Stretchable nanocomposites with tunable acoustic impedance for ultrasound devices

Wearable ultrasound devices hold great promise for continuous health monitoring, yet their long-term continuous monitoring performance is often limited by the short lifetime of coupling gel and variable operating environments. As a result, the stable acoustic properties of ultrasonic sensors are important for their signal transmission efficiency and operational lifetime. This paper introduces a stretchable Ecoflex-based nanocomposite as an acoustically and mechanically compliant interface material, which can achieve acoustic impedance matching with human skin while maintaining low acoustic attenuation. The composite exhibits high stretchability (>600%) and a skin-like Young’s modulus (around 0.15 MPa), enabling stable operation under body movement. A theoretical investigation into the effective acoustic impedance of composites is also presented. Based on an effective medium model with different calculation methods, the Reuss lower bound provides a simple and accurate prediction of acoustic impedance in systems with a large modulus difference between the elastomeric matrix and rigid fillers. Additionally, the stability under complex operating conditions is investigated by a portable ultrasound system, demonstrating its potential for reliable performance in real-life scenarios. These findings reveal the potential of these nanocomposites as an acoustically and mechanically compliant interfaces for wearable ultrasound sensors, offering a pathway toward high-performance, skin-conformal ultrasound imaging devices.