Research On Sensor Array Structure And 3D Image Reconstruction Of Electromagnetic Tomography

Electromagnetic tomography (EMT) is a new process tomography (PT) which is based on the principle of electromagnetic induction. According to the principle of electromagnetic, when conductive material is being excited by alternating magnetic from different directions, it will induce eddy current and in turn to change the electromagnetic characteristics of the original object space. The data from the detector coils around the object space will be used to reconstruct the conductive material distribution images.In this thesis, based on the study of electromagnetic tomography theory, EMT forward problem and inverse problem are analyzed. A variety of sensor modules are proposed, which are more suitable for industrial application. And the feasibility and effectiveness of the sensor modules are verified by the quality of the reconstructed images. At the same time, by studying the 2D EMT algorithms,3D EMT method is proposed, and is proved to be effective by the simulation experiments.The specific contents of this thesis are as follows.1.Combining with the research status of electromagnetic tomography at home and abroad, and according to the basic theory knowledge of electromagnetic tomography, principles and models of electromagnetic tomography forward problem and inverse problem are researched.Finite element method is adopted for solving electromagnetic tomography forward problem. By using the simulation software Ansys, the forward problem is simulated to obtain the prior knowledge of solving the inverse problem.2.By researching the array structure characteristics of the EMT sensor models, and breaking the limit of the whole surrounded O-shaped sensor structure of traditional EMT, a variety of semi-enclosed sensor modules of EMT are proposed to adapt to industrial applications.Lots of simulation experiments have proved that those semi-enclosed EMT sensor structures can work well in reconstructing images, it is a certain work for the electromagnetic tomography technology to extend to a wider range of industrial fields.3.Based on the characteristics of EMT technology, a real three-dimensional image reconstruction method in process tomography is used to research the 3D imaging of EMT. Namely the 3D images are reconstructed directly by measuring the induced voltage between the single-layer and different layers of coils, without processing a series of 2D tomographic images.In this thesis, the 3D model of EMT system and finite element method are described, and then the sensitivity of the axial and radial directions are analyzed, finally the feasibility of 3D imaging of EMT is proved by the reconstructed 3D images.