RF interferometric wearable wrist pulse detection system

This study presents a novel wrist pulse detection system based on the variation of transmission coefficient ( S 21 ) of coupled resonators. Radiated signal from one resonator is modulated by the wrist pulse and transmitted to the other resonator. To improve sensitivity of the system, a radio-frequency (RF) interferometer concept is employed and its validity is mathematically analysed. Full-wave electromagnetic simulation is conducted with the wrist phantom model to predict the transmission coefficient between resonators. The peak level of the S 21 is around −10 dB and the resonance frequency shifts to higher frequency as the distance between the resonator and wrist increases. A prototype of the system is fabricated and tested to show sensitivity enhancement around the 2.4 GHz industry-science-medical (ISM) band. Experimental results reveal that the wrist pulse signal measured by the RF interferometer system is in exact coincidence with the reference finger sensor. Also, the sensitivity is enhanced about 23 dB with the RF interferometer system based on the measurement results.