Acquisition And Processing Of Vital Signs Based On Microwave Radar

The vital sign parameters are important indicators of human health.Real-time detection of vital sign signals has great research value.At present,the life signs detection device on the market is not only difficult to meet the requirements of ordinary users in terms of price and volume,but also restricted by the cable connection itself.Non-contact vital signs detection device does not need to be worn by human body.It is a new detection method with friendly user interface.The detection of vital signs based on microwave radar does not need to contact the human body,is not easily affected by the surrounding environment,and its penetration is very strong.These advantages make microwave doppler radar has wide application space in clinical monitoring of burn patients,family routine medical monitoring and disaster relief.At present,there are some problems to be solved in the research of non-contact signs detection based on microwave radar,such as linear reduction of cardiopulmonary activity signals,real-time processing of vital signs collected by radar,and obtaining cardiopulmonary signals from radar echo signals with a lot of clutter interference.This paper is mainly aimed at the health monitoring in daily life and the application of noncontact physical sign detection device in medical treatment:(1)According to Doppler principle and the requirement of detecting sign signal,orthogonal zero intermediate frequency radar,which is aimed to avoid mirror and zero problem,is selected in this paper by comparing the advantages and disadvantages of superheterodyne radar and zero intermediate frequency radar.Considering the requirements of resolution and signal-to-noise ratio(SNR),the radar operating frequency is selected.(2)Because the amplitude of the received sign signal is very small.In order to successfully observe the signal,it is necessary to filter and amplify the signal.A signal preprocessing circuit is therefore designed and manufactured.A 14-bit high-precision ADC is used to sample the signals.Through the preliminary signal processing and refer the actual cardiopulmonary signal,the successful acquisition of heartbeat signal and respiratory signal is proved.(3)In order to meet the needs of daily vital signs detection,real-time extraction of vital signs information from radar echo signals is required,and the algorithm complexity is kept as low as possible.The method of combining short-time fourier transform(STFT)with interpolation processing is used to extract the heart rate information of human body.(4)In order to meet the requirement of high precision in extracting parameters of sign signals in medical applications,wavelet transform is used to reconstruct signals and the heart rate information is obtained by combining the above real-time signs detection method.Then,in order to effectively separate the cardiopulmonary signals and prevent the occurrence of modal aliasing,the ensemble empirical mode decomposition(EEMD)is used to successfully obtain the heartbeat and respiratory signals.The test results of the designed human body signs detection device show that the detection system can effectively detect the breathing and heartbeat of a single stationary human body,and the maximum effective working distance is 100 cm.