Novel methods of Lamb wave detection for material damage detection and location

We describe and compare two novel methods of detecting ultrasonic Lamb waves used for damage detection and location, and then go on to compare their characteristics with those of more conventional PZT transducers. The two methods are measurements of the change in polarization state of the light in an optical fibre and the changes in reflected power from a fibre Bragg grating. Since different transducers measure different properties of Lamb waves by different methods, their relative sensitivities to the S0 and A0 modes can also vary. This can be of interest because, for instance, the A0 mode is more sensitive to the presence of delaminations in a sheet due to the larger shear strain component that this mode contains. We also describe the directional properties of the sensors and demonstrate the ways in which these can be used to advantage in the detection and location of damage.