共查询到20条相似文献,搜索用时 15 毫秒
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Multidomain pseudospectral time-domain simulations of scattering by objects buried in lossy media 总被引:2,自引:0,他引:2
Guo-Xin Fan Qing Huo Liu Hesthaven J.S. 《Geoscience and Remote Sensing, IEEE Transactions on》2002,40(6):1366-1373
A multidomain pseudospectral time-domain (PSTD) method with a newly developed well-posed PML is introduced as an accurate and flexible tool for the modeling of electromagnetic scattering by 2-D objects buried in an inhomogeneous lossy medium. Compared with the previous single-domain Fourier PSTD method, this approach allows for an accurate treatment of curved geometries with subdomains, curvilinear mapping, and high-order Chebyshev polynomials. The effectiveness of the algorithm is confirmed by an excellent agreement between the numerical results and analytical solutions for perfectly conducting as well as permeable dielectric cylinders. The algorithm has been applied to model various ground-penetrating radar (GPR) applications involving curved objects in a lossy half space with an undulating surface. This multidomain PSTD algorithm is potentially a very useful tool for simulating antennas near complex objects and inhomogeneous media. 相似文献
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Gang Zhao Yan Qing Zeng Liu Q.H. 《Microwave and Wireless Components Letters, IEEE》2003,13(5):184-186
A three-dimensional (3-D) multidomain pseudospectral time-domain (PSTD) method with a well-posed PML is developed as an accurate and efficient solver for Maxwell's equations in conductive and inhomogeneous media. The curved object is accurately treated by curvilinear coordinate transformation. Spatial derivatives are obtained by the Chebyshev collocation method to achieve a high-order accuracy. Numerical results show an excellent agreement with solutions obtained by the FDTD method under fine sampling. 相似文献
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In order to deal with the stability problem restricted by the finite-difference time-domain (FDTD) and conventional pseudospectral time domain (PSTD), the multidomain PSTD algorithm based on alternating-direction implicit (ADI) technique is proposed in this paper. This algorithm improves the stability and efficiency of conventional PSTD, while it maintains the accuracy and flexibility of conventional PSTD for an accurate treatment of arbitrarily curved objects. A compact matrix form is derived to effectively describe two-dimensional ADI multidomain pseudospectral time domain (ADI-MPSTD) algorithm. Numerical results show an excellent agreement with analytical solutions as well as results obtained by the FDTD algorithm, and fully demonstrate a remarkable improvement in stability and efficiency. 相似文献
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Chai M. Tian Xiao Gang Zhao Qing Huo Liu 《Antennas and Propagation, IEEE Transactions on》2007,55(5):1398-1406
We propose a hybrid technique combining the pseudospectral time-domain (PSTD) method with the alternating-direction implicit conformal finite-difference time-domain (ADI-CFDTD) method to solve 3-D mixed-scale problems in computational electromagnetics. A mixed-scale problem contains both electrically large and relatively homogeneous regions and electrically small fine details, thus poses a significant computational challenge to any single computational method if it is utilized alone. In particular, the ADI-CFDTD method is an unconditionally stable time-domain method with second-order spatial accuracy, and allows the time step to be increased beyond the Courant-Friedrichs-Levy limit; it is suitable for electrically small problem (structure details much smaller than a wavelength) but is inefficient and suffers from large numerical errors for electrically large-scale regions. The PSTD method, on the other hand, is accurate and efficient for regions with large, relatively homogeneous materials, but loses its efficiency for electrically small structures. The hybrid PSTD/ADI-CFDTD method overcomes these disadvantages and is potentially more useful than the individual solvers. The implementation details and numerical accuracy of this hybrid method are examined. Numerical examples demonstrate the advantages of the hybrid PSTD/ADI-CFDTD method 相似文献
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This letter presents a new time-domain method for Maxwell's equations, in which the unconditionally stable techniques, the alternating direction implicit (ADI) and the split-step (SS) schemes, are developed for the pseudospectral time-domain (PSTD) algorithm to maintain stability while achieving higher accuracy and efficiency over the FDTD method. The multidomain strategy is employed to allow for a flexible treatment of internal inhomogeneities. Numerical results demonstrate the unconditional stability and the second-order accuracy for both ADI- and SS-PSTD algorithms. 相似文献
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结合PML边界条件的傅立叶时域伪谱(PSTD)算法已广泛用于模拟电磁波传播和目标散射,但传统的PSTD方法在每个坐标方向上需要均匀分布的空间坐标网格点,从而不能够很好地模拟曲面目标和与网格空间尺寸不一致的目标,基于变空间的PSTD方法可以很好地克服这些不足。文中将CFS-PML边界条件在PSTD算法中实现并将它与TSNU-PSTD方法结合模拟了大范围有耗媒质中2D\3D曲面介质体目标的电磁散射,部分结果与FDTD计算结果进行了比较。仿真结果表明,基于变空间的PSTD只需平均每波长分成3个网格就可以达到较好的精度,可高效模拟电大尺寸空间曲面形状目标体的电磁散射。 相似文献
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伪谱时域(PSTD)方法可以处理电大尺寸目标电磁散射问题。本文介绍了一种能够把入射波有效引入PSTD计算区域的新方法——加权总场法。该方法通过引入类似于FDTD中连接边界的连接层,将计算区域划分为总场区、连接区和散射场区。为了总场区和散射场区的连续,在连接区引入窗函数.通过设置8—10层连接区就可以将入射波有效地引入到PSTD总场区。这样使入射波和目标分离,实现了复杂目标的单独建模,从而使PSTD便于模拟复杂目标的电磁散射。文中以高斯脉冲为入射波,通过二维情况下目标散射宽度的数值结果,验证了加权总场法应用于PSTD算法时的有效性和计算精度。 相似文献
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Jongkuk Park Jungwon Lee Heeduck Chae Sangwook Nam 《Microwave Theory and Techniques》2001,49(11):2147-2151
A finite-element method (FEM)-based hybrid method (or iterative FEM) is successfully applied to a three-dimensional (3-D) scattering problem without the effect of internal resonance. With only a small number of meshes around a 3-D scatterer, this FEM is shown to give an accurate result through several iterative updates of the boundary conditions. To confirm the efficiency of this method, scattering from a 3-D cavity-backed aperture is analyzed and the results obtained are compared with the same obtained by another conventional method 相似文献
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In this paper, we present a multidomain and multi-method coupling scheme called FACTOPO, based on generalized scattering matrix computations on three-dimensional (3-D) subdomains. The global target Ω is split in NV subdomains (Vi)(i=1, NV), separated by NI fictitious surfaces (Γ j)(j=1,NI). We use a modal representation of the tangent fields on the interfaces. In each domain, the generalized scattering matrix Si is computed with different methods such as the 3-D finite-element method (FEM) or the electric field integral equation (EFIE). This coupling scheme leads to an important reduction in computational resources, especially for cavities with one dimension much larger than the other two. The advantages of this formulation for parametric studies is illustrated by two cases: computing the RCS of an air-intake terminated with a flat PEC or a fan (CHANNEL) and of an antenna structure coupled to an electronic feed with a varying parameter (DENEB). Numerical as well as experimental results are presented 相似文献
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Kai Li Xiaodong Wang 《Vehicular Technology, IEEE Transactions on》2005,54(2):580-590
We investigate the effective temporal diversity property of a multiantenna system employing the phase sweeping transmit diversity (PSTD) scheme in a slow fading channel. We analyze how the number of transmit antennas used for phase sweeping and the sweeping frequency spacing affect the normalized time mean-square covariance (NTMSV) value which characterizes the temporal diversity of a channel. It is revealed that, in some situations, given the maximum sweeping frequency, there is an optimal antenna number that maximizes the temporal diversity, and the NTMSV can be used to find the optimal antenna number. Although the temporal diversity provided by PSTD is at the expense of the spatial diversity, we show by analyzing the fundamental tradeoff between the spatial diversity and the temporal diversity that the overall diversity gain can be maintained when applying the PSTD technique. Numerical results show that, with low complexity receivers, the coded PSTD multiple antenna system is a promising candidate to exploit the possible diversity in slow fading channels. 相似文献
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In this paper, an approximate solution for electromagnetic scattering by a very thin planar homogeneous dielectric object is presented. This solution is obtained from a volumetric integral equation using Fourier transform and is shown to be uniformly valid from low to high frequencies at all incidence angles including edge-on incidence. Validity of the solution is demonstrated through a comparison with canonical objects such as an infinite dielectric slab, and a number of two-dimensional (2-D) and three-dimensional (3-D) dielectric scatterers. For 2-D, and 3-D scatterers, the approximate solution is compared with a method of moments solution. In all cases examined the approximate formulation provides very accurate results except for situations where the dielectric constant is very high. 相似文献
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《IEEE transactions on medical imaging》1997,16(5):630-641
The recovery of a three-dimensional (3-D) model from a sequence of two-dimensional (2-D) images is very useful in medical image analysis. Image sequences obtained from the relative motion between the object and the camera or the scanner contain more 3-D information than a single image. Methods to visualize the computed tomograms can be divided into two approaches: the surface rendering approach and the volume rendering approach. In this paper, a new surface rendering method using optical flow is proposed. Optical flow is the apparent motion in the image plane produced by the projection of real 3-D motion onto the 2-D image. The 3-D motion of an object can be recovered from the optical-flow field using additional constraints. By extracting the surface information from 3-D motion, it is possible to obtain an accurate 3-D model of the object. Both synthetic and real image sequences have been used to illustrate the feasibility of the proposed method. The experimental results suggest that the proposed method is suitable for the reconstruction of 3-D models from ultrasound medical images as well as other computed tomograms 相似文献
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基于造影图像的冠状动脉三维定量分析的研究 总被引:6,自引:4,他引:2
由于X射线造影成像把血管三维空间结构投影到二维图像上,基于二维造影图像的传统诊治方法存在很大局限性.本文在冠状动脉树三维重建的基础上,研究了冠状动脉的三维定量分析方法,提出血管直径、分支夹角和血管段长度的三维测量方法.并利用冠状动脉树实物模型进行实验,对二维和三维定量分析结果进行了比较.实验结果表明,三维定量分析能够有效地提高临床医学参数的测量精度.因此,在冠心病的临床诊断和介入治疗中,该方法能够可靠地诊断血管狭窄及选择和放置支架. 相似文献
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Markerless real-time 3-D target region tracking by motion backprojection from projection images 总被引:3,自引:0,他引:3
Rohlfing T Denzler J Grässl C Russakoff DB Maurer CR 《IEEE transactions on medical imaging》2005,24(11):1455-1468
Accurate and fast localization of a predefined target region inside the patient is an important component of many image-guided therapy procedures. This problem is commonly solved by registration of intraoperative 2-D projection images to 3-D preoperative images. If the patient is not fixed during the intervention, the 2-D image acquisition is repeated several times during the procedure, and the registration problem can be cast instead as a 3-D tracking problem. To solve the 3-D problem, we propose in this paper to apply 2-D region tracking to first recover the components of the transformation that are in-plane to the projections. The 2-D motion estimates of all projections are backprojected into 3-D space, where they are then combined into a consistent estimate of the 3-D motion. We compare this method to intensity-based 2-D to 3-D registration and a combination of 2-D motion backprojection followed by a 2-D to 3-D registration stage. Using clinical data with a fiducial marker-based gold-standard transformation, we show that our method is capable of accurately tracking vertebral targets in 3-D from 2-D motion measured in X-ray projection images. Using a standard tracking algorithm (hyperplane tracking), tracking is achieved at video frame rates but fails relatively often (32% of all frames tracked with target registration error (TRE) better than 1.2 mm, 82% of all frames tracked with TRE better than 2.4 mm). With intensity-based 2-D to 2-D image registration using normalized mutual information (NMI) and pattern intensity (PI), accuracy and robustness are substantially improved. NMI tracked 82% of all frames in our data with TRE better than 1.2 mm and 96% of all frames with TRE better than 2.4 mm. This comes at the cost of a reduced frame rate, 1.7 s average processing time per frame and projection device. Results using PI were slightly more accurate, but required on average 5.4 s time per frame. These results are still substantially faster than 2-D to 3-D registration. We conclude that motion backprojection from 2-D motion tracking is an accurate and efficient method for tracking 3-D target motion, but tracking 2-D motion accurately and robustly remains a challenge. 相似文献
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Hemmendorff M Andersson MT Kronander T Knutsson H 《IEEE transactions on medical imaging》2002,21(12):1536-1543
We present a method for accurate image registration and motion compensation in multidimensional signals, such as two-dimensional (2-D) X-ray images and three-dimensional (3-D) computed tomography/magnetic resonance imaging volumes. The method is based on phase from quadrature filters, which makes it robust to noise and temporal intensity variations. The method is equally applicable to signals of two, three or higher number of dimensions. We use parametric models, e.g., affine models, finite elements or local affine models with global regularization. Experimental results show high accuracy for 2-D and 3-D motion compensation. 相似文献