Non-contact Fingertip Microwave Plethysmography Based on Near-Field Sensing with Super-regenerative Oscillator

In this article, a new kind of near-field sensor based on a super-regenerative oscillator (SRO) architecture is proposed to detect the pulse waveforms from fingertips without any direct contact. The designed sensor operates at the center frequency of 5.06 GHz, where a quench signal is imposed to modulate the drain voltage such that the SRO sensor operates in the logarithmic mode. Experiment results demonstrate that the pulse width (PW) as well as vital sign information, such as heartbeat rate, can be easily identified, which agree well with the ground truth measured by a commercial photoplethysmography (PPG) sensor. Furthermore, the proposed near-field SRO-based sensor exhibits higher sensitivity with reduced hardware complexity compared with conventional radar sensors based on homodyne or self-injection locked (SIL) schemes.