Thermal behavior of a metal embedded fiber Bragg grating sensor

Abstract

With embedded sensors, the structures are capable of monitoring parameters at such critical locations not accessible to ordinary sensors. Recently, fiber optic sensor emerges as one promising technology to be integrated with structures. Embedding of fiber optic sensors into composites and some metals, especially those with low melting points, have been reported. However, all reported embedding techniques so far are either complicated or difficult to achieve coherent bonding with low residue stresses. Thus, it is of strong interest to pursue some economical ways to embed fiber optic sensors into metallic structures with low residue stresses. In this work, a new technique is proposed for embedding fiber optic sensor into metallic structures, such as nickel, with minimized residue stress. Fiber Bragg Grating (FBG) sensors have been embedded into nickel structures. Thermal performance of such embedded FBG sensor is studied. Higher temperature sensitivity is demonstrated for the embedded FBG sensors. For temperature measurements, the embedded FBG sensor yields an accuracy of about 2 °C. Under rapid temperature changes, it is found that thermal stresses due to the temperature gradient in the metallic structures would be the main cause for errors.

Does Integrated-Circuit Fabrication Show the Path for the Future of Mechanical Manufacturing?

“…The embedding sequence, with the exception of the electrical-insulation step, was shown to be practical for encapsulating fiber-optic sensors into steel structures. 6 …”

V-groove-based compact FBG package for thermal tuning and mechanical stability

“…More importantly, the coefficient of thermal expansion (CTE) value of packaged FBGs has been replaced by that of the substrate material. Bragg wavelength (λ 0 ) is related to refraction index n 0 and grating period (d 0 ) through the equation [8] By differentiating Eq. (1), the thermal wavelength shift ∆λ is given by Thermal sensitivity of FBG (temperature dependent Bragg wavelength λ 0 ) is then dependent on two parts: temperature dependence of the refraction index (dn 0 /dT) of the fiber and the CTE of the substrate material (α) as Because the V-groove can be constructed on various kinds of materials, such as plastics, ceramics, glass,…”

“…Bimaterial packages have been proposed for a-thermal design [3][4][5][6], but those packages increased the original length of the FBG. Metallization of the FBG can increase the thermal sensitivity and mechanical stability, but it is difficult to maintain the original spectrum [7,8]. Polymer FBGs (PFBGs) have also been developed with high thermal and moisture sensitivity, but some research is still needed for manufacturing and packaging [9].…”

Double-layer silicon photonic crystal fiber tip temperature sensor

“…Fiber Bragg grating (FBG) sensors have been most extensively investigated, but their thermal sensitivity is low (~0.01nm/°C) and modifications to enhance sensitivity, e.g., metal or polymer coatings, sacrifice stability and compactness because of residual stress and bulky encapsulation [2,3,4]. We have previously reported on a compact and robust point sensor where a monolithic singlelayer silicon (Si) photonic crystal (PC) is attached on a tip of a single mode optical fiber (SMF) [5].…”