Guided waves based damage localization using acoustically coupled optical fibers and a single fiber Bragg grating sensor

Fiber Bragg grating (FBG) sensors have long been thought of as the ideal sensors for structural health monitoring (SHM) due to their small size, light weight, ability to be embedded and ability to be multiplexed. So, FBG sensors have been commonly used for strain based SHM. In recent times, a renewed interest is seen in the use of FBG sensors for GW measurements using the edge filtering approach which increases the sensitivity several fold. The remote bonding configuration has also been proposed to enhance this sensitivity further. But in order to achieve damage localization, a multi-sensor network is needed. The FBG sensors and the equipment for employing them in the edge filtering configuration is expensive. As a result, their use for SHM in large structures is still limited. Recent studies have shown that the acoustic wave in an optical fiber may be transferred from one optical fiber to another through an adhesive based acoustic coupler. In this study, this phenomenon is used to develop an SHM system which is capable of damage localization using a single FBG sensor. The paper presents a proof-of-concept of the use of the acoustically coupled optical fibers and single FBG for damage localization. The paper also highlights the design considerations of an acoustic coupler and discusses them in detail. The proposed approach has a potential to radically reduce the equipment costs (factor of 3) which is one of the limiting factors in the widespread acceptance of SHM systems in structures.