The use of fibre Bragg gratings for ultrasonic Lamb wave detection and source location

There is an increasing interest in the use of ultrasonic Lamb waves for materials characterisation and the detection of structural defects. Fibre Bragg gratings offer some significant advantages over more traditional transducers such as piezoelectrics for ultrasound detection and are also dual purpose, since the same sensors can also be used for strain mapping.. We describe the use of fibre Bragg gratings to detect ultrasound signals and thereafter to determine both their direction of propagation and source location. The main aspects that will be concentrated upon will be – optimising FBG interrogation techniques; maximising the efficiency of strain transfer from the sample to the FBG sensors; describing the directional response of FBGs; how this allows them to be configured into rosettes to determine the direction of the received ultrasound signal and, finally, how an array of 2 or more rosettes can be used to determine the source of the ultrasound.