羰基铁和FeSiAl共混制备宽频吸波材料

为提高材料在低频段(1～4GHz)下的吸波性能和拓宽吸波频带,选择羰基铁和FeSiAl颗粒作为吸收剂、石蜡作为粘结剂制作吸波材料,采用矢量网络分析仪测试材料的电磁参数,并在给定厚度(0.5和1mm)下分析吸波材料的吸波性能。随着质量添加比的增加,两类材料的介电常数和磁导率均升高,添加比相同下含FeSiAl颗粒吸波材料在1mm厚时具有优异的低频吸波性能(-8.6～-1.2dB),而高频段(14～18GHz)时不及羰基铁(-16.0～-10.1dB);两类颗粒共混后,通过改变FeSiAl颗粒的含量能获得具有良好低频吸收性能(-4.5～-1.1dB)和宽频带(<-4dB频带为3.8～18GHz)的吸波材料。该结果对于通过混合其它优良低频和高频吸波材料以获取宽频带的吸波材料具有指导意义。     

Trends in radar absorbing materials technology

The research in the area of Radar Absorbing Materials (RAMs) has been actively pursued for at least four decades. Although resonant RAMs were originally designed by transmission line approach, and the broad band RAMs were obtained by multilayering, the quest for ultrawide band performance has led to novel approaches such as chirality and even exploring biochemical products. It is observed that radome materials are frequently used as RAMs. The understanding of the underlying principles of electromagnetic analysis and design, fabrication and the trends in RAMs reviewed in this paper could lead to indigenisation, and even pioneering next generation of RAM technology.     

雷达吸波材料的研究进展

根据电磁波在介质中的传播理论,详细地介绍了雷达吸波材料的吸波原理;综述了各种雷达吸波材料的特点、性能、应用现状以及发展趋势;列举了几种新型雷达吸波材料的吸波原理、吸波性能与应用现状;展望了雷达隐身材料的发展趋势。     

Liquid phase epitaxy of hexagonal ferrites and spinel ferrites on non-magnetic spinel substrates

Using a PbOBaOB₂O₃ fluxed melt which had been employed previously to grow hexagonal ferrite Zn₂Y films on hexagonal ferrite M substrates, isothermal dipping liquid phase epitaxy produced epitaxial films on non-magnetic spinel substrates. The substrates studied were single crystals of three different compositions: MgAl₂O₄, MgGa₂O₄ and Mg(In,Ga)₂O₄. Two different film phases were identified: a lightly Zn-substituted M-type hexagonal ferrite and a heavily Zn-substituted magnetite.     

A versatile software tool for microwave planar radar absorbing materials design using global optimization algorithms

A computer-aided design (CAD) tool for the design of planar multi-layer coatings with high absorption for a desired frequency and angle range is presented. The tool uses deterministic and evolutionary optimization design methods. Both single and multi-objective design algorithms can be used and a single absorber design or the Pareto front can be found accordingly. A novel design technique utilizing PSO is also presented. A user-defined or a pre-defined design case can be selected interchangeably. The choice of selecting materials from pre-defined database is also available. The tool can be useful for both educational and research purposes. The efficiency of the tool is demonstrated through several design cases that are in agreement with existing literature data.     

吸收剂形状对雷达吸波材料性能的影响研究

以片状铁、针状多晶铁纤维、球形羰基铁粉吸收剂为原材料分析探讨了磁性吸收剂形状对其微波电磁参数的影响。结果表明，2GHz时磁导率实部最大的为片状，其次是针状，最小的为球形吸收剂，片状铁吸收剂磁导率实部在2GHz时可达4．65，磁导率虚部2～18GHz均高于多晶铁纤维和羰基铁粉。模拟其吸波性能发现片状铁吸收剂吸波性能在2～9．6GHz优于多晶铁纤维和羰基铁粉，可用于提高吸波材料的低频吸波性能。     

Fast and accurate radar cross-section computation over a broad frequency band using the best uniform rational approximation

The method of moments (MOM) in conjugation with the best uniform rational approximation is applied to predict the broad-band radar cross-section of arbitrarily shaped three-dimensional (3D) bodies. The surface integral equations are solved using MOM to obtain the equivalent surface currents at the frequency points corresponding to the Chebyshev nodes, and then the surface current within the given frequency band is represented by the Chebyshev series. To improve the accuracy, the Chebyshev series is matched via the Maehly approximation to a rational function, which can be as good as the best uniform rational approximation. Using the rational function, the surface current is obtained at any frequency point within the frequency band. Numerical results for 3D arbitrarily shaped perfectly electric conducting objects and homogenous dielectric bodies are considered. Compared with the asymptotic waveform evaluation technique and the model-based parameter estimation, the proposed technique is accurate in much broader frequency band with lower memory required.     

Development of radar absorbing nano crystals by microwave irradiation

Single phase M-type barium hexaferrite nano crystals of radar absorbing material i.e., BaFe₁₂O₁₉ were synthesized by a modified flux method under cyclic microwave irradiation. Uniform and ultrafast morphological transformation from spherical to pyramidal-faced nano crystals were noticed in field emission electron microscopy during the cyclic microwave irradiation power for constant time. The reflection loss of nano crystals in Ku band (12.4-18.0 GHz) were measured. Significant increments in reflection loss from − 15.23 to − 53.63 dB over a wide bandwidth were noticed during symmetric morphological growth of single phase nano crystals.     

Electromagnetic and absorption properties of carbonyl iron/rubber radar absorbing materials

We measured the effective complex magnetic permeability /spl mu//sub eff//sup */ and dielectric permittivity /spl epsiv//sub eff//sup */ spectra in rubber radar absorbing material (RAM) with various carbonyl iron volume fractions by using the transmission/reflection method with a vector network analyzer. We studied the effects of carbonyl iron content and rubber thickness on the microwave absorption properties in the frequency range of 2.6 to 18 GHz. Our mathematical analysis is based on electromagnetic theory. The results indicate that the effective complex magnetic permeability and dielectric permittivity values of the RAM increase as the carbonyl iron volume fraction increases. For sample thickness of 3.0 mm, an increase in carbonyl iron content reduces the minimum reflection loss from -1.3 to -23.9 dB and shifts the frequency of the minimum reflection loss from 15.5 to 3.5 GHz. For an equal volume fraction of carbonyl iron, the frequency of the minimum reflection loss decreases as the thickness is increased. However, the dip in the reflection loss plot (in decibels) initially decreases to a minimum value before it increases with a further increase in thickness. We determined the value of the reflection loss for the samples by the impedance matching degree (reflection coefficient), which depends on the thickness and composition of the RAM.     

Broad bandwidth of thin composite radar absorbing structures embedded with frequency selective surfaces

The three-layer ultrathin radar absorbing structure (RAS) involving a frequency selective surface (FSS) exhibiting excellent broad bandwidth properties is designed and fabricated. The EW and flaky carbonyl iron powders were used to produce two kinds of silicone rubber matrix magnetic composites for the top and the bottom layer, respectively. The electromagnetic parameters of the composites were measured in the frequency range of 2–18 GHz. The middle layer is an FSS in the form of double-square loops with four micro-split gaps in the middle of the outer loop. The results show that the proposed RAS can provide a 10 dB absorbing bandwidth of 13.2 GHz from 4.8 to 18 GHz (1.7 mm thickness) and a 10 dB absorbing bandwidth of 14.1 GHz from 3.9 to 18 GHz, covering C-band, X-band and Ku-band (2.0 mm thickness). A good match between simulation and measurement results demonstrates the validity of our design.     

纤维复合吸波材料的研究进展

从损耗机理出发,分类介绍了纤维复合吸波材料的研究情况,对国内外关于以磁性纤维、导电纤维、介电纤维、混杂纤维作为吸收剂的研究现状作了总结和评价,提出了纤维复合吸波材料的发展方向。     

基于材料电磁特性测量的雷达吸波材料性能分析方法研究

吸波材料的性能测试分析对于研究吸波材料和改造吸波材料的生产工艺具有重要意义。通过分析雷达吸波涂层的工作原理及吸收型吸波涂层的设计与电磁特性到吸波性能的转换分析原理，提出了一种基于材料电磁特性测量的雷达吸波材料性能测试分析方法，并选取引进的两种吸波材料对该测试分析方法进行实例分析。     

尖晶石结合氧化铝空心球隔热材料的研制

以氧化铝空心球为骨料,Al2O3微粉和MgO细粉为基质,以纸浆废液为结合剂,经1700℃烧成尖晶石结合的氧化铝空心球隔热材料.研究基质中不同的MgO含量(质量分数)(9％,12％,15％,18％)对材料的抗热震性及其它性能的影响.结果显示:随着MgO含量的增加,材料中镁铝尖晶石生成量呈增加趋势,材料抗热震性先提高后降低;当MgO含量为15％时,材料的抗热震性最好,是空白样热震次数的3倍左右;随着尖晶石的生成,尖晶石结合氧化铝空心球隔热材料的常温耐压强度稍有降低,但其它性能没有受到影响.     

Formation and magnetic properties of ultrafine spinel ferrites

Investigations of the formation and magnetic properties of MnδCo1-δFe2O4formed in alkaline aqueous solution by the coprecipitation method are covered. The lattice constant of these ferrites apparently reduced with decreasing average particle size below about 500 Å. The coercive force ratio of MnFe2O4and Co-Fe2O4is 1 to 50 and equal to that of the crystal magnetic anisotropy coefficient K1of sintered ferrites. As the average particle size became larger, the coercive force and the apparent remanence increased linearly, and superparamagnetic critical size was determined. The sizes range, for example, from 50 to 100 Å for CoFe2O4and from 150 to 200 Å. for MnFe2O4. From the correlation between the average particle size and their magnetization, the limit size of ferromagnetic critical particle was also determined. Results obtained in this experiment are approximately in accord with Néel's Version of the theory on thermal fluctuation aftereffect of magnetic fine particles.     

微遗传算法优化多层ZnOw雷达吸波涂层

采用微遗传算法对以四针状ZnOw为主要成分的多层雷达吸波材料(RAM)进行优化设计.在给定最大厚度的情况下,在2～18GHz频率范围内,采用对不同频段给定不同吸收率的方案,对多层吸波涂层建立了快速优化设计方法.讨论了吸波涂层的厚度、层数对吸收效果的影响.此外,对于不同频段改变给定的吸收率,分析对于优化结果的影响.     

Thermoelectric power properties of Zn substituted Cu-Ga spinel ferrites

Composition and temperature dependence of dc conductivity and Seebeck coefficient for Cu_1−xZn_xGa_0.5Fe_1.5O₄ (0.0 ≤ × ≤ 0.5) are discussed. Thermoelectric power studies of this ferrite series are investigated from room temperature to well beyond the Curie temperature by the differential method. The Seebeck coefficient φ is found to be positive for compositions with x ≤ 0.2 indicating that these ferrites behave as p-type semiconductors, while compositions with x ≥ 0.3 show n-type semiconductors with φ negative. Results of the dc conductivity display semiconducting behavior of these materials. Transition temperatures obtained from both studies are in good agreement and was found to be decreased linearly with Zn content. Some physical properties of the samples such as density and porosity are also discussed. The obtained results are discussed in the light of the interactions over the metal sites in the spinel unit cell.     

铁氧体吸波材料的制备研究进展

铁氧体吸波材料具有价格低廉、吸收效率高、涂层薄、频带宽等优异特性,具有广泛的应用前景.本文重点对共沉淀法,水热法,溶胶-凝胶法,自蔓延燃烧法,低温固相反应前驱体法,沸腾回流反应法等铁氧体吸波材料制备技术的研究进展进行了分析和讨论,并结合相关行业的发展,指出了铁氧体吸波材料今后的研究重点和发展方向.     

Triple-layer broad band antireflection coatings using homogeneously mixed dielectric coatings

Mixtures of ZnS and MgF₂ of different compositions were successfully used for the innermost and intermediate layers in triple-layer (quarter-half-quarter) antireflection coatings. The suitability of this mixture for optical interference coatings is discussed. The transmittance of the sample was found to be 99–99.25% over a broad range in the visible region (490–725 nm). This is in good agreement with theoretical predictions.