Design And Implementation Of Non-Contact Vital Signs Detection Device

Respiration and heartbeat are two important physiological parameters that characterize the normalcy of the human respiratory and circulatory systems.The real-time detection of these physiological parameters plays an important role in disease diagnosis and prevention,as well as in guiding people’s daily activities such as exercise and health care.Traditional vital sign detection devices need to contact the human body through electrodes or sensor cables to detect and extract physiological parameters,which is difficult to meet the needs of diagnosis and monitoring of diseases,daily health monitoring,and monitoring of special groups(such as infants and children,patients with severe burns,athletes in training,etc.)under the free movement of the human body.In order to solve the problems of high monitoring limit for contact vital sign detection,easy to fall off the electrode sensor lead wire,and the monitored signal is easily disturbed by the environment,this paper designs a non-contact vital sign detection device based on Doppler radar,which does not need to contact the human body and can extract the human respiratory and heartbeat physiological parameters in real-time within a certain distance,even in the presence of obstacles.The device has good penetration,high sensitivity,and strong anti-interference ability,and can be us-ed in health monitoring applications to achieve cardiopulmonary activity monitoring.The non-contact vital sign detection device designed in this paper extracts and separates the human respiration and heartbeat signals from the signals detected by Doppler radar in real time through an embedded microcontroller to achieve long-distance non-contact human vital sign parameters detection.The hardware system of the device mainly consists of a microcontroller,Doppler radar sensor signal ampli-fication,filtering,voltage boosting,power supply circuit,and waveform display.The software system and function implementation mainly include the design of the algorithm for separation and extraction of respiration and heartbeat signals,real-time spectrum analysis of signals,and calculation of respiration and heartbeat count display.The work of this paper mainly includes:(1)Hardware system design.The experimental circuit is built for the 24 GHz Doppler radar CMD324 as the radar sensor,and after analyzing the characteristics of the collected human echo signal,the hardware implementation scheme based on the STM32F429 with Cortex-M4 core as the control core is determined.In order to reliably extract the radar echo signal,the signal conditioning circuit based on CMD324 Doppler radar(mainly including signal amplification,filtering,voltage boost and other funct-ional circuits),as well as the system power management circuit are designed.(2)Design of respiratory heartbeat signal separation algorithm.The human vital signs signals extracted by the radar conditioning circuit are mixed signals containing breathing and heartbeat,and they need to be separated from the mixed signals by digital signal processing methods.In this paper,five signal processing methods,namely,Empirical Modal Decomposition(EMD),Ensemble Empirical Modal Decomposition With Adaptive Noise Addition(CEEMDAN),Modified Ensemble Empirical Modal Decomposition(MEEMD),Variational Modal Decomposition(VMD)and IIR digital filtering,are used to separate the signals for research experiments.The IIR bandpass filter was selected for the real-time detection and separation of respiratory and heart-beat signals.(3)Signal separation and function implementation based on embedded system.Firstly,the digital filter coefficients were calculated using Matlab tools and the STM32 driver was configured.Then,the IIR bandpass filter was implemented on the STM32 to separate and extract the respiratory and heartbeat signals,and finally,the results of respiratory and heartbeat counts were calculated using the FFT transform and modulo,to realize the real-time detection of human vital signs signals.Finally,the effect of breathing and heartbeat parameters extracted by the non-contact vital sign detection device was tested several times in the laboratory on diff-erent subjects and at different distances.The experimental test results show that the maximum mean error of respiration count at an effective distance of 200 cm from the Doppler radar sensor is 4.7%,and the maximum mean average error of heartbeat count is 9.14%.Therefore,the detection device designed in this paper can accurately detect respiration and heartbeat signals in real-time without contacting with the human body.