absorption properties. ZnO nano-material attaching to the carbonyl iron surface may introduce a variety of other types of loss, making system in a relatively high magnetic loss in the same time, added additional loss and improves the microwave absorbing properties of the composites materials.The magnetic spectra of two magnetostatic coupled ferromagnetic stripes with different distances were investigated by the three-dimensional Object Oriented Micromagnetic Framework (OOMMF) code. The studied systems exhibit two resonance peaks. The higher peak can be identified with the bulk mode predicted by the macroscopic LL model. The lower peak originates from edge magnetic moments. Influence of magnetostatic interaction on the two resonance models was studied in detail. As the distance between two stripes increases, the magnetic spectrum of two stripes is close to the case of a single stripe.