Abstract
Fibre optic sensors (FOSs) are nowadays widely adopted in structural health monitoring (SHM) of mechanical and aeronautical components thanks to their high sensitivity, reduced size, electro-magnetic immunity, and ease of being embedded in composite materials, enabling the realization of smart structures. SHM refers to the identification of damages due to both fatigue loads and impact occurrence. Regarding this latter case, the feasibility of FOSs for high frequency SHM has been recently proved in both passive impact detection (localization and energy estimation) and active damage monitoring, e.g. by generation and analysis of ultrasonic Lamb waves [1]. Most of the works reported in literature have been performed by means of Fibre Bragg Gratings (FBGs) [2], which guarantee good reliability and high signal-to-noise ratios (SNR). Nevertheless, associated acquisition systems become all more demanding as the frequencies generated by the impact increase. A valid alternative for acoustic and ultra-acoustic sensing is represented by optical fibre interferometers whose monitoring capabilities with bandwidth up to MHz have been extensively proved [3]. In this work, the interferometric approach is proposed for the detection of ultrasonic Lamb waves in metallic structures, exploiting a novel sensing solution based on standard optical fibres associated to a phase-diversity coherent detection scheme [4], which retrieves in a completely passive way the high-frequency phase information of received optical signals. In order to prove the feasibility of the proposed solution for high-frequency SHM, the experimental setup depicted in Fig. 1(a) has been arranged.
© 2017 IEEE
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