共查询到19条相似文献,搜索用时 140 毫秒
1.
2.
3.
轴对称二维位场的变形玻恩迭代反演 总被引:3,自引:0,他引:3
本文将变形玻恩迭代方法用于处理轴对称二维非均匀介质分布的电导率反演问题众所周知,横磁场的反演比横电场的反演的非线性程度更高.本文选用了收敛速度快而效果好的变形波恩迭代反演方法.而离散非线性积分方程所得矩阵方程的病态特性用古洪诺夫正则化方法来克服,再用共轭梯度方法求解在每次选代过程中采用了快速的半解析半数值的高效正演方法,本文用它半解析地表达出反演中所需计算的格林函数的偏导数;并在此基础上半解析地求出了反演的非线性积分方程中的积分运算,从而大大提高了反演速度和精度 相似文献
4.
5.
分层粗糙面下方介质目标散射的快速算法 总被引:2,自引:0,他引:2
为快速获取分层粗糙面与下方介质目标的复合电磁散射特性,提出了一种基于前后向迭代算法(FBM)和双共轭梯度法(Bi-CG)的快速互耦迭代算法。推导了一维分层粗糙面与下方介质目标(二维散射问题)的耦合边界积分方程组,用FBM求解分层粗糙面的表面积分方程,而用Bi-CG求解目标的表面积分方程,目标和粗糙面的相互耦合作用通过更新两方程的激励项来迭代求解。应用该算法计算了下方存在介质目标时双层介质粗糙面的双站散射系数,与传统矩量法得到的结果相吻合,验证了该算法的正确性;分析了不同极化波入射时该算法的收敛性,讨论了目标尺寸和位置变化对双站散射系数的影响。 相似文献
6.
7.
8.
9.
10.
传统的2维大规模滤波器组的设计方法具有复杂度高的缺点。该文提出一种设计2维双原型滤波器组的快速方法,该方法利用近似完全重构的条件,并采用完全过采样的离散傅里叶变换(DFT)调制滤波器组来设计。新算法将两个原型滤波器的设计问题归结为一个无约束优化问题,其中目标函数为滤波器组的总体失真(传递失真和混叠失真)与原型滤波器阻带能量的加权和,利用目标函数的梯度向量,通过双迭代机制求解该优化问题。单步迭代中,利用矩阵求逆的等效条件和块Toeplitz矩阵求逆的快速算法,显著地降低了计算复杂度。理论分析和数值实验表明,新算法可以得到整体性能更好的滤波器组,计算复杂度大幅度降低,故可以快速设计大规模的2维滤波器组。 相似文献
11.
提出一种基于B样条小波的偏微分方程图像去噪方法.先对图像进行B样条小波变换,将得到的高频系数采用偏微分方程方法去噪,迭代次数采用去相关最优停止准则进行控制;将得到的低频系数进行阈值处理,阈值选取采用基于信息熵的阈值选择策略,然后对处理后的小波系数进行B样条小波逆变换,得到去噪后的图像.数值实验表明,改进算法能克服B样条小波变换与偏微分方程去噪的不足,增强去噪能力,同时有效保护图像边缘和细节信息. 相似文献
12.
Zhang ZQ Liu QH Xiao C Ward E Ybarra G Joines WT 《IEEE transactions on bio-medical engineering》2003,50(10):1180-1189
Active microwave imaging (MWI) is emerging as a promising technique for the detection of biomedical anomalies such as breast cancer because of the high electrical contrasts between malignant tumors and normal tissue. Previously, we have developed fast two-dimensional forward and inverse scattering algorithms for MWI systems. In this paper, we report the full three-dimensional (3-D) forward scattering simulation in order to account for 3-D effects and to provide a fast solver in future 3-D nonlinear inverse scattering methods. The 3-D fast forward method is based on the stabilized biconjugate-gradient fast Fourier transform (BCGS-FFT) algorithm. The method has been validated for various MWI measurement scenarios. Using this fast simulation method, we demonstrate the importance of accounting for 3-D effects in MWI, and we compare numerical results with the measurements from an experimental prototype. 相似文献
13.
Zero-crossings of a wavelet transform 总被引:19,自引:0,他引:19
Mallat S. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1991,37(4):1019-1033
The completeness, stability, and application to pattern recognition of a multiscale representation based on zero-crossings is discussed. An alternative projection algorithm is described that reconstructs a signal from a zero-crossing representation, which is stabilized by keeping the value of the wavelet transform integral between each pair of consecutive zero-crossings. The reconstruction algorithm has a fast convergence and each iteration requires O ( N log2 (N )) computation for a signal of N samples. The zero-crossings of a wavelet transform define a representation which is particularly well adapted for solving pattern recognition problems. As an example, the implementation and results of a coarse-to-fine stereo-matching algorithm are described 相似文献
14.
A novel technique, called the spectral-iteration approach, for analyzing the problem of scattering from periodically perforated screens which find useful applications as radomes, optical filters, artificial dielectrics, and so on is applied. The formulation is carried out in the spectral domain where a set of algebraic equations is obtained directly for the spectral coefficients of the aperture field distribution (or the induced current density) rather than via an integral equation formulation. These equations are then solved simultaneously using an iterative procedure developed in this paper that circumvents the need for matrix inversion. Because the matrix solution is avoided in the spectral approach, it is capable of handling large aperture sizes in a computationally efficient manner. The efficiency of computation results from the use of the fast Fourier transform (FFT) algorithm which is employed in the derivation of the algebraic equations and in the iteration procedure. A unique feature of the spectral-iteration approach is that it has a built-in boundary-condition check which provides a reliable indication of the accuracy of the solution. It is also shown that the spectral domain technique can be applied to even a wider class of geometries, e.g., the step discontinuity in a waveguide. 相似文献
15.
提出一种基于电磁等效原理的一组积分方程,应用变分方法和傅立叶变换理论,得到了时域散射场与目标电磁参数之间非线性关系的频域表示式,即反演自由空间中二维电磁目标的时域非线性迭代方法的反演方程。列举了一些典型的数值反演实例,对反演性能进行了多方面的考察,指出本法是一种具有良好反演性能的时域非线性反演方法。 相似文献
16.
17.
一种新的GNSS快速定位算法 总被引:1,自引:0,他引:1
GNSS定位的经典算法Gauss-Newton迭代法对初始位置依赖性强,若初值设置不当则迭代次数增加,而每次迭代涉及矩阵乘法和矩阵求逆,计算量剧增,直接影响系统冷启动首次定位时间。直接解算定位法无需初值和迭代计算,计算量小但定位精度较差。针对上述问题,本文提出了一种两步快速定位法,首先用直接解算法解算出用户的概略位置,然后将距离方程组在该位置处进行泰勒展开,用加权最小二乘算法计算用户位置的修正量,概略位置修正后即为用户位置。新算法与传统Gauss-Newton迭代定位算法相比,在保证相同定位精度前提下大幅降低运算量,具有重要的工程意义。仿真结果证明了新算法的有效性。 相似文献
18.
Rubk T. Meaney P.M. Meincke P.. Paulsen K.D. 《Antennas and Propagation, IEEE Transactions on》2007,55(8):2320-2331
Breast-cancer screening using microwave imaging is emerging as a new promising technique as a supplement to X-ray mammography. To create tomographic images from microwave measurements, it is necessary to solve a nonlinear inversion problem, for which an algorithm based on the iterative Gauss-Newton method has been developed at Dartmouth College. This algorithm determines the update values at each iteration by solving the set of normal equations of the problem using the Tikhonov algorithm. In this paper, a new algorithm for determining the iteration update values in the Gauss-Newton algorithm is presented which is based on the conjugate gradient least squares (CGLS) algorithm. The iterative CGLS algorithm is capable of solving the update problem by operating on just the Jacobian and the regularizing effects of the algorithm can easily be controlled by adjusting the number of iterations. The new algorithm is compared to the Gauss-Newton algorithm with Tikhonov regularization and is shown to reconstruct images of similar quality using fewer iterations. 相似文献
19.
用变形玻恩迭代法反演电导率的二维非均匀分布 总被引:1,自引:1,他引:0
本文把变形玻恩迭代方法用于求解二维轴对称逆散射问题。该方法提供一种迭代收敛较快的反演成像算法。利用对称轴上20kHz电场的测量值在二维非均匀介质中对电导率分布进行反演。首先给出对于未知电导率分布的非线性积分方法,并用玻恩近似使积分方程线性化,然后用吉洪诺夫与正则化方法求出电导率分布。在迭代过程中,数值模式匹配法用于求解正演场.数值实例表明,用简单的对称轴上测量场能得到好的好的成像结果。 相似文献