School of Electronic Information Engineering, Beihang University, Beijing 100191, China.
Key Laboratory of Microwave Perception & Safety Application, Beihang University, Beijing 100191, China.
Sensors (Basel). 2021 Apr 13;21(8):2732. doi: 10.3390/s21082732.
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.
采用窄波束毫米波雷达设计了一种非接触式心率/呼吸率监测系统。该系统在频率调制连续波（FMCW）系统的 120GHz 频段中，在收发天线的前端配备了特殊的低旁瓣和小型天线透镜，实现了雷达的窄波束控制，减少了测量背景中其他物体反射引起的干扰，提高了中频信号（IF）的信杂比（SCR），降低了后续信号处理的复杂性。为了解决心率容易受到呼吸谐波干扰的问题，应用自适应陷波滤波器滤除呼吸谐波。同时，通过使用相邻元素的比值对快速傅里叶变换（FFT）得到的心率进行修正，有助于提高心率检测的准确性。实验结果表明，当监测系统与人距离 1m 时，八位志愿者的呼吸率检测误差在±2 倍内的概率可达 90.48%，心率检测的准确率可达 90.54%。最后，通过改进的经验模态分解和快速独立分量分析算法实现了短期心率测量。
