一维多通道正常金属结构的透射几率

本文考虑一个严格一维的正常金属多分支结构,指出把Büttiker等人处理两分支结构的方法加以改进。即可解决这种多分支结构问题。我们给出了多分支结构的透射系数公式,作为一个简单的例子,求出了一个对称三分支结构的具体结果,并表明在这种结构中存在透射几率的共振现象。 关键词：     

Sound transmission by coupled structures: Application to flanking transmission in buildings

In the paper a new formulation for sound transmission by coupled structures with special application to flanking transmission is presented. As distinct from other approaches in which the couplings are considered to be similar, this method treats each type of coupling specifically: the mechanical/mechanical coupling is rigorously treated; the mechanical/acoustic coupling is considered to be weak, this hypothesis being generally admissible when air is the acoustic medium fluid. The formulation proceeds from the general to the specific; in this way, it is easier to measure the effect of the hypothesis introduced. The theoretical procedure for defining the transmissions leads to an experimental method in which measured data of the energy and spectral densities of the forces is used. The application of this method to the case of sound transmission in buildings was carried out to serve as an example. The proportions of the energy transmitted by the dividing wall and the flanking walls were calculated to diagnose the situation and thereby to improve the insulation between the rooms. An interactive computer program is being proposed and will be available to users.     

Band structures of Fibonacci phononic quasicrystals

The paper studies the band structures of a two-component Fibonacci phononic quasicrystal which is considered as a phononic crystal disordered in a special way. Oblique propagation in an arbitrary direction of the in-plane elastic waves with coupling of longitudinal and transverse modes is considered. The transfer matrix method is used and the well-defined localization factors which are used to study the ordered and disordered phononic crystals are introduced to describe the band gaps of the phononic quasicrystals. The transmission coefficients are also calculated and the results show the same behaviours as the localization factor does. The results show the merits of using the localization factors. The band gaps of the phononic quasicrystal and crystals with translational and/or mirror symmetries are presented and compared to the perfect phononic crystals. More band structures are exhibited when symmetries are introduced to the phononic quasicrystals.     

等截面消声管道传递损失计算的简化方法

本文提出了等截面消声管道传递损失计算的简化方法,方法利用消声管道截面形式的特点,将三维声学计算问题简化为二维问题,消声管道的传递损失可以表示为与轴向波数有关的表达式,轴向波数可以通过计算截面的特征值得到。对于规则截面结构,使用传递矩阵法计算特征值;复杂非规则截面的特征值使用二维有限元方法得到,进而可以计算消声管道的传递损失。仿真结果与文献中的数值方法及实验值在较宽的频率范围内吻合较好,说明了方法的正确性,此外,该方法可以考虑均匀流对消声管道声学性能的影响。方法的计算效率高,对消声管道的前期优化设计具有实际意义。     

Scattering Parameters of FSS on Anisotropic Layers at Millimeter Wave Frequencies

The analysis of periodic structures on anisotropic substrates is presented for incident millimeter waves. Frequency selective surface structures composed by a periodic array of conducting crossed dipoles on anisotropic layers are analyzed. A full-wave analysis for the problem of scattering is performed. The formulation uses the moment method in combination with the immitance approach, in the Fourier domain, to determine the scattering parameters of the considered structures. A set of entire-domain type basis functions is used in the expansion for the unknown induced current. This analysis is computationally efficient, and its accuracy is verified by the agreement between results obtained in this work and those available in the literature, for particular cases.     

Sound transmission loss of foam-filled honeycomb sandwich panels using statistical energy analysis and theoretical and measured dynamic properties

Comparisons between the experimental and predicted sound transmission loss values obtained from statistical energy analysis are presented for two foam-filled honeycomb sandwich panels. Statistical energy analysis (SEA) is a modeling procedure which uses energy flow relationships for the theoretical estimation of the sound transmission through structures in resonant motion. The accuracy of the prediction of the sound transmission loss using SEA greatly depends on accurate estimates of: (1) the modal density, (2) the internal loss factor, and (3) the coupling loss factor parameters of the structures. A theoretical expression for the modal density of sandwich panels is developed from a sixth-order governing equation. Measured modal density estimates of the two foam-filled honeycomb sandwich panels are obtained by using a three-channel spectral method with a spectral mass correction to allow for the mass loading of the impedance head. The effect of mass loading of the accelerometer is corrected in the estimations of both the total loss factor and radiation loss factor of the sandwich panels.     

矩形槽同轴布拉格结构的模式匹配分析方法及实验验证

基于模式匹配法建立了矩形槽同轴布拉格结构的全波耦合分析模型, 推导出了不同模式反射率和传输率的计算式, 并采用公开报道的实验数据验证了该理论模型. 在此基础上就本文理论与其他相关的理论方法进行了比较, 发现以前的理论近似模型由于忽略了矩形槽中的消失模而使传输率的频率响应曲线发生偏差. 本文建立的理论方法有望为矩形槽同轴布拉格结构的特性研究和工程实践提供一种理论分析手段. 关键词： 同轴布拉格结构 矩形波纹 模式匹配法 模式耦合     

Dynamics of bi-periodic structures

Many structures considered for space applications are bi-periodic in their construction. Bi-periodicity means that two types of structural subassemblies, alternating in one or more directions, make up the structure. To gain insight into the dynamics of bi-periodic space structures a variety of one and two dimensional bi-periodic structures are considered. Results indicate that bands in which natural frequencies lie for periodic structures are further subdivided as a consequence of the bi-periodicity. Analytical solutions for the modes and frequencies of finite length one dimensional bi-periodic structures are obtained for general boundary conditions. A transmission method is developed to simplify the application of boundary conditions. It is found that some modes occur at frequencies which are outside the frequency bands predicted for bi-periodic structures. Two dimensional bi-periodic crossed beam grillage and truss structures are considered in this study. For cases where a separation of variables solution is possible the two dimensional structures exhibit similar properties to the one dimensional bi-periodic structures. Analytical solutions for the one and two dimensional bi-periodic structures considered above lead to a compact solution form similar to that of periodic structures analysis.     

Electrical and structural characterization of inhomogeneously doped semiconductors by infrared spectroscopy

An optical method is presented for thenon-destructive electrical and structural characterisation of multilayer structures. The presented concept yields the complex refractive index profiles within an arbitrary composed layer system by using the symmetrical transmission and the asymmetrical reflectivity caused by the optical inhomogeneity of a material. This method includes the superimposition of coherent multiple reflections within the refractive index profile as well as incoherent multiple reflections within the whole wafer. This analysis yields the spacial distribution of free carrier density profiles within the sample as well as the transitions between different crystal phases by using the least squares fit procedures. The results of the optical analysis are compared with other methods used to quantitatively determine density profiles and phase transitions such as SIMS, spreading resistance, stripping Hall and RBS.     

Investigations on the acoustic transmission characteristics of underwater perforated panel structures

Perforated panel structures have a wide potential in underwater applications. However, up to now there has been little related research. The acoustic impedance of an underwater perforated panel is obtained based on the theories for air perforated panel sound absorption. In this paper sound transmission characteristics of underwater perforated panel structures are theoretically analyzed by the transfer matrix method. A formula for normal incidence sound transmission coefficients is given. The main factors that have effects on the acoustic transmission coefficient are analyzed by numerical simulations. The perforated panel structures made by ourselves are tested in a standing-wave tube by the four-sensor transfer-function method. The experimental results are well in accord with the results obtained by the numerical method, which proves that the theoretical analysis is correct. This paper has provided theoretical and experimental bases for the design of underwater perforated panel structures.     

Composition determination for complex and transmitting samples in x‐ray quantitative analysis

In this work, quantitative analysis of x‐ray fluorescence measurements of transmitting samples with complex chemical composition is considered. A method is presented for analytical solution of sample composition including matrix effects, independent of sample thickness and requiring no standards. The method uses fundamental parameters and measured fluorescence signal intensities, and is applicable to transmission geometry measurements for which standard analyses are not applicable. Limitations of the analysis presented here are discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Object image correction using an X‐ray dynamical diffraction Fraunhofer hologram

Taking into account background correction and using Fourier analysis, a numerical method of an object image correction using an X‐ray dynamical diffraction Fraunhofer hologram is presented. An example of the image correction of a cylindrical beryllium wire is considered. A background correction of second‐order iteration leads to an almost precise reconstruction of the real part of the amplitude transmission coefficient and improves the imaginary part compared with that without a background correction. Using Fourier analysis of the reconstructed transmission coefficient, non‐physical oscillations can be avoided. This method can be applied for the determination of the complex amplitude transmission coefficient of amplitude as well as phase objects, and can be used in X‐ray microscopy.     

光纤光栅法布里-珀罗腔的V-I传输矩阵法研究

快速有效地获得多级联光纤光栅法布里-珀罗(F-P)腔的光谱特性,是优化设计基于上述结构建立的级联多波长激光器、放大器等各种光器件以及复杂分布式传感网络的重要基础和保障.将V-I传输矩阵法用于光纤光栅F-P腔反射光谱特性的分析,并建立了V-I传输矩阵模型.采用该模型对三种不同结构的光纤光栅F-P腔在不同参数下的光谱特性进行分析,并与传统多层膜法的分析结果相比较,表明V-I传输矩阵法能够在保证分析精度的前提下大大节省运算时间.实验结果表明,V-I传输矩阵法对光纤光栅F-P腔谱特性的分析结果比耦合模法更准确.     

Electron microscopy study of incommensurate modulated structures in misfit ternary chalcogenides

The study of misfit structures by means of transmission electron microscopy and associated techniques is reviewed. It is complementary to X-ray crystallography and provides a local and direct view of the beautiful complexity of these systems. Three different types are presented in this work. Misfit columnar structures can be contemplated as a case of one-dimensional misfit structures while misfit layer structures are considered as two-dimensional misfit structures. Some extra dimensionality is added when these misfit layer structures wrap to give rise to tubular crystals. Electron microscopy/diffraction shows clearly in many examples the presence of structural modulations as weak satellite reflections that are very difficult to detect by X-ray diffraction methods. Besides, high-resolution images show the presence of stacking defects in some of these misfit layer structures.     

基于微环谐振器阵列与马赫-曾德尔干涉仪的反射型滤波器性能分析

理论分析了一种将微环谐振器阵列与马赫-曾德尔干涉仪(MZI)相结合实现的反射型滤波器结构。将此结构类比为两类四端口网络级联模型,利用传输矩阵法推导出其通用函数形式,并给出单环及三环结构下的能量反射系数具体公式。通过传输函数矩阵模拟计算了取不同耦合系数值情况下的反射谱形变化,给出了原因分析及讨论。并模拟了引入传输损耗对三环结构谐振峰反射率的影响。数值结果表明:适当选取直波导与微型环以及微型环间耦合系数幅值时,此结构能够作为反射型滤波器件应用于密集波分复用(DWDM)系统,也可实现激光器反射镜面的功能;由于传输损耗增加而引起的谐振峰反射率下降程度依赖于所选取的耦合系数值。     

开环全光混沌通信系统中的光纤信道结构

根据外光反馈半导体激光器及光纤传输方程,构建了基于光纤信道的开环全光混沌通信系统.考虑混沌调制和混沌键控两种信息加密方法,采用先进的校正相减解调法恢复信息,并且通过解调Q因子衡量系统性能.以不同次序排列单模光纤和色散补偿光纤构成4种结构的光纤信道,通过数值仿真分析信道结构对系统通信性能的影响.结果表明,为光纤信道保留少量的负累积色散有利于改善远程传输性能;两端补偿和中间补偿这两种对称结构的性能一致,对称结构优于非对称结构即预补偿和后补偿,适用于远程高速开环全光混沌通信.另外,无论光纤信道结构怎样,在远程高速激光混沌通信中混沌调制方法总是优于混沌键控方法.     

开环全光混沌通信系统中的光纤信道结构

根据外光反馈半导体激光器及光纤传输方程,构建了基于光纤信道的开环全光混沌通信系统.考虑混沌调制和混沌键控两种信息加密方法,采用先进的校正相减解调法恢复信息,并且通过解调Q因子衡量系统性能.以不同次序排列单模光纤和色散补偿光纤构成4种结构的光纤信道,通过数值仿真分析信道结构对系统通信性能的影响.结果表明,为光纤信道保留少量的负累积色散有利于改善远程传输性能;两端补偿和中间补偿这两种对称结构的性能一致,对称结构优于非对称结构即预补偿和后补偿,适用于远程高速开环全光混沌通信.另外,无论光纤信道结构怎样,在远程高速激光混沌通信中混沌调制方法总是优于混沌键控方法.     

一种半环形表面等离子体光波导滤波器的传输特性研究

本文设计并提出一种基于金属-介质-金属结构的带有半环形共振腔的表面等离子体光波导滤波器,利用数值模拟的方法研究了其传输特性。结果表明,在该结构传输谱曲线中形成的滤波阻带位置可以通过改变半环形共振腔的半径来调整。另外由于结构固有的特性,在传输谱曲线上还可以观察到类似等离子体感应透明的传输特性,而且这一特性可以通过改变半环形共振腔与直波导之间的耦合间距和采用面对面放置的双半环结构进行调节。本文所设计的结构可以动态控制光的传输,并可以应用于紧凑型纳米光学器件集成领域。     

Effects of structural factors on filtering operation of photonic band gap air bridges with circular and square shape holes

Applying the finite element analysis on the photonic band-gap materials with a cavity at the center for two types of structures, circular and square shape holes with the same cross section, filtering operation of these structures is simulated and compared. Any variations in the structure parameters, such as cavity length, period and hole dimensions, change the transmission peak and frequency bandwidth of these structures. The effects of rotation of square holes and ellipticity of circular holes on filtering operation are studied. Other new structures such as tapered, shortened and non-uniform rotated structures are proposed and filtering characteristics of them are discussed. It is found that, by rotating the square holes around their axis, it is possible to have a blue-shift in the transmission peak wavelength without notable variations in the filter peak and bandwidth. It is concluded that the increase of elliptical holes diameters length causes the decrease of transmission peak and increase of bandwidth with blueshift of the peak wavelength. This shift is larger for one of the elliptical diameter values considered that is along the waveguide length.