柱状结构中多层各向异性吸波材料的电磁分析

通过对圆柱状结构中多层各向异性薄层吸波材料的电磁分析－柱体由金属柱芯和包围其外的多层各向同性介质材料组成,在各层之间和外表面涂覆各向异性薄层。考虑各薄层的输入阻抗,得出曲面结构内部及表面涂覆各向异性吸波材料散射场。根据级联矩阵和算法,在一定波段上进行ＲＣＳ（Ｒａｄａｒ Ｃｒｏｓｓ Ｓｅｃｔｉｏｎ）减缩,获令人满意的计算结果。     

DF31导弹各向异性材料涂覆RCS缩减优化设计

在目标表面合理涂覆各向异性吸波材料,能够有效缩减目标的雷达散射截面.文章以DF31导弹为例子,提出了一种适用于复杂几何外形的各向异性吸波材料涂覆目标雷达截面缩减的优化设计方法.该方法由通用几何建模方法、各向异性材料电磁散射高频计算方法、常用遗传算法三部分组成,以各向异性阻抗为优化参量.仿真结果表明,采用各向异性吸波材料涂覆能够显著降低目标的雷达散射截面.     

圆孔形FSS对复合材料吸波效能的影响

利用拱形法对制备出的由频率选择表面(FSS)和两层吸波材料组成的夹层复合结构吸波材料的吸波效能进行了测试,研究了频率选择表面对复合吸波材料吸波效能的影响.结果表明:频率选择表面的加入改变了吸波材料的工作频段,拓宽了吸波材料的带宽,并且频率选择表面单元尺寸和电磁波入射角度不同,对其吸波效能的影响也不同.     

一种基于多层电阻膜的超宽带超材料吸波体

本文提出了一种基于多层电阻膜的超带宽超材料吸波体的设计模型.该吸波体的结构单元由一种环形电阻膜片在含导体底面的平面分层介质基板上多层叠加而成,各层电阻膜片的外形相同,但表面阻值不同.一件四层吸波体的仿真分析结果表明:该吸波体对6.8GHz~59.6GHz频段之间的垂直入射波吸波率均大于90%;同时对入射角为45度的TE和TM斜入射波仍能保持超宽带吸波,具有极化不敏感和宽入射角特性.另外,对不同层次吸波体的分析表明:随着电阻膜片层次的增加,其吸波效果更好,吸波频带变宽,带内吸波效果更稳定.     

金属衬底多层吸波材料表面等效电磁流的研究

基于Maxwell方程的一阶状态矢量微分方程描述。推导出均匀平面波入射下金属衬底多层各向异性材料表面上等效电磁流的一般解析表达式及其相互关系。以此为基础给出了两层涂覆电大尺寸平板导体的散射结果，为我层各向异性材料涂覆导体目标电磁散射的近信计算提供了理论基础。     

多向定向铁纤维吸波材料的雷达反射特性研究

基于电磁场理论用传输矩阵方法数值计算具有金属基底多向定向铁纤维吸波材料的雷达反射特性.结果表明具有强各向异性的单定向铁纤维材料,通过多向定向铺层在铺层层数不是很小时(通常大于10层)该吸波材料表面的反射场近似各向同性特性;指出它的反射特性可用反射系数平行分量(R//)0表征;通过等效电磁参数的计算和实验验证了数值分析的正确性.     

开缝腔体场强增强效应抑制方法研究

开缝屏蔽腔体不能完全阻断能量耦合,导致在腔内局部区域、特定频点附近形成场强增强效应,对敏感器件或线路构成威胁。以分析腔内场强增强效应及研究抑制方法为出发点,建立3 种开缝腔体数值模型,提出并验证腔体涂覆吸波材料、内置吸波柱、内置双层PCB 板等谐振抑制方法的有效性。结果表明:在3 种腔体模型内表面涂覆吸波材料均能有效抑制场强增强效应,并且涂覆磁损耗型吸波材料效果最好;随着涂覆厚度的增加,谐振抑制效果也增强;腔体中心放置吸波柱,应使用电损耗型吸波材料。腔体内置PCB 板既能实现对电子器件和线路的承载功能,还可整体大幅度提升腔体屏蔽效能,对谐振效应的抑制体现在迫使腔体主谐振点偏移,结合使用吸波材料,高阶第2 谐振点处谐振抑制效果也明显改善。     

随机分布贴片构成频率选择表面的吸波特性研究

探讨了随机分布贴片构成的频率选择表面在吸波材料应用中的原理,提出了用随机分布的电阻贴片来拓展吸波带宽和提高吸收率.用有限元方法仿真分析了这种频率选择表面应用于吸波材料设计的可行性.讨论了表面占有率、表面电阻率以及分布形式对复合材料反射率频率特性的影响.仿真结果证明包含这种新型FSS结构的吸波材料可以很好地改善材料的吸波性能.     

用遗传算法设计宽带薄层微波吸收材料

针对雷达吸波材料(RAM)的吸收频带宽和厚度薄的优化目标,引入动态跟踪变量约束条件和可动态扩展编码长度等技术,采用基本遗传算法建立了在任意给定的厚度范围内对电磁波的吸收达到特定的反射损耗值有最大合格带宽的多层RAM的优化设计方法.并结合研制的实际吸波材料建立的电磁参数数据库优化设计出了宽带、薄层的涂敷型RAM.用本文建立的优化设计方法可以实现宽带薄层RAM的优化设计.     

多涂覆目标的RCS可视化计算

涂覆雷达吸波材料技术(RAM)是隐身技术中重要的技术之一,在现代隐身武器设计中得到广泛应用.GRECO方法使用Phong光照模型获取法矢等几何参数,只能处理目标表面单一涂覆的情况.使用索引法即用像素的颜色表示索引序号的方法,就可以处理目标表面不同部位有不同涂覆参数的多种涂覆情况.计算结果与相关文献进行比较,结果令人满意.     

Experimental Evidence of Anisotropic and Stable Charged Excitons (Trions) in Atomically Thin 2D ReS2

Experimentally observed, stable trions with large binding energy (≈25 meV) in atomically thin monolayer 2D transition metal dichalcogenides MX₂ (M = Mo, W, X = S, Se, and Te) with an isotropic crystal structure have been extensively studied. In contrast, the characteristics of trions in atomically thin 2D materials with an anisotropic crystal structure are not completely understood. Low‐temperature photoluminescence (PL) spectroscopy in few‐layer ReS₂ with an anisotropic crystal structure by applying a gate voltage is described. A new PL peak that emerges below the lower‐energy side of neutral excitons obtained by tuning the gate voltages is attributed to emission from negative trions. Furthermore, the trion binding energy that is strongly dependent on the layer thickness reaches a large value of ≈60 meV in 1L–ReS₂, which is ≈2 times larger than that in other isotropic 2D materials (MX₂). The enhancement of the binding energy reflects the quasi‐1D nature of the trions in anisotropic atomically thin ReS₂. These experimental observations will promote a better understanding of the optical response and applications in new categories of the anisotropic atomically thin 2D materials with a quasi‐1D nature.     

Quantitative mobility spectrum analysis (QMSA) for hall characterization of electrons and holes in anisotropic bands

An extension of the quantitative mobility spectrum analysis (QMSA) procedure, which determines free electron and hole densities and mobilities from magnetic-field-dependent Hall and resistivity measurements, to materials exhibiting anisotropic conduction is presented. As test cases, the fully computer-automated procedure is used to analyze magnetotransport data from Bi thin films and Bi/CdTe superlattices. Using the results of the QMSA procedure, the thermoelectric properties of these films can be accurately modeled. As a second exmaple, an electron mobility anisotropy ratio of ≈4.5 is derived from the QMSA treatment of the Hall data for bulk Si samples.     

Tuning Dichroic Plasmon Resonance Modes of Gold Nanoparticles in Optical Thin Films

A simple method is presented to tune the gold surface plasmon resonance (SPR) modes by growing anisotropic nanoparticles into transparent SiO₂ thin films prepared by glancing angle deposition. In this type of composite film, the anisotropy of the gold nanoparticles, proved by gracing incidence small angle X‐ray scattering, is determined by the tilted nanocolumnar structure of the SiO₂ host and yields a strong film dichroism evidenced by a change from an intense colored to a nearly transparent aspect depending on light polarization and/or sample orientation. The formation in these films of lithographic non‐dichroic SPR patterns by nanosecond laser writing demonstrates the potentialities of this procedure to develop novel optical encryption or anti‐counterfeiting structures either at micrometer‐ or macroscales.     

Development and evolution of thin film microstructures: A Monte Carlo approach

A computer simulation procedure based on the Monte Carlo algorithm has been developed to study the thin film microstructure evolution in the Zone II regime. This is accomplished by letting the grain boundary movement on the film surface couple with the microstructure in the interior of the film. The grains when viewed in cross-section are found to reach a limiting size at which point all grain boundary motion ceases despite the presence of capillarity driving force. This results in a columnar morphology for the thin film. The cross-sectional size distribution function is found to be approximately log-normal in shape. The introduction of anisotropic solid-vapor interfacial energy is found to induce abnormal grain growth at the expense of the normal grain which has a relatively higher solid-vapor energy. An analytical model is proposed in which the formation of the columnar structure is explained in terms of the grain boundary drag at the growing interface due to sub-surface boundaries.     

Scattering of plane waves by an anisotropic dielectric half-plane

Scattering of plane waves by a semi-infinite anisotropic thin dielectric layer is investigated, which can be considered as an example for electromagnetic energy absorbing materials. A pair of second-order boundary conditions is used to simulate an anisotropic thin dielectric layer as an infinitesimally thin sheet. Formulation is based on the Fourier integral transform technique, which reduces the scattering problem to two decoupled scalar Wiener-Hopf equations. Diffracted, reflected, and transmitted field terms are evaluated by using the Wiener-Hopf solutions that is obtained by the standard method. The uniqueness of the solution is satisfied by imposing an edge constraint in addition to the classical edge condition     

A Simple Artificial Anisotropic Dielectric Medium

The anisotropic properties of an infinite stack of thin dielectric sheets separated by another set of thin sheets with a different dielectric constant is investigated. It is shown that the anisotropic properties are brought about because of the two distinct modes of propagation which can exist in such a stacked array of sheets. The limiting forms of the wave solutions and second-order results for the equivalent dielectric constants are given.     

光学薄膜的各向异性折射率

本文从光学薄膜的实际结构出发,根据电磁场理论,给出了光学薄膜折射率与光线传播方向的关系。     

用液晶与聚合物混合材料的各向异性相分离制备快速响应液晶盒

展示一种新型含有超薄液晶层(小于1μm)的快速响应液晶盒．总的响应时间(τon τoff)可以达到1．3ms。这种液晶器件可以通过对一种液晶和聚合物混合材料的各向异性相分离制备获得。偏光显微镜和扫描电子显微镜的观测结果确认了一种液晶／聚合物的双层膜机构的形成。实验结果表明液晶层的厚度可以简单地通过改变液晶在混合材料中的含量来精确调节。这种制备方法可以用来制作含有超薄液晶层的快速显示液晶器件用于视频显示方面的应用。     

Generalized Analysis of Microstrip-Like Transmission Lines and Coplanar Strips with Anisotropic Substrates for MIC, Electrooptic Modulator, and SAW Application

A unified variational expression is presented for the line capacitance of a general, multilayer anisotropic structure. The propagation characteristics of a variety of striplines, microstriplines, and coplanar strips, in isolated and coupled configurations, with anisotropic substrates having optical axis aligned along the axis of the substrate, are computed. The characteristics of these structures with anisotropic substrates having tilted optical axis are also studied. Using the formulas presented, the study of structures with anisotropic substrates having aligned or tilted optical axis, for various applications including MIC, electrooptic modulator, and SAW IDT, reduces to the determination of a single admittance parameter. This parameter can be obtained from the transmission-line equivalent circuit of the structure almost by inspection.