Research On Mechanism And Cancellation Algorithms Of Motion Artifact Based On The Fabric ECG Electrodes

The prevalence of cardiovascular disease(CVD)is on the rise in China,including hypertension,coronary heart disease,and acute myocardial infarction(AMI).Long-term and dynamic monitoring to capture transient,non-sustainable abnormal ECG changes is critical for diagnosing heart disease,judging efficacy,and saving lives.However,currently there is no textile sensor(electrode)for dynamically acquiring ECG signals that can be worn comfortably for a long time.One of the main reasons is that the gel wet electrode is not suitable for long-term adherent to skin.,and it is easy to cause adverse reactions such as allergies,drop off.Flexible electrode or fabric electrode is a promising solution with obvious advantages in long-term dynamic acquisition.However,the clinical application of electrodes is facing severe theoretical and technical challenges.It is mainly manifested that the long-term dynamic ECG detection should be wearable and non-obtrusive,which requires better mechanical properties close to ordinary clothing or fabric,such as high elasticity,flexibility,elasticity and breathability.However,when detecting the ECG signals under daily activities,it is likely to cause sliding,deformation,and shedding of the electrode.Besides it may be subjected to the vertical pressure,and the skin topology under motion may be easily deformed,thereby causing motion artifacts.Therefore,it is necessary to remove the motion artifacts of the fabric electrode.In this thesis,the characteristics of the contact surface of the flexible fabric electrode,the motion artifact generation mechanism and the motion artifact cancellation methods are studied.The main work and innovations are as follows:1)The characteristics of the contact surface of fabric electrodeAn equivalent circuit model of the fabric electrode-skin interface is proposed by the electrochemical,electrical and human skin characteristics of the fabric electrode-skin interface.The model is based on the textile texture structure of the flexible fabric electrode contact surface,no gel when in contact with the skin,only a thin layer of sweat or moisture on the skin surface acts as an electrolyte,and the electrode is regarded as a contact type paralleled with a non-contact electrode.The interface equivalent circuit component is a function of the effective area of the electrode,which is equivalent to the analysis of motion artifacts.The model is verified and evaluated by electrochemical impedance spectroscopy,and the relationship between the parameters and the area of the model is analyzed.The results show that the model parameters are fitted with errors,and the equivalent parameters have reasonable physical meanings.Then the parameters of the interface equivalent circuit model are used to analyze the influence of the impedance,phase and electrode area of the fabric electrode contact surface(or interface)on ECG signals.The results show that the fabric electrode-interface impedance is larger than that of the standard disposable gel Ag/AgCl electrode.The ECG signals collected by a circular fabric electrode with a radius of 2-3 cm when the person is stationary can be compared with the standard electrode.2)Motion artifacts of fabric electrodesThe mechanism of interface potential difference is analyzed by the principle of electrode process,metal phase and liquid phase interface theory,and then the electric double layer capacitor charge and discharge and its charge distribution are analyzed.Then,using the interface electric double layer charge distribution and its redistribution and combining the theory of fluid dynamics and electrochemical kinetics,a dynamic model of motion artifacts of fabric electrode and skin relative motion is established.The model is used to analyze the mechanism,source and motion artifacts of motion artifacts.According to the analysis of skin characteristics,the main source of motion artifacts of fabric electrodes is the inter-electrode potential change between the electrodes and the changes of the internal and external potentials of the epidermis;There are many factors,the main one is that the relative movement of the fabric electrode and the skin causes the electric double layer disturbance and the change of the effective area of the electrode and the skin deformation.According to the source of origin and the causative factors,it is proposed to increase the cushion and expand the support area to buffer the relative movement of the electrode and the skin,and to reduce the deformation of the skin,and to optimize or prevent the movement of the electrode structure from the source.The results show that the method can effectively reduce the motion artifacts of the fabric electrodes.3)Motion artifact cancellation algorithmsAccording to the three sources of motion artifacts,motion artifacts and motion artifacts of fabric electrodes,three methods are proposed to deal with the motion artifacts of dynamic ECG,which can effectively remove or reduce motion artifacts.Firstly,the auxiliary fabric electrode adaptive motion artifact elimination algorithm is proposed,the skin potential change near the working electrode is directly detected by the auxiliary fabric electrode as the reference signal,and based on the large variation of the motion artifact energy spectrum.In this thesis,a transform domain adaptive cancellation algorithm is proposed to deal with motion artifacts based on traditional algorithms.Secondly,a multi-sensor adaptive algorithm is proposed to deal with motion artifacts based on single sensing.Multiple inertial sensors are used to acquire multiple motion signals and then combined with wavelet transform to improve the correlation with motion artifacts.Finally,the diversity of factors caused by motion artifacts.Lastly,a semi-blind source separation algorithm is used to constrain the independent component analysis algorithm to reduce motion artifacts.