Towards Remote Monitoring of Vital Signs without Body Instrumentation

Abstract

This research presents two approaches using microwave signals to detect vital signs of humans equipped with an m-health application. The first approach utilizes phase locked loop (PLL) to multiply the frequency of a very accurate Direct Digital Synthesizer (DDS), generating a FMCW signal. The second approach multiplies the generated DDS signal using a frequency multiplier (F12). Counter-intuitive existence of low power harmonics (F13, F14, F11, F10, etc.) in the frequency multiplier added improvements in our tests. Tiny variations in environment are easily observed on specific bars in FFT of down-converted signals in the frequency multiplier approach. Both approaches work by sending a Frequency Modulated Continuous Wave (FMCW) that reflects off objects present in the room. Based on the reflected signal, we calculate distances and movements, from which we then extract breathing and heart rates. In both approaches, we try two sets of microwave signals: Triangular FMCW and Sawtooth FMCW. Both approaches showed more obvious variation for body movement. In the case of the Triangular FMCW signal, interpreting data is more challenging. On the other hand, the Sawtooth FMCW signal resulted in clear output but lower power and harder to directly observe.