Study On Capacitive Coupling Human Vital Signs Measurement

With the rapid development and application of the mobile internet,the portable and wearable human vital signs sensor technology in a noninvasive and unobtrusive manner has become an important research hot spot in recent years.It is attracting comprehensive attention in the home healthcare detection field.Capacitive coupling measurement with measuring electrodes as the sensing element has advantages of simple structure,and high sensitivity non-contacting mensurement.Based on the analysis on capacitive coupling human bioimpedance and biopotential measurement principles,application technology on capacitive coupling human vital signs acquisition.Capacitive coupling measurement and signal processing algorithm on the bioimpedance of human skin surface,electrocardiogram(ECG),impedance plethysmogram(IPG),and blood pressure are investigared as the key research.The following research has been done.1.For the measurement on human bioimpedance and the biopotential,a model for capacitive coupling human vital signs measurement is establised and theoretically analyzed.The measurement methods are proposed and analyzed,including the contacting multi-parameters measurement on the human skin surface impedance,the capacitive coupling electrocardiogram pick-up technique,and the non-contacting impedance plethysmogram measurement.2.For the portable measurement on the health status of human skin surface,an interdigital electrode(IDE)is used as the sensing element,and the electrode-skin model between skin tissue and contacting electrodes is establised.The phenomenon that equivalent capacitance and equivalent resistance correspond to the electrical property of skin surface and subcutaneous tissue respectively has been found and studied.As a result,a dual-parameter measurement method driven by dual-frequency square wave is proposed to detect and assess properties of human skin quantificationally.3.For the non-contacting measurement on electrocardiogram and impedance plethysmogram,the sensing electrodes are made from standard printed circuit board(PCB).The pickup circuit for capacitive coupling biopotential sensing electrodes is designed using a reversely connected diode which provides high bias resistance.Electrical signals on human body surface can be obtained through thin clothes using the capacitive coupling electrodes.Besides,in the ECG measurement,the effect of the reference configuration on the signal quality are analyzed.Therefore,three different configurations of reference electrodes are proposed.Experiments verify the feasibility on signal extraction of biopotential and impedance plethysmogram with the proposed capacitive coupling measuring electrodes.4.For noise interference during the human surface electrical signals measurement,singular spectrum analysis and the selection of its critical parameters are studied and analyzed theoretically,such as length and principal component indices.By analyzing the relationship between singular value decomposition and Fourier transformation in matrix form,the design formula on the selection of window length is proposed.By analyzing and studying the features of every principal component in time domain and frequency domain,two indices selecions are proposed.Thus a non-supervision de-noising algorithm based on singular spectrum analysis is proposed.Moreover,Combining the Golub-Reinch alogrithm and rank-onematrix perturbation,a fast algorithm on singular spectrum analysis is proposed.Besides,a new singular spectrum analysis based on network layer is proposed to enhance the performance on extracting the feature of the signals.5.The practical application on the original signals processed by the modified singular spectrum analysis are studied and analyzed.Meanwhile,by stuyding and analyzing the non-contacting measurement on feet ECG and feet IPG experimentally,the characterization paramter for blood pressure is obtained during experiments.Besisdes,the performance that modified singular spectrum analysis is applied in feature extraction and noise reduction on respiration and electromyography,is further discussed.