A nanocomposite-inspired smart sensing coating for acousto-ultrasonics-based structural health monitoring: Modeling, validation and application

An innovative smart sensing coating based on the nanocomposites made of carbon black (CB) and polyvinylidene fluoride (PVDF) is developed. This coating exhibits high fidelity, fast-response and high sensitivity to broadband acousto-ultrasonic waves (from static to high frequency up to 400 kHz). Making use of the tunneling effect [1], the nanostructure of the developed nanocomposites allows the coating to perceive low dynamic disturbance induced by acousto-ultrasonic waves. Morphological characterization is implemented on the prepared nanocomposites to reveal the sensing mechanism of the sensor. For the sake of balancing conductivity and sensitivity, 6.5 wt% of CB nanofiller is determined based on morphological characterization. Performance of the coating is demonstrated by using the sensing coating to capture acousto-ultrasonic waves from low-frequency vibration, through medium-frequency impact signals to high-frequency ultrasonic waves, to show good coincidence, frequencyindependence and higher gauge factor compared with conventional piezoelectric transducers and strain gauges [2]. Lightweight and flexible, the developed sensing coating offers superior designability and tailorablilty, allowing it to be embedded in engineering structures of various geometries and materials, whereas with minimum weight penalty. In addition, a nano-scale model is developed, to facilitate understanding of the sensing mechanism and to corroborate experimental results. Last, the developed sensing coating is applied to acousto-ultrasonicsbased structural health monitoring (SHM), including passive impact localization and active damage identification, highlighting that the coating has paved a new path for implementing insitu SHM, by striking a compromise between "sensing cost" and "sensing effectiveness".