基于PMP的岩芯样品裂缝三维重构方法

提出了一种对岩芯样品内部裂缝进行高精度三维重构的新方法.该方法运用相位测量轮廓术(PMP)测得岩芯两裂面的三维面形,利用高度信息提取两裂面的边缘轮廓,避免了传统的基于灰度信息提取边缘受背景和阴影的影响,采用相关度最值算法实现两裂面的轮廓匹配和高度匹配,以岩芯表面裂纹特征为基础获取了岩芯内部裂缝的宽度和体积,实现了岩芯裂缝的三维重构,三维重构重复精度优于20 μm,为裂缝性油气藏开发中面临的裂缝预测提供了一种有效方法.实验证明了该方法的可行性和实用性.     

计算周期性导波结构的时域有限差分方法

本文提出一种计算周期性导波结构的时域有限差分方法.由Floquet定理建立边界条件,在电场边界和磁场边界上两次使用Floquet定理,从而将计算域限制在一个周期结构内,并且在导波结构侧面引入吸收边界条件,保证了计算精度.通过预先给出传播常数,经FDTD迭代计算,其谐振频率就是该传播常数所对应的工作频率.     

Numerical scattering analysis for two-dimensional dense randommedia: characterization of effective permittivity

A new numerical method for determining effective permittivity of dense random media in two dimensions is presented. The core of the method is to compare the average scattered field of a random collection of scatterers confined within an imaginary boundary with the scattered field from a homogeneous dielectric of the same shape as the imaginary boundary. The two-dimensional (2-D) problem is aggressively studied to provide insight into the dependence of the method's convergence on particle size, boundary shape, and boundary dimension. A novel inverse scattering method is introduced based on the method of moments (MoM), which greatly reduces the computation time and increases the flexibility of the procedure to analyze a variety of geometries. Results from this 2-D method may be used directly to compare with theoretical methods for determining effective permittivity such as the Polder-Van Santen (1946) mixing formula or field techniques such as the quasi-crystalline approximation     

Extended boundary condition integral equations for perfectly conducting and dielectric bodies: Formulation and uniqueness

The equivalence theorem is used to derive novel generalized boundary condition (GBC) integral equations for the tangential components of the electric and magnetic fields on the interfaces of a finite number of dielectric or conducting scatterers. Closed surface, plane, and line extended boundary conditions (EBC) equivalent to the GBC are introduced. The GBC integral equations can now be replaced by any of these EBC integral equations whose solutions are unique and easy to obtain numerically using the moment method. A perfectly conducting sphere and a dielectric sphere in the electrostatic field of two equal and opposite point charges are presented as simple examples of the general procedure.     

Analysis of optical waveguide discontinuities

A novel approach for analyzing discontinuity problems in optical waveguides is presented. The method is a combination of the vector-finite-element method and the least-squares boundary residual method. The vector-H-field-finite-element method is capable of providing accurate eigenvalues and eigenvectors for a wide range of optical waveguide problems, including arbitrary shape, arbitrary index distribution, and anisotropic materials. The least-squares boundary residual method matches the continuity of tangential fields in the least-squares sense, taking into account many modes at the discontinuity plane, to give the general scattering matrix. A few results are presented to show the usefulness of the approach     

一种有效的数值吸收边界条件与MEI方法的比较

本文给出了一种新的吸收边界条件，并与不变性测试方程法（ＭＥＩ）、矩量法在计算时间、存贮空间方面进行比较，结果表明运用这个条件在计算时间和存贮空间上都具有优点，是计算电大尺寸媒质柱体电磁散射特性的一种有效手段。     

Novel finite element analysis of optical waveguide discontinuity problems

In this paper, a novel finite-element method (FEM) to rigorously and efficiently solve the optical waveguide discontinuity problems is presented. Instead of performing the time-consuming modal solutions on both discontinuity sides, the square root of the characteristic matrix is efficiently approximated using Taylor's series expansion, and then the interface boundary conditions are enforced at the discontinuity plane to solve for the reflected and transmitted fields. The high numerical precision and effectiveness of the proposed method is demonstrated through the analysis of various discontinuity problems, and the excellent agreement of the results obtained using the present finite element method and those obtained using other rigorous approaches in the literature.     

用边界元法提取VLSI版图电阻

介绍了ＶＬＳＩ版图验证中电阻提取的基本原理和主要方法，给出了一种新颖的基于边界元法的电阻提取算法。该算法采用变节点单元，较好地解决了实际问题中经常出现的角点问题。通过应用该算法对几个实例进行提取，证明使用本文的算法不仅在精度上而且在占用ＣＰＵ时间上都取得了令人满意的效果     

非线性方程法确定低空探测机载激光雷达消光系数边界值

提出了机载激光雷达进行低空探测时确定消光系数边界值的非线性方程法。首先根据机载激光雷达方程推导出消光系数边界值与机载激光雷达回波信号之间的函数关系,构建一个以消光系数边界值为变量的非线性方程。然后采用改进Jarratt法求此非线性方程的数值解,得到消光系数边界值。使用地基激光雷达真实回波信号数据模拟得到的机载激光雷达回波信号,进行了实验验证,并与斜坡法进行了比较。结果表明,本方法确定边界值的相对误差比斜坡法减小5.9%,由于其具有六阶的收敛特性,迭代次数仅为3次。该方法不需辅助测量设备,精度较高,收敛速度快,迭代次数少,具有良好的应用前景。     

Novel Methods for Modeling of Multiple Vias in Multilayered Parallel-Plate Structures

This paper presents novel modeling methods for accurate and efficient analysis of coupling of multiple vias in finite-sized multilayered parallel-plate structures. The new modeling methods address two open problems related to the modal expansion with the T-matrix method for the analysis of via coupling. First, a novel boundary modeling method, called the frequency-dependent cylinder layer (FDCL), is proposed to resolve the open problem of boundary modeling. In the FDCL, virtual cylinders with dynamic radii are postulated to approximate the original finite-sized boundary of parallel-plate structures. Second, a generalized T-matrix model, which is derived by the mode-matching technique, is created to characterize the coupling effect for vias penetrating more than one layer in a multilayered structure. With the two open problems successfully solved, the modal expansion with the T-matrix method incorporating the FDCL boundary modeling method and the generalized T-matrix model can now be fully utilized for efficient and accurate analysis of finite-sized multilayered parallel-plate structures with a large number of vias. Both numerical and experimental verifications are presented to validate the new modeling methods.      

Translation, rotation, and scale-invariant object recognition

A method for object recognition that is invariant under translation, rotation and scaling is addressed. The first step of the method (pre-processing) takes into account the invariant properties of the normalized moment of inertia and a novel coding that extracts topological object characteristics. The second step (recognition) is achieved by using a holographic nearest-neighbor (HHN) algorithm, in which vectors obtained in the pre-processing step are used as inputs to it. The algorithm is tested in character recognition, using the 26 upper-case letters of the alphabet. Only four different orientations and one size (for each letter) were used for training. Recognition was tested with 17 different sizes and 14 rotations. The results are encouraging, since we achieved 98% correct recognition. Tolerance to boundary deformations and random noise was tested. Results for character recognition in “real” images of car plates are presented as well     

Fuzzy inference-based plaque boundary extraction using image separability for intravascular ultrasound image of coronary artery

A novel plaque boundary extraction method for an intravascular ultrasound (IVUS) image employing image separability and Takagi-Sugeno's fuzzy inference model is presented. The membership functions are allocated heuristically with special consideration of the features of the IVUS image. The method has not only improved the accuracy of plaque boundary extraction but has also reduced the workload of medical doctors.     

运动薄板的平均边界条件

考虑到利用精确边界条件处理电磁屏蔽问题的复杂性,为简化电磁屏蔽边值问题的分析与计算,该文在平均边界条件的基础上给出了运动薄板电磁屏蔽边值问题求解的一种新的近似方法。通过编程上机计算,得到了运动薄板近似传输系数的值,经与精确边界条件下运动薄板准确传输系数的值比较,发现两种结果符合得很好。这表明本文中的方法不仅是简便易行的,且可以足够准确地描述薄板两侧电磁场的分布情况。     

Accurate characterization of planar printed antennas usingfinite-difference time-domain method

The finite-difference-time-domain method (FD-TD) is used to characterize complex planar printed antennas with various feed structures, which include coaxial probe feed, microstrip line feed, and aperture coupled feed structures. A coaxial probe model is developed by using a three-dimensional FD-TD technique. This model is shown to be an efficient and accurate tool for modeling coaxial line fed structures. A novel use of a dispersive absorbing boundary condition is presented for a printed antenna with a high dielectric constant. All the numerical results obtained by the FD-TD method are compared with experimental results, and the comparison shows excellent agreement over a wide frequency band     

Complex multipole beam approach to electromagnetic scatteringproblems

A novel approach to reducing the matrix size associated with the method of moments (MoM) solution of the problem of electromagnetic scattering from arbitrary shaped closed bodies is presented. The key step in this approach is to represent the scattered field in terms of a series of beams produced by multipole sources located in a complex space. On the scatterer boundary, the fields generated by these multipole sources resemble the Gabor basis functions. By utilizing the properties of the Gabor series, guidelines for selecting the orders as well as locations of the multipole sources are developed. It is shown that the present approach not only reduces the number of unknowns, but also generates a generalized impedance matrix with a banded structure and a low condition number. The accuracy of the proposed method is verified by comparing the numerical results with those derived by using the method of moments     

Vectorial wave analysis of uniform-core optical fibers using anovel boundary integral method

Vectorial wave analyses of uniform-core optical fibers using a boundary integral method that does not use Green's function are presented. The expansion of the electromagnetic field on the boundary, the selection of the weight function, and the method for giving boundary conditions are discussed. By using the formulation obtained, the propagation characteristics of elliptical-core optical fibers are analyzed. The effect of the boundary shape on the numerical results is also investigated through analyses of rectangular-core fibers. It is found that the boundary integral method can easily be applied to solve vectorial wave boundary value problems     

Scattering analysis of a large body with deep cavities

A numerical scheme is presented for simulating electromagnetic scattering from a large and arbitrarily shaped body, coated with inhomogeneous composite materials, with large and deep cavities. This numerical scheme employs the higher order vector finite-element method (FEM) to discretize the fields inside the cavities and coatings and the higher order boundary integral (BI) method to terminate the FEM computational domain. A highly efficient special solver is designed to eliminate the unknowns inside the cavities, which yields a computed relation (CR) matrix over the cavity's aperture between the tangential electric and magnetic fields. This CR matrix is then combined with the finite element-boundary integral (FE-BI) matrix equation to form a complete linear system for the discrete fields everywhere in the computational domain. The resulting system is solved iteratively using a novel preconditioner derived by replacing the BI with a corresponding absorbing boundary condition (ABC).     

A novel TEM waveguide using uniplanar compact photonic-bandgap(UC-PBG) structure

A novel waveguide using a photonic bandgap (PBG) structure is presented. The PBG structure is a two-dimensional square lattice with each cell consisting of metal pads and four connecting lines, which are etched on a conductor-backed Duroid substrate. This uniplanar compact PBG structure realizes a magnetic surface in the stopband and is used in the waveguide walls to provide magnetic boundary conditions. A relatively uniform field distribution along the cross section has been measured at frequencies from 9.4 to 10.4 GHz. Phase velocities close to the speed of light have also been observed in the stopband, indicating that TEM mode has been established. A recently developed quasi-Yagi antenna has been employed as a broad-band and efficient waveguide transition. Meanwhile, full-wave simulations using the finite-difference time-domain method provide accurate predictions for the characteristics of both the perfect magnetic conductor impedance surface and the waveguide structure. This novel waveguide structure should find a wide range of applications in different areas, including quasi-optical power combining and the electromagnetic compatibility testing     

A Variational Theory for Wave Propagation in Inhomogeneous Dielectric Slab Loaded Waveguides

A novel numerical technique based on the variational formulation defined only in the slab is developed to study the loaded rectangular waveguide with an inhomogeneous dielectric slab. The variational equation for the boundary value problem is formulated and solved numerically, using the finite element method with piecewise quadratic trial functions. A comparison of this new technique with the conventional variational ones is presented. Various propagation characteristics, such as the phase constant, useful bandwidth, power handling capacity, and attenuation constants due to conductor and dielectric losses, are investigated for the waveguide centrally loaded with a slab of parabolic dielectric profile. The effects of changes in dielectric profiles are discussed by examining the results for the slabs with constant and parabolic profiles.     

Functional Approximations for Solving Boundary Value Problems by Computer

The use of functional (as opposed to numerical) approximations in solving electromagnetic boundary value problems is presented. Galerkin's method is modified to simplify the choice of trial functions by permitting use of trial functions which do not satisfy certain boundary conditions. A test problem, the dielectric loaded rectangular waveguide, is worked using both the modified and unmodified Galerkin's method with identical results. This method is then applied to the arbitrary waveguide. The cutoff frequencies and computer drawn contour plots are presented for circular, rectangular, triangular and star-shaped waveguides.