嵌入频率选择表面的薄层宽带磁性吸波材料研究

Research on thin and broadband magnetic absorbing materials with embedded frequency selective surfaces

介绍一种在两层磁性材料之间嵌入频率选择表面的薄层复合吸波结构的宽带吸收特性.频率选择表面由金属方环阵列和低耗介质板构成,其上层、下层磁性材料为不同电磁参数的羰基铁复合物.不加频率选择表面的传统磁性吸波材料若想在宽带取得良好的吸收效果,需要较大的厚度和面密度,导致其应用范围受限.引入频率选择表面能够增强复合吸波结构的吸收频带,并有效减薄吸波结构的厚度.在阻抗匹配条件下,电磁能量主要通过金属单元的欧姆损耗和底层磁性材料的磁损耗进行吸收.为了验证该复合吸波体的吸波性能,在电磁仿真软件HFSS 15.0上搭建模型,而后根据仿真结果对结构参数不断进行优化.最终的仿真结果表明,复合吸波材料厚度为2 mm,2 GHz处反射率可达-5.5 dB,在3.4 G^9 GHz频段反射率为-10 dB,在9 G^18 GHz频段反射率依旧达到-8 dB以下.而无频率选择表面的复合吸波材料,在同等条件下,虽然峰值吸收率较大,但在12 GHz以上吸波性能快速恶化,难以满足宽带吸波的要求.因此,含频率选择表面的复合吸波体具有吸收频带宽的优势,具有广泛的应用前景.

Microwave absorption properties of thin composites containing frequency selective surfaces(FSS)embedded in magnetic absorbing material(MAM)are presented in this paper. The FSS is composed of a regular array of square loop elements and a low-loss dielectric flat as the substrate. The top and bottom magnetic absorbing materials are carbonyl iron composites with different electromagnetic parameters. It is difficult to obtain good microwave absorption properties only using the conventional magnetic absorber without FSS embedded in a broadband frequency range. The thickness of the magnetic absorber will be too large,and subsequently the surface density of the absorber will be greatly increased,which will limit its application regions. Introducing FSS can enhance the microwave absorption ability of magnetic composites,especially in the low frequency range,and hence broaden the absorption band as well as effectively reduce the thickness of the absorber. Under the condition of surface impedance matching,the ohmic dissipation originating from metal elements of FSS and the magnetic loss originating from the bottom layer are the main mechanism to absorb electromagnetic energy. In order to investigate the microwave absorption properties of the composite structure,we built the model using the electromagnetic simulation software HFSS 15.0,and then continuously optimized the structural parameters based on the simulation results. The final simulation results show that the composite microwave absorber with the thickness of 2 mm has an operating bandwidth with the reflectivity below-10 dB in the frequency range of 3.4 G^9 GHz and-8 dB in the frequency range of 9 G^18 GHz. The absorber obtains-5.5 dB reflectivity at 2 GHz. Compared with the absorber without FSS inserted under the same condition,though the higher peak absorption could be achieved using the absorber without FSS,the microwave absorption properties become worse and worse,and hardly meet the requirement of broadband absorption. The composite microwave absorber with FSS inserted,which has a broad absorption band and excellent low-frequency absorption characteristics,has a wide application prospect.