Feasibility of Fiber Bragg Grating and Long-Period Fiber Grating Sensors under Different Environmental Conditions

Abstract

This paper presents the feasibility of utilizing fiber Bragg grating (FBG) and long-period fiber grating (LPFG) sensors for nondestructive evaluation (NDE) of infrastructures using Portland cement concretes and asphalt mixtures for temperature, strain, and liquid-level monitoring. The use of hybrid FBG and LPFG sensors is aimed at utilizing the advantages of two kinds of fiber grating to implement NDE for monitoring strains or displacements, temperatures, and water-levels of infrastructures such as bridges, pavements, or reservoirs for under different environmental conditions. Temperature fluctuation and stability tests were examined using FBG and LPFG sensors bonded on the surface of asphalt and concrete specimens. Random walk coefficient (RWC) and bias stability (BS) were used for the first time to indicate the stability performance of fiber grating sensors. The random walk coefficients of temperature variations between FBG (or LPFG) sensor and a thermocouple were found in the range of −0.7499 °C/ h to −1.3548 °C/ h. In addition, the bias stability for temperature variations, during the fluctuation and stability tests with FBG (or LPFG) sensors were within the range of 0.01 °C/h with a 15–18 h time cluster to 0.09 °C/h with a 3–4 h time cluster. This shows that the performance of FBG or LPFG sensors is comparable with that of conventional high-resolution thermocouple sensors under rugged conditions. The strain measurement for infrastructure materials was conducted using a packaged FBG sensor bonded on the surface of an asphalt specimen under indirect tensile loading conditions. A finite element modeling (FEM) was applied to compare experimental results of indirect tensile FBG strain measurements. For a comparative analysis between experiment and simulation, the FEM numerical results agreed with those from FBG strain measurements. The results of the liquid-level sensing tests show the LPFG-based sensor could discriminate five stationary liquid-levels and exhibits at least 1,050-mm liquid-level measurement capacity. Thus, the hybrid FBG and LPFG sensors reported here could benefit the NDE development and applications for infrastructure health monitoring such as strain, temperature and liquid-level measurements.

A fuel level sensor for aeronautical applications

“…Conically shaped [4] or angled and retroreflecting-type optical fiber tip [5][6] have been also proposed. Sensors based on Fiber Bragg Grating (FBG) [7] and Long Period Fiber Grating (LPG) sensors with mm resolution have also been reported [8]. FBG and LPG partially simplify the multiplexing problems but they are fragile and non cost-effective technologies when thousands of sensors are required.…”

Application study on FBG sensor applied to hull structural health monitoring

“…As early as 1996, IMO (The Maritime Safety Committee) had recommended that hull stress monitoring system should be installed to improve safety performance of cargo ship. Fiber Bragg grating (FBG) sensor, encoded with wavelength, has advantages of anti-electromagnetic interference, corrosion resistance, light weight, small size, geometrical versatility, electrical, and optical multiplexing [1]. It has incomparable advantage over traditional sensors when used in the hull structural health monitoring.…”

Application of CCG Sensors to a High-Temperature Structure Subjected to Thermo-Mechanical Load

“…Over the past two decades many fibre Bragg grating (FBG)-based sensors have been developed for applications in high-temperature environments due to their unique features [1,2,3,4]. Some examples of the interesting characteristics that characterise FBGs are their low weight, compact size, electromagnetic and radiofrequency compliance, durability, long-distance transmission capabilities and good heat resistance [5,6].…”