Surface Modification Technology Of High Performance Magnetic Absorber

The noise and electromagnetic pollution due to the integrated circuit are more and more serious in the high frequency integrated circuit. The high performance magnetic absorbers are good candidates to realize electromagnetic shielding due to their high frequency characteristic and larger microwave magnetic permeability. Surface modification technology is a simple, economic and efficient way to solve the problems of the high performance magnetic absorber on the fact of difficult dispersing, bad impedance matching. In this paper, we prepares core/shell material of coated agent/alloy magnetic powders, by the technology of mechanical ball mill, sol-gel, polymer packages and so on, and focuses on the change of microwave electromagnetic properties bring by the surface modification.In the way of experiment, we have coated the alloy magnetic powder with coupling agent, oxide, polymer and so on, studied the modifier chemical composition, reactive groups and dosage, multiple coated, reaction environment etc on the coated effect.Firstly, silane coupling agent (KH-550) coated alloy powder can effectively reduce the permittivity, reduce mismatch of permittivity with magnetic permeability. Secondly, prepared SiO₂ / FeSiAlCr compound material. At the 2 GHz, real part of permittivity dropped by 40, and in the range of 2 18 GHz, the change of imaginary part trend evidently, falling by roughly half. Absorption peak of the imaginary part is at about 5 GHz, and solution concentration in PH = 9, reaction temperature in 40℃are the most for experiment. Thirdly, compared the modified effect of KH-550 with SiO₂, SiO₂ is much better. This may be because it has more effective reactive groups. Adding epoxy resin can modify powdery surface. Fourthly, we had repeatedly done the experiment of SiO₂ coating alloy powder three times. The results show that the modification effects change slow with the time increased. In 2 GHz, the real part of permittivity were down 25﹪,33﹪,21﹪respectively for three times, and the imaginary part of permittivity were down 66﹪,60﹪,50﹪respectively, and at the same time, magnetic permeability had very small amounts of decline. What's more, increasing the amount of coated agent in an experiment does not meet the requirements of the effect. Then, we had used the method of high-energy ball mill to coat FeSiAl alloy powder with ZnO. The method can get the uniform coating, and can adjust electromagnetic parameters. Finally, with polymer nylon 6 coating magnetic alloy powder for example, we studied the modification effect of polymer package method. In addition, dry and annealing processing also help to realize the uniform coating and improve the stability of the alloy particle.In theory, we analysed the principle of surface modification and the influence factors by chemical bonding, and calculated the core-shell structure particles'microwave magnetic spectrum, through the effective medium theory model. The simulated results show that surface coated treatment can effectively increase the magnetic permeability of alloy magnetic powder,and magnetic permeability will reduce with the increasing of coated thickness, in addition, natural resonance frequency moves to high frequency. The simulation results with typical experiment results are consistent, so the theoretical model of core-shell structure can guide designing and researching of surface modification.