Metal Defect Detection Method Based On Electromagnetic Tomography

The demand for metals is largely increased with the development of industry.There is a current need for detection of metal defect with high speed and visualization..Visual detection of metal defects can not only improve the detection speed and accuracy,but also reduce the requirements of the inspectors.Electromagnetic tomography(EMT)is a visualized electromagnetic non-destructive testing technology that has emerged in recent decades.EMT has the advantages of being non-radiant and non-intrusive,rapid response,flexible sensor position,simple structure and low cost.It is very suitable for visualization of metal defects.In this paper,an EMT system for detection of metal defects is designed.The visualization of metal defects is realized by sparse imaging algorithm.The following work is mainly completed in this paper:1.In order to realize the visualization of metal defects,a new planar sensor is designed.The sensor consists of 6 coils,which increases the amount of data acquisition;the coils are parallel to each other,the mutual inductance between the coils is enhanced.2.Because of the sparse distribution of the defects in the measured objects,traditional image reconstruction algorithms have seriously smoothing effect and affect image quality.This paper proposes an EMT image reconstruction algorithm based on sparse imaging algorithm.The L1 regularization method is applied to solve the inverse problem of EMT,and the mathematical model of EMT is transformed into the convex quadratic problem,with linear inequality constraints.The newton method is used to solve the problem,and the regularization parameter selection method is also discussed.Simulation and experimental results show that the EMT system can obtain high quality reconstructed images by L1 regularization algorithm.Compared with the traditional image reconstruction method,the L1 regularization algorithm can better represent the edge information of the reconstructed image and improve the quality of the reconstructed image.3.In view of the current majority of EMT systems are using the acquisition card for data acquisition,the price is relatively expensive.The data acquisition module for EMT is designed based on FPGA and ARM.FPGA is designed to control acquisition chip,ARM is designed to transfer the data between the host computer and FPGA.Since the module makes full use of the advantages of FPGA and ARM,the cost of the system is effectively reduced.The performance of the module was tested.It can meet the requirements of the EMT system.The performance of the module was tested.It can meet the requirements of the EMT system.The performance of the module was tested.It can meet the requirements of the EMT system.Experiments were conducted based on the EMT system,the experimental results show that the system has high SNR and good channel uniformity,the system works stably and has good performance.