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The use of fibre optic sensors to compare the internal strains and pressures produced by different Lamb wave modes

Lamb waves are a type of guided ultrasound wave that propagate in plate material and have found applications in the fields of structural health monitoring and material properties evaluation. They have modal properties and are divided into two categories, symmetric and antisymmetric. Normally they are measured through detection of surface movement; however analysis shows that the greatest difference in particle motion between the modes is at the centre of the plate. In this paper the use of fibre Bragg gratings and polarimeters, embedded at different locations within the plate, to detect the differences in strain and pressure these ultrasound modes produce by is described.