The possibility of inscribing a Bragg grating in conventional optical fibers (FBG), opens a new field for optical sensing, selleck chemicals llc being the subject of considerable research in recent years due to their advantages over conventional electronic Inhibitors,Modulators,Libraries devices. When used in structural monitoring, FBG sensors can monitor deformations and stresses in reinforced concrete elements, urban infrastructures, the curing process of concrete and mortars, RH, pH level, in geodynamic applications, among other variables and applications [33].In this work we present an innovative RH sensor based on FBGs coated with an organo-silica hybrid material known as di-ureasil [34], which will be used to monitor the RH level in concrete blocks exposed to environmental conditions, demonstrating Inhibitors,Modulators,Libraries its ability to be used in structure health monitoring (SHM) applications.
This paper is organized as follows: after an introduction showing the requirements Inhibitors,Modulators,Libraries and advantages of optical fiber sensors, namely those based on FBG’s, over conventional methods and devices, a brief description of FBG’s and how they have been used as RH sensors is described Inhibitors,Modulators,Libraries in Section 2. The experimental procedure for the implementation of the proposed sensor is described at Section 3, with three sub-sections referring to the hybrid material production, the FBG coating and the sensor characterization. Section 4 shows the results of a real field application of this type of sensor in SHM. Finally, in Section 5, the main conclusions are presented.2.
?Fiber Bragg Gratings: Fundamentals and RH SensorsA Bragg grating is a passive optical device based on the refractive index modulation of the optical fiber core, created through AV-951 the exposure of the fiber optics core to an optical interference pattern of ultraviolet radiation.The operation principle of a FBG is based on the signal reflection in each plane of the periodic structure. When the Bragg condition is match, all the reflected components are in phase and are added, otherwise, the components are out of phase and vanished. The Bragg wavelength, ��B, at which the central wavelength of the reflection mode satisfies the first order Bragg condition, is given by:��B=2��neff(1)where �� is the refractive index modulation period and neff is the optical fiber core effective refractive index [33]. The Bragg wavelength depends both on the neff and �� and, therefore, any external disturbance acting on these parameters can be measured by analyzing the Bragg wavelength of the reflected signal.
The application of a mechanical deformation selleck Sunitinib or a temperature variation gives rise to a change in the refractive index and in the period values.Several methods can be used to induce the fiber core refractive index modulation, being the most frequent ones the phase mask recording, the interferometric method, and the interferometric method with phase mask [33]. The latter one was selected to be used in the present work.