Design And Implementation Of A Non-Contact Vital Signs Monitoring System Based On Continuous Wave Radar

The physical condition of human body can be mirrored by many physiological parameters,including height,weight,blood pressure,heart rate,respiratory rate,blood sugar,etc,and the accurate acquisition of such data is of great importance to the judgement of the state of health.Respiration and heartbeat signals are two obvious signals among many physiological ones and both of them are directly related to cardiopulmonary function.Particularly,cardiopulmonary health are more significant for people who are always kept in long-term working status at desk.Since cardiopulmonary-related symptoms often occur suddenly,in order to ensure the timely treatment,the monitoring of high risk group requires accuracy,durability,real time capability and no interference while traditional contact measurement methods are not feasible.With the purpose of making it suitable to the utmost extent for certain people,it is necessary to apply non-contact measurement methods for better acquisition.The non-contact measurement methods,among which the Doppler radar is a representative one,are convenient and have no interference in the detection of vital signs,therefore,the popularity and increasing application of such methods have been existing.Recently,relevant researches have mainly focused on the comparison of data quality corresponding to different radar frequencies,and the processing of radar signals based on different algorithms.Some existing plans were inexpensive but the accuracy could be improved.Some well-known manufacturers proposed high quality radar plans for weak signal detecting,which are based on experimental algorithm and customized hardware,however the application is limited by cost and complexity.As a complete system capable of being put into use,indicators such as the reliability,practicability,and cost of the system require more research and implementation.In this paper,a biological signal detection system based on 24 GHz continuous wave Doppler radar is designed.It is capable of detecting the respiratory and heartbeat signals represented by body surface displacement,as well as filtering out the noise interference introduced by the environment and equipment.The complete radar system is consisted of radar hardware system with high integration,low noise,high anti-interference ability,and a computer-based upper computer interface.It can be applied to indoor occasions and can accurately obtain movement results.Specifically,key biological signals such as human breathing and heartbeats in either sleeping or clear-headed states can be measured.The radar principle,designing of hardware system,signal processing,overall reliability and accuracy of the system are analyzed and verified.The change of Doppler phase shift caused by the displacement of the chest surface is analyzed from the perspective of signal acquisition.The frequency domain analysis method such as Fast Fourier Transform(FFT)is used with bandpass filter.Both respiratory rate and heartbeats are obtained after the frequency domain information of received signal is extracted.Theoretical analysis and experimental results show that the non-contact radar measurement system proposed in this paper provides accurate results.In the experiments in which several health subjects participated,data collected from radar was compared with that from traditional measurements such as Biopac and its breathing belt,it is also verified that the signals are detectable within the allowable range and this actually further verifies the accuracy and feasibility of the system.