Three-dimensional optical correlator with general complex filters

A new type of electro-optical three-dimensional (3-D) correlator is proposed and demonstrated. A 3-D object scene, observed by multiple cameras from several points of view, is correlated with a 3-D complex computer-generated function. This correlator is a hybridization of the joint transform and the VanderLugt correlators, and, as such, it allows correlations to be made between 3-D real-world objects and 3-D general complex functions. Experimental results are presented.     

Object recognition using three-dimensional optical quasi-correlation

A novel method of three-dimensional (3-D) object recognition is proposed. Several projections of a 3-D target are recorded under white-light illumination and fused into a single complex two-dimensional function. After proper filtering, the resulting function is coded into a computer-generated hologram. When this hologram is coherently illuminated, a correlation space is reconstructed such that light peaks indicate the existence and locations of true targets in the observed 3-D scene. Experimental results and comparisons with results of another 3-D object recognition technique are presented.     

3-D eddy-current computation with a self-adaptive refinementtechnique

A method for the adaptive computation of 3-D eddy-current problems is presented. The 3-D eddy-current problem is formulated in terms of the electric intensity (E formulation). Edge elements that impose tangential continuity of the approximation function are employed for the discretization of the problem with the finite element method. An a-posteriori error estimation technique is proposed with the introduction of two error criteria: a) the tangential discontinuity of the magnetic intensity H, and b) the normal discontinuity of the eddy current density J_e. The proposed error estimation technique is employed in a 3-D self-adaptive refinement procedure. Sufficient approximation of the skin effect and calculation of the eddy current distribution is obtained with the proposed method. The implementation of the proposed technique in a problem of 3-D eddy-current computation in a multiply connected conducting body is discussed     

Optical image recognition of three-dimensional objects

A three-dimensional (3-D) optical image-recognition technique is proposed and studied. The proposed technique is based on two-pupil optical heterodyne scanning and is capable of performing 3-D image recognition. A hologram of the 3-D reference object is first created and then is used to modulate spatially one of the pupils of the optical system; the other pupil is a point source. A 3-D target object to be recognized is then scanned in two dimensions by optical beams modulated by the two pupils. The result of the two-dimensional scan pattern effectively displays the correlation of the holographic information of the 3-D reference object and that of the 3-D target object. A strong correlation peak results if the two pieces of the holographic information are matched. We analyze the proposed technique and thereby lay a theoretical foundation for optical implementations of the idea. Finally, computer simulations are performed to verify the proposed idea.     

高速旋转物体的频闪结构光三维面形测量系统

提出了一个用于测量高速旋转物体三维面形的频闪结构光照明系统。系统自动跟踪检测旋转物体的转动信息,再用该信息同步控制光源发光和摄像系统工作,记录下旋转物体在闪光时刻的瞬间“静止”图像。使用该系统产生持续时间为424s的同步频闪结构光,对转速为每分钟1080转的家用电风扇旋转叶片三维面形进行测量,证明该系统能够准确地获得旋转叶片的瞬间静止图像,便于重建旋转叶片每个瞬间时刻的三维面形。同时,该系统还具备人工设定光源发光频率的功能,可以拓宽应用到无重复特征信号的高速运动物体三维面形测量。     

基于3/2维谱的螺栓松动非线性检测及定位

提出基于3/2维谱分析的螺栓松动非线性检测及定位方法,用多尺度法分析螺栓松动产生非线性相位耦合的机理,研究3/2维谱分析处理信号的过程并分析其识别非线性二次谐波原理,以铝板上螺栓结构为实验对象,利用粘贴在铝板表面的压电作动/传感元件进行实验,对结构响应信号进行3/2谱分析,有效判断螺栓的连接状态;为实现松动螺栓的定位,定义螺栓松动的非线性指标,引入径向基插值函数,实验获得粘贴在铝板上压电列阵响应信号的非线性指标,利用径向基插值函数拟合损伤定位图像。实验结果表明,该方法能有效检测螺栓松动非线性,实现松动螺栓定位。     

A multiparametric and multiresolution segmentation algorithm of 3-D ultrasonic data

An algorithm devoted to the segmentation of 3-D ultrasonic data is proposed. The algorithm involves 3-D adaptive clustering based on multiparametric information: the gray-scale intensity of the echographic data, 3-D texture features calculated from the envelope data, and 3-D tissue characterization information calculated from the local frequency spectra of the radio-frequency signals. The segmentation problem is formulated as a maximum a posterior (MAP) estimation problem. A multi-resolution implementation of the algorithm is proposed. The approach is tested on simulated data and on in vivo echocardiographic 3-D data. The results presented in the paper illustrate the robustness and the accuracy of the proposed approach for the segmentation of ultrasonic data     

Theoretical quality assessment of myocardial elastography with in vivo validation

Myocardial elastography (ME), a radio frequency (RF)-based speckle tracking technique with one-dimensional (1-D) cross correlation and novel recorrelation methods in a 2-D search was proposed to estimate and fully image 2-D transmural deformation field and to detect abnormal cardiac function. A theoretical framework was first developed in order to evaluate the performance of 2-D myocardial elastography based on a previously developed 3-D finite-element model of the canine left ventricle. A normal (control) and an ischemic (left-circumflex, LCx) model, which more completely represented myocardial deformation than a kinematic model, were considered. A 2-D convolutional image formation model was first used to generate RF signals for quality assessment of ME in the normal and ischemic cases. A 3-D image formation model was further developed to investigate the effect of the out-of-plane motion on the 2-D, in-plane motion estimation. Both orthogonal, in-plane displacement components (i.e., lateral and axial) between consecutive RF frames were iteratively estimated. All the estimated incremental 2-D displacements from end-diastole (ED) to end-systole (ES) were then accumulated to acquire the cumulative 2-D displacements, which were further used to calculate the cumulative 2-D systolic finite strains. Furthermore, the cumulative systolic radial and circumferential strains, which were angle- and frame-rate independent, were obtained from the 2-D finite-strain components and imaged in full view to detect the ischemic region. We also explored the theoretical understanding of the limitations of our technique for the accurate depiction of disease and validated it in vivo against tagged magnetic resonance imaging (tMRI) in the case of a normal human myocardium in a 2-D short-axis (SA) echocardiographic view. The theoretical framework succeeded in demonstrating that the 2-D myocardial elastography technique was a reliable tool for the complete estimation and depiction of the in-plane myocardial deformation field as well as for accurate identification of pathological mechanical function using established finite-element, left-ventricular canine models. In a preliminary study, the 2-D myocardial elastography was shown capable of imaging myocardial deformation comparable to equivalent tMRI estimates in a clinical setting.     

Fast ultrasound imaging simulation in K-space

Most available ultrasound imaging simulation methods are based on the spatial impulse response approach. The execution speed of such a simulation is of the order of days for one heart-sized frame using desktop computers. For some applications, the accuracy of such rigorous simulation approaches is not necessary. This work outlines a much faster 3-D ultrasound imaging simulation approach that can be applied to tasks like simulating 3-D ultrasound images for speckle-tracking. The increased speed of the proposed simulation method is based primarily on the approximation that the point spread function is set to be spatially invariant, which is a reasonably good approximation when using polar coordinates for simulating images from phased arrays with constant aperture. Ultrasound images are found as the convolution of the PSF and an object of sparsely distributed scatterers. The scatterers are passed through an anti-aliasing filter before insertion into a regular beam-space grid to reduce the bandwidth and significantly reduce the amount of data. A comparison with the well-established simulation software package field II has been made. A simulation of a cyst image using the same input object was found to be in the order of 7000 times slower than the presented method. Following these considerations, the proposed simulation method can be a rapid and valuable tool for working with 3-D ultrasound imaging and in particular 3-D speckle-tracking.     

Green’s function for KI determination of axisymmetric elastic solids containing external circular crack

A new Green’s function is derived to determine the mode-I stress intensity factor for axisymmetric solids containing external circular crack. The formulated boundary integral equation is applied to a finite cylindrical bar with an external crack, and the obtained solution is compared with existing published results, indicating good agreement. The proposed method compared with the finite element method or the conventional application of the boundary element method provides the following main advantages: (a) it does not require discretization of the crack surface, (b) it does not require multi-region modeling and (c) it reduces the 3-D discretization of the solid to 1-D resulting in substantially reduced effort.     

A Grid-based integral approach for quasilinear problems

For non-homogeneous and nonlinear problems, a major difficulty in applying the Boundary Element Method is the treatment of the volume integrals that arise. A recent proposed method, the grid-based integration method (GIM), uses a 3-D uniform grid to reduce the complexity of volume discretization, i.e., the discretization of the whole domain is avoided. The same grid is also used to accelerate both surface and volume integration. The efficiency of the GIM has been demonstrated on 3-D Poisson problems. In this paper, we report our work on the extension of this technique to quasilinear problems. Numerical results of a 3-D Helmholtz problem and a quasilinear Laplace problem on a multiply-connected domain with Dirichlet boundary conditions are presented. These results are compared with analytic solutions. The performance of the GIM is measured by plotting the L₂-norm error as a function of the overall CPU time and is compared with the auxiliary domain method in the Helmholtz problem.     

Free surface flow through rock-fill dams analyzed by FEM with level set approach

 A stabilized-finite element formulation is coupled with a level set technique for computations of incompressible non-linear flow with interfaces between two immiscible fluids. An interface capturing formulation (ICF) for non-linear, free surface, seepage flow in rock-fill dams is proposed. The formulation is derived for two- and three-dimensional flow within a fixed mesh domain. The resulting formulation is general and applicable for various steady and transient two-phase flow problems. FE-refinement is processed for the entire fixed mesh domains. A general solver is also reviewed for large and non-symmetric non-positive definite linear system of equations with the GMRES-update technique based on a Newton-iterative method. The computational procedure has been implemented in MATLAB. A comparison is performed between the 2-D computed test problem for coarse and refined meshes together with some proposed analytical solutions for nonlinear seepage flow with free surface in rock-fill dams. An expansion of the 2-D program code to a 3-D one for a rectangular rock-fill dam is also developed and simulated in MATLAB. The performance of the computations in 3-D is very promising and its opening the future for possible industrial applications using the same simple technique. Computations for a simple 3-D seepage flow problem with free surface in rock-fill dam are included in present paper. A general mesh generator and solver for large scale and complex 3-D flow problems in a real embankment dam is also under construction in C++.     

Sub-sample displacement estimation from digitized ultrasound RF signals using multi-dimensional polynomial fitting of the cross-correlation function

A widely used time-domain technique for motion or delay estimation between digitized ultrasound RF signals involves the maximization of a discrete pattern-matching function, usually the cross-correlation. To achieve sub-sample accuracy, the discrete pattern-matching function is interpolated using the values at the discrete maximizer and adjacent samples. In prior work, only 1-D fit, applied separately along the axial, lateral, and elevational axes, has been used to estimate the sub-sample motion in 1-D, 2-D, and 3-D. In this paper, we explore the use of 2-D and 3-D polynomial fitting for this purpose. We quantify the estimation error in noise-free simulations using Field II and experiments with a commercial ultrasound machine. In simulated 2-D translational motions, function fitting with quartic spline polynomials leads to maximum bias of 0.2% of the sample spacing in the axial direction and 0.4% of the sample spacing in the lateral direction, corresponding to 38 nm and 1.31 μm, respectively. The maximum standard deviations were approximately 1% of the sample spacing in both the axial and the lateral directions, corresponding to 193 nm axially and 4.43 μm laterally. In simulated 1% axial strain, the same function fitting leads to mean absolute displacement estimation errors of 255 nm in the axial direction and 4.77 μm in the lateral direction. In experiments with a linear array transducer, 2-D quartic spline fitting leads to maximum bias of 458 nm and 6.27 μm in the axial and the lateral directions, respectively. These results are more than one order of magnitude smaller than those obtained with separate 1-D fit when applied to the same data set. Simulations and experiments in 3-D yield similar results when comparing 3-D polynomial fitting with 1-D fitting along the axial, lateral, and elevational directions.     

A Boundary Integral Formulation on Unstructured Dual Grids for Eddy-Current Analysis in Thin Shields

A 3-D boundary integral method (3-D BIM) capable of analyzing eddy currents in thin shields is presented. This novel approach is formulated in terms of loop currents in order to implicitly fulfill the div-free condition for quasi-magnetostatic problems. Using nonorthogonal dual grids unknowns are defined on nodes, resulting in a very efficient formulation with limited memory requirements. The proposed method is tested on an axisymmetric model showing a good agreement with the analytical solution. 3-D BIM is then applied to analyze a real case of low-frequency magnetic shielding     

Design Optimization of NEMS Switches for Suspended-Gate Single-Electron Transistor Applications

The operation of nanoelectromechanical switches is investigated through simulation. A simple methodology based on a 1-D lumped model taking account of the Casimir effect is first proposed to determine a low-voltage actuation window for conventional cantilevers. Results show good agreement with 3-D simulation and prove to be helpful for systematic design. The conventional cantilever shape is then optimized to a cross-like design that is fully studied in a 3-D environment. Static and dynamic behaviors as well as effect of the oxide layer thickness are investigated with a view to suspended-gate single-electron transistor applications. The proposed structure successfully combines low actuation voltage and low power consumption, and it is shown that the switching speed is the limiting factor for the considered applications.      

网格投影式立体视觉三维表面重建系统

提出了一种基于立体视觉的三维表面重建的新方法。该方法以立体视觉为基础,结合网格投影,把被动的立体视觉与主动的非结构光网格投影相结合,采用一种算法简单的由粗到精网格图像立体匹配方法,有效地解决了常用的立体视觉系统中存在的算法复杂、处理时间长、容易产生误匹配等问题。基于该方法的三维表面重建系统具有结构简单、操作方便、数据采集速度快、实时性强等优点。实验结果表明该系统能够有效地对三维表面,特别是对无明显特征的光滑自由三维曲面进行重建。     

Modeling of porous piezoelectric structures by the meshless local Petrov-Galerkin method

A meshless method based on the local Petrov-Galerkin approach is proposed to solve initial-boundary value problems of porous piezoelectric solids. Constitutive equations for porous piezoelectric materials possess a coupling between mechanical displacements and electric intensity vectors in both solid and fluid phases. Stationary and transient 2-D and 3-D axisymmetric problems are considered in this article. Nodal points are spread on the problem domain, and each node is surrounded by a small circle for simplicity. The spatial variation of displacements and electric potentials for both phases is approximated by the moving least-squares scheme. After performing the spatial integration, one obtains a system of ordinary differential equations for certain nodal unknowns. The resulting system is solved numerically by the Houbolt finite-difference scheme as a time stepping method. The proposed method is applied to bending problems associated with a porous piezoelectric 2-D plate and 3-D axisymmetric cylinder under simply supported and clamped boundary conditions.     

基于固定扫描点的建筑物三维测量方法

提出一种基于固定激光扫描点的三角投影法测量建筑物大目标三维尺寸的方法。利用线结 构光旋转扫描形面和对投影图像进行处理分析,实现三维重建和测量。导出了三维几何尺寸的计算公式,进行了仿真实验,获得满意的数据。在进行建筑物等大目标三维测量时,不需激光器和传感器平行移动,减少误差来源,提高精度,方便可行。     

基于自适应前景分割及粒子滤波的人体运动跟踪

提出了在图像序列中用自适应前景分割及粒子滤波对人体的3-D运动轨迹进行跟踪的方法．首先建立了像素点的高斯模型,并结合图像帧间的差分信息以及灰度分布的先验概率等因素完成了图像中人体的自适应分割．根据所得到的分割结果建立了透视投影下的运动平面跟踪模型．根据投影过程的非线性以及图像中噪声分布的未知性,提出了粒子滤波的跟踪方法,并最终得到了人体运动平面的3-D轨迹．实际人体运动图像序列的实验证明,本文方法能有效地跟踪人体运动的3-D轨迹,并反映出在此跟踪问题上粒子滤波比传统的扩展卡尔曼滤波更具优势．     

Three-dimensional object recognition by fourier transform profilometry

An automatic method for three-dimensional (3-D) shape recognition is proposed. It combines the Fourier transform profilometry technique with a real-time recognition setup such as the joint transform correlator (JTC). A grating is projected onto the object surface resulting in a distorted grating pattern. Since this pattern carries information about the depth and the shape of the object, their comparison provides a method for recognizing 3-D objects in real time. A two-cycle JTC is used for this purpose. Experimental results demonstrate the theory and show the utility of the new proposed method.