A study of wavelets for the solution of electromagnetic integralequations

The use of wavelet basis functions for the efficient solution of electromagnetic integral equations is studied. It has previously been demonstrated that the use of wavelets for expansion and testing functions produces a sparse moment-method matrix. Here, this effect is examined and analyzed in terms of the radiation/receiving characteristics of the wavelet basis functions. The limitations of wavelets as an efficient solution technique are discussed, and a comparison is made to other fast algorithms     

Fast spectral domain algorithm for rapid solution of integralequations

A fast spectral domain algorithm is presented for rapid solution of planar surface integral equations. The method of moments coupling integral matrix is formulated in the spectral domain but not explicitly calculated. Thus, in conjunction with an iterative equation solver, the pertinent matrix/vector products are evaluated with complexity O(n) where n is the number of unknowns. Validation and timing results are presented for an array analysis approach using a hybrid finite element (FE)-boundary integral implementation     

Finite-difference approach to the solution of time-domain integralequations for layered structures

A numerical algorithm for the analysis of transient electromagnetic fields in planar structures is proposed based on the time-domain magnetic-field integral equation (MFIE), electric-field integral equation (EFIE), and the marching-on-in-time approach. The field vectors are represented in terms of vector potential functions which are calculated either by integration or by the three-dimensional (3-D) wave equation according to the geometry of the structure. Thus, the algorithm combines the advantages of integral equation techniques and finite-difference schemes. While this approach is applicable to any geometries, it is especially suitable for multilayered planar structures and is competitive to the finite-difference time-domain (FDTD) method in the case of open and radiating problems. Theoretical results are verified by the analysis of a pulse propagation in a homogeneous open-end microstrip line     

用小波变换快速求解三维电磁散射问题

在三维电磁散射问题中,用小波变换对由Ｒａｏ面片生成的阻抗矩阵进行稀疏化和求逆,比较了两种小波变换对阻抗矩阵的稀疏效果,由此指出了三维散射问题与二维散射问题中小波变换选取有所不同。通过分析和算例,表明小波变换可以有效减少阻抗矩阵的求逆时间,这对于计算电大尺寸散射体的ＲＣＳ是很有益的。     

Wavelet packets feasibility study for the design of an ECG compressor

Most of the recent electrocardiogram (ECG) compression approaches developed with the wavelet transform are implemented using the discrete wavelet transform. Conversely, wavelet packets (WP) are not extensively used, although they are an adaptive decomposition for representing signals. In this paper, we present a thresholding-based method to encode ECG signals using WP. The design of the compressor has been carried out according to two main goals: (1) The scheme should be simple to allow real-time implementation; (2) quality, i.e., the reconstructed signal should be as similar as possible to the original signal. The proposed scheme is versatile as far as neither QRS detection nor a priori signal information is required. As such, it can thus be applied to any ECG. Results show that WP perform efficiently and can now be considered as an alternative in ECG compression applications.     

Wavelet packets and spatial adaptive intraband coding of images

In this work, we present a coding scheme based on a rate-distortion optimum wavelet packets decomposition and on an adaptive coding procedure that exploits spatial non-stationarity within each subband. We show, by means of a generalization of the concept of coding gain to the case of non-stationary signals, that it may be convenient to perform subband decomposition optimization in conjunction with intraband optimal bit allocation. In our implementation, each subband is partitioned into blocks of coefficients that are coded using a geometric vector quantizer with a rate determined on the basis of spatially local statistical characteristics. The proposed scheme appears to be simpler than other wavelet packets-based schemes presented in the literature and achieves good results in terms of both compression and visual quality.     

一种非组合的电磁目标快速识别算法

针对电磁目标识别算法中辐射源组合的本质是避免同一辐射源的多个可能识别结果同时参与一个目标识别模板的匹配置信度计算的问题,提出了一种非组合的快速电磁目标识别方法。依据目标平台与辐射源的搭载关系,建立辐射源识别和平台识别的两级识别体系,基于两点和三点模板匹配法对辐射源进行识别,然后使用非组合的快速模板匹配法对目标平台属性进行识别。仿真实验表明使用该方法计算目标的识别置信度简单易行,可用于实际工程中电磁目标的识别。     

Numerical solution of electromagnetic problems

Modern high-speed digital computers have made possible the solution, by theoretical-numerical techniques, of many problems in electromagnetics that have traditionally been solvable only by experimental methods. Formulated in terms of integral equations, the techniques described yield answers, with an accuracy and completeness unobtainable by experimental methods, in a small fraction of the time and at much less cost than by the experimental approach. Computer programs utilizing these techniques have been developed in the areas of radiation and scattering from arbitrary wire-antenna structures, bodies of revolution, and cylindrical bodies of arbitrary cross section.     

Multilevel fast multipole algorithm for electromagnetic scatteringby large complex objects

The fast multipole method (FMM) and multilevel fast multipole algorithm (MLFMA) are reviewed. The number of modes required, block-diagonal preconditioner, near singularity extraction, and the choice of initial guesses are discussed to apply the MLFMA to calculating electromagnetic scattering by large complex objects. Using these techniques, we can solve the problem of electromagnetic scattering by large complex three-dimensional (3-D) objects such as an aircraft (VFY218) on a small computer     

The fast multipole method (FMM) for electromagnetic scatteringproblems

The fast multipole method (FMM) developed by V. Rokhlin (1990) to efficiently solve acoustic scattering problems is modified and adapted to the second-kind-integral-equation formulation of electromagnetic scattering problems in two dimensions. The present implementation treats the exterior Dirichlet problem for two-dimensional, closed, conducting objects of arbitrary geometry. The FMM reduces the operation count for solving the second-kind integral equation from O(n³) for Gaussian elimination to O(n^4/3) per conjugate-gradient iteration, where n is the number of sample points on the boundary of the scatterer. A sample technique for accelerating convergence of the iterative method, termed complexifying k, the wavenumber, is also presented. This has the effect of bounding the condition number of the discrete system; consequently, the operation count of the entire FMM (all iterations) becomes O(n^4/3). Computational results for moderate values of ka, where a is the characteristic size of the scatterer, are given     

A fast Discrete Wavelet Transform algorithm for visual processing applications

For visual processing applications, the two-dimensional (2-D) Discrete Wavelet Transform (DWT) can be used to decompose an image into four-subband images. However, when a single band is required for a specific application, the four-band decomposition demands a huge complexity and transpose time. This work presents a fast algorithm, namely 2-D Symmetric Mask-based Discrete Wavelet Transform (SMDWT), to address some critical issues of the 2-D DWT. Unlike the traditional DWT involving dependent decompositions, the SMDWT itself is subband processing independent, which can significantly reduce complexity. Moreover, DWT cannot directly obtain target subbands as mentioned, which leads to an extra wasting in transpose memory, critical path, and operation time. These problems can be fully improved with the proposed SMDWT. Nowadays, many applications employ DWT as the core transformation approach, the problems indicated above have motivated researchers to develop lower complexity schemes for DWT. The proposed SMDWT has been proved as a highly efficient and independent processing to yield target subbands, which can be applied to real-time visual applications, such as moving object detection and tracking, texture segmentation, image/video compression, and any possible DWT-based applications.     

用于深空探测快速反射镜的电磁驱动

为了实现深空探测系统对成像光束的高速和高精度控制,以?50 mm×4 mm的单晶硅反射镜作为负载,采用理论和仿真分析相结合的方法,对音圈电机驱动的快速反射镜进行了理论分析和实验验证。给出了该快速反射镜的一般构成、工作原理及数学模型,采用有限元法分析计算了音圈电机线圈、永磁体和气隙尺寸对驱动力矩的影响,最后设计、制作了快速反射镜样机,并进行了测试。结果表明,快速反射镜的转角范围大于±1°,带宽(3 dB)大于500 Hz。该研究结果有助于推广光学快速反射镜在深空探测、激光通信、光电对抗等领域的应用。     

用于电磁散射分析的积分方程快速直接求解法研究及进展

介绍了一系列用于电磁散射分析的积分方程快速直接求解方法,旨在显著缓解或避免积分方程迭代求解收敛缓慢甚至不收敛的问题,为积分方程提供一个快速稳定的数值求解手段.文中详细介绍了快速直接求解方法的优点、应用以及国内外的研究动态;重点讨论了几种不同的方法,分别为分级矩阵（hierarchical matrices,-matrices）以及分级非对角低秩矩阵（hierarchically off-diagonal low-rank matrices,HODLR）,包括每种方法的构建以及分解求逆方式;对各个方法的优缺点展开了进一步讨论;给出了各个方法的分解以及内存复杂度和复杂飞机模型的电磁散射分析数值算例来证明各个方法的效率和精度.最后,对快速直接求解方法当前仍然存在的主要挑战和可能的策略进行了简略的讨论以及展望.     

Closed solution of Berlekamp's algorithm for fast decoding of BCHcodes

A decision tree solution is presented for the most complicated step in decoding binary BCH codes, namely, the computation of an error location polynomial over GF(2^m) from the syndrome vector of received data. The author runs S. Lin's (1970) iterative version of the Berlekamp-Massey algorithm symbolically, keeping the results at each level in the form of branches of a binary decision tree. A decoder can then be constructed that uses the derived formulas to evaluate a decision variable at each level. Complete traversal of the tree using the decision variables leads to the correct polynomial coefficients for the received vector. The decoder can be implemented in a very straightforward way with a simple processor or program that performs extension field arithmetic, or it can be realized entirely in hardware using lookup tables for multiplications, inverses, and exponents, and exclusive OR operations for addition     

A fast convergent method in electromagnetic inverse scattering

The authors present a fast convergent technique of the Born iterative method for nonlinear two-dimensional lossless object profile inversion using time-domain data. The magnitudes of the scattered fields at different frequencies are weighted according to the properties of the object. It is shown that the technique can speed up the convergence of the Born iterative method     

WAVELET ALGORITHM FOR INTEGRAL OPERATOR EQUATION AND ITS APPLICATIONS TO ELECTROMAGNETIC PROBLEMS

A brief summary of the basic theory of wavelet is proposed. The properties of wavelet function are discussed. The possible applications of wavelet to electromagnetics are given. Examples show that the wavelet method is feasible and effective for solving electromagnetic problems.     

大规模有限周期结构电磁特性的快速算法研究进展

周期结构在阵列天线、频率选择表面和超材料方面都有着广泛的应用,而针对大规模有限周期结构电磁散射、辐射特性的快速算法也一直是计算电磁学的热点与难点.本文中,简要介绍了矩量法中几类分析大规模有限周期结构电磁特性的有效算法,并对这几类方法的优缺点做了说明,最后讨论了计算电磁学在分析大规模有限周期结构领域未来的可能发展方向.     

A fast solution of banded circulant systems

The solution of banded circulant systems based on structured factorisation is presented. The structured factorisation of banded circulant matrices is obtained by solving a set of non-linear equations. When the matrix is strictly diagonally dominant, the corresponding non-linear system can be solved by an iterative algorithm, e.g., a non-linear SOR or Newton's iteration. Both approaches are presented. The computational complexity of algorithms for computing the structured factorisation depends on the matrix bandwidth and not on its dimensions. A coupled system obtained by the factorisation is solved using a rank-annihilation formula. The structured approach is competitive to the deconvolution one based on the FFT. Moreover, in many practical applications where large matrices with narrow bandwidths occur the structured approach is the most efficient.     

起爆方式对反应式脉冲发生器的影响试验

反应式脉冲发生器是一种利用快速化学反应变化而产生高功率电磁脉冲的脉冲发生系统,其工作的核心是通过爆炸产生化学反应所需的环境,为了研究起爆方式对其产生的脉冲影响情况,以典型Φ26 mm脉冲发生器为研究对象,设计了端面点起爆、两端起爆和中心起爆3种起爆方式,并进行了试验,试验结果表明,充电电压为5 kV时,中心起爆能产生最大的脉冲电压,两端起爆次之,点起爆最小;试验得到的电压与反应材料的冲击波历经时间成二次曲线变化。     

填充旋波媒质矩形波导电磁场的解析求解

提出了一种获得填充旋波媒质矩形波导电磁场解析解的新方法.从旋波媒质本构方程和麦克斯韦方程出发,讨论了电磁波在旋波媒质中的传播特性.经过矢量变换,将难以解析求解的波动方程化简为常规的波动方程,并对其进行了求解.利用矢量变换关系和场矢量的边界条件,求得了电磁场分量表达式和求解传播常数的特征方程组.