Research Of Microwave Absorption Property Of Iron-based Magnetic Alloy Powders

With the rapid development of computer science, mobile communication and satellite communication, the Electromagnetic Interference (EMI) technology has been greatly applied in military and civil fields of the electronics and information. In order to communicate in high speed, the clock-pulse frequency was raised, followed by increasing of the EMI frequency. Electromagnetic absorbing materials with high frequency and high loss are required to absorb the noise energy, aiming at restraining the electromagnetic leak induced by high-frequency emission noise. The theory of absorbing electromagnetic wave by EMI resistance materials is introduced in this paper, and the absorbing performances of different materials are discussed. The metal magnetic material was adopted to satisfy EMI resistance equipment in GHz frequency, due to its higher saturation magnetic susceptibility than the ferrite material, lamella structure and higher frequency in Snoek limit than that of the ferrite material. Meanwhile, the temperature stability of the metal magnetic material is much better than that of the ferrite material after oxidation, as a result of the higher Curie temperature. Then soft magnetic metal powders with the Fe-Si-Al composition are employed in recent years, with the felt dope of latex or the epoxy colophony. The electromagnetic interference resistance characteristic of the Fe-Si-Al magnetic alloy powder was improved by flattening the metallic materials and chemical coating method in this paper. Two kinds of technical flows for improving the absorbing performance of the powder were introduced in detail. SEM analysis of the sample was carried out and the influence of the grain morphology on the performance of the material was observed, as well as the influence of different boll-milling time and different additive contents of isolative medium on the electromagnetic performance of the powder. The formulas of reflection coefficient of absorbing materials with electric substrates were analyzed and the reflection coefficient of different material sample was computed. The result shows that the proposed boll-milling flattening and isolative coating technology will dramatically improve the performance of absorbing materials in the frequency of 1.0-3.5GHz, which makes it possible to apply the material to EMI resistance.