Feasibility of an all-optical scalable network architecture for non-destructive testing of composite plates

With the energy transition, increasing numbers of windmills are built. They are often placed in harsh and difficult to reach environments. Regular inspection of these assets is needed for maintenance and remaining lifetime assessment. Traditional piezoelectric-based monitoring is vulnerable to lightning strikes and requires local signal pre-amplification to deal with long electrical cabling which increases costs and complexity. Here, we present a scalable network architecture consisting of all-optical Fiber Optic Photonic Ultrasound Transducers (FOPUTs) organized in unit cells to provide efficient ultrasonic area coverage. A cut-down unit cell was implemented on a composite plate to monitor plate stiffness using A0 and S0 guided waves and measurement results are provided using receiver FOPUTs consisting of π-Shifted Fiber Bragg Gratings (PS-FBG) and a transmitter consisting of a piezoelectric transducer. The wave propagation in the composite plate was modeled using Finite Element Modeling and the wave speed was estimated using a cross-correlation based algorithm. The four tested PS-FBGs were successfully read out, and the expected S0 mode identified for all of them with an SNR ranging from 52 to77 dB. The measured group velocities were in good agreement with the modeled group velocities. This measurement, on a cut-down unit FOPUT cell, demonstrates the feasibility of the FOPUT system architecture principle.