Research On Image Reconstruction For Electrical Capacitance Tomography Based On Combined Electrode Excitation Measurement Strategy

Electrical capacitance tomography(ECT)is a process tomography technology based on the principle of capacitance sensing,which is suitable for measuring mixed fluids composed of a variety of insulating media,such as oil/gas two-phase flow.Electrical capacitance tomography has broad application prospects in the chemical and medical fields for the advantages of fast response,non-invasiveness and low cost.The object field measured by ECT technology has"soft field"characteristics,and different excitation measurement modes have certain differences in the detection ability of the medium distribution in the sensitive field.This topic focuses on the combined electrode excitation measurement mode of ECT technology to carry out in-depth research,and the main work and results are as follows:1.Research on the sensitive field characteristics of the combined electrode ECT system.Firstly,based on the 24-electrode electrical capacitance tomography(ECT)sensor model,a combined 8-electrode and 12-electrode ECT sensor array was constructed.Secondly,the sensitivity field characteristics of the 8-electrode and 12-electrode ECT sensors,such as capacitance measurement value,sensitivity field distribution and equipotential line distribution,are analyzed by finite element simulation.Finally,image reconstruction simulations were carried out on the two combined electrode schemes,The results show that the sensitivity distribution of the8-electrode ECT system in the central area is stronger than that of the 12-electrode system,while the 12-electrode ECT system has more independent measurement values,and the reconstructed image quality in the non-central area is better.2.Research on the fusion of reconstructed images based on the combined electrode ECT system.In this paper,four flow patterns are selected,and the reconstructed image of the combined 8-electrode and 12-electrode ECT system is used as the source image.Moreover,the image fusion simulation is performed using the weighted average,pixel gray value selection method and wavelet transform method.The results show that the combined 8-electrode and 12-electrode ECT system has complementary detection capabilities for the distrib ution of objects in the sensitive field,and the use of image fusion algorithms can improve the accuracy of image reconstruction.3.An image reconstruction algorithm based on optimization algorithm for electrical capacitance tomography(ECT)is proposed.In order to approximate the regularization minimization problem,the traditional regularization algorithm is transformed into the least squares problem by the l_p-norm,and the iterative calculation is performed by the re-weighting method.Based on the traditional 12-electrode and combined 8-electrode system,simulation and static experiments were carried out.The presented optimization reconstruction algorithm is compared with the commonly used LBP,Landweber iteration and Tikhonov regularization algorithm.The results show that lower image relative error and obviously improved shape fidelity of the reconstructed images can be obtained using the presented algorithm for the flow patterns which contain the object in the center of the pipe or many objects in th e pipe.In addition,the optimization algorithm is also applicable to the combined electrode ECT system,which shows that the algorithm has good versatility.