Accurate Sensing of Arbitrary Displacement Motions Based on Polar Chord Accumulation With Interferometric Radar

In recent decades, the noncontact displacement motion detection via interferometric radar, especially for monitoring vital signs like heartbeat and respiration, has become a significant research area. This article introduces an advanced time-domain phase demodulation technique that overcomes the limitations of frequency-domain features by reconstructing detailed motion patterns. Facing the challenges posed by the inevitable dynamic dc offset of complex scatterers and the complex calibration steps required for time-domain demodulation, our method utilizes chord length to recover the magnitude of the Doppler phase and introduces a cross-product-based technique for determining polarity, thus constructing polar chords. This separate calculation of Doppler phase magnitude and direction is insensitive to stringent central optimal conditions and circumvents complex calibration steps. In addition, this article introduces a pioneering adaptive segmentation method capable of detecting motion details of complex scatterers, thereby expanding the application scope of our algorithm. Both simulations and experiments show that the proposed phase demodulation technique based on polar chord accumulation can accurately reconstruct the normalized motion without phase ambiguity and improve the accuracy with a root mean square error two times lower than other conventional methods. The computational efficiency is 15 times faster than other methods when processing pendulum motion signals within 2 min. In addition, this method is also able to recover similar feature points to photoplethysmography (PPG) in heartbeat signal detection.