Fiber Bragg gratings were used to measure stress caused by the orthodontic appliance in an experimental model
reproducing the maxilla and dentition. This study brings light to the understanding of the way forces are dissipated on the
dentition and propagate to the adjacent bone. Results show deformations on the order of 4 με and a linear relationship
between strain and the applied load in the incisor, canine and molar teeth.
Experimental results of the thermal regeneration of Bragg gratings recorded in hydrogen loaded high birefringence fibers
are presented. The thermal characterization of saturated and non saturated recorded gratings is described, as well as
results of the changes in the birefringence of these types of fibers when subjected to temperature variations.
In this work the behavior of an optical fiber Long Period Grating (LPG) refractometer with the variations of the
surrounding refractive index is discussed. The objective is to characterize optical fiber refractometers sensitive to
surrounding refractive index, higher and lower than the cladding. For values of surrounding refractive index higher than
the cladding, the LPG does not show enough sensitivity. For this reason, a nanolayer of an organic material was coated
onto the fiber, using the Langmuir-Blodgett technique. We characterized LPG covered with different nanolayers
thickness (110 and 120 nm) relatively to changes in surrounding refractive index.
This paper presents a structural health monitoring system, based on fibre Bragg gratings, developed for the church of
Santa Casa da Misericordia of Aveiro. This system comprises 19 displacement sensors and 5 temperature sensors. All
the sensors were custom made according to the monitoring points' characteristics. The results obtained over the first
months are presented. The objective of this work is to gather data that will bring a deeper knowledge of how this
structure behaves and to help planning the recovering interventions in this historical building.
The use of fibre Bragg grating sensors to study mortars' dimensional variations during the setting process is reported.
When determining a mortar's potential to fissure, it's important to know its total retraction. This means it is necessary to
know not only the mortar's retraction after hardened, but also to know how much it retracts during the plastic phase.
This work presents a technique which allows to measure dimensional variations, either expansion or retraction, during
the whole setting process. Temperature and strain evolution during both plastic and hardened phase of the mortar were
obtained, allowing the determination of dimensional variations and setting times.
Due to its high-speed, ease of implementation and low operation costs, this technique will allow to get a deeper
knowledge of the effects of several additives on the mortar's behaviour, allowing to improve its mechanical properties
through the determination of the proper chemical composition.
The use of Fibre Bragg Grating sensors to study the setting expansion of dental materials like resin based composites and gypsum is reported. Temperature and strain evolution during the hardening phase of the material are obtained.
A new class of structures based on fibre Bragg gratings enable the next generation of lightwave communication systems. However, these devices require precise recording and determination of the fibre Bragg gratings characteristics for optimized performance. In this paper we present a technique for a precise spatial characterization of gratings based structures. A theoretical model as well as the corresponding experimental setup are presented and compared.
Bragg gratings written in high birefringence (HiBi) fibre optics can be used as sensors for multiple parameters, such as stress along different axis and temperature. Their use as sensors require the characterization of the HiBi fibres, because the specific fibre parameters can induce different responses to the sensor system. In this work we analyse, using finite elements methods, stress effects over three types of the HiBi fibres: Bow tie, PANDA and internal elliptical cladding. We also characterize the spectral response of gratings written in HiBi fibre as a function of the input states of the polarization. The obtained results are discussed.
Fiber Optic Bragg Grating Sensors are modeled and studied in high birefringence fiber. Coupled mode theory and multilayer approach are used to predict the spectral characteristics of the structure. Results are compared with experimental characterization of devices produced by UV light using the external method.
A review of current activities in the development of fiber optic Bragg grating sensors under a joint agreement of Brazilian and Portuguese Institutes is presented. Numerical simulation, experimental development, calibration procedures and application result are presented for sensor in mechanical, electrical and biomedical engineering.
In Brazil several groups develop Optical Fiber Sensors based on Wavelength Division Multiplexed Optical Bragg Gratings. We present a review of recent results obtained at our groups in the development of Optical Fiber Sensors to measure deformation (strain) or temperature in high voltage power transmission lines.