A Non-contact Vital Signs Retrieving Method for Aviation Safety Personnel Using TVF-EMD

Conducting real-time monitoring of aviation safety personnel’s vital signs during their duty, like respiration and heart rate, is essential for ensuring the safety of civil aviation operations, especially in promptly detecting fatigue-related anomalies. Traditional contact or wearable measurement systems are inevitably inconvenient and even bring new operational hazards when applied in working scenarios. The Linear Frequency Modulated Continuous Wave Radar (FMCW) provides a non-contact vital signal monitoring means for pilots and air traffic controllers in their working environments. The Empirical Mode Decomposition (EMD) method is a typical time domain solution to retrieve time-varying vital sign signals. However, this method is subjected to the modal aliasing effect due to the respiration rate and heartbeat rate being close in frequency. The Time-Varying Filtered Empirical Mode Decomposition (TVF-EMD) method is then introduced to address this issue, which enhances signal separation performance by adaptively adjusting the local cutoff frequency of the signal. This method successfully resolves the issue of modal aliasing in retrieving respiration and heartbeat signals from mm-wave radar echoes. In addition, heartbeat waveforms are effectively reconstructed using the Instantaneous Mode Functions (IMFs) decomposed by TVF-EMD. This enables precise estimation of Inter-Beat Interval (IBI) and various Heart Rate Variability (HRV) metrics. Simulations and experiment results validate the effectiveness of the TVF-EMD method in accurately extracting vital sign information from millimeter-wave radar measurement signals.