Research On Design Of Hardware Platform For Human Lung Electrical Impedance Tomography

The excitation module in the multi-frequency bioelectrical impedance tomography(EIT)technology can dynamically adjust the frequency of the excitation signal,and can obtain richer electrical impedance imaging information,which expands the scope of application.Based on the research of bioelectrical impedance imaging technology,this paper focuses on designing a multi-frequency human lung tissue electrical impedance imaging data acquisition platform,and studies the data processing methods of bioelectrical impedance imaging signals.Hardware platform design.It mainly includes excitation channel design and detection channel design.Excitation channel part: adopt DDS technology to design waveform generator,adopt enhanced How Land current pump technology to design voltage-controlled current source,and convert DDS voltage signal into current signal(current <5m A)through voltage-controlled constant current source and input into human tissue.Detection channel part: design amplifying,filtering and high-speed A/D acquisition circuits to obtain EIT detection signals.In order to reduce the interference of common-mode signals and solve the problem of gain uncertainty,instrumentation amplifiers and program-controlled amplifiers are designed.The conduction of 16 electrodes is controlled by analog switches,and the electrodes are time-division multiplexed.Simulate and test the designed circuit respectively.Data acquisition platform software: mainly includes hardware driver,digital demodulation algorithm and host computer debugging interface.The hardware driver is composed of DDS control module,program-controlled amplifier control module and analog switch control module.Aiming at the problems of too many multiplications and long demodulation time in the digital demodulation algorithm,the characteristics of the EIT detection signal are used to improve the FFT demodulation algorithm,and the amplitude of the EIT signal can be demodulated with only 8 real number multiplications.With phase information,the host computer is mainly responsible for the parameter configuration and data display and storage of the acquisition platform.Design an experimental model to verify the EIT collection platform,and conduct data collection on the human body.Experiments show that the frequency range of the excitation signal is within 10KHz-100 KHz,and the relative frequency error is within 0.5%.The common mode rejection ratio of the detection channel reaches-40 d B,and the gain is adjustable from-20 d B to 20 d B.Through the adjacent excitation mode,208 sets of bioelectrical impedance imaging signals are obtained.The demodulation time of one frame of data is 9.7ms,which meets real-time requirements.