General theory of sub-quarterwave multilayers with highly absorbing materials

A general theory of multilayers with enhanced reflectance has been developed based on the superposition of sub-quarterwave layers of various highly radiation-absorbing materials. The theory has been developed by second-order expansion of the multilayer reflectance with respect to the optical-constant differences between the materials in the multilayer. The current paper completes and improves the theory that was developed in a previous paper [J. Opt. Soc. Am. A 18, 1406 (2001)] by including the case of nonnormal incidence and general radiation polarization and by providing more-accurate film thickness values of the optimized multilayer than with the previous theory. The theory provides an accurate approach to the design of a new concept of multilayer coatings with more than two materials. The new multilayers are adequate to enhance the reflectance of the materials particularly in the far and the extreme ultraviolet.     

Reflectance enhancement in the extreme ultraviolet and soft x rays by means of multilayers with more than two materials

Sub-quarterwave multilayer coatings with more than two different materials are shown to provide a reflectance enhancement compared with the standard two-material multilayer coatings when reflectance is limited by material absorption. A remarkable reflectance enhancement is obtained when the materials in the multilayer are moderately absorbing. A simple rule based on the material optical constants is provided to select the most suitable materials for the multilayer and to arrange the materials in the correct sequence in order to obtain the highest possible reflectance. It is shown that sub-quarterwave multilayers generalize the concept of multilayers, of which the standard two-material multilayers are a particular case. Various examples illustrate the benefit of sub-quarter-wave multilayer coatings for highest reflectance in the extreme ultraviolet. Applications for sub-quarterwave multilayer coatings are envisaged for astronomy in the extreme ultraviolet (EUV) and soft x rays and also for future EUY lithography.     

Inreflectance: a new function for the optimization of multilayers with absorbing materials

A new magnitude is unveiled from the fact that a multilayer can be optimized for the largest reflectance in a layer-by-layer sequence: This magnitude has been named inreflectance. Inreflectance equals the modulus of the complex reflectance once elevated to the inverse of the complex refractive index of the next outer layer, including the inclination term. The maximization of inreflectance at every internal layer, proceeding sequentially starting with the innermost layer, results in a multilayer with the largest reflectance. At a given layer in the multilayer, inreflectance is different from reflectance when the next outer material absorbs radiation, whereas the two magnitudes are coincident when the next outer layer is transparent. The outermost layer of the multilayer is intrinsically different from the internal layers, and its optimization is performed through reflectance and not through inreflectance. Every maximum of inreflectance is found at a layer thickness that is larger than that for the reflectance maximum. The new magnitude is illustrated with some examples in the extreme ultraviolet, a spectral range in which all materials absorb radiation. Inreflectance can also be used to design multilayers in which some layers have fixed thicknesses and the rest of the layers have to be optimized taking into account the fixed layers.     

Interaction of lamb modes with delaminations in plates coated by highly absorbing materials

A theoretical study of Lamb mode propagation through an absorptive bilayer consisting of a steel plate coated by highly absorptive rubber with a finite delamination dividing these layers is presented. Essentially, in such a bilayer structure, steel-like A0 and S0 modes still propagate, although with moderate absorption. Two different types of delaminations are taken into consideration: slip delaminations in which noncontact boundary conditions are assumed only for shear displacement and stress, and stress-free delaminations in which noncontact boundary conditions are assumed for all mechanical displacements and stresses. The calculations, which are based on a modal decomposition method, show that delaminations in absorptive bilayers result in a considerable change of the normal displacement amplitude at the bilayer surfaces inside the delamination region, and for an incident mode steel-like A0 mode, also in the transmission region. Stress-free and slip delaminations can be distinguished exploiting their different effect on the steel-like A0 and S0 incident modes.     

静电自组装法制备的纳米多层膜的吸波性能

配制了钡铁氧体溶胶和PSS（聚苯乙烯磺酸钠）溶胶,并利用静电自组装的方法在硅片上组装了纳米多层膜。利用紫外-可见分光光度计测出了单层最佳组装时问及每个双层的层厚。用SEM和XPS考察了纳米多层膜的表面形貌和铁元素的价态。对纳米多层膜进行吸波测试,结果显示：总层数为45个双层、总厚度为300nm左右的纳米多层膜有显著的吸波效应,在频率为8～18GHz范围内,最大吸波率达到16．85dB。基于量子理论探讨了纳米多层膜的吸波机理。     

Magnetoresistance enhancement of amorphous CoNbZr-buffered magnetoresistive multilayers

Amorphous CoNbZr alloys are thermally stable and thus have been intensively studied as soft layers of a pseudo-spin-valve (PSV). By depositing a wedge-shaped Co inset layer (IL) between the CoNbZr and Cu layer, we were able to simultaneously fabricate CoNbZr(t_CNZ)/Co(0-3 nm)/Cu/Co PSVs with various CoNbZr and Co IL thicknesses. We have investigated the dependence of magnetic properties, giant magnetoresistance (GMR) effect, and microstructure on the thickness of the amorphous CoNbZr buffer layer. The GMR enhancement behaviour of the PSVs with different CoNbZr thickness was also studied along the inset Co wedge. By optimizing the thickness of CoNbZr and Co IL, a maximum GMR ratio of 7% was obtained in the stack of CoNbZr(4 nm)/Co(1.2 nm)/Cu(2.2 nm)/Co(4 nm).     

手性吸波材料研究进展

手性吸波材料是近年来发展起来具有良好吸波性能的隐身材料,它具有手性参数可调、吸波频带宽等优点。通过对材料手性参数的调整,可以达到预期吸波效果,使吸波材料的制作更具有针对性。对手性吸波材料的吸波机理进行了阐述,综述了3种常见的手性吸波材料——金属手性微体、螺旋炭纤维和手性导电高聚物的研究进展,并对其发展前景进行了展望。     

核壳吸波材料的研究进展

核壳吸波材料作为一种新型复合吸波材料,与单一类型的吸波材料相比在结构、吸波性能和应用上有着明显优势,本文总结了核壳吸波材料的基本类型、制备方法及提出了一种新的制备方法-自反应淬熄+表面改性法。指出核壳吸波材料有望满足新型吸波材料"薄、轻、宽、强"的要求,并对今后核壳吸波材料的研究提出展望。     

多孔层叠宽频吸波材料研究

根据电磁波传输线理论,将传统片状结构吸波材料设计为梯度渐变多孔层叠吸波结构,增加雷达波在涂层中的传输距离和损耗;采用轻质超高导电炭黑和短切碳纤维复合吸收剂技术,将电磁波损耗由吸收剂单一作用扩展到结构/功能填料吸波一体化,吸波材料随厚度的不同可实现在2～18GHz的雷达波反射率-15dB,在26～100GHz的雷达波反射率-20dB,大幅提高材料的宽频吸波性能,为实现雷达隐身材料的"薄、轻、宽、强"提供了新的技术途径。     

Progress in low-frequency microwave absorbing materials

Electromagnetic wave equipment and devices working at low frequency of 0.5–8 GHz have been extensively used in wireless data communication systems, local area network, household appliances and so on. It is found that the extensive use of such devices have a terrible pollution to their surroundings and moreover threaten the health of human being by weakening biological immune systems, breaking DNA strands, promoting cancers. A key solution to this problem is to develop materials that are able to attenuate the harmful electromagnetic waves pollution. This review aims at summarizing the progresses obtained in conventional materials and new emerging structures for microwave absorption at low frequency. The ultimate aim of these materials is to realize a wider effective absorption frequency bandwidth (f_E) at a thinner coating thickness (d). Typical and well-received component and construction of composite, synthesis methods, and f_E are summarized in several tables in detail. The different characteristics of different types of absorbing materials are given much attention in this review.     

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.     

干涉型多层吸波材料研究

综合介绍了干涉型多层吸波材料的吸波原理及其国内外研究现状，并分别研究了干涉型多层吸波材料三种基本类型：一般干涉型吸波材料、Jauman吸收体和频率选择表面（FSS）吸收体的一般结构、应用以及分析与方法，得出FSS吸收体较之其他类型具有更优的吸收性能和更高的实用价值，最后指出了干涉型吸波材料发展的新方向是有源FSS吸收体。     

新型填充式吸波材料的研究

针对聚氨酯在工艺和应用上的缺陷,提出一种用珍珠岩和聚苯乙烯泡沫（EPS）颗粒为载体,涂挂碳粉制成颗粒状散料,填充到特定形状的模型中制成新型吸波材料。这种填充式吸波材料的初步测试结果与聚氨酯泡沫锥体吸波材料相当。     

Special issue on electromagnetic wave absorbing materials

Journal of Materials Science: Materials in Electronics -     

介电损耗型微波吸收材料的研究进展

随着无线信息技术的飞速发展,电磁干扰问题日益突出,在全球范围内引起广泛关注.解决这一挑战的关键是开发能够吸收电磁波的材料.理想的吸波材料应为集承载、防热和强吸收于一体的结构性材料.本文总结了近年来碳基、陶瓷基复合材料及其电磁波吸收性能,这些吸收剂的最终目的是在较薄的涂层上实现更宽的有效吸收频率带宽;介绍了几种典型的、广受欢迎的复合材料的制备方法、结构及其电磁波损耗机制;阐述了现今吸波材料的优势、研究现状及存在的问题.最后,预测了吸波材料未来潜在的发展方向,采用理论、模拟计算以及实际实验紧密结合的手段设计和构筑碳基复合材料将会是必然趋势.     

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。     

电磁屏蔽与吸波材料研究进展

分析了电磁屏蔽与吸波材料的工作原理,综述了电磁屏蔽材料与吸波材料国内外研究进展与应用.     

电磁屏蔽与吸波材料

首先阐述了电磁屏蔽材料与吸波材料研究的重要意义，分析了电磁屏蔽与吸波材料的工作原理，综述了电磁屏蔽材料与吸波材料的种类及其性能，最后指出了其研究方向。