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Lamb wave detection and source location using fiber Bragg grating rosettes

Betz, D. and Thursby, G.J. and Culshaw, B. and Staszewski, W. (2003) Lamb wave detection and source location using fiber Bragg grating rosettes. In: Smart Structures and Materials 2003 Conference, 2003-03-02 - 2003-03-06.

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Abstract

We describe a novel fiber-optic system that is able to detect both ultrasonic Lamb waves and the location of their source. The aim of the system is to detect damage in structures such as those found in aerospace applications. Our system involves the use of fiber Brag gratings, which may be either bonded to the surface of the material or embedded within it in order to detect the linear strain component produced by the acoustic waves. Interrogation of the Bragg gratings is carried out using a laser, which is tuned to the wavelength that gives the maximum sensitivity on the grating response curve. An amplitude modulated signal is produced by the interaction of the Lamb wave with the grating. ne well defined directional properties of the Bragg grating (compared to the isotropic response of the more commonly used piezoceramic disc transducers) are used to determine the direction of propagation of the acoustic waves by mounting three of the gratings in a rosette configuration. Two suitably spaced rosettes are used to locate the source of the ultrasound by taking the intersection of the directions given by each rosette. This will become important when we extend the technique to include the study of the use of changes in the propagation properties of Lamb waves as a method of damage detection. We will present both theoretical and practical results on the interaction of the Lamb waves with the grating and the extraction of directional information from the response of the rosettes.