三维电容层析成像组合电极激励测量模式

针对3层电容阵列电极传感器,基于三维仿真,研究了两种组合电极激励测量模式,并与传统的单电极激励单电极测量模式进行了比较,包括电容测量值大小及其动态范围、敏感场分布均匀性以及重建图像质量。基于COMSOL软件及Matlab软件进行了仿真实验,结果表明:相较于传统的单电极激励单电极测量模式,组合电极激励测量模式所得图像重建效果更好,测量电容值较大且动态范围较小,敏感场分布更加均匀,对中心物体的成像质量明显提高。     

双电极联合循环工作模式下阵列电极的传感能力分析

同面阵列电极主要基于边缘电场工作使其敏感场分布呈现软场特性,其传感能力易受外部多因素影响而降低。为了提高同面电容传感器的检测能力和检测效率,本文针对3×4同面阵列电极,提出了一种两极板联合循环激励的测量模式。通过对同面电极电势分布的有限元仿真,分析了该激励模式下的电场穿透深度。求解了阵列电极的灵敏度矩阵,根据其数据离散系数评判敏感场的均匀性。通过建立3种不同被测物场的模型,分别分析其电容数据的动态范围,并进行图像重建,采用图像相关系数比较图像质量的提升效果。结果表明,在联合循环电极激励测量模式下,阵列电极穿透深度和敏感场分布均匀性均好于单电极激励模式,重建图像更清晰地反映了待测物体的实际形态和轮廓,综合验证了阵列电极传感能力得以提高。     

基于旋转电极的电容层析成像技术图像融合算法

针对固定电极的电容层析成像技术独立测量值较少,且由于电极位置的影响而导致重建图像失真等问题,提出了一种基于16旋转电极的电容层析成像技术系统模型及对应的图像融合方法。模型对16电极的电容层析成像技术模型进行4次旋转,得出的数据分别采用线性反投影算法和修正共轭梯度法算法进行图像重建,再将重建的5张图像进行小波变换,变换得到的低频和高频成分分别采用加权平均和主分量分析的融合准则进行图像融合。实验结果表明:提出的电容层析成像技术旋转模型通过增加测量电容数,结合图像融合方法可明显提高重构图像质量,降低成像误差。     

电容层析成像系统阵列电极三维优化设计

基于COMSOL软件构建了电容层析成像传感器三维有限元模型,并实现其正问题求解,在此基础上,进行了电容层析成像3层分布的阵列电极传感器参数的无量纲优化设计。首先,分析了传感器的屏蔽层半径R3、电极高度h、电极宽度w及电极层间距l对灵敏度均匀性指标P及电容值动态范围D的影响规律;然后,通过设计正交试验,综合分析各结构参数对优化指标的影响;最终,得到一组电容层析成像三维传感器的优化结构参数:R3=1.50,h=0.20,w=0.20,l=0.06。     

电容层析成像系统中电容传感器参数优化设计

电容层析成像系统中,图像重建的质量主要依赖于电容敏感场分布的均匀性,这一性质又由传感器的几何和材料参数决定,因此传感器的设计尤为重要．根据敏感场颁上的均匀性,灵敏程度和电容测量技术,确定了传感器的优化参数;在多因素轮换的基础上,采用正交设计法进行电容传感器参数的计算机辅助设计,从而快速地获得一组最优参数．在实际应用中,概据此优化参数制造的电容传感器获得了较为理想的重建图像．     

数字化电容层析成像系统

基于电容敏感原理设计的数字化电容层析成像（ECT）系统,利用有限元法,分析了阵列电极结构对敏感场分布的影响,通过优化设计和仿真试验,改善了敏感场分布的均匀性;构建了以数字信号处理器（DSP）为核心、现场可编程门阵列（眦）协同工作的12电极的数字化ECT系统,提出了由离线预迭代和在线一步成像所构成的新的图像重建算法——预迭代法,其成像速度及精度均明显得到提高。     

一种组合电极电容层析成像重建图像融合方法

提出一种基于电容层析成像(ECT)组合电极重建图像及层次聚类的ECT图像融合方法。首先,构建组合8电极及12电极ECT阵列传感器,研究2种组合传感器激励测量方案;其次,采用层次聚类法对两种组合电极ECT重建图像进行聚类,从而消除重建过程中产生的伪影;最后,将聚类后的2种图像再进行小波融合重建。实验结果表明,相较于原始重建图像,所提方法重建图像平均相对误差最小,最大降幅达到23.4%,平均相关系数最大,最大增幅达到10.56%。     

基于ECT的航空复合材料缺陷检测研究

针对航空复合材料制件在生产和服役过程中产生的缺陷损伤,提出了一种基于电容敏感原理的同面多电极阵列传感器无损检测方法。基于电容边缘效应,设计了一套同面电极阵列的胶粘缺陷检测系统,模拟航空复合材料缺陷的真实分布。电容层析成像(ECT)系统以单电极激励方式工作,根据缺陷材料介电特性变化引起的电容测量值的变化,采用共轭梯度成像算法复现缺陷位置和形状。实验结果表明,所述方法能够准确地判断出胶粘缺陷的位置和大小,能够对2mm厚度碳纤维复合材料内侧的8mm胶粘结构缺陷进行可视化检测,ECT检测系统重建图像质量较高、边缘伪影较少,为航空复合材料缺陷检测提供了一种新的研究方向。     

电容层析成像系统的仿真与研究

针对电容层析成像系统中的8电极电容传感器,通过电磁场有限元分析软件ANSYS建立了其仿真模型,实现了传感器电容值的快速获取,并分析了传感器的灵敏度特性.在此电容传感器结构下,对层流、核心流、泡流三种典型流型利用RBF神经网络进行了辨识.提出了以层流、核心流、泡流的特征参数作为BP神经网络图像重建的主要依据,实验结果表明利用特征值作为神经网络的输出可以重构出满意的图像.     

基于均匀设计及非线性偏最小二乘法的非闭合电极ECT传感器参数优化设计

提出了一种非闭合电极电容层析成像(ECT)传感器结构参数的优化方法.采用均匀设计结合非线性偏最小二乘(NPLS)回归,提取传感器结构参数(电极极板的宽度 L、绝缘外壳的壁厚δ1.、屏蔽罩与绝缘外壳间距δ2及绝缘外壳材料的相对介电常数ε)与待优化指标(敏感场的均匀度及灵敏度指标p1、最大与最小电容的比值 K)间的函数关系,建立相应的优化目标泛函,通过对优化目标泛函的求解,最终获得传感器结构参数的最优值.并以 10 电极非闭合电极 ECT 传感器为研究对象,进行了结构参数的优化设计,根据优化结果设计制作了非闭合电极 ECT 传感器,对其成像进行了仿真与实测.结果表明,参数优化后的传感器图像重建质量优于未优化的传感器.     

三角波激励ECT测量电路

电容层析成像系统测量电路须有极高灵敏度及动态测量范围。提出一种采用三角波代替传统正弦波作为激励信号的方法,利用C/V转换电路的微分特性,使其输出为方波信号且幅值与被测电容值呈线性关系。瞬态仿真表明,电路的稳定时间缩短为0.65μs;此外,因其不需要相敏解调的环节,电容测量速率大幅提高,将其用于12电极ECT测量,可使测量速度提高到3124帧/s。实测结果表明,该电路的测量灵敏度峰峰值达0.8 V/pF,动态测量范围可达到69 dB。     

Image reconstruction algorithm based on the extended regularised total least squares method for electrical capacitance tomography

Electrical capacitance tomography (ECT) is a non-invasive imaging technology that aims at the visualisation of the cross-sectional permittivity distribution of a dielectric object based on the measured capacitance data. Successful applications of ECT depend greatly on the precision and speed of the image reconstruction algorithms. ECT image reconstruction is a typical ill-posed problem, and its solution is unstable, that is, the solution is sensitive to noises in the input data. Methods that ensure the stability of a solution while enhancing the quality of the reconstructed images should be used to obtain a meaningful reconstruction result. An image reconstruction algorithm based on the regularised total least squares (TLS) method that considers the errors in both the sensitivity field matrix and the capacitance data for ECT is presented. The regularised TLS method is extended using a combination robust estimation technique and an extended stabilising functional according to the ill-posed characteristics of ECT, which transforms the image reconstruction problem into an optimisation problem. In addition, the Newton algorithm is employed to solve the objective functional. Numerical simulations indicate that the algorithm is feasible and overcomes the numerical instability of ECT image reconstruction; for the cases of the reconstructed objects considered here, the spatial resolution of the reconstructed images obtained using the algorithm is enhanced; as a result, an efficient method for ECT image reconstruction is introduced.     

Electrical Capacitance Volume Tomography

A dynamic volume imaging based on the principle of electrical capacitance tomography (ECT), namely, electrical capacitance volume tomography (ECVT), has been developed in this study. The technique generates, from the measured capacitance, a whole volumetric image of the region enclosed by the geometrically three-dimensional capacitance sensor. This development enables a real-time, 3-D imaging of a moving object or a real-time volume imaging (4-D) to be realized. Moreover, it allows total interrogation of the whole volume within the domain (vessel or conduit) of an arbitrary shape or geometry. The development of the ECVT imaging technique primarily encloses the 3-D capacitance sensor design and the volume image reconstruction technique. The electrical field variation in three-dimensional space forms a basis for volume imaging through different shapes and configurations of ECT sensor electrodes. The image reconstruction scheme is established by implementing the neural-network multicriterion optimization image reconstruction (NN-MOIRT), developed earlier by the authors for the 2-D ECT. The image reconstruction technique is modified by introducing into the algorithm a 3-D sensitivity matrix to replace the 2-D sensitivity matrix in conventional 2-D ECT, and providing additional network constraints including 3-to-2-D image matching function. The additional constraints further enhance the accuracy of the image reconstruction algorithm. The technique has been successfully verified over actual objects in the experimental conditions     

方形电容层析成象系统的仿真研究

本利用自行开发的软平台,引入方形管道电容成象系统的模型,用限元法计算了敏感场的分布,并结合多种图象重建算法针对１２电极方形ＥＣＴ系统进行了仿真实验,得到了令人满意的结果。     

Online Voidage Measurement of Two-Phase Flow Based on the Ant System Algorithm

Based on the 12-electrode electrical capacitance tomography (ECT) system and the ant system algorithm (ASA), a new method was proposed for online voidage measurement of oil-gas two-phase flow. In practical voidage measurement, based on the 66 measurement capacitances obtained from the ECT system, the real-time flow pattern of oil-gas two-phase flow was first identified. Then, according to the flow pattern identification result, an appropriate measurement model was selected, and the measurement voidage value was calculated. The measurement models related to the flow pattern were developed in advance using the ASA. Static and dynamic experimental results show that the proposed voidage measurement method is effective. Moreover, the real-time performance and measurement accuracy are satisfactory.     

基于梯度投影稀疏重建算法的电容层析成像图像重建

为解决两相流中存在中心物体、物体比较小或存在多个物体且相距较近时电容层析成像(ECT)重建图像精度较差的问题,基于稀疏分布的流型其介电常数分布满足稀疏性的先验条件,采用梯度投影稀疏重建(GPSR-BB)算法进行ECT图像重建。仿真及实验测试结果表明:GPSR-BB算法对于流体中小目标以及复杂流型的图像重建质量较好,重建图像的形状保真度高。