A Novel Microwave Measurement Technique for Non-Contact Vital Sign Monitoring

Using microwave to monitor vital signs is becoming a common research topic now a days. People have attempted to use continuous wave radar extensively to monitor heart rate and breathing rate. However, this often suffers from a common problem of measurement non-linearity (i.e. presence of harmonics) due to phase wrapping if the amplitude of vibrating object (in our case the movement of chest wall) exceeds certain threshold when compared against the probing wavelength. This limits the selection of probing wavelength which in turn limits the antenna size. Further miniaturization of the antenna size is not possible because further reduction of probing wavelength will create harmonic frequencies (even if the radar is placed at optimal point) that may completely mislead the measurement. Here, we propose a novel technique based on amplitude modulation of continuous microwave (AMCW) signal that overcomes this limitation and gives independent handle to design the antenna dimension while preventing generation of any harmonics in the baseband. Our concept of using AMCW has been supported well by the simulation result.