Nowadays, smart composite materials embed miniaturized sensors for structural health monitoring (SHM) in order to mitigate the risk of failure due to an overload or to unwanted inhomogeneity resulting from the fabrication process. Optical fiber sensors, and more particularly fiber Bragg grating (FBG) sensors, outperform traditional sensor technologies, as they are lightweight, small in size and offer convenient multiplexing capabilities with remote operation. They have thus been extensively associated to composite materials to study their behavior for further SHM purposes. This paper reviews the main challenges arising from the use of FBGs in composite materials. The focus will be made on issues related to temperature-strain discrimination, demodulation of the amplitude spectrum during and after the curing process as well as connection between the embedded optical fibers and the surroundings. The main strategies developed in each of these three topics will be summarized and compared, demonstrating the large progress that has been made in this field in the past few years.

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Fiber Bragg grating sensors toward structural health monitoring in composite materials: challenges and solutions.

This paper describes steps involved in the design and realization of a new type of pressure sensor based on the optical fiber Bragg grating. A traditional pressure sensor has very limited usage in heavy industrial environments, particularly in explosive or electromagnetically noisy environments. Utilization of optics in these environments eliminates all surrounding influences. An initial motivation for our development was the research, experimental validation, and realization of a complex smart pressure sensor based on the optical principle. The main benefit of this solution consists of increasing sensitivity, resistance to electromagnetic interference, dimensions, and potential increased accuracy.

https://www.mdpi.com/1424-8220/10/12/11212/pdf

Design of a Pressure Sensor Based on Optical Fiber Bragg Grating Lateral Deformation

When FBG sensors are embedded in CFRP laminates, the reflection spectrum from the FBG sensors splits into two peaks because of the non-axisymmetric thermal residual stress. This deformation of the spectrum will lead to misreading in strain measurements or crack detection in the laminates. In the present research, three types of FBG sensors: uncoated normal, polyimide-coated normal, and polyimide-coated small-diameter FBG sensors, were embedded in CFRP cross-ply laminates, and reflection spectra from the sensors were measured during the fabrication process of the laminates. Through the comparison of results obtained for the three FBG sensors, it was found that the effect of thermal residual stress on the reflection spectrum could be decreased when the optical fiber was coated with polyimide and its diameter was small in the present laminate configuration and embedment position. Furthermore, these changes of the spectra during the curing process could be simulated by theoretical calculation considering the birefringence effect.

Effect of thermal residual stress on the reflection spectrum from fiber Bragg grating sensors embedded in CFRP laminates

Preface Editors Contributors Introduction to Optical Fiber Sensors Ginu Rajan Optical Fiber Sensing Solutions: From Macro- to Micro-/Nanoscale Yuliya Semenova and Gerald Farrell Interferometric Fiber-Optic Sensors Sara Tofighi, Abolfazl Bahrampour, Nafiseh Pishbin, and Ali Reza Bahrampour Polymer Optical Fiber Sensors Kara Peters Surface Plasmon Resonance Fiber-Optic Sensors Kent B. Pfeifer and Steven M. Thornberg Photonic-Crystal Fibers for Sensing Applications Ana M.R. Pinto Liquid Crystal Optical Fibers for Sensing Applications Sunish Mathews and Yuliya Semenova Optical Microfiber Physical Sensors George Y. Chen and Gilberto Brambilla Fiber Bragg Grating Sensors and Interrogation Systems Dipankar Sengupta Polymer Fiber Bragg Grating Sensors and Their Applications David J. Webb Acousto-Optic Effect and Its Application in Optical Fibers Alexandre de Almeida Prado Pohl Distributed Fiber-Optic Sensors and Their Applications Balaji Srinivasan and Deepa Venkitesh Fiber Laser-Based Sensing Technologies Asrul Izam Azmi, Muhammad Yusof Mohd Noor, Haifeng Qi, Kun Liu, and Gang-Ding Peng Active Core Optical Fiber Chemical Sensors and Applications Shiquan Tao Optical Fiber Humidity Sensors Muhammad Yusof Mohd Noor, Gang-Ding Peng, and Ginu Rajan Medical Applications of Fiber-Optic Sensors Vandana Mishra Optical Fiber Sensors for Smart Composite Materials and Structures Manjusha Ramakrishnan, Yuliya Semenova, Gerald Farrell, and Ginu Rajan Future Perspectives for Fiber-Optic Sensing Brian Culshaw Index

Optical fiber sensors : advanced techniques and applications

Fiber grating laser sensors have been attracting great interest because of their high signal-to-noise ratio and narrow linewidth that permit high resolution sensing. According to the working principle, fiber grating laser sensors can be classified into two types: wavelength encoding sensor and polarimetric heterodyning sensor. The former responds to external perturbations in terms of shift in the operation wavelength of the fiber laser, which is similar to that of fiber grating sensor. The latter converts measurand into change in beat frequency between the two orthogonal polarization modes from the fiber laser. The polarimetric fiber grating laser sensor not only has almost all advantages of passive fiber grating sensors, but also has a distinctive advantage of ease of interrogation. This is because the beat frequency is in the RF domain, which avoids the employment of expensive wavelength measurement devices. This type of sensor has been demonstrated for measurement of temperature, axial strain, lateral force, hydrostatic pressure, bending, displacement, acceleration, electric current, and acoustic and ultrasonic signal. In this paper, we review the principle, fabrication, characterization, and implementation of the polarimetric heterodyning fiber grating laser sensors, and the sensor multiplexing in the RF domain.

Rachid Gafsi

Papers

Analysis of Induced-Birefringence Effects on Fiber Bragg Gratings