Skin-conformal PMN-PT ultrasonic sensor for cuffless blood pressure sensing via eutectic solder integration

Wearable ultrasonic systems are emerging as promising tools for noninvasive cardiovascular monitoring, enabling the real-time assessment of vascular dynamics without the need for cuff-based measurements. However, the integration of high-performance piezoelectric materials into flexible, skin-conformal arrays poses challenges in terms of mechanical stretchability, acoustic fidelity, and scalability. In this study, we present a flexible 5 × 4 ultrasonic transducer array (UTA) based on 1-3 lead magnesium niobate-lead titanate (PMN-PT) composite elements for continuous blood pressure monitoring. To achieve reliable integration, we employed a dual-sided eutectic solder bonding method using an Sn-Bi alloy to ensure low-temperature attachment without depolarization. The fabricated UTA operates at a center frequency of 6.0 MHz with an acceptance angle of 45°, enabling acoustic signal acquisition under varying angular conditions. Time-of-flight simulations and in vitro testing of vascular phantoms demonstrated the accurate tracking of vessel diameters and the estimation of real-time blood pressure. The UTA achieved systolic and diastolic pressure measurements within 4 mmHg of those of a commercial reference sensor. These results highlight the feasibility of scalable and flexible ultrasound systems for wearable hemodynamic sensors, suggesting their potential for next-generation point-of-care diagnostics.