Wearable Bracelet Belt Resonators for Noncontact Wrist Location and Pulse Detection

This paper gives a complete evaluation of a new wearable microwave sensor module for pulse measurements. Three substantial contributions are reported. First, a frequency-multiplexed sensor array was developed using complementary split-ring resonators. Cylindrical bracelets can spatially resolve the positional changes of the wrist relative to the location of the sensors on the bracelets. Second, the proposed method requires only a transmission coefficient magnitude (decibels) response at the same frequency. The method does not need to track the resonance frequency shifts, but receives power at a selected frequency. Third, the mechanical movement of the artery perturbs the electrical field radiated from the source resonator; the proposed method detects this perturbation and verifies the biological information, which is utilized to modulate the signal. The proposed bracelet sensor combines position detection and pulse measurement to obtain a more accurate measurement of the pulse. The experimental results show that the bracelet can detect a relative distance change of 0-20 mm with a sensitivity of 1.16 (dB/mm). The bit rate of the measured pulse was verified through photoplethysmography.