Non-contact Vital Sign Detection Based On Microwave Doppler Method

Microwave Doppler radar has been used to sense physiologic movements since the early 1970s. The method that obtains kinds of physical information by detecting the micro-movements caused by physical activities is a very important method of non-contact detection. Besides the related information like respiration, circulation, metabolism and so on, the body's micro-movements may contain information that cannot be acquired by contact detection.In this thesis, Microwave Doppler radar has been applied to detect vital signs. Non-contact detection has a lot of applications, such as searching human subjects under earthquake rubble and monitoring of sleep apnea in both infants and adults.Doppler radar vital sign detection system typically transmits a continuous-wave (CW) signal, which is reflected off a target and then demodulated in the receiver. According to Doppler theory, a CW radar with the chest as the target will receive a signal similar to the transmitted signal but with its phase modulated by the time-varying chest position. Demodulating the phase will give a signal directly proportional to the chest position, which contains information about chest movements, from which heart and respiration rates and signatures can be determined.In this thesis, a digital-IF Doppler radar system is designed. A CW carrier signal, generated by Agilent Signal Generator, is transmitted to the subject, which reflects the modulated waves to the receiver antenna. The Agilent Spectrum Analyzer, with an under-conversion module inside, demodulates the received signal to 70MHz IF signal, which is then sampled by a ADC module in Agilent Vector Signal Analyzer. Digital quadrature demodulation is used to convert IF signal to baseband. We could finally get the respiration and heartbeat signal by further analyzing the baseband signal.The afore-mentioned system proves a good sensitivity. Given transmitting power 0dBm, carrier frequency 2.36GHz, the maximum detection range extends to be 2.5m. The tunable carrier frequency helps avoid the detection null points and improve the system sensitivity.