Effect of fiber Bragg Gratings receivers' directivity on guided wave tomography of pipe

Abstract : Structural health monitoring (SHM) consists in embedding sensors in a structure like aircraft fuselages, pipes or ship hulls in order to detect defects (for example cracks or corrosion in metallic materials or delamination in composite materials) before a serious fault occurs in the structure. Guided elastic waves emitted by a sensor and propagating to another one are often used as the physical way of detecting the defect. However, the implementation of SHM systems is restricted in many situations by the necessity to store or to harvest the electric energy necessary to emit the waves and also by the intrusiveness of the sensors. Guided wave tomography imaging is able to localize and quantify the severity of the defect when it comes to loss of thickness such as corrosion or erosion. However, it needs many sensors (generally piezoelectric-PZT-transducers) and it has a cost, particularly in terms of intrusiveness. The idea in this paper is to use less intrusive sensors such as fiber Bragg Gratings (FBG) to perform guided wave tomography. The inspected area of a pipe is surrounded by two rings, one with PZT and the other one with FBG.