Hygieia: A Wearable Metamaterial Patch for Calibration-free Carotid Hemodynamics Monitoring

Abstract

Long-term, continuous cardiac monitoring is essential for early detection and risk prediction of cardiovascular diseases. Recently, electromagnetic-based monitoring methods have gained attention because they are not affected by skin tone or contact force compared to optical or pressure-based methods. While existing systems perform well, they typically rely on professional-grade RF transceivers or require subject-specific impedance tuning based on tissue composition, leading to high cost and per-user calibration that severely limit scalability in large-scale deployments. In this paper, we present Hygieia, a wearable, calibration-free, and low-cost electromagnetic patch that supports continuous, high-accuracy hemodynamic monitoring. Hygieia introduces an air-gap cavity sensing method that converts carotid-induced skin vibrations into resonant frequency shifts, effectively decoupling the hemodynamic measurement from individual differences. In addition, Hygieia combines spectral shaping with morphology-aware feature extraction to reconstruct fine-grained hemodynamic waveforms from noise and adaptively high-accuracy estimate hemodynamic indicators across heterogeneous users. We design and fabricate the Hygieia patch and readout hardware using commodity components at low cost, and validate the system through extensive experiments with 110 participants. Hygieia achieves 96.14% waveform similarity to medical-grade equipment and mean absolute errors below 0.04 s for time-based indicators on average, demonstrating high accuracy and robustness and continuous potential for practical monitoring.