Evaluation of the internal strains and stresses produced in a plate by propagating Lamb waves through the use of fibre optic sensors

Ultrasonic Lamb waves can be detected by various optical sensors, including polarimetric and FBG fibre sensors embedded within a sample plate. The difference between the responses of two types of optical fibre sensors, both positioned at different depths within a carbon fibre composite plate, to the first symmetric (S0) and antisymmetric (A0) Lamb waves are described. These responses illustrate the differences in internal strains and pressures characteristic of the two modes and may be used to identify phenomena such as mode conversion that might be caused by either structural features or damage within the material.