In this paper, we present the design and analysis of chirped fiber Bragg grating (CFBG) sensors, optimized for temperature measurements. The transfer matrix method has been used to simulate the CFBGs and to study their thermal response. The simulations have been carried out with different temperature profiles in order to understand how the CFBG thermal response varies as a function of the grating design parameters and, thus, to optimize the design for the specific application. Finally, to assess the numerical simulations, a series of experimental tests was performed showing very good agreement.

In this work, we report the in-field demonstration of a liquefied petroleum gas monitoring system based on optical fiber technology. Long-period grating coated with a thin layer of atactic polystyrene (aPS) was employed as a gas sensor, and an array comprising two different fiber Bragg gratings was set for the monitoring of environmental conditions such as temperature and humidity. A custom package was developed for the sensors, ensuring their suitable installation and operation in harsh conditions. The developed system was installed in a real railway location scenario (i.e., a southern Italian operative railway tunnel), and tests were performed to validate the system performances in operational mode. Daytime normal working operations of the railway line and controlled gas expositions, at very low concentrations, were the searched realistic conditions for an out-of-lab validation of the developed system. Encouraging results were obtained with a precise indication of the gas concentration and external conditioning of the sensor.

Temperature mapping is a key asset in supporting the clinician during thermal ablation (TA) treatment of tumors without adding additional risk to the TA procedure. Herein we report our experiments on multidimensional thermal mapping during radio frequency (RF) thermal ablation treatments of an ex-vivo animal organ. The temperature was monitored using several arrays of fiber Bragg gratings properly positioned around the RF applicator. The results show the effectiveness of our proposed method at assessing the TA probe depth and demonstrating how the insertion depth directly influences the maximum temperature and the treated area of the radio frequency ablation.

This paper reports results related to early age temperature and shrinkage measurements by means fiber Bragg gratings (FBGs), which were embedded in geopolymer matrices. The sensors were properly packaged in order to discriminate between different shrinkage behavior and temperature development. Geopolymer systems based on metakaolin were investigated, which dealt with different commercial aluminosilicate precursors and siliceous filler contents. The proposed measuring system will allow us to control, in a very accurate way, the early age phases of the binding systems made by metakaolin geopolymer. A series of experiments were conducted on different compositions; moreover, rheological issues related to the proposed experimental method were also assessed.

In this paper, we report on the experimental assessment of real-time temperature and shrinkage early age monitoring of geopolymer matrices, by means of embedded fiber Bragg gratings (FBGs). The FBG sensors were properly designed and packaged in order to discriminate shrinkage and temperature behaviors. The proposed system allows for controlling the rheology of the binding systems made by metakaolin geopolymer. Hence, a series of experiments were conducted on different kind of materials, and confirms that FBGs represent a valid method for simultaneous temperature and shrinkage measurements with a temperature resolution of 0.1 ∘C and strain resolution of 1με.

In this work, we present and discuss on the deflection estimation of a bi-dimensional panel by using Fiber Bragg Gratings (FBGs) as strain sensors embedded in the structure and a method based on the classical beam theory. The existing difficulties in the direct measure of the deflection are overcome thanks to the proposed technique and a real-time indirect structural monitoring is possible both on small and large structure. In many tests the estimated deflection with the proposed method has been compared with direct deflection measurements obtained with a mechanical comparator showing good agreement. A resolution of few tens of microns over a surface of the order of 1 m² has been reached.