Research On Portable Electrical Impedance Tomography Hardware Syste

Electrical Impedance Tomography(Electrical Impedance Tomography,EIT)is a research hotspot in the field of imaging in recent decades.It is a kind of imaging technology with non-invasive,non-invasive,low-cost and other advantages.It has a very broad application prospect.At present,several companies in the world have developed commercial EIT equipment.The attractive prospect of electrical impedance tomography technology is the driving force of continuous research by scientific research teams all over the world,but the solution of its inverse problem is seriously ill-conditioned,and small interference will lead to great changes in the final calculation results.EIT reconstruction algorithm needs a lot of computation,so it is difficult to guarantee real-time performance.At the same time,the measurement accuracy and anti-fabrication performance of the hardware system are also the key to imaging,which are all factors hindering the development of EIT technology.In this paper,the traditional EIT system is optimized for its complex hardware design and large equipment volume.A set of portable EIT equipment is built based on FPGA.The system adopts modular design,which mainly includes main control module,incentive module and acquisition module.The system uses rechargeable lithium battery for power supply,and uses serial port to send voltage data to the host computer for imaging.The main work of this paper is as follows:1.In order to improve the accuracy of current source in EIT system,an adaptive current source based on FPGA is proposed.The current source can adjust the output current according to the stray impedance in the circuit and reduce the error caused by current shunt.The current source is in the frequency range of 1KHz-1MHz.After adaptive compensation,the output impedance is kept around 10 M Ω,and the output capacitance is reduced to less than 0.8p F in the whole frequency range.2.In order to improve the data acquisition rate of EIT system,this paper adopts the combination of four-channel synchronous ADC and analog intersection switch to realize semi-parallel acquisition in 16-electrode system.Only by switching the analog switch array four times,the voltage acquisition of all electrode pairs under one excitation can be completed,and the switching times can be greatly reduced and the acquisition time can be reduced.3.In order to further improve the acquisition rate,a fast digital demodulation method is proposed.This method is improved on the basis of traditional digital demodulation,and the amplitude and phase information of the boundary voltage can be obtained in less time.In this paper,the algorithm is implemented in the form of Verilog code,which reduces the resources occupied by using a lot of IP cores.4.Build the physical simulation model and test the performance of the hardware system.The signal quality of the current excitation source and the signal-to-noise ratio of the EIT measurement system are tested.Finally,the conductivity reconstruction image of the simulation model is completed by related algorithms.