Research On Three-Dimensional Electrical Impedance Imaging System And Its Application

Electrical impedance tomography(EIT:Electrical Impedance Tomography)technology is a kind of new non-destructive testing imaging technology to obtain internal media information image of the measured object,which is based on the characteristics of different media inside the measured object or the same media under different environmental conditions have different conductivity.EIT technology has great prospects in the field of industrial two-phase flow detection and biomedical research because of its advantages such as no damage for the measured object,high efficiency,visual measurement,and low price.Based on the physics and mathematics model of EIT technology,this article studied the measurement process and image reconstruction mechanism of three-dimensional EIT system from multiple angles.Firstly,based on the three-dimensional circuit model of EIT technology,we proposed and constructed the three-dimensional EIT circuit model.Then,we proposed and designed a hardware data acquisition system that used FPGA as the main controller and used power module,signal excitation and acquisition module,and multiplexer module as the core.Finally,a two-phase flow pattern detection experiment was conducted on a square field experimental platform,which fully verified the high efficiency and reliability of the EIT system.The specific research works are as follows:(1)The 3D-EIT circuit model was proposed based on the 2D-EIT circuit model.By designing the circuit network structure,simplifying the measurement circuit model,determining the excitation mode,and deriving the expression of the measured voltage,the circuit simulation data curve was obtained.The imaging area imaging target was simulated by changing the circuit network parameters.The conjugate gradient algorithm was used to obtain the reconstructed image.The comparison of the three indicators of image relative error,image correlation coefficient and structural similarity determined the feasibility of the circuit model.(2)We designed a set of 3D-EIT hardware system which is based on FPGA.The hardware of the system was mainly composed of power module,signal excitation and acquisition module,and multiplexer module.Finally,the three components were combined together by a motherboard to complete the data acquisition function,and then communicated with the host computer through the UART to upload data.The GUI interface written by Lab VIEW was responsible for the sending and receiving of the instruction on the host computer and the image was rebuild by the MATLAB software after the uploaded data was processed.(3)We used LAB VIEW language to complete design and development of the GUI interface on the host computer,proposed and designed a square field experimental device,and completed the simulation and image reconstruction of the 2D and 3D model for the square field.(4)The detection experiments of the two-dimensional and three-dimensional two-phase flow were implemented on a square field experimental platform.Using the sensitivity matrix calculated of the square field platform to complete data acquisition and imaging of the two-dimensional bubble flow and three-dimensional laminar flow and wavy flow on the square field platform while excitation current was 5mA and the frequency was 100KHz.The imaging results accurately reflected the positional and morphological characteristics of the water-gas two-phase flow in the bubbly flow state.