Wearable RFID Sensor for Simultaneous Heartbeat and Respiration Monitoring

Novel sensing and communication techniques have created new opportunities for unobtrusive vital sign monitoring. Due to the features of wireless power and data transfer and non-line-of-sight interrogation of radio frequency identification (RFID), its innovative integration with different sensing elements has become a promising solution. Since the heartbeat and respiration signals are weak and their measurement is time-consuming, a lightweight and flexible solution for their unobtrusive wearable sensing remains a challenge. This investigation presents a novel capacitive pressure sensor (CPS)-augmented RFID solution for simultaneous and wearable sensing of heartbeat and respiration. The main contributions include: first, proposal of an innovative RFID-based vital sign monitoring scheme, which integrates a CPS for heartbeat sensing and employs RFID phase signals for respiration sensing; second, design and fabrication of a polydimethylsiloxane (PDMS)-based flexible and porous slotted CPS for continuous heartbeat sensing; and third, development of respiration signal reconstruction algorithm using the weak and noisy RFID phase integrating phase disambiguation, denoising, baseline removal, and peak detection. Experimental studies are conducted to verify the feasibility and effectiveness of the presented techniques.