Non-Contact Extraction of Seismocardiogram From FMCW Radar Signals Using Variational Mode Decomposition

The Seismocardiogram (SCG) is a mechanical signal caused by the vibrations of the chest surface due to heartbeats. SCG is closely related to cardiac activities, including myocardial contraction and relaxation, as well as the opening and closing of heart valves. Therefore, SCG provides a new method for monitoring cardiac function in addition to the Electrocardiogram (ECG). This paper proposes a method for measuring SCG signals using a 77 GHz frequency-modulated continuous wave (FMCW) radar, which can non-invasively measure SCG signals with a high signal-to-noise ratio (SNR) and capture seven prominent feature points. The method begins by extracting raw vital signs from the radar signal, followed by median filtering to remove pulse noise. Then, a Variational Mode Decomposition (VMD) algorithm is applied to decompose the raw vital signs into 20 modes. After analysis, modes 11 to 15 are selected and reconstructed to obtain the SCG signal. We collected synchronized radar and ECG data from five subjects and validated the proposed method. The results show that the method can extract SCG signals with a higher signal-to-noise ratio, with the SCG signal clearly exhibiting seven characteristic points of cardiac activity. Notably, the aortic opening (AO) point corresponds to the R-wave peak of the ECG, and the Interbeat Interval (IBI) derived from the SCG signal is nearly identical to that calculated from the ECG signal.