Wrist pulse detection system based on changes in the near-field reflection coefficient of a resonator

This letter presents a wrist pulse sensor based on reflection coefficient (S₁₁) from a resonator which is applicable to existing wearable communication devices. The compact resonator is designed on flexible substrate as an RF signal radiator. Since the reflection coefficient from the resonator depends on the distance between the resonator and the wall of the major artery, slight changes in radial artery diameter can be utilized to obtain pulse rate at the wrist. The sensor system is implemented and tested at 2.4 GHz ISM band, and reveals excellent performance in terms of sensitivity as well as convenience as a wearable device compared to conventional piezoelectric or photoplethysmography (PPG) sensor.