Efficient FDTD method for analysis of mushroom-structure based left-handed materials

A finite-difference time-domain method, combined with thin-wire and thin-slot algorithms, which is used to analyse a metamaterial based on periodic mushroom structures, is proposed. This proposed method is suitable for analysing problems involving large structures with fine structural details. Several composite right/left handed (CRLH) metamaterial mushroom-based structures are investigated. A 19 times 8 flat lens and a parabolic lens structure composed of 410 unit mushroom cells are investigated and they demonstrate negative-refractive-index characteristics while operating in the LH region. The simulation and measurement results of one- and two-dimensional CRLH mushroom-based structures are compared. The periodic analysis for mushroom structures is also introduced. Only a single unit mushroom cell is required to present the phenomena of infinite periodicity with periodic boundary conditions     

左手材料研究进展及应用前景

详细介绍了左手材料(同时拥有负磁导率和负介电常数)存在的理论依据、实现方法和基本电磁特性,针对其出现的新颖电磁特性介绍了它在隐身、光学和微波等领域的潜在应用,及其需进一步加强的工作和发展方向.     

Stability of surface integral equation for left-handed materials

In recent years, left-handed materials (LHMS) have been a hot and debated research topic. Electromagnetic simulation is usually performed for prediction as well as for design. The stability of the surface integral equation method through an insightful and rigorous procedure is analysed. The conclusion is that the PMCHWT formulation at perfectly matched LHM-RHM interface has stability problem, which comes from the plasmon resonance condition. Adding a small amount of loss can greatly improve the condition number of the matrix. Physical and consistent numerical results are shown followed by a brief conclusion     

左手材料薄板波导中的传导模

推导了左手材料薄板波导中传导模的色散方程,分析了波导中存在传导模与波导材料和包敷材料参数取值范围之间的关系.数值算例证实了这些关系.     

左右手材料构成的双层结构的转移矩阵

推导出了由左右手材料构成的双层结构的转移矩阵.利用这个转移矩阵,推导出了由左右手材料交替构成的一维光子晶体的色散关系.     

Frequency selective characteristics of gratings with arbitrary profiles composed of left-handed materials

The frequency selective surface (FSS) of gratings with arbitrary profiles composed of left-handed materials is systematically analysed by a method that combines the staircase approximation and the multimode network theory with the rigorous mode matching procedure. The effects of different periodic groove profiles, such as rectangle, ellipse and trapezoid on the reflection characteristics of the FSS are carefully studied and compared with each other. The variations of the frequency selective characteristics with dielectric loss and the comparisons between left-handed and right-handed gratings are also presented with the physical explanations of the related phenomena.     

YIG/SRR结构的磁可调太赫兹左手材料

利用钇铁石榴石(YIG)在外加磁场作用下,等效磁导率为负值和电谐振环结构可以实现负介电常数的性质,组合设计出了一种新型磁可调左手材料.通过理论分析与计算表明,该结构在太赫兹频段范围内实现了左手通带,且左手通带可以随着外加磁场的增大而产生蓝移,达到了磁可调的目的.该结构具有通带性能良好、损耗低、制作方便等优点,在未来太赫兹波功能器件设计中具有广泛的应用前景.     

Chiral mesoporous materials based on the self-assembly

Ordered mesoporous materials with various structures are synthesized based on the self-assembly of surfactant and inorganic precursors and covered by several excellent reviews. However, less work has been directed to chiral structured mesoporous materials, although these could have wide-ranging applications on the manufacturing of enantio-pure chemicals and pharmaceuticals as catalysts and separation media with both shape selectivity and enantioselectivity. This short review will address the synthesis of chiral mesoporous materials by chiral organic compounds templating route, covering single and 2-dimensional ordered chiral channel mesoporous materials. Non-porous helical fiber, atomic-scale enantio-morphism and zeolite-like materials with three-dimensional helical pores are beyond the scope of this paper.     

掺合材对水泥基材料雷达吸波效能实验研究

采用弓形法,对以水泥为基体,以掺合材硅灰和粉煤灰、石墨和碳纤维、纳米TiO2和钢纤维为吸波剂的试样,在8～18GHz频段内的吸波性能进行了分析,实验表明硅灰和粉煤灰、纳米TiO2和钢纤维与水泥复合制成的吸波材料具有良好的吸波效能,在8～18GHz频段内,其吸波效能随掺合材的含量增加而增大,但有一极限值。石墨和碳纤维与水泥复合制成的吸波材料的吸波效能较差,当石墨和碳纤维掺量为6%(质量分数)以上时,材料的吸波性能下降。硅灰和粉煤灰混合的最佳含量为30%(质量分数)左右,而纳米TiO2和钢纤维的最佳含量为纳米TiO24%(体积分数)、钢纤维4%(质量分数)左右。掺合材超过一定极限后,材料的透波能力增强,吸波性能便会下降。     

Functional materials based on the complex compounds of germanium

A new class of functional materials based on the coordination compounds of germanium is developed and studied. The materials are capable of forming transparent films from aqueous solutions at room temperature and exhibit high technological properties. Physicochemical and electrophysical characteristics of some samples are presented.     

Position-sensitive detectors based on two-dimensional materials

Nano Research - Two-dimensional (2D) materials have attracted great attention in optoelectronics because of their unique structure, optical and electrical properties. Designing high-performance...     

Waveguide lasers based on dielectric materials

Fifty years since the invention of the laser have been witness of the development of many different laser systems and designs. Among them, miniaturized versions of solid sate lasers based on rare-earth-doped dielectric materials have been proposed and demonstrated during the last 20 years. They are based on confined radiation provided by optical waveguide structures. Although many materials and techniques have been studied for producing planar and channel waveguides, only a few of them have shown to be adequate routes for fabricating waveguide lasers. Here we summarize the theory and specific technologies developed for characterizing waveguide structures, and we present some common fabrication techniques already successfully applied to fabricate dielectric waveguide lasers, where relevant examples of demonstrated working devices are outlined.     

Analysis of the left-handed corrugated circular waveguide

Infinite circular corrugated waveguide is analysed to investigate its ability to support modes with backward wave behaviour. Such waveguides provide an alternative structure, easier to manufacture than those already reported based on rectangular symmetry with corrugated walls or filled with frequency selective surfaces. The corrugations if sufficiently deep provide a guiding structure with the required series capacitance and shunt inductance to allow left-handed propagation within some frequency bands. These backward waves are analysed using the surface impedance model of propagation in corrugated waveguides to predict their properties. Interpreting the physical meaning of the analysis, the authors discuss how backward waves are related to resonances in corrugated structures. The relationship between power flows in the guide and the behaviour of the group velocity for such guides is shown. A full wave simulator is also applied to validate these results and the case of a dielectric filled waveguide is considered showing the improved ability to support left-handed modes. The authors present the results of a parametric study of how left-handed propagation depends on the corrugation depth. Potential applications of backward waves in corrugated circular waveguides are proposed.     

On the use of nanoindentation for cementitious materials

Recent progress in experimental and theoretical nanomechanics opens new venues in materials science for the nano-engineering of cement-based composites. In particular, as new experimental techniques such as nanoindentation provide unprecedented access to micromechanical properties of materials, it becomes possible to identify the mechanical effects of the elementary chemical components of cement-based materials at the scale where physical chemistry meets mechanics, including the properties of the four clinker phases, of portlandite, and of the C-S-H gel. In this paper, we review some recent results obtained by nanoindentation, which reveal that the C-S-H gel exists “mechanically” in two different forms, a lowdensity form and a high-density form, which have different mean stiffness and hardness values and different volume fractions. While the volume fractions of the two phases depend on mix proportions, the mean stiffness and hardness values do not change from one cement-based material to another; instead they are intrinsic properties of the C-S-H gel.

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Résumé Les récents progrès en “nanomécanique”, aussi bien sur le plan théorique qu’expérimental, ouvrent de nouvelles perspectives en science des matériaux pour la nano-ingénierie des composites à base de ciment. Grace à de nouvelles techniques expérimentales telles que la ‘nanoindentation’, qui permet d’avoir un accès sans précédent aux propriétés micromécaniques des matériaux, il devient notamment possible d’identifier les effets mécaniques des composants chimiques élémentaires à l’échelle où la chimie rejoint la mécanique; cela inclut les propriétés des quatre phases de clinkers, de la portlandite et du gel de C-S-H. Dans le présent article, nous analysons quelques résultats récents obtenus par nanoindentation; ces résultats révèlent que le gel de C-S-H existe “mécaniquement” sous deux formes différentes, l’une à faible densité et l’autre à forte densité. La valeur moyenne du module d’élasticité, de la dureté, ainsi que la fraction volumique de ces deux formes sont différentes. Alors que la fraction volumique des deux phases dépend de la formulation du mélange, les valeurs moyennes du module d’élasticité et de la dureté sont identiques d’un composite à l’autre; il s’agit de propriétés intrinsèques du gel de C-S-H.

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Editorial Note Prof. Franz-Josef Ulm is a RILEM Senior Member. He was awarded the 2002 Robert L’Hermite Medal. He is Associate Editor forConcrete Science and Engineering.     

仿生UHMWPE软骨材料的制备和性能研究

模拟天然软骨的"多孔渗透"和"梯度功能" 特征,利用T-L法制备出多孔UHMWPE试样和梯度多孔UHMWPE/普通UHMWPE试样.观察了试样表面和断面的形貌,并对试样的相关性能进行测试.多孔UHMWPE仿生软骨材料具有与天然软骨材料类似的孔隙性质,孔径多分布在50～100μm左右,多孔UHMWPE的机械性能均不同程度低于普通UHMWPE,且多孔结构能提高试样与水和牛血清之间的可润滑性能.梯度UHMWPE仿生软骨材料的多孔层和实心层之间具有明显的梯度分界,但在界面连接处具有良好的融合性和结合强度.     

Items on base nanocomposite materials for medical use

Developed principles in designing of organ equivalents and created composite materials were made real and utilized in several constructions of endoprostheses and implants namely prostheses of blood vessels, trachea and bronchus, dental implants, etc. Based on designed bioactive materials, a construction of enzyme electrode, drainage was developed, and antiseptic bandages were created.     

Porous carbon materials based on exfoliated graphite

We have prepared low-density composites of exfoliated graphite and coke. The distribution of the coke particles in the composites and their structural perfection have been studied by scanning electron microscopy and Raman spectroscopy. The specific surface area of the materials have been determined as a function of burnoff value using low-temperature nitrogen adsorption measurements. The results demonstrate that the highest specific surface (400 m²/g) is offered by the composite with a burnoff value of 35%, which contains micropores of 1.4-nm radius.     

沥青型阻尼材料的性能研究

以蛭石为阻尼剂,SBS、硅烷偶联剂(WD-50)等为改性剂制备了沥青型阻尼材料.结合正交试验法研究了主要影响因素(SBS、蛭石)对阻尼性能的影响,并进行了实际降噪模拟测试.结果表明,随SBS用量的增加,材料的损耗因子呈下降趋势;随蛭石用量的增加,损耗因子呈先降低后增加的趋势;当WD-50、蛭石、SBS的量分别为5.2%、13.0%、5.0%时,制备的阻尼材料性能最佳,降噪率高达26.1%.     

多面体低聚倍半硅氧烷(POSS)杂化材料

POSS作为一种特殊的有机-无机杂化材料,在结构上具有很强的可设计性,为新材料的研究提供了极大的便利,在近几年的研究中备受人们关注.介绍了POSS合成的研究进展,重点综述了近几年POSS杂化材料在光电材料、聚合物阻燃和材料表面改性等领域的应用.指出基于POSS的杂化材料发展前景广阔,在未来材料科学发展中将发挥重要作用.