Stretchable nanocomposites with tunable acoustic impedance for ultrasound devices

This paper presents the design, fabrication, and theoretical modelling of a highly stretchable Ecoflex-based nanocomposite that achieves acoustic impedance matching and low attenuation for wearable ultrasound devices, enabling improved signal transmission, skin conformity, and high-performance ultrasound imaging. • A highly stretchable (>600%), soft Ecoflex-based nanocomposite is developed with skin-like modulus (∼0.15 MPa), enabling stable, conformal contact for wearable ultrasound devices. • Nanoparticle incorporation increases acoustic impedance from 1.06 to ∼ 1.4 MRayl (32% improvement), reducing reflection losses from 17.2% to 3.4% while maintaining low acoustic attenuation. • Effective medium models (Reuss, Voigt-Reuss, HS, Mori–Tanaka) accurately predict composite impedance, and experimental demonstrations confirm improved imaging and blood-flow measurement capability. 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.