非闭合电极电容层析成像传感器的敏感场计算及仿真成像研究

本文提出了一种新型的非闭合电极电容传感器，以满足利用电容层析成像技术来测试冻土中水分迁移、物质组成及其动态变化特性的要求，对该电容传感器的敏感场进行了计算，并对其进行了成像仿真研究。结果表明，该种电容传感器可以实现测试区域内不同形状物体的测量及图像重建，其中Landweber成像算法对该传感器成像质量最好，从而为利用电容层析成像技术来进行冻土测试提供了实验基础。     

非闭合电极电容传感器在电容层析成像中的应用

提出了一种新型的非闭合电极电容传感器，以满足利用电容层析成像技术来测试冻土中水分迁移、物质组成及其动态变化特性的要求，对该电容传感器的敏感场进行了计算，并对其进行了成像仿真研究。结果表明：该电容传感器可以实现测试区域内不同形状物体的测量及图像重建，其中Landweber成像算法对该传感器成像质量最好，从而为利用电容层析成像技术来进行冻土测试提供了实验基础。     

电容层析成像系统阵列传感器的优化设计

电容层析成像系统的结构参数对电容敏感场灵敏度的分布有重要影响,进而影响重建图像的质量.本文提出了一种灵敏场均匀性的评价指标,并据此对电容层析成像系统阵列传感器进行了优化设计.     

循环流化床上ECT传感器灵敏场的有限元分析

电容层析成像传感器的敏感场受多相流介质分布的影响,软场特性给图像重建带来很大困难,为了提高重建图像质量,对敏感场分布进行分析是非常必要的.该文以12电极方形电容传感器为基础,对电容层析成像技术应用于循环流化床研究做了简单阐述,着重研究了用有限元法对方形电容传感器敏感场分布的计算机仿真,讨论了负敏感场的处理方法.     

一个基于1范数的电容层析成像图像重建迭代算法

电容层析成像因具有快速、廉价、非侵入传感等优点而被认为是具有广阔发展前景的过程成像技术.电容层析成像图像重建是一个典型的病态问题,它的解是不稳定的.为了获得有意义的重建结果,能够保证解的稳定性而又能提高重建图像质量的方法应该被采用.本文提出了一个基于1范数稳定的电容层析成像图像重建算法.将图像重建问题转化为一个最优化问题,并对目标泛函采用光滑逼近.在此基础上用Newton法求解该目标泛函.数值实验表明该算法是有效的,能够有效克服ECT图像重建的数值不稳定性,就本文所考察的重建对象而言,该法所获得的重建图像的质量有了一定的提高,从而为ECT图像重建引入了一种有效的方法.     

微型电容层析成像传感器的设计及应用

本文提出一种电容层析成像微型传感器,实现脉动热管内两相流的可视化监测及液膜厚度的测量.该传感器也作为流动管道,具有和测量管道基本相同的传热和流动特性.同时,建立基于图像灰度的液膜厚度测量方法,并采用最大类间方差法对重建图像进行处理.实验结果表明：可视化监测图像与实际相符,液膜厚度测量结果与Nusselt理论计算结果吻合较好.相比普通电容层析成像传感器,其测量精度和空间分辨率都有一定提高,从而拓宽了电容层析成像技术的应用范围.     

基于ECT/EST双模信息融合的磨粒图像重建算法

电容层析成像(ECT)技术因其非侵入、无辐射、可视化、响应快、成本低等优势在两相流测量中获得了广泛应用,但在发动机油路中,因摩擦产生的能量释放使磨粒荷电,对ECT传感器电容值的测量产生扰动,严重影响成像质量。为提高荷电颗粒存在情况下电容层析成像的图像重建质量,提出电容层析成像(ECT)与静电层析成像(EST)双模信息融合成像方法。该方法通过测量荷电颗粒在传感器矩形电极上感应的电荷值,得到荷电磨粒的信息;通过ECT系统得到一组电容值,并利用加权融合的修正方法,对ECT中畸变的电容值进行修正;用修正后的电容值进行图像重建。仿真实验证明:该方法能够弥补单一ECT模态的成像质量不高的不足,减弱荷电颗粒对ECT电容值测量的干扰,明显提高了图像重建质量,降低了成像误差;采用双模态重建图像方法可正确识别环状流、泡状流、核心流等几种典型流型。     

两相流电容层析成像中图像重建的研究

电容层析成像(Electrical Capacitance Tomography,ECT)技术是目前最具发展前景的多相流参数检测方法,它可重建两相流在其流经管道横截面上的分布图像.对12电极的电容传感器进行了数学描述,建立了电容敏感场分布的数学模型及其有限元模型,分析了敏感场的算法,利用有限元法实现了敏感场的仿真,并且研究了敏感场分布的规律.在此基础上利用灰度图像重建的方法重现出不同流体分布状态下油管横截面的灰度图像,为两相流在线检测仪器的设计提供了理论依据.     

提高ECT系统成像质量和速度的方法

在电容层析成像(ECT)技术的应用中,图像重建的质量和速度是电容传感器,并通过一种改进的正则化算法和利用DSP系统来实现快速高质的图像重建.     

电容层析成像系统中径向电极的研究

由于电容层析成像系统中电容测量非常困难,常采用在相邻电极间嵌入径向电极的方法来改善电容敏感场的分布.文中对8电极电容层析成像系统进行了具体的仿真实验和理论分析,并对径向电极及其嵌入尺寸对电容传感器的电容值及敏感场分布的影响进行了研究,根据各项参数对电容传感器性能的影响以及传感器结构参数的优化目标函数,确定了径向电极的最优嵌入尺寸.实验结果表明:采用径向电极最优嵌入尺寸的电容层析成像系统,能够缩小测量电容值的动态变化范围,降低数据采集电路的设计难度,同时还能够提高电容响应的灵敏度,改善电容传感器敏感场的分布,提高电容层析成像系统的性能.     

Decoupling the joint effect of moisture and mass in dense phase pneumatic conveying

Electric capacitance tomography (ECT) is advantageous for online imaging of pneumatic conveying of solids. From the ECT images, the spatial distribution of the mass of the material can be displayed at a very fast speed. However, as the mass distribution and the permittivity of the solids simultaneously affect the values of the measured capacitance arrays, they cause a coupled effect on the ECT images. In situations where the permittivity of the solids is influenced by the moisture, and this influence cannot be separated from the influence of the mass, or cannot be accounted for by an appropriate means, the measurement will be erroneous, as ECT images are usually interpreted as the distribution of the mass alone. This study aims to tackle the problem by an attempt to decouple the combined influence of the mass and the permittivity. A sensor of narrow electrodes is designed for the purpose of detecting only the variations in the permittivity. Simulation and experimental results both demonstrated that the influence of the permittivity and the mass of the solids can be decoupled under certain conditions, which provide a mechanism to correct the possible errors due to the unknown variation of the solids permittivity, or moisture.     

Imaging conductive materials with high frequency electrical capacitance tomography

Electrical capacitance tomography (ECT) is known as an imaging technique for dielectric permittivity imaging. A novel ECT sensor model at a high excitation frequency is proposed to examine the capability of the ECT system to image both conductivity and permittivity contrasts. The proposed model uses a complex impedance forward model for the ECT system. This new model indicates that in higher excitation frequency both conductive and dielectric imaging may be feasible. Normally, capacitance tomography is designed for the measurements of imaginary part and resistance tomography is used to take the measurements of real part. The drawback of a typical capacitance tomography at a low excitation frequency, such as 200 kHz is that it cannot be used to measure the conductive phase of a conductive/dielectric mixed fluid, e.g. the gas/water flow. By increasing the excitation frequency, the capacitive impedance of the conductive material decreases and dielectric phenomena of the conductive fluid dominates so that it is possible to use capacitance tomography to characterise the dielectric/conductive flows. This paper presents a development of capacitance tomography with a high excitation frequency in measuring the gas/liquid mixture i.e. gas/water and gas/oil multiphase distributions. Both theoretical and experimental results are presented to verify this feasibility study.     

介电常数分布对电容层析成像传感器灵敏度的影响

电容层析成像技术（ECT）近年来发展迅速。ECT传感器属“软场”传感器，其灵敏度分布受被成像介电常数分布的影响。由于“软场”特性的复杂性，图像重建时常忽略其影响，其结果是重建图像中有较大的“软场”误差。为获得高质量的图像重建，必须研究ECT传感器的软场特性。本文通过典型介电常数分布下灵敏度分布的计算与比较，分析了ECT传感器的“软场”特性，给出了介电常数分布对灵敏度分布影响的主要规律。     

Adaptive calibration of a capacitance tomography system for imaging water droplet distribution

A highly sensitive electrical capacitance tomography (ECT) system based on an HP4284 impedance analyser has been developed and used to quantify low concentration multi-phase flows in wet gas separation processes. The system hardware provides high accuracy (0.05%) and high resolution (10⁻¹⁷ F). The sensor was calibrated in an environmental chamber with solid samples of known permittivity over ranges of temperature and humidity. Adaptive calibration and adjacent electrode pair correction techniques were applied to image very low concentration profiles. This paper describes the techniques used and presents the experimental results obtained from a test flow rig called Twister, which has been designed to separate liquid droplets from wet gas streams. The test results over a range of operating conditions (20–95% humidity) demonstrate that the ECT system is capable of reconstructing clear images of the droplet distribution inside Twister. Changes as small as 1 gWater/kgAir in the form of liquid droplets were detectable. It has also been shown that the concentration of the condensable phase can be estimated quantitatively within 20% in comparison with the reference measurements.     

Preconditioned Landweber iteration algorithm for electrical capacitance tomography

Electrical capacitance tomography (ECT) has been used to obtain the cross-section images of processes with different dielectric materials inside. Image reconstruction with ECT is to retrieve the permittivity distribution of materials inside the sensor from the capacitance measurements. Algorithms for ECT image reconstruction should be both precise and fast in order to satisfy the requirements of real-time monitoring of the dynamic behavior of processes. Several algorithms have been developed for ECT image reconstruction. The Landweber iteration is the most precise one. However, the low convergence rate of the Landweber iteration limits its application for on-line imaging.This paper introduces an iterative algorithm based on the Landweber method with preconditioning for ECT image reconstruction. A preconditioner, which is equivalent to a filter, is applied to the Landweber iteration. The convergence of this algorithm is analyzed. Its performance is evaluated by using simulated and experimental data corresponding to certain typical permittivity distributions. Preliminary numerical and experimental results show that this algorithm converges more rapidly than the Landweber iteration without preconditioning. Therefore, image reconstruction iteration can be accelerated, which makes on-line quantitative image reconstruction possible.     

基于改进ECT的隔热材料胶层无损检测研究

电容层析成像(ECT)技术是能显示被测物场的二维或三维介质分布图像的实时检测技术,基于平面阵列传感器的ECT系统为陶瓷多孔隔热材料缺陷检测提供一种新的技术途径。本文针对陶瓷多孔隔热材料粘结胶层的缺陷无损检测问题,提出了一种基于改进的电容层析成像方法。首先在分析平面阵列传感器ECT检测系统模型及成像原理的基础上,提出了一种改进初值的Landwebe迭代图像重建算法;进一步将该算法应用到基材表层与隔热材料之间的粘结胶层的缺陷检测领域,并通过实验验证了采用基于改进ECT的无损检测方法在陶瓷多孔隔热材料粘结胶层缺陷检测中应用的有效性;同时与采用传统ECT成像算法的检测实验进行比较。结果表明本文提出的改进ECT算法对胶层缺陷图像重建质量具有较大幅度的提高。     

Application of ECT and relative change ratio of capacitances in probing anomalous objects in water

Nowadays electrical capacitance tomography (ECT) is mainly adopted for detecting dielectrics of low permittivity in chemical and petroleum industries. In these fields, to meet the demand of measuring capacitances within the range of low values, ECT still needs relatively high requirements of designing its system. In this work, an ECT system is simplified to probe anomalous objects in water with high permittivity. Additionally, the relative change ratio (RCR) of capacitances is presented for image reconstruction in terms of the high permittivity background. RCR is the change value of a capacitance divided by its background value. To verify the effectiveness of the simplification of an ECT system and the method of RCR for image reconstruction, simulations and experiments associated with media of high permittivity (i.e. water) were conducted. The obtained results demonstrate that the simplified ECT system based on RCRs of simulated and measured capacitances is capable of effectively probing anomalous objects in tap-water and sodium chloride solutions with different concentrations. Therefore the RCR is recommended when the sensing domain of ECT is of the high permittivity background. Besides the simplification of ECT systems can be appealing and beneficial to introduced ECT into other fields associated with water flows, such as hydrology, hydrogeology, hydroponics, environment science, etc.     

3D ECT reconstruction by an improved Landweber iteration algorithm

Electrical capacitance tomography (ECT) is a relatively mature non-invasive imaging technique that attempts to map dielectric permittivity of materials. Recently, 3D ECT has gained interest because of its potential to generate volumetric images. The study of a fast and accurate image reconstruction algorithm is a challenge task, especially for 3D reconstruction. In this paper, we propose an improved Landweber iteration algorithm. We incorporate an additional acceleration term into the cost function and apply an adaptive threshold operation to the image obtained in each iteration for reducing artefacts. The algorithm proposed is tested by the noise-free and noise-contaminated capacitance data. Sensitivity matrixes and capacitance data of a 3D ECT sensor are obtained by using the finite element (FE) method. Extensive simulations in 3D reconstruction are carried out. The results verify the effectiveness of these improvements. Both the reconstruction time and the artefacts in the reconstructed image are reduced obviously. The experimental results of 3D reconstruction of objects in the shape of letters U and L confirm the effectiveness of the proposed algorithm further.     

电容层析成象系统中微小电容测量法

电容层析成象技术（ＥＣＴ）是一种最早发展起来的过程成象技术。由于为重建图象所需测量的电容变化量相对于ＥＣＴ传感器的固有电容非常小,总的杂散电容值又远大于待测电容,因此ＥＣＴ对电容检测提出了极为严格地要求。本文介绍了ＥＣＴ系统中最常用的３种微小电容检测电路—充电／放电电路、带反馈补偿的交流测量电路以及自平衡电容测量电路,并指出了它们的优缺点。     

Window function-based regularization for electrical capacitance tomography image reconstruction

Image reconstruction for electrical capacitance tomography (ECT) is to retrieve the permittivity distribution of materials inside the sensor from the capacitance measurements outside. It is a typical inverse problem and has long been a challenge for its nonlinearity and ill-posedness. This paper discusses the application of Tikhonov regularization, widely used for ill-posed problems, to the image reconstruction for electrical capacitance tomography. Two methods using different regularizations are investigated, which are the standard Tikhonov regularization and the Tikhonov regularization based on the second order derivative operator. Particularly, a combined method using the linear back projection (LBP) result as the prior constraint for the Tikhonov regularization with the second order derivative operator is suggested. Simulation and experiment results show that this combined method takes advantages from both the linear back projection and the Tikhonov regularization and provides reconstructions better than those from the LBP and the Tikhonov regularization. In addition, considering the essence that the Tikhonov regularization can be described as a spectral filter characterized by its corresponding window function, we propose the possibility of applying other window functions to the ECT image reconstruction, which include the Gauss window, the Hanning window, the Blackman window, and the cosine window. Results also show the feasibility of using window functions as regularization, which presents a new strategy for the regularization of ECT image reconstruction.