PSI - Issue 78

Alessandra Marino et al. / Procedia Structural Integrity 78 (2026) 1753–1758

1757

4.3. FBG fiber optic sensors In recent years, fiber optic has been the main physical means of transmitting and receiving information in telecommunications. Fiber Bragg Grating (FBG) fiber optic sensor technology meets the requirements for use in plants with a major accident hazard. In fact, it is a dynamic and continuous pre- and post-earthquake monitoring system that is robust, multi-functional and remotable. A sensor based on FBG technology can measure the strain, and therefore the stress, of the structures on which it is installed or integrated. The deformation of the structure automatically leads to a deformation of the grating and therefore to a change in the reflected wavelength. A particular feature of using Bragg gratings in the sensor is that the information about the unknown parameter is coded as a change in the peak wavelength, so it is not affected by noise or power loss in the line. Another advantage of this technology is its inherent multiplexing capability. In fact, hundreds of Bragg gratings can be placed on a single optical fibre, a few millimetres apart or a few kilometres apart. By means of special transducers, each of these grating can be made sensitive to different physical quantities such as pressure, acceleration, displacement, shape change (3D shape sensing), making an FBG array a multi-functional sensor chain. There is also a non-secondary aspect, which is the safety of operation thanks to the dielectric characteristics and the ATEX certification. In fact, they use light instead of electrical current to transmit measurements from the field to the NOC (Network Operation Center). This means that they can be used at a distance of several kilometres for the management and control of SHM, EWWS and PM (Predictive Maintenance) operations.

Fig. 2: FBG fiber optics sensors metrological chain

The FBG fiber optic sensors are multifunctional transducers capable of detecting vibrations, deformations, temperatures, length variations, dynamic pressures, 2D and 3D geometry variations and accelerations at high sampling rate, with high accuracy and over a long distance, along a single-mode optical fiber interfaced with the structure or component to be monitored. The FBG fiber optic sensors are completely immune to electromagnetic interference, are ATEX certified, do not require a power supply and are considered non-invasive measurement systems due to their limited weight and dimensions. The material they are made of makes them chemically inert: they are insensitive to oxidative and erosive phenomena, guaranteeing correct operation in all environmental and operating conditions, even when immersed in a liquid. They allow measurement data to be transmitted over long distances with low signal loss: kilometer long measurement chains can be easily structured with simple wiring and extremely lean control hardware. The operational and functional characteristics of the optical fiber sensors allow the development of distributed architecture measurement chains, with connections in series and in parallel, depending on the layout of the plant, pipeline or tank farm to be monitored. The multifunction sensors - as will be described below - can be interrogated at kilometer distances by ATEX certified multichannel optoelectronic control units capable of receiving data from the sensors relating to deformations, temperature variations, attitude variations, pressures, 2D/3D geometry variations, liquid leaks, recording them in cloud on secure servers and transmit them to remote NOC and mobile devices, in the form of graphics, numerical values, 3D digital twins, acoustic and visual geo-referenced alarms.