Research On Wearable ECG Signal Measurement Based On Optical Theory

With the improvement of public living standards,people began to pay more attention on health problems.Application of wearable medical equipment for heath monitoring is becoming a new lifestyle.The electrocardiogram?ECG?signal as one of the most important vital signs of the human body,is a record of the electrical activities of the heart.The ECG signal can be used to determine if a patient is suffering from any form of cardiac ailment.The wearable ECG monitoring system can perform signal processing on a patient's ECG to detect these irregular heartbeats.The recent main method to detect ECG signal is based on electronic sensors,which is difficult to integrate and poor measurement safety.In the complex electromagnetic environment,electronic sensors are sensitive to signal distortion and loss,so that it cannot obtain accurate ECG signal and miss those irregular heartbeats or get wrong results.The wearable ECG signal measurement system based on optical theory with anti-EMI performance is suitable for ECG monitoring in MRI,war field and other complex electromagnetic environment.The main research aim is to design a wearable ECG signal monitoring system using the Lithium Niobate?LiNbO₃?electro-optical modulator,which is based on the linear photoelectric effect and the Mach-Zehnder interference principle,and realize the measurement of chest lead ECG.The main work of this paper is as follows:1.The working principle of LiNbO₃ electro-optical modulator with MZ structure is proposed.The factors influencing the sensitivity of ECG monitoring system are analyzed,and the theoretical sensitivity of the system is given.The signal processing circuitry including photoelectric conversion,filtering and amplification is designed.The sensitivity test system is built,and the system sensitivity is 0.041mW/V by experiment.The error between experimental and theoretical is 3.3%.2.The ECG waveform at V2 and V4 position is tested in real time using the designed optical wearable ECG monitoring system,and the experimental results are compared with those obtained by ECG acquisition channel of Biopac system.The experimental results show that the ECG waveforms obtained by optical wearable ECG signal monitoring system is clear,and the characteristic waveform such as QRS wave group,P wave and T wave can be distinguished,which is consistent with the results of the electrical acquisition system under the same experimental conditions.In order to test the anti-electromagnetic interference ability of the system,ECG acquisition experiment is conducted by two systems respectively under the electromagnetic environment.The experimental results show that ECG waveform obtained by Biopac system is abnormal and the SNR difference is 24.07dB at the V2 position,while the SNR difference is 16.75dB at the V4 position.The optical system can still work normally and the SNR difference is 0.54dB and 0.54dB,which is at the V2 position and V4 position respectively.3.A multi-channel ECG signal acquisition system based on parallel principle is designed to monitor the ECG waveform of V2 position and V4 positon at the same time.A multi-channel ECG signal acquisition based on time division multiplexing is designed,and the experimental result of multi-channel ECG acquisition system based on parallel principle is compared with it to verify the feasibility of its ECG signal acquisition.