Second Harmonic Weighted Reconstruction for Non-Contact Monitoring Heart Rate

Achieving high-accuracy and non-contact heart rate monitoring via radar is a non-trivial task under the interference from respiration and its harmonics. In order to eliminate the interference, we propose a weighted reconstruction method of the second harmonic signal of the heartbeat for the heart rate estimation. The proposed method combines the Variational Modal Decomposition (VMD) algorithm with the prior information about the second harmonic of the heartbeat. Namely, after a sophisticated endeavor for preprocessing, the chest wall displacement signal is decomposed into several quasi-orthogonal components by VMD and then those components whose spectrum are within the second harmonic frequency band of the heartbeat are selected to reconstruct the second harmonic signal of the heartbeat. For highlighting more likely second harmonic components and suppressing undesired noise components, the energy of each selected component is used as a weight to adjust its proportion in the reconstructed signal. Consequently, the heart rate estimation is achieved indirectly by estimating the spectral peak of the second harmonic signal. The proposed method not only avoids the strong interference from the respiratory signal and its higher harmonics on heart rate estimation, but also predigests the parameter setting in the spectral peak estimation model. Experimental results from 15 subjects demonstrate that the proposed method can achieve higher measurement accuracy compared with other several methods based on a 77 GHz FMCW radar.