Non-Contact Vital Sign Monitoring With a Metamaterial Surface

Vital sign monitoring is important for determining the health status and well-being of an individual. Despite their high level of accuracy, clinical sensing methods for vital signs, such as heart or respiration signals, often require direct skin contact and the use of wires, making them restrictive and inconvenient. In contrast, alternative sensing approaches using wireless means can be comfortable for users and are suitable for long-term, continuous health monitoring scenarios. Recent advances in physiological sensing using Doppler radars present great potential for non-contact vital sign monitoring, but face many challenges due to background clutter and large body motions. In this work, we develop an integrated system for non-contact vital sign monitoring based on microwave metamaterials and software-defined Doppler radar. Our sensor is thin, flexible, and able to monitor health through clothing. We demonstrate our system's capability in respiration and cardiac sensing through experiments on a healthy volunteer and validate its cardiac sensing accuracy against electrocardiography as the gold standard. Validation results show a Pearson's correlation coefficient
$r\approx 0.9$
and Bland-Altman agreement limits of ±37.1 ms between our sensor's and the gold standard's estimation of heart beat-to-beat intervals.