mmHvital: A Study on Head-Mounted mmWave Radar for Vital Sign Monitoring

Vital signs, such as heart rate (HR) and respiratory rate (RR), are essential indicators of human health. Millimeter-wave (mmWave) radar has emerged as a promising non-contact sensing technology due to its high resolution, penetration capability, and robustness to varying lighting conditions. However, existing mmWave-based systems require placement at chest height, which reduces mobility performance and requires user compliance. Head-mounted devices---such as smart glasses, headphones, and helmets---offer a wearable alternative but introduce challenges related to sensor positioning, distance variations, and obstruction effects. This study investigates the feasibility of using head-mounted mmWave radar for HR and RR monitoring. To assess waveform quality beyond statistical accuracy, we introduce VITAL-KL, a novel metric that quantifies differences in signal morphology. Results show that front-facing placements achieve higher signal similarity with reference signals, whereas back-facing positions suffer from degraded performance due to reduced chest motion detection. Despite these variations, HR accuracy remains high, reaching approximately 97% for standing and 93% for sitting, as peak-based detection remains robust against waveform distortions. These findings validate the feasibility of head-mounted mmWave radar for vital sign monitoring and provide insights into optimizing sensor placement in wearable sensing systems.