Wearable biometric authentication wristbands based on ultrasonic signatures of identity-gesture fusion

Wearable electronics have been widely adopted in health monitoring, human-computer interaction, and fitness tracking. However, the accompanying risks of personal information leakage, including physiological data, payment details, and communication records, have become increasingly prominent, raising an urgent demand for high-security identity authentication solutions. Here, we present a wearable biometric authentication wristband (WBA-band) that integrates a flexible ultrasonic patch with an adaptive airbag interface, leveraging identity-gesture fusion-based ultrasonic signatures to achieve hardware-level identification. The system employs the ultrasonic patch composed of piezoelectric 1–3 composites to probe deep wrist anatomical structures and extract user-specific ultrasonic signatures. By coupling intrinsic anatomical features with gesture-induced dynamic modulation, the system generates a unique identity-gesture fusion key for secure verification. To ensure stable operation under practical wearing conditions, an elastic airbag is introduced between the ultrasonic patch and an elastic strap, forming the three-layer architecture of adaptive airbag interface. This design provides effective pressure compensation and eliminates interfacial air gaps caused by wrist curvature and tendon undulation, thereby enabling dynamic acoustic impedance matching and robust acoustoelectric transduction. Experimental results demonstrate that wrist ultrasonic echoes exhibit highly distinguishable time-domain and envelope features across users and gestures, enabling highly accurate single-user multi-gesture recognition and user-specific authentication in multi-user scenarios. Notably, this work establishes wrist ultrasound as an implicit biophysical-level biometric modality and introduces a novel paradigm for secure next-generation wearable authentication and reliable human-computer interaction.