Design Of Active Electrode With Feedback For High Quality Bioelectric Signal Detection

The bioelectric signals of human body can reflect the health condition of the body to a great extent.The commonly used electrodes for monitoring bioelectrical signals are standard wet electrodes,contact dry electrodes and non-contact capacitive coupling electrodes.In practice,the bioelectric signals collected by electrodes are greatly affected by noise interferences,especially in the application of non-contact capacitive coupling method to acquire signals.In order to obtain bioelectric signals with high signal-to-noise ratio(SNR),a new kind of active electrodes,called active electrodes with feedback,is proposed and investigated in this paper.In the second chapter of this paper,a preliminary design scheme of active electrodes with feedback is proposed and implemented on the circuit board.the experiments of contact ECG measurement show that the active electrodes can effectively restrain power frequency interference,motion artifact,radio frequency signal of mobile phone and so on.However,it is found that the stability and quality of the signals obtained by the electrodes are not high in the non-contact ECG measurement experiment.In the third chapter,the design of active electrodes with feedback is optimized.Firstly,the circuit structure of the active electrodes is optimized according to the principle of non-contact measurement of bioelectrical signals and the circuit model of capacitive active electrodes,and adds the shielding protection to the input of active electrodes.Then,through theoretical calculation and analysis of the output noise of the active electrodes circuit,the circuit parameters are optimized.By using TINA software to simulate the active electrodes circuit,the total output noise and the frequency characteristics of the transfer function are understood.The fourth chapter analyzes the problems of rigid sensing surface and the advantages of flexible plate sensing surface in the process of measuring bioelectrical signals,and re-designs the flexible plate sensing surface of active electrodes with feedback.The experiments of ECG measurement show that the optimized active electrodes with feedback can output high quality ECG signals no matter in contact with skin or in non-contact with insulating materials.In the fifth chapter,the output impedance,the input impedance and the bottom noise of the active electrodes with feedback are measured.At the end of the paper,we summarize the whole work and give the prospects of the next step.