Guided wave imaging of a composite plate using passive acquisitons by Fiber Bragg Gratings on optical fibers

Abstract : In this work are presented imaging results of defects in composite panels using guided wave imaging algorithms with Fiber Bragg Gratings (FBG) receivers and no piezoelectric actuation. Guided wave imaging is commonly applied to active data: each sensor acts successively as a source whereas other sensors measure the propagated signals. Here the imaging is obtained from passive data, that is, the signal corresponding to each emitter-receiver couple is reconstructed thanks to the crosscorrelation of the ambient noise measured simultaneously by every couple of sensors. The passive imaging approach allows the use of sensors unable to generate guided waves, namely FBG in optical fibers. FBGs present a much smaller intrusiveness compared to traditional piezoelectric sensors while allowing dense multiplexing and are much more robust to harsh environments. Results are shown for two instrumentations, the first one using piezoelectric transducers for actuation and FBG for reception while the second one uses FBG sensors only. The imaging results presented here show the feasibility of passive imaging in composite panels and the possibility of using FBG at ultrasonic frequencies, reducing the intrusiveness of the sensors integrated in the structure in the context of Structural Health Monitoring (SHM).