Skin-adaptive focused flexible micromachined ultrasound transducers for wearable cardiovascular health monitoring

Continuous monitoring of cardiovascular vital signs can reduce the incidence and mortality of cardiovascular diseases, yet cannot be implemented by current technologies because of device bulkiness and rigidity. Here, we report self-adhesive and skin-conformal ultrasonic transducer arrays that enable wearable monitoring of multiple hemodynamic parameters without interfering with daily activities. A skin-adaptive focused ultrasound method with rational array design is proposed to implement measurement under wide ranges of skin curvatures and depths with improved sensing performances. We introduce a self-adhesive hydrogel layer to enhance the acoustic impedance matching, biocompatibility and contact reliability at device-skin interfaces, and a microelectromechanical systems-compatible process for batch-to-batch and high-consistency manufacturing. The resultant transducer array, with a frequency of 2.4 megacycles per second and a -6 dB bandwidth of 47%, implements accurate and continuous detection of cardiovascular signs, including blood pressure (BP) waveforms of various arteries, heart rate and BP during exercises, and arterial stiffness, validated clinically.