| With the continuous development of the social economy,great changes have taken place in people’s lives,and unhealthy lifestyles have led to the cardiovascular disease becoming the primary disease threatening human health.Cardiac diseases have shortterm and sudden characteristics,the traditional short-term ECG monitoring is easy to miss abnormal ECG,while clinical long-term dynamic ECG monitoring has high cost and imbalance between supply and demand,its popularity and application are low.Traditional disposable Ag/Ag Cl wet electrodes will reduce the signal-to-noise ratio of ECG signals in long-term ECG monitoring due to the reduction of gel moisture,and some patients are allergic to wet gels.The application of traditional dry electrodes to wearable devices has serious problems of baseline drift and motion artifacts.There are insufficient research on impedance modeling of wet and dry electrodes and pressure testing at low frequency.In view of the above problems,the paper establishes the skinelectrode interface impedance circuit model and electrode pressure test and designs an ECG monitoring system based on the flexible dry electrode to realize long-term dynamic monitoring of human ECG.The main research content and work of the paper:(1)The skin-electrode impedance comparison experiments and electrode drying experiments were carried out for flexible dry electrodes and disposable Ag/Ag Cl wet electrodes of 1～1000 Hz,the experimental results show that the skin-electrode impedance of the flexible dry electrode is close to that of the disposable Ag/Ag Cl wet electrode,and the overall impedance change of the flexible dry electrode after drying is small,demonstrates the superior performance of flexible dry electrodes.(2)The skin-electrode impedance circuit model of wet and dry electrodes is established,and the important determinants of the impedance of wet and dry electrodes are analyzed in the parallel equivalent capacitance and equivalent resistance formed by the epidermis layer and the electrode interface layer.The variation trend of absolute value,imaginary part value and the equivalent capacitance value of the skin-electrode impedance of four types of electrodes at different frequencies and different pressures are studied.The experimental results show that the indicators of dry electrodes are more sensitive to pressure changes than wet electrodes.The pressure test experiment verifies the wet and dry electrode impedance circuit models established in this paper.(3)Aiming at the defect that the reduction of the moisture of the disposable Ag/Ag Cl wet electrode gel leads to a significant increase in the skin-electrode impedance and introduces noise and interference,an ECG patch based on the flexible dry electrode is designed,and completed the software and hardware design of ECG patch.The low-noise single-lead input front end is designed,and the embedded software programming provides a solution for long-term ECG monitoring.The ECG patch is a patch configuration as a whole,which has the advantages of small size and low power consumption.The system only uses the 2-electrode mode to collect ECG signals,which improves the portability and comfort of the device.(4)A comparison experiment of various indicators was carried out between the ECG patch based on the flexible dry electrode and the Shimmer device.The comparison of ECG waveform shape and PSD shows that the ECG patch could collect high-quality ECG signals;the RR interval comparison results showed a high correlation(r=0.999);in order to evaluate the quality of ECG signals collected by the ECG patch,signal quality indices comparison experiment was conducted,the seven SQI parameters indicate that the quality of the ECG signals collected by the two devices is generally close;a long-term ECG monitoring experiment was carried out for the ECG patch,and the results showed that the ECG signal collected under the long-term working state of the ECG patch was clear,stable and reliable.The results of the paper enrich the research on wet and dry electrode impedance circuit modeling and electrode pressure testing;the ECG patch based on flexible dry electrodes is helpful for the early detection of cardiac diseases and has good application prospects. |
