Simultaneous Measurement of Temperature and Mechanical Strain Using a Fiber Bragg Grating Sensor

Abstract

Based on the shift of the Bragg wavelength, fiber Bragg grating (FBG) sensors have been employed to measure a variety of physical parameters such as stress, strain, displacement, temperature, vibration and pressure. In this work, a simple and easy way to be implemented FBG sensing methodology was proposed to measure the temperature and strain simultaneously. Half of the FBG was bonded on the host structure, while the other half of the FBG was left free. The host structure was an aluminum test specimen with dimensions of 20 × 3.8 × 0.5 cm3. As the host structure subjected to mechanical and thermal loadings, the Bragg wavelengths reflected from the bonded and unbonded FBGs are different. Theoretical predictions of the Bragg wavelength shifts of the bonded and unbonded FBGs were presented. Utilizing the Bragg wavelength shift of unbonded FBG, the temperature can be determined and is independent of mechanical strain. The Bragg wavelength shift of the bonded FBG allows the determination of the mechanical strain. The temperature measured by FBG sensor was compared with the result from a thermocouple, while the mechanical strain was validated with the theoretical prediction. Good agreement between the experimental measurement and theoretical prediction demonstrates that temperature-strain discrimination can be realized using the proposed method with one single FBG sensor.

Air Gap Fiber Bragg Grating for Simultaneous Strain and Temperature Measurement

“…chirped long-period grating [14], superstructure FBG [15], misaligning splicing a thin core fiber between two SMFs [16], combining few-mode fiber and FBG [17,18], combining FBG and multimode fiber [19], tilted FBG [20], specially packaged FBG [21], π-phase-shifted FBG [22], and a combination of different types of interferometers and FBG [23][24][25][26]. However, there are some flaws such as relatively high complexity, difficult fabrication process, or low sensitivity in some of those approaches, which restrict their practical applications.…”

“…Dan Su et al [ 9 ] proposed a measurement scheme for dual-parameter measurements using a double-fiber grating written by a single-mode fiber and a thin-core fiber. Furthermore, there are several other approaches such as polarization-maintaining few-mode Bragg gratings [ 10 ], sawtooth stressor-assisted highly birefringent FBG [ 11 ], cascaded long-period fiber grating or Bragg grating [ 12 , 13 ], multimode fiber chirped long-period grating [ 14 ], superstructure FBG [ 15 ], misaligning splicing a thin core fiber between two SMFs [ 16 ], combining few-mode fiber and FBG [ 17 , 18 ], combining FBG and multimode fiber [ 19 ], tilted FBG [ 20 ], specially packaged FBG [ 21 ], π-phase-shifted FBG [ 22 ], and a combination of different types of interferometers and FBG [ 23 , 24 , 25 , 26 ]. However, there are some flaws such as relatively high complexity, difficult fabrication process, or low sensitivity in some of those approaches, which restrict their practical applications.…”

“…tilted FBG [20], specially packaged FBG [21], π-phase-shifted FBG [22], and a combination of different types of interferometers and FBG [23][24][25][26]. However, there are some flaws such as relatively high complexity, difficult fabrication process, or low sensitivity in some of those approaches, which restrict their practical applications.…”

Simultaneous strain and temperature sensing with a compact dual fiber Bragg grating structure

“…Strain and temperature parameter measurements are important for tracking the health information in the fields of bridge engineering and aerospace [1] . Various configurations of fiber optic devices are reported to distinguish for the strain and temperature simultaneously, including fiber Bragg gratings (FBGs) [2,3] , various fiber interferometers [4][5][6] , long period fiber gratings (LPFGs) [7,8] , photonics crystal fiber sensors [9] , and other hybrid structures [10][11][12] . Among them, FBGs have attracted much attention from researchers because its small size, reflection mode operation and excellent wavelength division multiplexing capability [1] .…”

Wavelength Characteristic Analysis of a FBG Array Embedded in Quaternary Unconsolidated Strata during a Deep Borehole Installation

“…With the development of the fiber optic sensing technology, the fiber Bragg grating (FBG), as an all-fiber passive sensing element with high performance, is applied to the safety monitoring in civil engineering, petroleum and chemical engineering, and national defense, to name a few applications. Fiber Bragg gratings can be embedded in composite material or structural systems or can be used for real-time monitoring of internal stress, strain, and displacement distributions of a material or structure [1][2][3], temperature distributions [4], and humidity distributions [5]. Research has also been conducted using laboratory tests and simulations [6,7] on the transfer of fiber optic sensor strain [8,9] and the fiber Bragg grating transverse effects [10].…”