Jiamin Ye

Evaluation of Effect of Number of Electrodes in ECT Sensors on Image Quality

It is commonly assumed that the use of more electrodes in an electrical capacitance tomography (ECT) sensor would result in higher resolution images. In this paper, the issues with the number of electrodes will be discussed. To investigate the effect of the number of electrodes on the quality of reconstructed images, ECT sensors with different number of electrodes-4, 8, 12, 16, 20, 24, and 32-are investigated. The capacitance between different electrode pairs is calculated for some typical permittivity distributions using a finite element method. The obtained capacitance data are then used to reconstruct images using the projected Landweber iteration algorithm based on both linear and semi-linear ECT models. The sensitivity distributions for the ECT sensors with different number of electrodes are analyzed. The main conclusion is that limited new information can be obtained and little improvement in the quality of images be achieved if the number of electrodes is more than 12.

Image Reconstruction for Electrical Capacitance Tomography Based on Sparse Representation

Image reconstruction for electrical capacitance tomography (ECT) is a nonlinear problem. A generalized inverse operator is usually ill-posed (unbounded) and ill-conditioned (with a large norm). Therefore, the solutions for ECT are not unique and highly sensitive to the measurement noise. To improve the image quality, a new image reconstruction algorithm for ECT based on sparse representation is proposed. An unconventional basis, i.e., an extended sensitivity matrix consisting of some normalized capacitance vectors corresponding to the base permittivity elements is designed as an expansion frame. The permittivity distributions to be reconstructed can have a natural sparse representation based on the new basis and can be represented as a linear combination of the base elements. Another sparsity regularization method-the standard Landweber iteration with a threshold is also conducted for comparison. The proposed algorithm has been evaluated by both simulation (with and without noise) and experimental results for different permittivity distributions.

Optimization of Helical Capacitance Sensor for Void Fraction Measurement of Gas-Liquid Two-Phase Flow in a Small Diameter Tube

A helical capacitance sensor is proposed to measure the void fraction of gas-liquid two-phase flow in a small tube with 5 mm diameter in this paper. The structure of helical capacitance sensor is analyzed by using the finite-element method (FEM) and the orthogonal array testing strategy. According to simulation, the optimal structure of helical capacitance sensor is suggested. The results of simulation and experiments show that the optimized sensor has a more homogeneous sensitivity field. The helical capacitance sensor demonstrates a good linearity between the capacitance value and the void fraction to be measured. In addition, the helical capacitance sensor has a good adaptability to different flow patterns.

Evaluation of Electrical Capacitance Tomography Sensors for Concentric Annulus

Electrical capacitance tomography (ECT) sensor is commonly used with circular or square pipes or vessels. In this paper, an ECT sensor of concentric annulus shape is presented. To investigate the effect of the configuration of electrodes and the measuring strategy on the quality of reconstructed images, the ECT sensors with internal-external electrodes (IEE) and external electrodes (EE) are investigated. For the IEE sensor, six different measuring strategies are considered. The capacitance between different electrode pairs is calculated for some typical permittivity distributions using a finite element method (FEM). The obtained capacitance data are then used to reconstruct images using Landweber iteration algorithm. The sensitivity distributions for the IEE and EE sensors are analyzed. Simulation results show that the IEE sensor with 12 external electrodes and four internal electrodes combining with an external-opposite strategy can reconstruct good images for most permittivity distributions.

Characterization of Electrical Capacitance Tomography Sensors With Different Diameter

In electrical capacitance tomography (ECT), the excitation frequency, excitation voltage, and the number of excitation electrode(s) can be chosen. The aim of this paper is to investigate their effect on ECT sensors with different diameter to improve the image quality and stability. Experimental studies have been carried out to understand the effect. To evaluate the experimental results objectively, the normalization models of capacitances are also examined. Using the linear back projection algorithm, images are reconstructed for six typical permittivity distributions, and the concentration is calculated based on the reconstructed images. Preliminary conclusions are given based on the experimental results.

A sparsity reconstruction algorithm for electrical capacitance tomography based on modified Landweber iteration

To improve the image quality and reduce the computational cost for electrical capacitance tomography (ECT), a sparsity reconstruction algorithm based on a modified Landweber iteration is presented in this paper. A soft-thresholding function is constructed for permittivity distributions with a continuous phase of low and high permittivity, respectively. An optimal step length is used during the iterative image reconstruction process. The effect of the regularization parameter, the noise level in data, and the permittivity distribution on the performance of the proposed algorithm is discussed according to the correlation coefficient. The modified Landweber iteration with a zero regularization parameter is also implemented for comparison. Simulation and experimental studies were carried out and the corresponding computational costs were estimated, showing the sparsity reconstruction outperforms the Landweber iteration.

Helical Capacitance Sensor-Based Gas Fraction Measurement of Gas–Liquid Two-Phase Flow in Vertical Tube With Small Diameter

A helical capacitance sensor for gas fraction including void fraction and volumetric void fraction measurement of gas-liquid two-phase flow in a vertical tube of 5 mm in diameter is presented in this paper. The structure of the helical capacitance sensor is optimized using a finite element method to achieve a homogeneous sensitivity field distribution. A calibration device using the quick closing valve method is designed and used to calibrate the void fraction measurement. Experiment results show that the relative error of gas fraction is less than 10%. The reason for the nonlinearity between the sensor output and gas fraction to be measured is discussed. The linear model describing the relationship between capacitance and gas fraction is obtained by removing the wall capacitance.

Concentric-annulus electrical capacitance tomography sensors

The aim of this research is to investigate the unique shape (concentric-annulus) electrical capacitance tomography (ECT) sensors. This is motivated by the desire to improve the contrast and spatial resolution of the images reconstructed using ECT sensors with internal?external electrodes (IEEs). Both numerical simulation and experimental study were carried out with the goal of providing an improved understanding of the configuration of IEE sensors, the internal shield and the measurement strategies. Simulation results are in agreement with the experimental results. Using the linear back projection algorithm, the IEE sensor with 12 external electrodes and 4 internal electrodes with the external?opposite?internal measurement strategy can reconstruct high-quality images. In experimental studies, the internal shield may reduce the quality of capacitance measured from the internal electrodes.

Image Filtering With Associative Markov Networks for ECT With Distinctive Phase Origins

The images reconstructed by electrical capacitance tomography (ECT) for two-phase flows are usually blurry at the phase interface. To improve the image quality, image filtering with associative Markov networks (AMNs), which support efficient graph-cut inference for insulation segmentation, is presented. An ECT sensor with 12 electrodes is investigated and the capacitance between different electrode pairs is calculated for some typical permittivity distributions using a finite element method. The initial images are reconstructed by liner back-projection and Landweber iterative algorithm, respectively. The obtained images are then processed using AMNs. Simulation results show significant improvement in the quality of images.

An evaluation of the rotation of electrodes in multi-plane electrical capacitance tomography sensors

The structure of electrodes in a multi-plane electrical capacitance tomography (ECT) sensor is vital for obtaining high-quality capacitance measurements and good images. In this paper, issues with the relative position of electrodes on each plane in three-plane ECT sensors are discussed. Five ECT sensors with different structures are compared by numerical simulation. For the five sensors, the electrodes on the second and third planes are arranged with rotation angles of 0 degrees and 0 degrees, 0 degrees and 15 degrees, 0 degrees and 30 degrees, 0 degrees and 45 degrees, and 22.5 degrees and 45 degrees, respectively, relative to the electrodes on the first plane. The capacitance data obtained from different sensors by numerical simulation are used for image reconstruction using linear back projection and Landweber iteration algorithms. The image quality is evaluated quantitatively in terms of image error. The sensitivity distributions of all the ECT sensors are compared.