Non-Contact Detection of Vital Signs Based on Improved Adaptive EEMD Algorithm (July 2022)

Figures

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  Figure 1. FMCW radar block diagram.

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  Figure 2. Spectrum of chirped signal frequency with time.

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  Figure 3. Flow chart of human heartbeat and respiration signal detection.

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  Figure 4. Spectrum of simulated phase signal. Respiration rate fre = 0.32 Hz, heartbeat rate fhr = 1.54 Hz. The 2nd, 3rd, 4th and 6th breath harmonics have been added. The original signal has respiratory harmonics in the range of 0.8~2.0 Hz.

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  Figure 5. (a) EMD decomposition results of simulated signals, the red line is the component close to the respiratory rate, and the blue line is the component close to the respiratory rate. (b) Spectrums of simulated signals, respiratory and heartbeat spectrums. Respiration rate Fre = 0.32 Hz, heartbeat rate Fhr = 1.54 Hz. The 2nd, 3rd, 4th, and 6th breath harmonics have been added. IMF2 and IMF1 are considered to be the closest respiratory and heartbeat components, respectively. In (b), false peaks exist in both the original signal and the heartbeat spectrum within 0.8−2.0 Hz, making it difficult to estimate the heartbeat frequency.

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  Figure 6. (a) EEMD results of simulated signals, the red line is the component close to the respiratory rate, and the blue line is the component close to the respiratory rate. (b) Simulated signal spectrum, respiratory spectrum and heartbeat spectrum. (c) Spectral details of simulated signals, respiratory and heartbeat domains. The respiratory rate and heartbeat rate are set as shown in Figure 4, that is, Fre = 0.32 Hz and Fhr = 1.54 Hz. The second, third, fourth and sixth breath harmonics were added, and the SNR was set to 0.2. IMF5 and IMF3 are considered to be the closest respiratory and heartbeat components, respectively. The heart rate can be estimated from the IMF3 spectrum of (c).

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  Figure 7. (a) Decomposition results of simulated signals using the improved EEMD, the red line is the component close to the respiratory rate, and the blue line is the component close to the respiratory rate. (b) Spectrum comparison of heartbeat IMF obtained from simulated signals using EMD, EEMD and the improved EEMD. The respiratory rate and heartbeat rate are set as shown in Figure 5, that is, Fre = 0.32 Hz and Fhr = 1.54 Hz. The second, third, fourth and sixth breath harmonics were added, and the SNR was set to 0.2.

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  Figure 8. (a) Experimental setup, which included volunteers, FMCW radar (IWR1843) component, and a laptop. (b) Radar chirp parameter setting.

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  Figure 9. Before (a) and after (b) static clutter filtering technology for echo signal, the raised lines in the figure represent targets detected by radar, it can be seen that, before processing, the radar detects moving targets and stationary objects, and it is difficult for us to distinguish the location of the subject target. After processing, we can see that only the subject target exists in the whole picture.

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  Figure 10. Target range, radar target distance is 0.65 m, radar range resolution is C/2B, range resolution is 4 cm.

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  Figure 11. (a) EMD decomposition results of actual signals, the red line is the component close to the respiratory rate. (b) Spectrograms of actual signals, respiratory spectrograms, and (c) heartbeat spectrograms. IMF3 and IMF2 are considered to be the closest respiratory and heartbeat components, respectively. In (c), there are false peaks in the range of 0.8−2.0 Hz in both the original signal and the heartbeat spectrum, making it difficult to estimate the heartbeat frequency.

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  Figure 12. (a) Decomposition results of actual signals using the method proposed in this paper, the red line is the component close to the respiratory rate, and the blue line is the component close to the respiratory rate. (b) spectrograms of actual signals, respiratory spectrograms and (c) heartbeat spectrograms. IMF5 and IMF3 are considered to be the closest respiratory and heartbeat components, respectively. The heart rate of 1.2 Hz can be estimated from the IMF3 spectrum of (c) in the range of 0.8−2.0 Hz.