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     

A compressive sensing algorithm using truncated SVD for three-dimensional laser imaging of space-continuous targets

For traditional array 3-D laser radars, the resolution of the intensity image and range profile is limited by the number and accuracy of sensors. Moreover, for a space-continuous target, peak detection in the pulsed time of flight is no longer suitable for super-resolution reconstruction algorithms. Hence, a compressive sensing algorithm for 3-D laser imaging is proposed. A range observation matrix composed of time interval basis vectors is constructed to acquire the range information regarding a target. However, the range observation matrix is generally ill-posed owing to the spatial continuity of the target. To address this shortage, truncated singular value decomposition is utilized to extract the peak values of echo pulses for image reconstruction. Simulation results demonstrate the effectiveness and performance of the proposed algorithm.     

Magnetic Field-Based Eddy-Current Modeling for Multilayered Specimens

Eddy-current inspection for nondestructive evaluation has traditionally been investigated in terms of coil impedance signals via theoretical and experimental methods. However, advanced eddy-current techniques use solid-state sensors such as Hall devices, giant magnetoresistive sensors, anisotropic magnetoresistive sensors, and superconducting quantum interference devices for magnetic field measurement to achieve better sensitivity and high temporal and spatial resolution in material evaluation and characterization. Here, we review the Dodd and Deeds integral model and use the truncated region eigenfunction expansion (TREE) method for computation of the magnetic field. This results in series expressions instead of integral ones. Thus, the computation is both simplified and speeded up so that it becomes convenient for solving one-dimensional eddy-current inverse problems. We compare the theoretical results from the analytical model with the results from a numerical simulation based on the finite-element method in terms of accuracy and computation time.     

近程光电视觉传感器感知物体空间信息的研究

本文论述了二种新型光电近程视觉传感器的工作原理、计算方法和系统构成。一种是由多个点光源和位置敏感器(PSD)构成的传感器,文中从误差分析、统计运算的角度出发推导出确定被测对象空间信息的算法;另一种是由多个点光源和单个探测元件构成的传感器,这种传感器通过对位相信息的测定来感知物体的三维信息。两种传感器都能得到被测点到传感器之间的距离信息及被测表面空间取向的信息。所论及的传感器可用于机器人对三维物表面轮廓的追踪运动以及提供物体形状的三维描述信息等方面。     

Solution of three dimensional eddy current problems by integral anddifferential methods

A differential T, Ω formulation using nonconformal elements is presented. It is an extension of the T integral formulation. The method has been used as the basis of a finite-element code that handles the open boundary problem of eddy-current analysis in fully 3-D conductors. The results obtained with this formulation for different treatments of the boundary conditions at infinity are shown and compared among themselves and with respect to a T integral formulation. The efficiencies are compared in terms of storage occupation, CPU time, and accuracy     

ANN-based error reduction for experimentally modeled sensors

A method for correcting the effects of multiple error sources in differential transducers is proposed. The correction is carried out by a nonlinear multidimensional inverse model of the transducer based on an artificial neural network. The model exploits independent information provided by the difference in actual characteristics of the sensing elements, and by an easily controllable auxiliary quantity (e.g., supply voltage of conditioning circuit). Experimental results of the correction of an eddy-current displacement transducer subject to the combined interference of structural and geometrical parameters highlight the practical effectiveness of the proposed method     

矢量线阵二维波达方位估计的方法

声矢量传感器南声压传感器和质点振速传感器组成,它可以空间共点、时间同步测量声场的声压标量和振速矢量信息。钏对声压线阵无法同时分辨目标的方位角和俯仰角,而三维矢量传感器线阵会带来成本的增加和工程应用上的困难．利用二维矢量传感器组成的直线阵对目标的二维波达方位进行联合估计,详细推导了矢量阵MUSIC算法的数学表达式,并着重对矢量线阵在三维坐标不同轴上时对方位估计的影响进行了研究。仿真结果表明二维矢量线阵布放在水平的X轴或Y轴上时存在方位模糊．而布放在垂直的Z轴上时可以实现全空间无模糊定向,且对双目标也有较高的分辨率。     

Three-dimensional eddy current analysis by the boundary elementmethod using vector potential

A boundary-element method using a magnetic vector potential for eddy-current analysis is described. For three-dimensional (3-D) problems, the tangential and normal components of the vector potential, tangential components of the magnetic flux density, and an electric scalar potential on conductor surfaces are chosen as unknown variables. When the approximation is introduced so that the conductivity of the conductor is very large in comparison with the conductivity of air, the number of unknowns can be reduced; also, for axisymmetric models the scalar potential can be eliminated from the unknown variables. The formulation of the boundary-element method using the vector potential, and computation results by the proposed method, are presented     

Modeling Magnet Length In 2-D Finite-Element Analysis of Electric Machines

Two-dimensional finite-element-method (2-D FEM) calculations are widely used in electric machine modeling instead of three-dimensional calculations because of their faster calculation time and simplicity. However, the 2-D calculations ignore end effects, causing a large error in calculating eddy currents in permanent magnets of synchronous machines. In this paper, we develop three analytical models and one curve-fitting model based on numerical calculations. The models improve the eddy-current loss calculation accuracy in 2-D FEM. The method adjusts the resistivity of a magnet material according to magnet dimensions. The adjustment takes into account the resistivity, the temperature dependence, and anisotropy of the resistivity of rare-earth magnet materials. We compare the models against FEM calculations in two and three dimensions and show that all the models improve the eddy-current loss calculation accuracy significantly, especially when the time-harmonic caused eddy-current losses in permanent magnets are considered.      

0-D thermo-hydraulic approach for predicting pressure and temperature along HELIOS SHe closed loop under pulsed loads

Cryogenic systems for future large superconducting tokamaks (e.g. JT-60SA or ITER) are expected to cope with large pulsed heat loads due to cycling plasma operation. Their superconducting magnets are cooled down with forced flow supercritical helium.The aim of this paper is to verify to what extent a 0-D thermo-hydraulic model can well reproduce in space and time, the variations of pressure and temperature along a supercritical helium closed loop, subjected to pulsed heat loads.A 0-D model has been developed and the paper will present the corresponding equations and assumptions will also be justified. A pulsed heat load tokamak relevant scenario has been tested and the resulting variations of pressure and temperature have been compared with experimental data. The results of the 0-D model demonstrate the relevance of such approach for predicting transient behaviors in response of pulsed heat loads in a closed loop.This simple approach is also a justification to use process modeling codes where dynamics of the cryogenic circuits can be simulated with cryogenics components.     

SAW Sensor Network Fabricated on a Polyvinylidine Difluoride (PVDF) Substrate for Dynamic Surface Profile Sensing

A combination of two 2-D sensor networks is proposed as a dynamic surface profile sensor network for biomimicing applications. A surface acoustic wave device fabricated on a polyvinylidine difluoride substrate has been investigated as the elementary 1-D bending curvature sensor used in the network. The device was tested under an injected signal and it shows the variation in amplitude and phase angle of output signal with respect to the injected signal in response to the bending curvature. These dual outputs provide opportunity to make an intelligent sensor with self error limit determination capability. Finally, a network of such sensors is proposed as a dynamic surface profile sensor     

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.     

基于FBG的三维编织复合材料制件状态健康监测研究

介绍了将FBG嵌入三维编织复合材料的方法,提出了三维编织复合材料状态健康监测方法,分析了材料在拉伸承载下的内部应变与FBG变化关系,提出了信号采集和处理方式。实验结果表明,FBG传感器具有优异的传感特性,复合材料的编织角对FBG的信号有一点影响,植入光纤对复合材料的力学性能影响不大。本课题的研究为先进智能复合材料的研发与应用提供了依据。     

Analysis and design of ferrite cores for eddy-current-killedoscillator inductive proximity sensors

Finite element modeling of ferrite cores used in the design of eddy-current-killed oscillator inductive proximity sensors was performed. Based on contemplation of the practical operation of the sensors, ferrite core geometries were compared with a reference core by the eddy-current power loss in a metal target at a fixed distance from the face of each transducer. Several of these cores were experimentally evaluated for sensing distance to verify the results of the simulation. It was observed that, for fixed coil, fixed target distance, and given target, the low-frequency sensing distance of a particular transducer is approximately proportional to the fourth root of eddy-current power loss in the target     

Time-Harmonic Induction-Machine Model Including Hysteresis and Eddy Currents in Steel Laminations

We have studied electromagnetic losses of a frequency-converter-fed cage-induction motor by using a numerical machine model that includes eddy-current and hysteresis phenomena in electrical steel sheets. We used the model to solve the two-dimensional (2-D) time-harmonic field and winding equations of a cage-induction machine, utilizing a finite-element method and phasor variables. We used complex reluctivity to couple the hysteresis and eddy currents in the sheets with the 2-D analysis. The model modifies the absolute value of the reluctivity according to a one-dimensional (1-D) eddy-current solution developed in the lamination thickness. To define the argument of the reluctivity, we applied both the 1-D field solution and measured hysteresis data. We compared computations of additional electromagnetic losses in a 37-kW test machine due to the higher harmonics of a frequency-converter supply with experimental results. The agreement is found to be reasonable.      

Boundary element analysis for the three-dimensional eddy currentproblem

The numerical implementation of the boundary-element method formulated for 3-D eddy-current problems is presented. In particular, the algorithm for solving these problems, together with the formulation for the magnetic vector potential and the electric potential using the Lorentz gauge, is discussed in detail. Based on accurate calculations of the numerical solution at interior points in the neighborhood of the boundary, the revised integration method shown earlier by the authors (1988) is extended to this 3-D magnetic field analysis for the steady-state     

Finite element scheme for transient 3D eddy currents

A transient 3-D finite-element model is presented. The method is based on the solution of the magnetic scalar potential in nonconducting regions and the magnetic vector potential and an electric scalar potential in eddy-current regions. Multiply connected regions of magnetic scalar can be avoided by extending the region modeled by the magnetic vector potential to fill any holes in the conducting regions. The model was used to simulate the FELIX brick experiment     

A 3-D PW ultrasonic Doppler flowmeter: theory and experimental characterization

A complete 3-D ultrasonic pulsed Doppler system has been developed to measure quantitatively the velocity vector field of a fluid flow independently of the probe position. The probe consists of four 2.5 MHz piezocomposite ultrasonic transducers (one central transmitter and three receivers separated by 120°) to measure the velocity projections along three different directions. The Doppler shift of the three channels is calculated by analog phase and quadrature demodulation, then digitally processed to extract the mean velocity from the complex spectrum. The accuracy of the 3-D Doppler technique has been tested on a moving string phantom providing an error of about 4% for both amplitude and direction with an acquisition window of 100 ms     

Theory and implementation of NDT data fusion

Scientific measurements from single or multiple sensors are usually incomplete and uncertain. A process making use of the concept of data fusion has been developed to try to encompass this problem by combining information from multiple sensors. The objective to synergistic use of information from multiple sources is to reduce uncertainty and increase the confidence level of a measurand. The implementation of data fusion to the field of NDT is relatively new. This paper summarizes the achievements of current research on data fusion applied to NDT. A theoretical data fusion strategy is described and experimental results generated from weld inspection are presented.     

图像传感器单粒子效应脉冲激光实验研究

针对设计研制的512×512 CMOS APS图像传感器,采用聚焦脉冲激光束研究了其空间单粒子效应特性。试验结果表明,CMOS APS器件图像传感器存在单粒子翻转（SEU）和单粒子锁定（SEL）现象。验证了CMOS APS图像传感器抗单粒子锁定设计的有效性。当对图像传感器移位寄存器区进行照射时,同时发生单粒子翻转和单粒子锁定,器件其它区域也有类似现象。分析了器件单粒子效应的敏感性,获得了器件发生单粒子翻转和锁定的脉冲激光能量阈值及器件锁定电流大小。