Investigation on in-situ sprayed, annealed and corona poled PVDF-TrFE coatings for guided wave-based structural health monitoring: From crystallization to piezoelectricity

Large-area, lightweight and flexible sensing networks are highly demanded in complex (either in structural topology or material property) structural health monitoring (SHM) applications. Development of piezopolymer offers a feasible solution. In pursuit of maximum exploitation of their functionality, the optimal fabrication technique requires to be investigated first. In this study, PVDF-TrFE coatings were in-situ fabricated and directly functionalized on structural surfaces in the consecutive processing steps as spray, thermal annealing, and corona poling. The processing conditions, including annealing temperature/time and poling voltage/duration, were correlated with their crystallinity, ferroelectric phase, morphology, polarization, and final piezoelectricity, through a systematic study. With the help of various characterization methods, the conditions of optimal functional performance were identified and rationalized. To study the feasibility of thus-prepared functional coatings in transducing guided waves, the host structures with sensors made of such coatings were interrogated by passive acoustic emission and active ultrasonic transmission to validate the sensing and actuation capability, respectively. The developed piezopolymer coatings possess excellent performance as a novel configuration of sensing networks, with lightweight, ultrathin, flexible, rapid-prototyping and adhesive-free features, manifesting high adaptability, high consistency, negligible inter-path interference, and minimal extra penalty for a robust SHM system.