Resumo O monitoramento estrutural pode detectar anomalias no tempo, permitindo a implementação de ações de manutenção e reparação mais eficientes em estruturas de obras de arte. Uma alternativa no monitoramento e avaliação de estruturas em engenharia civil é a utilização de fibras óticas inscritas com redes de Bragg (FBG ou Fiber Bragg Grating). Este trabalho visa comparar as técnicas disponíveis para estimar o módulo elástico de compósitos cimentícios, bem como contribuir para a aplicação de sensores de fibra ótica na avaliação da tensão, frequência natural de vibração, coeficiente de amortecimento e módulo elástico de vigas de argamassa. Os sensores FBG fabricados e calibrados pelos autores apresentaram uma boa precisão na medição destes parâmetros em amostras de argamassa. Os resultados mostram que os sensores FBG e strain gauges apresentam resultados semelhantes para a deformação específica e estimativa do módulo elástico (estático e dinâmico), portanto, FBGs nuas poderiam ser investigadas mais detalhadamente em testes não-destrutivos.

Abstract Structural health monitoring can detect anomalies in time, allowing the implementation of more efficient maintenance and repair actions in special engineering structures. An alternative in the monitoring and evaluation of structures in civil engineering is the use of optical fibers inscribed with Bragg gratings (FBG or Fiber Bragg Grating). This paper aims to compare available techniques to estimate the elastic module of cementitious composites, as well as contribute to the application of optical fiber sensors in the monitoring of strain, natural vibration frequency, damping coefficient and elastic modulus of mortar beams. The FBG sensors manufactured and calibrated by the authors presented a good precision for measuring those parameters in mortar samples. The results show that FBG sensors and strain gauge sensors present a similar result for strain and estimation of the elastic module (static and dynamic), therefore, bare FBGs could be further investigated for non-destructive testing.

Abstract This paper proposes the use of fiber Bragg gratings (FBG) in thermal monitoring of photovoltaic (PV) modules. Results acquired from FBG sensors were compared with two commonly used temperature sensing techniques in PV modules: PT100 sensors and infrared cameras. The experiments were performed using a PV module in actual operating conditions (varying ambient temperature and wind speed). Temperature changes in PV module were monitored with 27 FBG sensors installed on its front surface. During the experiments the ambient temperature, intensity of solar radiation and wind velocity were also monitored. The acquired results showed that FBG sensing technology has a potential for the proposed application.

This paper reports an effective method of packaging a fiber Bragg grating (FBG) for the simultaneous measurement of temperature and strain. The technique consists of embedding two fiber Bragg grating sensors inside a polymeric material with different geometrical characteristics. The mechanical and thermal characterizations of the optical transducer were performed. Then a matrix equation used measurements of the wavelength shifts from the two sensors and yielded information about the temperature and strain coefficients. The preliminary results demonstrate the feasibility of the encapsulation technique allowing measurements of temperature and strain in smart structures and harsh environments. The experimental procedure provides robustness to the sensor and the matrix equation approach has the potential to determine simultaneously the strain and temperature coefficients.

An alternative technique that uses a flame-brush at high temperature to enhance UV light photosensitivity in an optical fiber is described. An extreme low-cost air aspirated propane-butane mini-torch is used, which produces a lower temperature flame than the one in the flame-brush original technique. It is shown that this change in the previous technique is also capable of improving photosensitivity and allowing the fiber Bragg grating imprinting process to be accelerated. Since the flame-brush photosensitivity enhancement process is designed to operate in an automated fiber taper rig, the process was evaluated in optical fiber tapers with different diameters. In this case, changes in photosensitivity are observed in the tapers in addition to the intrinsic photosensitivity occurring in the pristine fiber without being tapered.