Simulation Research Of Key Technique For Electromagnetic Tomography

Electromagnetic Tomography (EMT) is a kind of Electrical Tomography (ET) based on the principle of magnetic induction. The adscititious AC excitation magnetic field is used to scan the sensing space with the distribution of medium of conductivity and permeability from different angles. The inductive signal is picked up through the detection coils. The image reconstruction algorithm is used to reconstruct 2D or 3D images, which reflect the distribution of the medium of conductivity and permeability.The theory and system of EMT is relatively complex because the solution of its sensing field changes with the excitation frequency. Via the simulations, the sensing field of EMT is investigated to select the information of the data and the sensitivity matrix is calculated by different methods, which are preconditions for researches of the image reconstruction. Furthermore, the imaging effect is also influenced by the shielding parameters of the EMT system. Via the optimization design, the optimal shielding parameters could be gained within a certain range, and then the design of the practical EMT system is also directed.Based on the advantages and the fundamental theory of EMT, the researches of key techniques were simulated via the finite element software Comsol in this paper. The main work is shown as follows:Firstly, 3D and 2D FEM simulation models of the EMT system were established respectively. Corresponding to the data selection of the image reconstruction for the properties of conductivity and permeability, 3D and 2D FEM simulative analysis were implemented and the relationships between the measured signal and the conductivity and the permeability were obtained. Moreover, the analytical solution validated the results of simulations. Then, the data for the image reconstruction were selected.Secondly, the sensitivity matrix of EMT system was calculated by the semi-analytical method and the FEM model simulation method respectively. Based on the two sensitivity matrix, images were reconstructed via qualitative sensitivity coefficient method based on the truncated singular value, Tikhonov regularization method and quantitative conjugate gradient iteration method, Newton-Raphson method. The reconstructed results for each algorithm were also analyzed.Thirdly, the electromagnetic coupling mechanism of EMT systems was analyzed. The simulation model for the optimization design of the shield of EMT systems was designed. Based on the optimization criterion, the influence of the height and inner radius of the shield to the shielding effect was investigated and the orthogonal analysis with three factors of the inner radius, height and material of the shield was implemented through the orthogonal test. And then the optimal parameters of the shield were obtained within a certain range. The necessity of the total shield was also researched at last.