A novel fibre Bragg grating sensor packaging design for ultra-high temperature sensing in harsh environments

Abstract

The aim of this article is to introduce a novel packaging of conventional Corning SMF-28 TM single-mode fibre Bragg grating sensors for ultra-high temperature sensing. The package is in a cylindrical shape made of yttria-stabilized zirconia tubes. The fibre optic sensor is epoxied to one end inside the tube to be protected from high external temperatures and also harsh environments. Highly-oriented pyrolytic graphite tube with an exceptional anisotropic thermal conductivity with higher conductivity in transverse than radial direction is positioned around the fibre to protect it from high temperatures. Air cooling system is also provided from the other end to dissipate the transferred heat from inside the tube. The shift in the Bragg wavelength is influenced by the thermal expansion of the package and internal temperature variations, which translates into thermal expansion of the fibre. The modelling and experimental results revealed that the Bragg wavelength shift increases to 1.4 pm • C −1 at higher temperatures with linear behaviour at temperatures above 600 • C. The finite element modelling and the experimental results are also in good proximity indicating the similar trend for the shift in the Bragg wavelength.

Measurement of the high-temperature strain of UHTC materials using chemical composition gratings

“…Prasad et al [39; 40] glued CCGs onto the surface of a metal plate, providing a useful simulation and experimental method to measure the temperature (up to 900°C) and strain response of a metal structure; the most suitable material to encapsulate the FBG for temperature sensing was also studied. Azhari et al [41] developed a simple optical sensor based on conventional FBGs using yttria-stabilised zirconia tubes, which can be used to measure the temperature up to 1100°C. This paper seeks to solve some aspects associated to the practical technology of these optical fibre sensors by using a type of adhesive to connect the RFBGs to the structure.…”

Measurement of high‐temperature strains in superalloy and carbon/carbon composites using chemical composition gratings

“…The value of K T1 in Table 3 is quite different with the values from the superalloy tests in Table 2 and the analogous values of UHTCs in the work of Xie et al 39 In this case, the parameter Relative variation with increasing temperature K T1 contains the effects of both the temperature changes on the CCGs itself and the strain provided by the thermal expansion of the structure, so its value should be larger than the temperature sensitivity coefficient of the bare fibers, which is 7.780 × 10 −6 as reported in the work of Du et al [50] For a silica-based pristine fiber, the parameter K T1 is theoretically equal to the sum of the thermal expansion coefficient α and the thermo-optic coefficient ζ, and it varies in a range between 7 × 10 −6 and 11 × 10 −6°C−1 . [37,[55][56][57] Since the value of K T1 in Table 3 is even lower than the minimum theoretical value, it can be inferred that the thermal strain of the C/C composite has a negative impact on the response wavelength of the CCGs. A major feature of C/C materials is the negative thermal expansion characteristic from room temperature to 400°C, 58,59 and even at 800°C.…”

“…Méndez et al, Selfridge et al, Mamidi et al, and Sai Prasad and co‐workers have bonded RFBGs onto metal substrates to measure the thermomechanical performance up temperatures of 900 °C. Reddy et al, Barrera et al and Azhari et al have attempted to encapsulate RFBGs within a metal or ceramic tube for usages up to 1100 °C. The packaging and installation of the sensors without damage on practical structures becomes however an import problem to the application of this technology, because silica‐based RFBGs are very brittle and fragile after the annealing process …”

2.1 - Adaption of Fibre Optic Sensors and Data Processing Systems for Flight Test on a Bulldog Light Aircraft

“…The use of this method for the measurement of strain is relatively mature, with FBGs finding application in areas including structural health monitoring [7], [8], temperature sensing [9] and in the oil and gas industry. In addition, the technique is now seeing increasing use in aerospace applications [10] including for the measurement of the shape of wings [11].…”