A Perturbation-Injection-Locked Sensor with Self-Oscillating Active CSRR for Vital-Sign Detection from Fingertip

A perturbation-injection-locked (PIL) sensor with the self-oscillating active complementary split-ring resonator (CSRR) is proposed in this paper to detect vital signs of the human subject from the fingertip. The output modulated signal of the active CSRR is demodulated by the differentiator-based envelope detector. Since the CSRR can concentrate the electric field in a near-field zone, it will significantly increase the sensor sensitivity. Therefore, one can easily detect respiration and heartbeat rates from the fingertip. The measured heartbeat agrees well with that acquired by the photoplethysmography (PPG) finger pulse sensor.