An addendum to “Numerical modeling of an enhanced very earlytime electromagnetic (VETEM) prototype system”

For original paper see Cui et al. (IEEE Antennas and Propagation Magazine, vol.42, no.2, p.17-27, 2000 April). Cui et al. proposed two numerical models to simulate an enhanced very early time electromagnetic (VETEM) prototype system, used for buried-object detection and environmental problems. In the first model, the transmitting and receiving loop antennas were accurately analyzed using the method of moments (MoM), and then conjugate gradient (CG) methods with the fast Fourier transform (FFT) were utilized to investigate the scattering from buried conducting plates. In the second model, two magnetic dipoles were used to replace the transmitter and receiver, because the working frequency for the VETEM system is usually low. Both the theory and formulation were correct, and the simulation results for the primary magnetic field and the reflected magnetic field were accurate. We have compared the simulation results for the magnetic field reflected by a wire-conductor mesh on the ground with measured data. They fit very well. However, the scattered magnetic fields in the simulation results were inaccurate, because we did not use a sufficient number of iterations in the CG-FFT algorithm when the frequency was very low     

Numerical modeling of an enhanced very early time electromagnetic(VETEM) prototype system

In this paper, two numerical models are presented to simulate an enhanced very early time electromagnetic (VETEM) prototype system, which is used for buried-object detection and environmental problems. Usually, the VETEM system contains a transmitting loop antenna and a receiving loop antenna, which run on lossy ground to detect buried objects. In the first numerical model, the loop antennas are accurately analyzed using the method of moments (MoM) for wire antennas above or buried in lossy ground. Then, the conjugate gradient (CG) methods, with the use of the fast Fourier transform (FFT) or MoM, are applied to investigate the scattering from buried objects. Reflected and scattered magnetic fields are evaluated at the receiving loop to calculate the output electric current. However, the working frequency for the VETEM system is usually low and, hence, two magnetic dipoles are used to replace the transmitter and receiver in the second numerical model. Comparing these two models, the second one is simple, but only valid for low frequency or small loops, while the first modeling is more general. In this paper, all computations are performed in the frequency domain, and the FFT is used to obtain the time-domain responses. Numerical examples show that simulation results from these two models fit very well when the frequency ranges from 10 kHz to 10 MHz, and both results are close to the measured data     

Detection of buried targets using a new enhanced very early timeelectromagnetic (VETEM) prototype system

In this paper, numerical simulations of a new enhanced very early time electromagnetic (VETEM) prototype system are presented, where a horizontal transmitting loop and two horizontal receiving loops are used to detect buried targets, in which three loops share the same axis and the transmitter is located at the center of receivers. In the new VETEM system, the difference of signals from two receivers is taken to eliminate strong direct-signals from the transmitter and background clutter and furthermore to obtain a better SNR for buried targets. Because strong coupling exists between the transmitter and receivers, accurate analysis of the three-loop antenna system is required, for which a loop-tree basis function method has been utilized to overcome the low-frequency breakdown problem. In the analysis of scattering problem from buried targets, a conjugate gradient (CG) method with fast Fourier transform (FFT) is applied to solve the electric field integral equation. However, the convergence of such CG-FFT algorithm is extremely slow at very low frequencies. In order to increase the convergence rate, a frequency-hopping approach has been used. Finally, the primary, coupling, reflected, and scattered magnetic fields are evaluated at receiving loops to calculate the output electric current. Numerous simulation results are given to interpret the new VETEM system. Comparing with other single-transmitter-receiver systems, the new VETEM has better SNR and ability to reduce the clutter     

一种有效的大规模数据的分类方法

本文提出了一种基于自组织特征映射神经网络(SOM)和支撑矢量机(SVM)相结合的复杂模式的大规模数据的分类方法.该方法首先利用自组织特征映射神经网络对待识目标进行聚类,然后应用支撑矢量机方法对其进行分类识别.通过对复杂异或(XOR)分类问题,以及实际的Iris和Appendicitis数据分类问题等的分类实验,且与仅用支撑矢量机的分类方法比较,结果表明,本文提出的方法对复杂模式的大规模数据的分类识别问题具有较好的效果,且训练时间大幅度减小.     

无深度反转的集成成像一次拍摄方法

针对传统集成成像显示技术存在深度反转,需要进行二次成像的问题,提出一种无深度反转的集成成像一次拍摄方法。该方法采用离轴平行式集成成像拍摄结构对三维(3D)场景进行拍摄,通过设计合理的拍摄参数,重排图像元,生成无梯形畸变的图像阵列(EIA),直接用于集成成像显示,解决了传统集成成像的深度反转问题,避免了复杂且繁琐的图像校正和二次成像过程,可快速生成具有正确深度信息的EIA。该方法所获取的EIA在集成成像3D显示实验中重建的3D图像具有正确的深度和逼真清晰的立体显示效果,验证了本文方法的正确性。     

Imaging of biomedical data using a multiplicative regularizedcontrast source inversion method

In this paper, the recently developed multiplicative regularized contrast source inversion method is applied to microwave biomedical applications. The inversion method is fully iterative and avoids solving any forward problem in each iterative step. In this way, the inverse scattering problem can efficiently be solved. Moreover, the recently developed multiplicative regularizer allows us to apply the method blindly to experimental data. We demonstrate inversion from experimental data collected by a 2.33-GHz circular microwave scanner using a two-dimensional (2-D) TM polarization measurement setup. Further some results of a feasibility study of the present inversion method to the 2-D TE polarization and the full-vectorial three-dimensional measurement will be presented as well     

双栅MOS场效应管精确的二维电势分布与V_（th）的解析模型

双栅（ＤｕａｌＧａｔｅ）ＭＯＳ场效应管所具有的完全对称的独特结构带来一系列电学特性变化引起了人们广泛的研究兴趣。本文利用格林函数法，采用合理的边界条件，得出ＤＧＭＯＳ体硅的二维电势解析表达式，并由此导出适用于亚微米沟道ＤＧＭＯＳ管阈值电压的解析表达式。阈值电压模型与有关实验数据符合甚好。对于进一步深入探讨ＤＧＭＯＳ管的体反型（ＶｏｌｕｍｅＩｎｖｅｒｓｉｏｎ）效应及其引起的电学特性变化，本模型提供了有效的途径。     

应变PMOS二维阈值电压解析模型

利用准二维方法求解二维泊松方程,建立了锗硅源漏单轴应变PMOS阈值电压的二维解析模型,理论计算结果和实验报道的结果能很好吻合。研究了不同沟道长度和漏压情况下的沟道表面势,分析了沟道长度、漏压及锗硅源漏中锗摩尔组分等参数对阈值电压的影响。利用TCAD工具进行仿真模拟,结果表明,沟道长度和漏压是单轴应变PMOS阈值电压漂移的主要影响因素,而锗摩尔组分在一定成分范围内影响较小。     

区域分裂法及其在三维散射中的应用

基于区域分裂（ＤＤＭ）和频域有限差分（ＦＤＦＤ）提出了一种分析三维散射问题的精确高效算法。用区域分裂法可以把原问题分解成若干子问题,可以大大缩小稀疏矩阵的规模,使得求解大尺寸三维散射问题成为可能。文中首先在小尺寸下计算了三维立体柱的散射特性,并和没有进行区域分裂时的ＦＤＦＤ法进行了对比,验证了本算法的正确性;然后又计算了尺寸比较大的三维矩形柱的散射特性,验证了它的高效性。     

A Hybrid Reconstruction Algorithm for 3-D Ionospheric Tomography

In this paper, a hybrid reconstruction algorithm (HRA) is presented to solve the ill-posed inverse problem associated with 3-D ionospheric stochastic tomography. In this new method, the ionospheric electron density (IED) can be inverted by using two steps. First, a truncated singular value decomposition (TSVD) method, whose value is independent on any initial estimation, is used to resolve the ill-posed problem of the tomography system. Second, taking into account the "approximation" of its solution, an iterative improvement process of the solution is then implemented by utilizing the conventional algebraic reconstruction algorithm (ART). The HRA, therefore, offers a more reasonable approach to choose an initial approximate for the ART and to improve the quality of the final reconstructed image. A simulated experiment demonstrates that the HRA method is superior to the TSVD or the ART alone for the tomographic inversion of IED. Finally, the HRA is used to perform GPS-based tomographic reconstruction of the IED at mid- and low-latitude regions.     

三维大纵横比目标散射的快速精确求解

采用积分方程法严格求解三维大纵横比目标的电磁散射。在积分方程法的迭代求解中用快速我极子法（ＦＭＭ）加速矩阵与矢量的相乘计算,同时运用快速傅里叶变换（ＦＦＴ）进一步提高快速多极子方法中的转换预计算,数值结果表明：这种快速多极子法－快速傅立叶变换方法（ＦＭＭ－ＦＦＴ）特别适合于三维大纵横比目标的散射求解。     

Incorporating a measure of local scale in voxel-based 3-D image registration

We present a new class of approaches for rigid-body registration and their evaluation in studying multiple sclerosis (MS) via multiprotocol magnetic resonance imaging (MRI). Three pairs of rigid-body registration algorithms were implemented, using cross-correlation and mutual information (MI), operating on original gray-level images, and utilizing the intermediate images resulting from our new scale-based method. In the scale image, every voxel has the local "scale" value assigned to it, defined as the radius of the largest ball centered at the voxel with homogeneous intensities. Three-dimensional image data of the head were acquired from ten MS patients for each of six MRI protocols. Images in some of the protocols were acquired in registration. The registered pairs were used as ground truth. Accuracy and consistency of the six registration methods were measured within and between protocols for known amounts of misregistrations. Our analysis indicates that there is no "best" method. For medium misregistration, the method using MI, for small add large misregistration the method using normalized cross-correlation performs best. For high-resolution data the correlation method and for low-resolution data the MI method, both using the original gray-level images, are the most consistent. We have previously demonstrated the use of local scale information in fuzzy connectedness segmentation and image filtering. Scale may also have potential for image registration as suggested by this work.     

Interior-point methodology for 3-D PET reconstruction

Interior-point methods have been successfully applied to a wide variety of linear and nonlinear programming applications. This paper presents a class of algorithms, based on path-following interior-point methodology, for performing regularized maximum-likelihood (ML) reconstructions on three-dimensional (3-D) emission tomography data. The algorithms solve a sequence of subproblems that converge to the regularized maximum likelihood solution from the interior of the feasible region (the nonnegative orthant). We propose two methods, a primal method which updates only the primal image variables and a primal-dual method which simultaneously updates the primal variables and the Lagrange multipliers. A parallel implementation permits the interior-point methods to scale to very large reconstruction problems. Termination is based on well-defined convergence measures, namely, the Karush-Kuhn-Tucker first-order necessary conditions for optimality. We demonstrate the rapid convergence of the path-following interior-point methods using both data from a small animal scanner and Monte Carlo simulated data. The proposed methods can readily be applied to solve the regularized, weighted least squares reconstruction problem.     

Nonseparable wavelet-based cone-beam reconstruction in 3-D rotational angiography

In this paper, we propose a new wavelet-based reconstruction method suited to three-dimensional (3-D) cone-beam (CB) tomography. It is derived from the Feldkamp algorithm and is valid for the same geometrical conditions. The demonstration is done in the framework of nonseparable wavelets and requires ideally radial wavelets. The proposed inversion formula yields to a filtered backprojection algorithm but the filtering step is implemented using quincunx wavelet filters. The proposed algorithm reconstructs slice by slice both the wavelet and approximation coefficients of the 3-D image directly from the CB projection data. The validity of this multiresolution approach is demonstrated on simulations from both mathematical phantoms and 3-D rotational angiography clinical data. The same quality is achieved compared with the standard Feldkamp algorithm, but in addition, the multiresolution decomposition allows to apply directly image processing techniques in the wavelet domain during the inversion process. As an example, a fast low-resolution reconstruction of the 3-D arterial vessels with the progressive addition of details in a region of interest is demonstrated. Other promising applications are the improvement of image quality by denoising techniques and also the reduction of computing time using the space localization of wavelets.     

Multiple target tracking using maximum likelihood principle

Proposes a method (tracking algorithm (TAL)) based on the maximum likelihood (ML) principle for multiple target tracking in near-field using outputs from a large uniform linear array of passive sensors. The targets are assumed to be narrowband signals and modeled as sample functions of a Gaussian stochastic process. The phase delays of these signals are expressed as functions of both range and bearing angle (“track parameters”) of respective targets. A new simplified likelihood function for ML estimation of these parameters is derived from a second-order approximation on the inverse of the data covariance matrix. Maximization of this likelihood function does not involve inversion of the M×M data covariance matrix, where M denotes number of sensors in the array. Instead, inversion of only a D×D matrix is required, where D denotes number of targets. In practice, D≪M and, hence, TAL is computationally efficient. Tracking is achieved by estimating track parameters at regular time intervals wherein targets move to new positions in the neighborhood of their previous positions. TAL preserves ordering of track parameter estimates of the D targets over different time intervals. Performance results of TAL are presented, and it is also compared with methods by Sword and by Swindlehurst and Kailath (1988). Almost exact asymptotic expressions for the Cramer-Rao bound (CRB) on the variance of angle and range estimates are derived, and their utility is discussed     

基于改进DPC和特征分区的点云去噪算法

针对三维激光扫描仪获取到的点云数据存在的多尺度混合噪声将严重影响后续的三维模型重建的问题,提出了一种基于改进的密度峰值聚类算法(DPC)和特征分区的点云去噪算法。首先通过改进的DPC算法去除远离点云主体的大尺度噪声;然后利用主成元分析法(PCA)和曲面变分获取点云法矢及曲率信息,同时采用邻域传播法调整法矢方向并根据曲率对点云进行划分,对特征区域点云与平坦区域点云分别采取自适应双边滤波和正交整体最小二乘平面拟合的方法进行光顺去噪。实验结果表明：在包含混合噪声的bunny与block模型下,利用该算法去噪后点云数据最大误差分别为0.235 mm和0.157 mm,平均误差分别为0.029 mm和0.009 mm,均能取得较好的去噪效果,且降低了去噪参数设置的复杂性。     

A general framework for nonlinear multigrid inversion.

A variety of new imaging modalities, such as optical diffusion tomography, require the inversion of a forward problem that is modeled by the solution to a three-dimensional partial differential equation. For these applications, image reconstruction is particularly difficult because the forward problem is both nonlinear and computationally expensive to evaluate. In this paper, we propose a general framework for nonlinear multigrid inversion that is applicable to a wide variety of inverse problems. The multigrid inversion algorithm results from the application of recursive multigrid techniques to the solution of optimization problems arising from inverse problems. The method works by dynamically adjusting the cost functionals at different scales so that they are consistent with, and ultimately reduce, the finest scale cost functional. In this way, the multigrid inversion algorithm efficiently computes the solution to the desired fine-scale inversion problem. Importantly, the new algorithm can greatly reduce computation because both the forward and inverse problems are more coarsely discretized at lower resolutions. An application of our method to Bayesian optical diffusion tomography with a generalized Gaussian Markov random-field image prior model shows the potential for very large computational savings. Numerical data also indicates robust convergence with a range of initialization conditions for this nonconvex optimization problem.     

采用精确三维控制场的wMPS全局组网定向方法

工作空间测量定位系统是一种基于激光扫描的三维坐标大尺寸分布式测量系统,目前已广泛应用于大尺寸测量领域。该系统可以通过增加发射站数目来扩展量程同时精度并不损失,其前提是有一套精确的全局定向参数。在系统多平面约束的数学模型基础上,阐述了一种基于三维控制场的wMPS全局组网定向方法。在标定空间内设置点位坐标已知的控制点组成控制场,给出了组网定向的模型及优化方法,并给出迭代初值生成方法。实验表明:通过基于控制场全局组网定向方法后,系统与激光跟踪仪对比后点位误差优于0.15 mm,在提高效率的同时大大提高了系统的精度。     

An efficient Fourier method for 3-D radon inversion in exactcone-beam CT reconstruction

The radial derivative of the three-dimensional (3-D) radon transform of an object is an important intermediate result in many analytically exact cone-beam reconstruction algorithms. The authors briefly review Grangeat's (1991) approach for calculating radon derivative data from cone-beam projections and then present a new, efficient method for 3-D radon inversion, i.e., reconstruction of the image from the radial derivative of the 3-D radon transform, called direct Fourier inversion (DFI). The method is based directly on the 3-D Fourier slice theorem. From the 3-D radon derivative data, which is assumed to be sampled on a spherical grid, the 3-D Fourier transform of the object is calculated by performing fast Fourier transforms (FFTs) along radial lines in the radon space. Then, an interpolation is performed from the spherical to a Cartesian grid using a 3-D gridding step in the frequency domain. Finally, this 3-D Fourier transform is transformed back to the spatial domain via 3-D inverse FFT. The algorithm is computationally efficient with complexity in the order of N ³ log N. The authors have done reconstructions of simulated 3-D radon derivative data assuming sampling conditions and image quality requirements similar to those in medical computed tomography (CT)     

A new fast method for the reconstruction of 2-D microwave images ofrotating objects

The problem of microwave imaging of rotating objects is approached from a digital signal processing point of view. Attention is focused on the reconstruction of the two-dimensional (2-D) image of an object obtained by processing complex samples of the continuous wave (CW) signal return received for different object aspect angles covering a 2pi total variation. The effects of a polar sampling of the Fourier transform (FT) of the target reflectivity function on the impulse response of the imaging system are analyzed. A criterion for the choice of the angular sampling interval in order to control the image blurring is given. Finally, a new and fast digital signal processing method for image reconstruction is proposed. This method reconstructs high resolution images of rotating targets illuminated by a CW electromagnetic signal or by a large bandwidth transmitted signal. This algorithm is suitable for processing wideband received signal of targets observed for a large variation of the viewing angle, so it is very attractive for the reconstruction of very high spatial resolution target images in SAR/ISAR systems. To show the performance of the method we finally present and discuss the results obtained by applying the proposed technique on simulated and experimental data.