| Electromagnetic tomography is a technique that uses the voltage measurements of an induction coil to reconstruct an image of the medium distribution in the area under test.In order to excite and collect signals from array sensors,an 8-channel electromagnetic data acquisition system based on ZYNQ was designed and used for electromagnetic imaging.In the imaging process,the quality of the sensitivity matrix directly affects the quality of the final image.Therefore,two methods are used to obtain the sensitivity matrix of the array sensor and correct them.The main work is as follows:(1)Analyze the principle of electromagnetic induction,theoretically analyze electromagnetic imaging and 8-channel coils,identify the data required for electromagnetic tomography,develop a method for obtaining the sensitivity matrix,and determine the image reconstruction algorithm used.(2)An electromagnetic imaging system was designed,including an excitation module,a receiving module,and an interface power supply.A digital phase sensitive detection algorithm was designed and time-sharing multiplexing was implemented for eight channels to complete the cyclic excitation and data reception of the array sensor.The induced voltage data was analyzed based on the excitation voltage and induced voltage signals obtained from the hardware system,Through digital phase sensitive detection algorithm,the induced voltage signal is decomposed by I/Q and filtered by a digital filter to obtain the real and imaginary parts of the induced voltage,and electromagnetic tomography is performed accordingly.(3)The model of the array sensor is established using comsol software,and the simulation sensitivity matrix of the array sensor is obtained by combining the perturbation method with finite element analysis.At the same time,an experimental platform is built using a high-precision mobile platform and an impedance analyzer.Wavelet transform is used to filter the collected signal.Finally,the measured sensitivity matrix is tested using the actual measurement method.And use a correction method to correct these two matrices.Using the obtained modified sensitivity matrix and using the global least square method as the image reconstruction algorithm,the electromagnetic tomography images were obtained.Through the analysis of the maximum values of the obtained images,five metals,titanium,copper,tin,aluminum,and copper,were classified.And establish polar coordinates to obtain the relationship between the classification effect and polar coordinates. |
