Research On Non-contact Human Body Sign Detection Technology Based On Capacitive Coupling

The health of people are seriously endangered by cardiovascular diseases.It is characterized by sudden and intermittent attacks.Patients have a high mortality rate because they do not receive timely treatment.Real-time monitoring and analysis of human vital signs can effectively improve patient survival rates.Contact anthropometric methods require direct contact with human skin and are often unsuccessful when dealing with patients with sensitive skin or large burns.The non-contact detection technology is not subject to this limitation and has the advantage of being insensitive to skin conditions and can be embedded in clothing for measurement,which meets the residents’ requirements for monitoring their cardiovascular lifecycle health status.Therefore,this paper proposes a scheme of non-contact human body sign detection based on capacitive coupling to achieve non-contact monitoring of human vital signs.This paper designs a non-contact hardware detection platform based on capacitively coupled electrodes for the simultaneous non-contact acquisition of electrocardiogram(ECG)and impedance plethysmography(IPG)signals based on the principle of capacitive coupling.The platform uses capacitively coupled electrodes as the front-end of signal acquisition,through which the electrodes form coupling capacitance with human skin and are processed by the back-end conditioning circuit to finally obtain higher quality ECG and IPG signals.The hardware platform’s non-contact capacitive coupling electrode and signal conditioning circuit are also simulated and verified to ensure the correctness of the circuit.In terms of data processing software,a digital filtering method with wavelet soft threshold is used to denoise the ECG and IPG signals,thus completing the filtering of noisy signals such as myoelectricity and baseline drift.In order to solve the problem that it is difficult to continuously and accurately monitor human blood pressure by cuff blood pressure measurement method,this paper proposes a non-contact blood pressure detection method based on the combination of Pulse Wave Transit Time(PWTT)and the time domain waveform characteristics of ECG and IPG signals.The blood pressure characteristic quantities were extracted from the time-domain relationship between ECG and impedance volume map,and a blood pressure prediction model based on five characteristic quantities,including PWTT,was established by multiple linear regression method.In addition,a data processing software interface was designed to visualize the ECG,impedance volume graph and blood pressure values of the subjects.Testing the functionality of the non-contact human sign detection system and designing experiments to measure sign parameters for 10 test persons.The mean relative error of systolic blood pressure and diastolic blood pressure was 3.56% and 6.69%,and the absolute error of both was within ± 5 mm Hg,meeting the AMMI criteria for blood pressure measurement.The experimental results show that the detection system can provide stable and accurate non-contact measurements of human ECG and IPG signals as well as blood pressure values and other vital signs.