Alignment-Free Liquid-Capsule Pressure Sensor For Cardiovascular Monitoring

Wearable pressure sensors enable long-term real-time health monitoring in a noninvasive and power-efficient way; however, the sensors are often required to be precisely applied at the optimal measurement spot, e.g., nearby radial artery, for signal acquisition, causing inconvenience for untrained users or the elders. In this paper, a wearable liquid-capsule sensor platform embedded with a piezo-resistive pressure sensor is presented for continuous, accurate, and alignment-relaxed physiological monitoring, i.e., heart rate (HR) and blood pressure (BP) tracking. The flexible capsule design ensures comfort and good device conformation to any skin regions. For HR and BP measurements, experiments are performed on 12 human subjects. The results show that the capsuled sensor can continuously track: 1) HR with a mean absolute difference (MAD) of 0.88 beats per minute (bpm) and 2) BP with a MAD<3 mmHg for both diastolic and systolic blood pressure. The new liquid-capsule-based sensor platform may help to realize an accurate, flexible, robust, and low-power solution for next-generation wearable health monitoring devices.