导电聚苯胺／羰基铁粉复合吸收效能的研究

利用软磁金属粉末羰基铁粉的良好电磁吸收特性,加入不等量的导电聚苯胺,制备成导电聚苯胺／羰基铁粉复合材料。在1．8mm厚的涂层中,随导电聚苯胺含量的增加,其吸波效能得到显著改善。分析表明,导电聚苯胺／羰基铁粉有利于发展成为轻质、宽频、强吸收的优良吸波材料。     

电磁波在周期性结构星型波导中的传输特性

提出一种新型波导结构,在二维周期性结构平板介质中引入两条线缺陷形成星型波导,在波导中加入介电常数不同的介质点阵形成缺陷,采用时域有限差分法(FDTD)对该结构的导波特性进行数值模拟。计算结果表明,该星型结构波导的透射频谱比入射波频谱的带宽更窄,说明此结构具有窄带滤波作用。当改变该星型波导中缺陷结构介电常数取值时,透射过该波导的电磁波中心频率随缺陷介质介电常数的增大而减小,呈良好的线性关系。当改变中心介质柱直径时,透射电磁波的中心频率随缺陷介质柱直径的增大而减小。这种周期性结构星型波导可作为一种窄带滤波和选频器件。     

基于熔融沉积成型的多层石墨烯吸波体的快速制备及其性能

在制备石墨烯/聚乳酸(PLA)复合材料的基础上,利用熔融沉积成型技术快速制备了单层均质样件,研究了石墨烯含量对其电磁参数的影响规律,并基于传输线理论计算分析了其吸波效果;选择石墨烯含量较低的复合材料作为透波层的打印材料,石墨烯含量较高的复合线材作为吸收层和再次吸收层的打印材料,并基于四分之一波长匹配理论确定了吸收层、再次吸收层的匹配厚度范围。设计制造了由不同石墨烯/PLA复合材料组合而成的三层吸波体,测试结果表明:三层吸波体的吸波效果远优于单层均质吸波体,且当选取石墨烯质量分数分别为5%、7%、8%的复合材料作为透波层、吸收层和再次吸收层打印材料时,可以获得最佳的吸收效果,此吸波体在13.3~18GHz频段内的反射率均小于-10dB,在17GHz时有-30dB的最大吸收峰值。     

A method for achieving electromagnetic wave absorption by low-loss stratified construction materials

For the safe and effective use of electromagnetic waves, a method for designing construction materials having selective electromagnetic wave absorption is needed. As an example, the characteristics of a stratified construction material consisting of two different low-loss materials (acrylic resin and glass) is evaluated by numerical simulation, and the electromagnetic wave absorption mechanism is determined. Furthermore, a method is developed for designing stratified construction materials to realize electromagnetic wave absorption at a desired frequency.     

Window materials for high power gyrotron

The room temperature application of sapphire as window material at higher frequencies is not feasible since its absorption coefficient increases almost linearly with increasing frequency in the millimeter wavelength region. At cryogenic temperature the absorption coefficient value decreases only by a few factors (factor of 2 to 3) in the 90 – 200 GHz region. The earlier reported temperature squared dependence (decrease) in the absorption coefficient or the loss tangent value is totally absent in our broad band continuous wave data we are reporting here (at 6.5 K, 35K, 77K and 300K) and one we reported at conferences earlier. Our results are verified by another technique. We utilize our precision millimeter wave dispersive Fourier transform spectroscopic techniques at room temperature and at cryogenic temperatures The extra high resistivity single crystal compensated silicon is no doubt the lowest loss material available at room temperature in the entire millimeter wavelength region At higher millimeter wave frequencies an extra high resistivity silicon window or an window made with extra high resistivity silicon coated with diamond film would certainly make a better candidate in the future. A single free standing synthetic diamond window seems to have higher absorption coefficient values at millimeter wavelength region at this time although it is claimed that it possesses good mechanical strength and higher thermal conductivity characteristics. It certainly does not rule out the use of diamond film on a single crystal high resistivity silicon to improve its mechanical strength and thermal conductivity     

多层旋波媒质平板的反射与透射

本文先利用电磁场的边界条件导出平面电磁波垂直入射于多层平板旋波媒质的透射场表达式。然后用传输线理论中的阻抗法,解决了多层平板旋波媒质的反射问题。最后对多层旋波媒质平板的一特例－双层结构型旅波吸波材料进行了计算机辅助设计分析,分析表明,双层代替单层可以在一定程度上改善涂层的吸波特性。     

Effective electromagnetic properties of honeycomb composites, and hollow-pyramidal and alternating-wedge absorbers

Closed-form expressions for the effective electromagnetic material properties of honeycomb composites and electromagnetic absorbers constructed in the shapes of alternating wedges and hollow pyramids are presented. These expressions can be used to efficiently calculate the interaction of electromagnetic fields with periodic structures of said geometries. The effective material properties from these expressions are compared to results obtained from a numerical solution of the actual cross-sectional geometry. Finally, we give guidance on how the expressions presented here and elsewhere can be used for other types of periodic geometries.     

基于太赫兹技术的葡萄糖及其同分异构体研究

太赫兹波对有机分子的分子内作用力(分子内氢键等)、分子间作用力以及分子本身的振动和转动现象等具有很好的分辨能力.糖类物质属于典型的有机分子,其中葡萄糖(C6H12O6)具有多种同分异构体且用途各不相同.本文利用太赫兹时域光谱技术,在频率为0.1～2.0 THz的范围内,对4种互为同分异构体的糖类进行测量,获得了固态时被...     

材料参数测量误差对吸波材料优化设计结果的影响

根据吸波材料电磁反射系数的传输线理论进行优化设计是微波吸收材料研究的重点,微波吸收材料的吸波效果与其电磁参数(介电常数与磁导率)和材料厚度密切相关,电磁参数测量的准确性与微波吸收材料厚度制作的精确性,对微波吸收效果有很大的影响。通过理论计算分析,探讨了电磁参数测量误差对微波吸收材料优化设计结果的影响,并讨论了微波吸收体厚度制作误差对微波吸收材料吸波效果理论计算值对优化值偏离的影响。     

Drag current for ionization of impurities by an electromagnetic wave in a semiconductor superlattice

The drag current for ionization of a shallow impurity by a strong electromagnetic wave in a semiconductor superlattice is found. It is shown that at low temperatures, when it is possible to ignore the equilibrium carrier density, the dependence of the drag current on the intensity of the electromagnetic wave is nonlinear and it oscillates with growth of the intensity of the electromagnetic field. These oscillations are a consequence of the many-photon character of absorption of the electromagnetic wave by the impurities and also of nonparabolicity of the energy spectrum of the superlattice. A comparison is made of the contributions to the drag current from the anisotropic part of the impurity ionization probability and from its isotropic part, with allowance for modification of the distribution function by the electromagnetic wave. It is found that for (Δ is the width of the conduction miniband) the main contribution to the drag current comes from the isotropic part of the ionization probability. Fiz. Tekh. Poluprovodn. 33, 1443–1446 (December 1999)     

卫星通信伞天线的研究与设计

随着材料科学的发展,轻型、可折叠、易携带的反射面天线逐渐推广和取代了一些特殊场合的金属固面反射面天线。文中利用FEKO中MOM与PO相结合的算法,仿真设计了一种理论值可达42 dB以上的单偏置抛物面天线,利用具有良好电磁波反射性能的银纤维布和雨伞结构制作了该天线。对反射面天线的轻便化、小型化、移动化提供了思路。     

Excitation of a V-antenna by a pulse electromagnetic field

In order to measure short electromagnetic field pulses in EMC problems, transducers in the form of strip line segments are used. Such transducers reproduce undistorted pulses within the time interval equal to a double run of the signal along the line. However, the strip line has a low sensitivity. The V-antenna seems to be reasonable for recording weak signals, since it is more sensitive when compared to a strip antenna. The equations of V-antenna excitation by a pulse electromagnetic field are derived from Maxwell's equations considered in a space-time domain. The role of the magnetic field of the wave as a source of excitation has been clarified. The transient response of a V-antenna is calculated as a function of the material of a dielectric interlayer between the electrodes, the antenna opening angle and the electromagnetic wave incidence angle. Based on a nonsymmetric version of the V-antenna, transducers were fabricated and experimentally investigated. The results of calculations and measurements are in good agreement with each other. It is shown that one can obtain a transient response of an approximate step shape by adding signals from two oppositely directed antennas. The antenna proposed allows nanosecond low-amplitude electromagnetic pulses to be detected     

表面等离激元电磁波吸收体研究进展

表面等离激元电磁波吸收体具有新颖的吸波机制、超高的吸收率、超薄的厚度、超小的单元结构、角度不敏感等特点, 使其在太阳电池、紫外防护、光电探测等领域受到广泛关注。文章围绕表面等离激元电磁波吸收体展开综述, 首先根据其吸波特性的不同, 将其分为窄带、多频带及宽带吸收进行概述, 接着详细介绍了窄带、多频带、宽带表面等离激元电磁波吸收体近年的研究进展, 最后对表面等离激元电磁波吸收体的发展前景进行了展望。     

Dyadic Green's functions inside/outside a dielectric elliptical cylinder: theory and application

Dyadic Green's functions in two regions separated by an infinitely long elliptical dielectric cylinder are formulated in this paper. As an application, the plane electromagnetic wave scattering by an isotropic elliptical dielectric cylinder is revisited by applying these dyadic Green's functions and the scattering-to-radiation transform. First, the dyadic Green's functions are formulated and expanded in terms of elliptical vector wave functions. The general equations are derived from the boundary conditions and expressed in matrix form. Then the scattering and transmission coefficients coupled to each other are solved from the matrix equations. To verify the theory developed and its applicability, we revisit the plane electromagnetic wave scattering (of TE- and TM-polarizations) by an infinitely long elliptical cylinder, and consider it as a special case of electromagnetic radiation using the dyadic Green's function technique. The derived equations and computed numerical results are then compared with published results and a good agreement in each case is found. Special cases where the elliptical cylinder degenerates to a circular cylinder and where the material of the cylinder is isorefractive are also considered, and the same analytical solutions in both cases are obtained.     

柔性可弯曲人工超构材料太赫兹波超吸收研究

近年来,由亚波长人工微结构单元组成的超构材料,因其具有自然材料所不具备的奇特物理性质,吸引了人们的广泛关注.其中最有趣的应用之一就是利用亚波长人工微结构增强对电磁波的吸收.设计并实现了一种人工超构材料柔性可弯曲的高性能太赫兹吸收器.为了实现最优的结构设计,分别对器件的结构周期、金属条宽度、介质层厚度和材料光学性质等关键结构及材料参数进行了系统优化.实验结果显示在频率3 THz附近器件峰值吸收率高达99%,与数值模拟结果相吻合.     

石墨烯/铜镍铁氧体复合材料的制备及性能研究

为制备出宽波段磁波衰减材料,采用水热法制备得到了石墨烯/铜镍铁氧体复合材料（CNFRGO）,并对其进行SEM、XRD、红外光谱和拉曼光谱表征分析;然后测量其2~18 GHz的电磁参数,并计算其损耗角正切值和反射损耗,进而分析其微波衰减性能;最后,测量其中远红外波段的复折射率,利用测量数据和T矩阵法计算分析其红外波段消光和吸收性能。结果表明,尖晶石型铜镍铁氧体纳米颗粒吸附在还原石墨烯上,粒径大部分约为20 nm;CNFRGO同时具有介电损耗和磁损耗两种机制,其反射损耗低于-10 dB的频宽为3.7 GHz,在11.8 GHz处有峰值-14.7 dB;CNFRGO在近红外波段消光较强主要由散射引起,中远红外波段则主要由吸收决定,而其吸收能力在近红外和中红外波段较强,但在远红外大气窗口内相对较弱。因此,CNFRGO可同时吸收微波和红外辐射,是一种良好的微波与红外兼容材料。     

新型多波段复合植被伪装材料

为满足多波段兼容伪装的需求,采用多种材料合理匹配与多功能层组合结构的方法,制备了一种可实现可见光、红外和雷达多波段兼容的新型复合植被伪装材料.用雷达波屏蔽效能和反射率测试实验对伪装材料的吸波性能进行了测试,用成像法对伪装材料的可见光和热红外伪装性能进行了试验检测.结果表明,研制的伪装材料有良好的雷达波衰减性能,大于5 ...     

电磁超材料吸收器的研究进展

基于电磁超材料的电磁谐振吸收器通过合理设计器件的物理尺寸及材料参数可对入射到吸收器的特定频率的电磁波实现100％的完美吸收,因而受到国内外学术界的高度关注.综述了当前国内外基于电磁超材料的电磁波完美吸收器在微波和太赫兹波段的研究进展,分类介绍了吸收器的结构及性能特点,最后对电磁超材料吸收器的发展趋势和待解决的问题作了探...     

烟幕扩散模型中任意光路电磁波透过率的计算

在烟幕扩散模型中,计算电磁波沿任意路径穿透烟幕云团时产生的衰减,需要准确计算出该路径下的烟幕积分浓度,从而得到电磁波的透过率。本文基于空间几何坐标变换原理、线性代数矩阵运算方法以及烟幕材料消光理论,推导了烟幕扩散模型中电磁波入射方向改变时的三维坐标系变换矩阵和二维积分浓度投影算法,实现了电磁波沿任意方向入射时的积分浓度分布及透过率的计算,为烟幕扩散模型的多角度(方向)数据分析、烟幕云团红外图像处理以及更多应用场景中的使用奠定了基础。     

飞秒激光的等离子体吸收太赫兹特性研究

在利用飞秒激光器产生太赫兹波的过程中,等离子体本身会对太赫兹波能量进行吸收,其吸收特性在太赫兹波雷达探测、等离子体隐身、电磁干扰研究等方面有着广泛的应用前景。结合理论分析设计了一种等离子体吸收太赫兹波的测量系统,提出等离子体粒子间相互碰撞吸收是导致等离子体吸收太赫兹波的主要原因,并在实验测量研究中发现等离子体密度大小、光学透镜焦距长短以及入射飞秒激光与倍频晶体晶轴角度是影响吸收程度的主要因素,这些研究为等离子体吸收应用提供了更加全面的理论支撑,有助于推动太赫兹波技术在军事及民用领域的快速发展。