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 durability, acoustic fidelity, and scalability. In this study, we present a flexible 5×4 ultrasonic transducer array (UTA) based on Lead magnesium niobate-lead Titanate (PMN-PT 1–3) composite elements for continuous blood pressure monitoring. To achieve reliable integration, we employed a dual-sided eutectic solder bonding method using an SnBi 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 robust 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.