包覆型纳米纤维吸收剂的电磁性能研究

采用化学镀方法制备出纳米磁性金属包覆碳纤维吸收剂, 分析比较了包覆前后纳米纤维长度对吸收剂电磁参数和比饱和磁化强度的影响. 在此基础上优化制备了雷达波吸收涂层样板, 检测结果表明, 制备的样板具有较好的雷达波吸收性能.     

多晶铁纤维吸收剂微波电磁参数的各向异性研究

由麦克斯韦方程出发,导出了多晶铁纤维吸收剂微波电磁参数的理论计算公式,通过数值分析,阐述了多晶铁纤维吸收剂微波电磁参数的各向异性.通过纤维取向样品的制备和测试,实验验证了电磁参数的各向异性.理论和实验研究均表明,多晶铁纤维吸收剂的微波电磁参数具有明显的形状各向异性,其轴向磁导率大于径向磁导率,轴向介电常数大于径向介电常数. 关键词：     

基于阻抗模拟的等效电磁参数研究

为能够较好的计算混合介质等效复介电常数和复磁导率, 提出了一种基于等效电路理论的阻抗模拟方法.导出了材料的电磁参数与材料容抗、感抗之间的对应关系, 并建立了能够较完整、精确地刻画实际复合材料的模型.通过求解混合介质的等效阻抗, 进一步反演其等效电磁参数.将计算结果与经典理论公式以及基于有限差分的数值方法进行了比较, 结果都符合得很好, 说明该方法可以用于计算材料的等效电磁参数.另外, 引入薄膜层结构来刻画表面效应等因素, 使得计算结果更加符合实验结果, 弥补了经典公式在这方面的不足, 同时也体现了该方法在刻画实际模型时所具有的优势. 关键词： 等效电磁参数 阻抗模拟 等效电路 混合介质     

复合介质等效电磁参数的数值研究

利用时域有限差分(FDTD)方法研究了掺杂介质材料等效电磁参数的反演方法.首先用FDTD方法计算掺杂介质的反射、透射系数,然后结合遗传算法和传播矩阵法反演不同掺杂比率的等效电磁参数,得到了等效电磁参数随掺杂比率变化的关系曲线.在复合材料的掺杂比率较低和较高时,等效电磁参数计算公式之间以及数值方法得到的结果比较一致;当掺杂比率处于中间值时,则稍有差别.结果显示用数值方法反演复合材料等效电磁参数具有可行性.     

基于电磁超材料的两种等效参数提取算法的比较分析

基于传统反演算法和Kramers-Kronig关系改进算法, 分别提取弱耦合和强耦合超材料渔网结构模型的等效参数, 并对两种算法的有效性及普适性进行了探讨.理论分析及计算结果表明, 传统的反演算法可以准确地反演弱、强耦合情形下电磁超材料结构的等效参数, 但计算复杂度较高;而基于Kramers-Kronig关系的改进算法巧妙地降低了计算的复杂度, 能简单准确地提取弱耦合情形下电磁超材料结构的等效参数, 但对于强耦合情形则不适用, 原因在于强耦合情形破坏了Kramers-Kronig关系的解析且连续性要求. 研究结果拓展了等效媒质理论并可为新的电磁超材料的设计提供理论参考. 关键词： 超材料 反演算法 Kramers-Kronig关系 等效参数     

含腔电大尺寸导体目标电磁散射的一体化数值模拟

应用等效原理，通过引入口面上等效磁流将含腔导电目标电磁散射简化为腔内、外两个等效 问题. 腔内问题分段求解并应用级联法获得口面等效导纳矩阵；腔内外的耦合关系应用近似 边界元方法描述并由此获得口面等效磁流；最后，这一具有混合源的腔体内外一体化散射问 题则应用所提出的广义混合场积分方程方法建立电磁模型，并用多层快速多极子方法实现高 效数值求解. 实例计算结果与测试结果具有很好的一致性. 关键词： 含腔目标 电磁散射 混合场积分方程 数值分析     

直线加速器同轴负载材料FeSiAl的电磁参数测试及仿真

 为获得直线加速器同轴负载材料FeSiAl的介电常数和磁导率,基于同轴传输反射法,利用矢量网络分析仪,对同轴负载磁性吸波材料FeSiAl的电磁参数进行了测试研究,同时利用电磁场分析软件Microwave Studio进行了测试仿真。研究表明,测量中加工样品与其夹具之间的装配间隙对电磁参数的测试值存在较大影响,进而制作了不同配比的FeSiAl微粉和固体石蜡混合样品,获得混合样品的稳定测试值。对求取电磁参数等效公式的适用性研究表明,Bruggeman,Looyenga,QCACP公式适用于描述该FeSiAl微粉的电磁特性,最后给出了FeSiAl材料的电磁参数。     

基于等效介质原理的宽角超材料吸波体的理论分析

目前,很少有文章就如何实现宽角度吸波材料进行详细的理论分析和设计指导,设计宽角度吸波材料仍然是一件很困难的事情.本文基于等效介质理论对带有反射地板的单层介质超材料吸波体进行较为详细的理论分析.从基础电磁理论出发,推导TE波(横电波,电场方向与入射面垂直的平面电磁波)和TM波(横磁波,磁场方向与入射面垂直的平面电磁波)照射下吸波体的反射系数,分析实现宽角度吸波效果所需的等效电磁参数,为宽角度超材料吸波体的设计提供了理论基础.此外,论文还理论分析了实现宽带宽角吸波等效电磁参数所要满足的条件,并做了计算检验.结果表明,当介质等效电磁参数按照特殊曲线随频率发生变化时,理论上能实现宽带宽角的吸波效果.     

涂层球体混合体系的等效介电常数计算及应用

采用一定的包覆工艺制备了炭黑包覆发泡型聚苯乙烯(EPS)颗粒，用包覆的颗粒作为填料制备了环境适应性强的吸波材料. 将涂层球体混合体系作为密实整体考虑，计算了炭黑含量1%时的等效介电常数，并用计算结果预测了吸波性能. 与实验值对比表明，计算值是基本准确的，可以应用于新型微波暗室用吸波材料的设计和优化. 关键词： 炭黑 吸波材料 等效介电常数 吸波性能     

球形壳层介质的光散射

本文以球形壳层介质为模型，根据电磁理论，求出了球形壳层介质散射系数的解析表达式。并在小颗粒近似条件下，给出了近似解及等效偶极矩。最后与实验结果进行了比较。     

制备条件对纳米晶吸收剂的吸波性能影响的实验研究

采用柠檬酸盐溶胶凝胶法制备出不同Co掺杂的Ba纳米晶铁氧体吸收剂,分析了制备条件对其物性、吸波性能等的影响,确定了最佳制备工艺条件. 研究了粒径对纳米晶吸波性能的影响,同时还测试了纳米晶吸收剂的雷达波吸收性能. 结果表明,纳米晶吸收剂是一种性能优良的雷达波吸收材料. 关键词： 纳米晶吸收剂 烧结温度 溶胶凝胶法     

纯天然植物紫外吸收剂的光谱特性研究

纯天然植物紫外吸收剂是一种高安全性、无副作用且有发展前景的化妆品新型紫外吸收添加剂。纯天然植物紫外吸收剂是由对紫外光有吸收作用的草本植物通过干品粉碎,用有机溶剂萃取、真空干燥后获得。新型紫外吸收剂固体呈现暗褐色,用乙醇和水配成溶液(紫外吸收剂原液)呈淡黄色。本文主要用紫外-可见分光光度计测定新型纯天然植物紫外吸收剂的紫外吸收光谱,分析结果发现,紫外吸收剂在UVC区和UVB区其相对透射率均小于0.2%,最大值出现在UVA区约375 nm处也仅为2.1%。说明新型天然植物紫外吸收剂对紫外线有较好的吸收,能屏蔽各种波长的紫外光。     

The Design and Electromagnetic‐Wave‐Absorbing Performance of a Broadband Four‐Layer Absorbing Composite

A four‐layer absorbing composite on millimeter scale is designed containing an absorbent with multilayer‐like structure on the microscale. In this four‐layer absorbing composite, epoxy resin acts as transparent layer, the multilayer‐like structure absorbent serves as the main absorbing layer; graphene/Ni composite acts as an impedance matching layer; and Fe₃O₄ nanoparticles serve as a magnetic‐loss absorbing layer. The reflection loss of the composites is simulated with CST Microwave Studio, and the absorbency of the composites is discussed in detail when the thickness of each layer is changed. The results show that when the thicknesses of the transparent layer, main absorbing layer, impedance matching layer, and magnetic‐loss absorbing layer are 2.5, 2, 1.5, and 2 mm, respectively, the minimum reflection loss of the composite is ?51.7 dB, the bandwidth below ?10 dB reaches 11.82 GHz, and the density of the composite is nearly 1.9 g cm^?3. Therefore, this new four‐layer absorbing composite possesses strong absorbency, broad absorbing bandwidth, thin thickness, and light weight. Thus, a new way to the development of multilayer absorbing composites is presented.     

红外光谱仪在红外电磁波吸收材料研究中的应用

以Lambere-Beer定律为基础．根据傅里叶变换红外光谱仪的特点，提出了红外电磁波吸收材料吸波性能的测试方法，并对非晶态SiO2粉末材料的红外电磁波吸收特性进行了讨论．实验结果表明。该方法简便、快速、可操作性强．     

Build-up processes of an optical cavity enclosing an absorbent thin film: computational study by the CIP method

Propagation of monochromatic light is analyzed by numerical calculations for an optical cavity enclosing a thin absorbent film. The computational study is performed by the CIP (constrained interpolation profile) method, which is shown to be able to solve temporal evolution of Maxwell’s equations even in a strongly absorbing medium. Simulations on build-up processes reveal that such a cavity exhibits transmittance even higher than the intrinsic transmissivity of the absorbent, i.e., the absorbent is virtually transparent, when the following requirements are satisfied: the film is much thinner than the wavelength, it is located at a node of a standing wave, and the cavity consists of a pair of mirrors with optimal reflectivity depending on the film thickness. Optimal conditions are discussed as well for maximizing absorption in the film.     

Diffraction of sound by a rigid screen with an absorbent edge

A solution is obtained for the problem of diffraction of a plane wave sound source by a semi-infinite plane. A finite region in the vicinity of the edge has an impedance boundary condition; the remaining part of the half plane is rigid. The problem which is solved is a mathematical model for a rigid barrier with an absorbing edge. It is found that the absorbing material that comprises the edge need only be of the order of a wavelength long to have approximately the same effect on the sound attenuation in the shadow region of the barrier as a semi-infinite absorbent barrier. Also the softer the absorbent lining the greater the attenuation in the shadow of the barrier. In the illuminated region a reduction in the sound intensity level can be achieved by a suitable choice of the absorptive material of the strip and its length. It is found that the effect of the absorptive strip is lost if its length is less than two wavelengths long. For a strip length of six wavelengths or more the system is equivalent to an absorbing half plane.     

Multilayer structures for the water-window spectral range on the basis of scandium

The problems of creating multilayer structures for the soft X-ray range are discussed. The search for an absorbing material for multilayer mirrors and phase shifters based on scandium for the water-window spectral range (wavelength of 2.3?C4 nm) is performed. A comparison of the reflection characteristics of normal-incidence mirrors and the properties of phase shifters during numerical simulation of different pairs of materials shows the possibility of using cobalt as an absorbent in a pair with scandium.     

Acoustic response of fibrous absorbent materials to impulsive transient excitations

The parameters used to characterize the acoustic behaviour of fibrous absorbent materials are usually the complex characteristic impedance and the complex wavenumber, which permit the calculation of the airflow resistance and vice versa. Different methods have been satisfactorily used by other authors in order to perform this characterization on the basis of a macroscopic modelling of the behaviour of these materials. In this paper, the suitability of this approach for predicting the acoustic response of absorbent materials to impulsive excitations is evaluated. The constant term of the airflow resistance equation for absorbent materials with different densities is quantified by means of a modified version of the impulse method. These values are then incorporated into one-dimensional acoustic calculations in order to predict the response of absorbing materials to pressure pulse excitation. The very good concordance observed between calculated and measured reflection and transmission coefficients shows the suitability of the proposed procedure for the characterization of absorbent materials.     

无毒紫外吸收剂的制备及光谱特性分析

对鸡蛋花树叶、芒果树叶、桂花树叶等几十种天然植物进行紫外吸收剂的提取,并对提取的紫外吸收剂进行光谱特性分析。通过对光谱特性分析结果的比较,选择紫外吸收效果最好的植物,探索提取紫外吸收剂的方法。结果显示,以芒果树叶为原料,蒸馏水为提取溶剂,乙醇为沉淀剂,得到的紫外吸收剂效果好,提取物配制成浓度为1％(w/w)的溶液,在整个紫外区(200～400 nm)紫外光透过率不超过1％。产物无毒,收率为1.5%。