A Compact Multimodal Patch for Continuous and Electrode-Free Cardiopulmonary Monitoring

Continuous and non-invasive cardiopulmonary monitoring is essential for the early detection and management of both chronic and acute health conditions. This study presents a compact, multimodal wearable patch that captures seismocardiogram (SCG), dual-wavelength photoplethysmogram (PPG), and skin temperature signals without requiring gel electrodes or form factor-limited designs. The system integrates low-noise sensors and a custom-designed PCB within a 3D-printed enclosure, resulting in a lightweight, electrode-free device suitable for a wide range of users. Experimental validation with 12 participants demonstrated accurate estimation of heart rate (HR), heart rate variability (HRV), respiratory rate (RR), and temperature, with low mean percentage errors across all modalities. HR and HRV were estimated with errors below 1%, RR with a mean error of 1.6%, and temperature within a 3.7% error margin. Additionally, the application of Teager-Kaiser energy operator improved the robustness of peak detection in SCG signals, leading to more accurate and reliable HR and HRV estimation. Unlike many existing wearables that rely on adhesive electrodes or single-signal modalities, this system offers a miniaturized, multi-sensor solution for continuous cardiopulmonary monitoring, suitable for both clinical environments and daily-life integration.