Noncontact Vital Sign Sensor Using Self-Injection-Locked (SIL) Technology and Frequency-to-Power Converter (FPC)

This study proposes a self-injection-locked (SIL) radar operating in the 2.36-2.39 GHz medical body area networks (MBAN) band for noncontact vital sign monitoring. The frequency-to-power converter (FPC), containing a surface acoustic wave band-pass filter (SAW BPF) and a power detector, is used to extract the SIL oscillator's (SILO) output frequency variation caused by the injection signal reflected from the environment. This work verifies that the FPC achieves the same SNR performance as the delay discriminator common in existing SIL radars, with a cost of merely 0.74% Moreover, the computation efficiency is also improved by 95% by resolving IQ mismatch and dc offset issues. Experimental results show that the prototype can provide exact cardiopulmonary information of the seated subject with a maximum sensing range of 3.5 m.