Seat Integration of RF Vital-Sign Monitoring

Abstract

Monitoring of the vital signs including heartbeat, respiration and blood pressure for long duration is critical for driver alertness, smart home, E-health and Internet of Things (IoT), especially when the user takes a seat as in the cases of seniors, patients, and car drivers. The sensing system should be integrated into the seat cushion and “invisible” to the users to provide continuous, comfortable and convenient monitoring. However, current vital-sign sensing technologies often require skin-touch electrodes or external readers with clear line-of-sight, and are hence difficult to be deployed into the chair setup. Piezoelectric, accelerometer and ultrasound sensors can suffer from mechanical damping in soft cushion and limited sensitivity. The radar-based system provides non-contact measurements based on signal reflection from body surfaces, but high areal resolution to accommodate multiple observation points on one user often incurs significant system cost. In this work, an active near-field coherent sensing (NCS) system is integrated into generic seat structures to assess the heartbeat, respiration and blood pressure of the occupant. With the improved balancing bridge design, the weak cardiopulmonary signals from the back and the femoral pulse from the thigh area can be accurately detected for the pulse transit time and the derived blood pressure. Variation of sensing positions due to different postures and body sizes is investigate for robust placement considerations.