The Study On Preparation And Microwave Absorbing Properties Of FeCo/Graphite Composites

In recent years,the research of microwave absorbing materials has made great progress.However,whether ferrite or carbonyl iron powder that have been used for many years,even for the newly developed microwave absorbing materials,all of them have many shortcoming such as narrow absorption band,weak absorption capacity,thick coating thickness,larger surface density and the absorption band which is difficult to control and so on.Therefore,the demands to develop more economical microwave absorbing materials with low density,wide and adjustable frequency region for the microwave absorption,and large reflection loss are ever increasing.In the long run,single microwave absorbing material is difficult to meet the requirements of "wide,thin,and strong".So the composite microwave absorbing material will become a hot spot in the research of absorbing materials.The electromagnetic properties of metamaterials can be controlled flexibly by its microstructure.So it is a potential technical approach for making up the deficiency of the single microwave absorbing materials.In addition,the equivalent impedance matching of composite materials can be improved by stacking different microwave absorbing materials,and it is also an effective method to compensate for the lack of a single material such as narrow absorption bandwidth.Firstly,with natural graphite flakes as raw materials,we prepared Graphite oxide by Hummers' method.With interlayer adsorption characteristics of graphite oxide,we prepared Fe Co/Graphite composites by hydrogen reduction.By analyzing the electromagnetic parameters such as refractive index and impedance,we found that in the preparation of Fe Co/Graphite composites,the ratio of Fe Co alloy and graphite,and the ratio of powder absorbing material and binder are the effective means to control the electromagnetic parameters of absorbing body and control the performance of microwave absorption.Secondly,we systematically studied the microwave absorbing properties of Fe Co/Graphite composites covered by copper sheets with different configurations such as strip copper,cross copper and double-coil copper.It is found that the surface plasmon excitation of the copper sheet plays an important role in enhancing the microwave absorption.Moreover,the scale and the lattice constant of the copper sheet affect the surface plasmon excitation dramatically and the scale is dominant.Oursimulation results show that the reflection losses of the Fe Co/Graphite composites covered by copper sheets always have two peeks.Relatively,covered by double-coil copper,the absorption peek at low frequency is much lower and the absorption bandwidth is much wider.At last,we improved the wave absorbing properties of Fe Co/Graphite composites through stacking carbonyl iron powder.When the total thickness is 2mm,we have calculated the wave absorption properties of material with the change of the thickness of carbonyl iron powder.It is found that when the thickness of carbonyl iron powder is 0.5mm,the absorbing material can realize a good absorption between 8.3 ~18GHz,i.e.,the bandwidth of reflection loss lower than-10 d B is near 10 G.