Numerical diffraction coefficients for surface waves

The numerical uniform theory of diffraction (UTD) is extended to include surface waves. A method for extracting surface wave diffraction coefficients from moment method data is given and Prony's method is applied to the problem of determining surface wave propagation constants. The method is validated through comparison with the exact solution of the problem of surface wave diffraction by a truncated dielectric slab recessed in a conducting surface. Examples are given for scattering from dielectric slabs and frequency-selective surfaces and for radiation from a conformal microstrip antenna with a truncated substrate. The accuracy obtained is demonstrated by comparison with moment method calculations     

微粗糙面下埋地地雷目标的极化滤波增强

首先采用了二维分数布朗运动来模拟实际地面,利用微扰法给出了微粗糙表面的散射矩阵;其次计算了微粗糙面下某型号地雷目标的极化散射特性,并与平坦地表下的极化特性进行了比较;最后,在考虑地杂波干扰时,研究了杂波环境中埋地地雷目标的极化滤波增强技术,给出了收／发天线的最优极化状态。     

Surface Waves on an Anisotropic Plasma Sheath

A treatment of the excitation of unidirectional plane surface waves on a perfectly conducting screen covered with an anisotropic plasma sheath is given for the case in which the external magnetic field is oriented parallel to the screen but perpendicular to the direction of propagation. The dispersion relations for the surface waves and their dependence on the strength of the external magnetic field and the sheath thickness, are discussed. For sufficiently small sheath thickness, backward surface waves are found to exist. The powers carried by the surface waves and the space waves are evaluated, and the efficiency of excitation of the surface waves are determined as a function of sheath thickness for a typical set of parameters. The power carried by the forward and backward surface waves are compared for two cases in which, in a given direction, either one or both of these exist.     

Tapping of Love Waves in an Isotropic Surface Waveguide by Surface-to-Bulk Wave Transduction

A theoretical study of tapping a Love wave in an isotropic microacoustic surface waveguide is given. The surface Love wave is tapped by partial transduction into a bulk wave at a discontinuity. It is shown here that, by careful design of the discontinuity, the converted bulk wave power and the radiation pattern may be controlled. General formulas are derived for the calculation of these important characteristics from a relatively general surface contour deformation.     

Radiation from a slot in an impedance surface

The effects of a lossy-ground plane on the radiation from a slot are analyzed by using a Green's function of an impedance surface. Numerical results of the radiation field, radiated power, and loss power are presented for various lossy ground planes. In particular, the radiation field and the radiated power from a short slot are given by simple closed expressions. The analytical model of a slot in an impedance surface is validated by radiation field measurements     

STUDY ON Zn DIFFUSION IN Ge

In this report the diffusion of Zn into Ge is investigated.The experiments are accomplishedin an evacuated and sealed quartz ampoule using Zn as the diffusion source.The relation of the X_j-t and C_s-(1/T)is given.The influence of the source temperature on the surface micrograph is investigated.It is foundthat using the two-temperature process a smooth surface layer can be obtained.The effect of the thickness ofthe SiO_2 films on the mask ability for Zn is given.The leakage current can be reduced by evacuation annealing,     

十字形频率选择表面单元的传输系数分析

传输系数是频率选择表面的一项重要技术指标。简要介绍了利用谱域Galerkin法计算平面频率选择表面传输系数的方法。该方法以平面波谱展开和傅里叶变换为基础,通过矩量法求解频率选择表面电流,进而求得传输系数。对一个十字形频率选择表面的传输系数进行了测量和计算,并将测量结果和计算结果进行了比较,两者吻合得较好,验证了本方法的正确性。     

Scattering by S-shaped surfaces

When an S-shaped surface possesses no derivative discontinuities, techniques such as the geometrical theory of diffraction are not applicable. However, if the radius of curvature is relatively large at every point on the surface, the physical optics approximation may be employed. The authors present a uniform physical optics (UPO) solution which remains valid at caustics occurring when two or more specular points coalesce at the inflection point of the S-shaped surface. The solution is developed by approximating the surface with a localized cubic expansion, leading to exact expressions in terms of Airy integrals. In contrast to other solutions, the one given here requires only a knowledge of the stationary phase points and the first three derivatives of the surface-generating function at those points. A major effort is devoted to the validation of the UPO solution, and this is accomplished with numerical models of the S-shaped surface. It is found that the given UPO solution is quite accurate in the specular and nonspecular regions     

深度图像分割中的面元优化描述

该文提出了一种新的参数化面元的优化描述方法,基于二次型面表示模型,物体表面参数由深度图像数据拟合得到,基于一种改进的纠偏曲面拟合方法,提出了一个正态分布概率模型来描述面元估计的统计性质,并显式定义了面元描述的可靠性度量,以面元提取为目的,提出了一种新的基于参数估计的深度图像分割方法,在建立区域一致性判别优化准则的同时,使得区域增长总是收敛于所提取面元的最可靠描述,文中给出了实际深度图像分割的实验结果。     

A method for the measurement of the parameters of a two-layer stratified earth

A two-layer stratified model is assumed for the earth. The distances involved are assumed to be sufficiently short that the earth can be considered flat. The measurement of the parameters of the top layer can easily be made from the surface, but the parameters of the lower layer are somewhat more difficult. A method is given for the evaluation of these quantifies in terms of measurements of propagation between two antennas located at the surface of the earth. The theoretical solution for the field of an antenna located at the surface of a flat stratified earth has been given by J. R. Wait. This solution is taken as the starting point; it is put into a form which explicitly shows the influence of the parameters of the lower layer. The method of least squares is then used to evaluate the unknown parameters in terms of the measurements. This process allows the use of a large number of measurements which are essentially subjected to an averaging procedure. This prevents localized irregularities in the earth's surface from unduly affecting the results.     

Effects of surface waves on the currents of truncated periodic arrays

The behavior of surface waves in truncated periodic arrays is examined through analysis of the currents. The surface waves to be studied are guided by the perfectly conducting elements of the array itself and are to be distinguished from the dielectric slab-guided surface waves encountered elsewhere in the literature. The conditions under which surface waves may arise are given. The surface wave currents are extracted from the method of moments solution for the finite by an infinite array using a least squares algorithm. Surface wave excitation and reflection coefficients are then be determined from the data and compared with the semi-infinite array solution.     

Target reconstruction from scattered far field data

The problem of finding the shape of a perfectly conducting cylinder when illuminated by an E-polarized incident electromagnetic wave is considered. The given problem is cast in the form of a penalized optimization problem in which we seek a surface in some suitably constrained class which minimizes a functional involving two terms. The first term measures the mean square deviation of the far field of the solution to the direct scattering problem for a surface in the admissible class from given, measured, far field data whilst the second term, penalty, measures the error in satisfying the imposed boundary conditions. An optimisation algorithm is used which does not require that a direct problem be solved in the updating process. Explicit reconstructions are presented which illustrate the effectiveness of the method. Some results indicating the sensitivity of the algorithm to the choice of penalty parameter and the number of incident waves are also given.     

Light scattering from periodic refractive-index fluctuations in asymmetric slab waveguides

We consider scattering of light out of the guiding layer into the substrate and the airspace of an asymmetric slab waveguide caused by periodic refractive-index fluctuations. Also discussed is the effect of backscattering of a guided wave into itself. The periodic index fluctuations may be caused by an acoustic surface wave. For this reason, we assume that the intensity of the index fluctuations decreases exponentially with increasing depth below the surface of the guide. However, out discussion is general, and the acoustic surface wave is used only as an example. Numerical results and graphic examples are given.     

The Transmission of TE/sub 01/ Wave in Helix Waveguides

Relations are investigated between the transmission characteristics of a helix waveguide and its surface impedance in regions where any simple approximate formulas are not available because of the magnitude of the surface impedance. The numericaf calculations show that, for any given value of the surface impedance and the angular mode index, there exist an infinite number of different modes which are distinguishable from each other by different values of the radial propagation content. Selecting a mode with minimum attenuation for each given surface impedance, we can draw the equiattenuation lines, connecting these points of equal attenuation on the complex surface impedance plane. At some point on the complex surface impedance plane, a maximum value of the minimum attenuation is found. For the TM/sub 0/ mode supported by a helix waveguide 50 mm in diameter, used at a frequency of 50 kmc, this minimax value of the attenuation constant is about 8 neper per meter, and the corresponding value of the surface impedance is about 57.6-j28.8 ohms. The attenuation constants of all the TM/sub 0/ modes corresponding to this optimum value of the surface impedance cannot be smaller than this minimax value. The same kind of calculations are also performed for the two lowest hybrid modes. Physical structures giving the best value of the surface impedance are also suggested.     

新型宽频带吸波涂层研究

本文介绍了一种在简单吸波涂层Dallenbach涂层中插入频率选择表面而构成的新型复合吸波涂层;采用等效电路法和传输线理论分析了这种涂层的吸收性能,证明其性能大大优于简单吸波涂层。     

改善环境光照对强反光体表面红外测温精度影响的补偿算法研究

针对铝业加工中的轧辊表面光滑,具有强反光特性,红外测温传感器测温易受环境光照影响,致使轧辊表面测温精度低,影响冷却控制系统对轧辊表面降温处理精度,进而造成产品质量差的现象,本文提出并构建了一种基于光照强度的红外测量温度补偿算法,以提高环境光照对强反光体表面温度测量的精度。实验结果证明本方法能较好地弥补光照强度变化对红外温度测量产生的测量误差,提高了测量精度。该补偿算法运算简单、适应性强,为改善光照强度变化对测量精度的影响提供了新的方法。     

Electromagnetic scattering for oblique incidence on impedancebodies of revolution

Combined field integral equations for the surface currents induced by an obliquely incident wave on a rotationally symmetric body are considered. The relative surface impedance is independent of the azimuthal angle but may vary along the profile of the scatterer in any plane containing the axis of symmetry; the currents are conveniently expressed in terms of Fourier series of uncoupled terms in the azimuthal angle. Simple integral expressions for the far field are given and a computer code is described and tested on a variety of scatterers. Geometry of scatterer, surface impedance and Fourier harmonics of induced currents are described by splines. The results are in agreement with physical interpretation     

Calculation of the surface-wave excitation in multilayeredstructures

A novel rigorous analysis of the surface waves excited by a Hertzian dipole embedded in a multilayered structure is presented. A transmission-line resonator equivalent circuit is used to calculate the surface wave's electromagnetic field components. It is shown that the power carried by the surface waves is related to the energy stored in the resonator. An analytical method for the calculation of the stored energy is given. A simple algorithm iterating over the layers of the structure is derived to analytically calculate the surface wave's electromagnetic field components and the power carried by surface waves. The need of numerical integration or calculation of residues is omitted. This benefits a reduction in computation time and an improvement in accuracy and versatility of computer-aided design (CAD) programs. The presented method has been implemented in a microwave CAD program. Numerical results for planar antennas are presented     

Scattering from bodies of revolution

The problem of scattering of a plane electromagnetic wave from an arbitrary metallic body of revolution is solved by a theoretical method for arbitrary incidence and polarization. The method permits numerical computations by high-speed digital computers, and examples are given. The incident wave is expanded in cylindrical modes, and an integral equation is solved for the induced current distribution of each mode. The scattering cross section, including the back-scattering or radar cross section, is found by summation of the mode scattered fields. The method is limited to a maximum perimeter length of twenty wavelengths. While the cases discussed in the paper pertain to perfectly conducting bodies, other surface boundary conditions, an arbitrary surface impedance or coatings by lossy dielectrics, can also be treated with equal precision.     

三维物体表面的小波平滑方法

用结构光方法获取物体表面的三维信息,由于其计算简单,易于实现,在计算机视觉领域获得了广泛的应用。然而由于物体表面反射特性的不均匀性、转台的机械扰动以及初始量化误差,实际得到的物体表面将存在一些形变,影响物体表面特性的计算,文中介绍用结构光获取的三维物体表面的小波平滑方法。首次,将物体表面轮廓线（激光扫描线和截面线）以弧长为参数沿Ｘ、Ｙ、Ｚ三个方向分解,并分别用小波进行平滑处理,然后再将这些平滑后的