Contactless Respiratory Waveform Estimation Using Ultrasound Planar Array

Accurate and contactless respiratory monitoring is essential for both clinical diagnostics and home healthcare, offering the potential for continuous, non-invasive observation. Ultrasound-based systems, particularly when integrated into home smart devices, provide a cost-effective solution. However, existing approaches are limited by poor directivity, inadequate clothing penetration, reliance on averaged respiratory rates without waveform details, and the inability to measure range due to continuous-wave Doppler techniques. To address these challenges, this study develops a novel 18-kHz, 16-channel two-dimensional (2-D) ultrasound array system employing adaptive beamforming to enhance sensitivity and accuracy in respiratory waveform detection. The system integrates pulsed and frequency-modulated continuous-wave (FMCW) excitation to improve the signal-to-noise ratio (SNR) by 20 dB, while the 2-D beamforming technique directly estimates delays from respiratory movements, boosting SNR by an additional 8.5 dB and eliminating the need for time-intensive volumetric scanning. Experimental results demonstrate sub-millimeter displacement accuracy in motor-controlled plate tests, surpassing wearable inertial measurement devices, and human trials reveal an average respiratory rate error of 0.13 breaths per minute across various clothing types and distances. The proposed system not only advances remote respiratory monitoring but also paves the way for enhanced health diagnostics in both clinical and home settings.