Research And Design Of Multi-frequency Excitation Driving Circuit For Electrical Impedance Tomography System

Electrical Impedance Tomography(EIT)injects safe current and measures the voltage signal,by placing a certain number of electrodes on the surface of the measured object.EIT is commonly used in biomedical science,it can obtain physiological or pathological information and functional images.EIT is safe,convenient and cheap.It is a kind of imaging technology developed rapidly in recent years.Firstly,in this paper,the background and significance of EIT,the research status quo in our country and abroad are reviewed,the biomedical basic,the electrical impedance model,the imaging theory and process of EIT are expounded,the components of the data measurement system and the two methods of image reconstruction are researched.The multi-frequency excitation and drive circuit of EIT system based on Walsh function are proved.Secondly,the definition about three sequences of Walsh function based on Rademacher function and the relationship among the sequences are researched,the method of generating multi-frequency excitation signals is studied.The conversions from H-sequence to W-sequence and P-sequence are realized in the Matlab software by bitset function and bitget function.The discrete states of multi-frequency excitation signal with arbitrary main harmonic number are obtained.Then,the multi-frequency excitation source and drive circuit based on FPGA are designed,the excitation source can obtain any frequency signal by infrared communication.The codes written by VerilogHDL are compiled for infrared signal demodulation module,LCD display module,clock generation module,signal generation module and drive circuit module.The relationship between measurement frequency and excitation signal is studied,and the simulations of each module are carried out.Several frequencies can be set instead of only one or a few fixed excitation frequency in the previous research.In addition,the counting frequency division and DDS frequency division are analyzed and compared,and the defects of DDS frequency division are pointed out through simulation.Finally,the hardware circuits of excitation source and drive system are designed,including the FPGA core circuit,excitation signal source circuit,drive circuit and affiliated circuits.The design and manufacture of circuit board are accomplished.The test results show that the excitation source meets the requirements of EIT system,and the multi-channel switch of drive system can achieve the gating of electrodes.