This paper presents a chest-worn health monitor based on continuous-wave Doppler radar technology. To achieve low complexity, low power consumption and simultaneous wireless transmission of Doppler information, the radar architecture is bistaic with a self-injection-locked oscillator (SILO) tag and an injection-locked oscillator (ILO) based frequency demodulator. In the experiments with a prototype operated in the 2.36–2.4 GHz Medical Body Area Networks (MBAN) band, the SILO tag is attached to the chest of a subject to transform the movement of the chest due to cardiopulmonary activities andbody exercises into a transmitted frequency-modulated wave.
The ILO-based frequency demodulator that is located 30 cm away from the subject receives and demodulates the wave to provide a waveform associated with the chest movement. This waveform is further analyzed using short-time Fourier transform (STFT) and ultimately displayed as time-frequency spectrograms. Promisingly, the experimental results as presented in this paper reveal that the proposed monitor is capable of tracking cardiopulmonary activity of a subject during exercise.