10 October 2006 Versatile fiber-Bragg grating arrays for strain mapping and ultrasound Lamb wave detection
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The possibility of combining load history with ultrasound signal information offers, potentially, an extremely powerful method for determining the structural health of a structure. Here we describe how suitably configured fibre Bragg grating arrays can be used to both monitor strain fields and to detect the magnitude and direction of ultrasound waves. The directional responses of fibre Bragg gratings to both static and ultrasonic strain fields have been investigated and the results used to enable the FBGs to be configured into rosettes. These can be interrogated to give both the magnitude and direction of either the principle static strain or an incident ultrasound Lamb wave. Measurement of the static strains enables us to perform strain mapping and hence determine load history, whilst ultrasound detection allows us to monitor a structure for defects such as cracks. If Lamb waves are generated by, for instance, PZTs bonded to the structure, comparing signals from the rosette with data previously obtained for the healthy structure allows possible defects to be identified and located. Location is carried out by calculating the intersection point of ultrasound direction from 2 or more rosettes. The geometry of the rosette configuration is described, together with the parameters affecting efficient strain transfer and the optimisation of FBG interrogation techniques.
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G. Thursby, G. Thursby, D. C. Betz, D. C. Betz, B. Culshaw, B. Culshaw, W. J. Staszewski, W. J. Staszewski, "Versatile fiber-Bragg grating arrays for strain mapping and ultrasound Lamb wave detection", Proc. SPIE 6379, Photonic Applications for Aerospace, Transportation, and Harsh Environments, 63790F (10 October 2006); doi: 10.1117/12.686823; https://doi.org/10.1117/12.686823

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