Analysis And Research On The Positive Problems Of Electromagnetic Tomography

Electromagnetic tomography(EMT)technology originated in the 1990 s.Compared with other process tomography technology,EMT has the advantages of non-invasive,non-contact,simple structure,real-time imaging and so on.It has more advantages for the spatial detection of multiphase flow field which can be represented by the distribution of conductivity and permeability,such as industrial process monitoring and medical imaging.The research significance and development prospect of EMT technology are analyzed in this paper.According to the current development of EMT technology at home and abroad,the physical model of EMT technology is determined,and its positive problems are optimized to provide theoretical basis for the establishment of physical model.The main components and working principle of EMT system are introduced.The research methods of positive and negative problems are elaborated.EMT positive problem is simulated by simulation analysis method.According to the electromagnetic characteristics of the measured object space,the physical model of EMT system is derived from Maxwell equations,and the second-order partial differential equation is solved by finite element method.Based on the COMSOL Multiphysics software,the simulation model of EMT system is established,and the free tetrahedron of the system is dissected.The influence of excitation current,space frequency of object field,disturbance target position and material,relevant parameters of sensor coil(wire turns,wire diameter,winding mode,coil number)on the measured value and measured phase are explored by using the control variable method.The conclusion is drawn: phase measurement is the necessary condition for establishing sensitivity field and image reconstruction;different frequency band excitation current should be used for objects with different conductivity,medium frequency band(kHz)excitation should be used for iron medium and other materials with high conductivity,and high frequency should be used for glass or other materials with low conductivity,such as biological tissue Segment(MHz)excitation;under the premise of not causing excessive load and electromagnetic interference to the system,tring to use a larger excitation current value;EMT system with a large number of coils,when the conductor adopts adouble-layer close wound structure with a smaller wire diameter and a large number of turns,the detection result is more ideal,which provides a basis for the design of hardware system according to the comparison diagram of the drawn detection results.The sensitivity matrix of 16 coil EMT system is established by using the field extraction method.The sensitivity matrix of 16 coil EMT system is established by using the method of field extraction.The reconstructed image of disturbance in the field is obtained by using Tikhonov regularization algorithm.