Abstract
A non-contact heartbeat/respiratory rate monitoring system was designed using narrow beam millimeter wave radar. Equipped with a special low sidelobe and small-sized antenna lens at the front end of the receiving and transmitting antennas in the 120 GHz band of frequency-modulated continuous-wave (FMCW) system, this sensor system realizes the narrow beam control of radar, reduces the interference caused by the reflection of other objects in the measurement background, improves the signal-to-clutter ratio (SCR) of the intermediate frequency signal (IF), and reduces the complexity of the subsequent signal processing. In order to solve the problem that the accuracy of heart rate is easy to be interfered with by respiratory harmonics, an adaptive notch filter was applied to filter respiratory harmonics. Meanwhile, the heart rate obtained by fast Fourier transform (FFT) was modified by using the ratio of adjacent elements, which helped to improve the accuracy of heart rate detection. The experimental results show that when the monitoring system is 1 m away from the human body, the probability of respiratory rate detection error within ±2 times for eight volunteers can reach 90.48%, and the detection accuracy of the heart rate can reach 90.54%. Finally, short-term heart rate measurement was realized by means of improved empirical mode decomposition and fast independent component analysis algorithm.
Highlights
With the development of medical technology and the continuous enhancement of people’s health consciousness, the measurement device which can obtain human physiological information anytime and anywhere has been brought to the fore in recent years
This paper presents a non-contact vital signs monitoring system based on narrow beam millimeter wave radar and the radar sensor system was implemented and integrated on printed circuit board (PCB)
This device possesses the following advantages: (1) the hardware structure of the radar system is compact; (2) millimeter wave lens antenna is used in the front end of radar to realize narrow beam control, which has a strong anti-jamming ability, high signal-to-clutter ratio (SCR) of intermediate frequency signal (IF) signal, and good acquisition performance of displacement of chest position points; (3) the mixer circuit is an orthogonal topology without zero point problems
Summary
With the development of medical technology and the continuous enhancement of people’s health consciousness, the measurement device which can obtain human physiological information anytime and anywhere has been brought to the fore in recent years. Calculating the signal frequency by means of fast Fourier transform (FFT) cannot solve the problem of respiratory signal harmonic and clutter interferences [12], affecting the accurate measurement of heartbeat signal frequency; (3) the FFT algorithm can only calculate the average heart rate over a period of time; its estimation accuracy for short-term heart rate is low As a result, it cannot judge abnormal physiological phenomena such as uneven heart rate, so its application value in medicine is limited. On the basis of what has been analyzed above, this paper presents a study on a kind of non-contact measuring device based on narrow beam millimeter radar for human respiratory/heart rate detection and the corresponding measuring methods for adopting frequency-modulated continuous-wave (FMCW) radar in the 120 GHz band.
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