A high-thermal-stability, fully spray coated multilayer thin-film graphene/polyamide-imide nanocomposite strain sensor for acquiring high-frequency ultrasonic waves

Abstract

Owing to their physical flexibility and exceptional sensitivity to ultrasonic waves, thin-film graphene-based nanocomposite sensors have been gaining prominence in ultrasonic testing-based structural health monitoring (UT-SHM) applications. However, both the electrical conductivities of this new class of sensors and their adhesion on monitoring targets have been found to be highly dependent on temperature. Consequently, under excessive temperature variations, signals that would be output would be disturbed and unable to reflect the health conditions of the monitoring targets, undermining the accuracy of the health monitoring. Herein, we propose a high-thermal-stability thin-film graphene/polyamide-imide sensor for acquiring ultrasonic waves under unstable temperature conditions. The sensor consists of three layers, namely a polyamide-imide-based insulation/adhesion layer (bottom), a graphene/polyamide-imide-based sensing layer (middle), and a silver-based electrode layer (top). It is fabricated by ultrasonic atomization-assisted spray coating and can be formed directly on monitoring targets. Thanks to the adoption of polyamide-imide, the sensor retains a steady electrical conductivity and a strong adhesion on monitoring targets up to 160 °C. As a result, its sensitivity to ultrasonic waves exhibits only marginal changes. All in all, this work further promotes the implementation of thin-film graphene-based nanocomposite sensors in real-life UT-SHM applications.