Ultrasonic-based submillimeter ranging system for contactless respiration monitoring

Wireless sensing technologies have exploited various methods for contactless respiration monitoring. One of the main methods is to use an acoustic beam to cover the chest and abdomen with real-time and high-resolution ranging. The system with high ranging resolution can detect small distance transformations, further affecting the precision of respiratory monitoring. However, the traditional range-based respiration monitoring systems are limited by an insufficient sampling rate and poor synchronization. The ranging resolution is between millimeters and centimeters. In this study, we introduced a novel, high-precision ultrasound-based system for contactless respiration monitoring. First, we developed a convenient and high-performance ultrasonic transceiver platform with universal serial bus audio architecture to eliminate the above limitations. The developed platform provides a foundation for acoustic sensing. Furthermore, based on this platform, we designed a cross correlation sine-frequency modulation continuous wave ranging method and a real-time respiration wave recovery method. The median error in monitoring respiration for 12 participants in three different sleep postures is 0 breaths/min, and the maximum error is 0.58 breaths/min. The proposed system has strong robustness concerning different respiration rates, long-term continuous respiration monitoring, and simulated apnea.