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Publicações

2020

Tuning of Fiber Optic Surface Reflectivity through Graphene Oxide-Based Layer-by-Layer Film Coatings

Autores
Monteiro, CS; Raposo, M; Ribeiro, PA; Silva, SO; Frazao, O;

Publicação
Photonics

Abstract
The use of graphene oxide-based coatings on optical fibers are investigated, aiming to tune the reflectivity of optical fiber surfaces for use in precision sensing devices. Graphene oxide (GO) layers are successfully deposited onto optical fiber ends, either in cleaved or hollow microspheres, by mounting combined bilayers of polyethylenimine (PEI) and GO layers using the Layer-by-Layer (LbL) technique. The reflectivity of optical fibers coated with graphene oxide layers is investigated for the telecom region allowing to both monitor layer growth kinetics and cavity characterization. Tunable reflective surfaces are successfully attained in both cleaved optical fibers and hollow microsphere fiber-based sensors by simply coating them with PEI/GO layers through the LbL film technique.

2020

Magnetostriction assessment with strain gauges and fiber bragg gratings

Autores
Linhares, CC; Santo, JE; Teixeira, RR; Coutinho, CP; Tavares, SMO; Pinto, M; Costa, JS; Mendes, H; Monteiro, CS; Rodrigues, AV; Frazão, O;

Publicação
EAI Endorsed Transactions on Energy Web

Abstract
Power transformers have an imperative role in the future developments of the electrical grids. Treated as crucial assets for transportation and distribution of electrical energy, transformers are currently being studied regarding to the integration of technologies aiming to diagnose problems and monitoring data of electrical power grid. Furthermore, environmental noise pollution has gained importance, especially in active units of the power grid, located near consumers, such as transformers. Transformers noise can be classified according to its source: core, windings and cooling. This study addresses an experimental characterization of one of the main causes of transformers core noise-magnetostriction of electrical steel. An evaluation of magnetostriction properties of electrical steel, including resistive strain gauges and Fiber Bragg Gratings (FBGs) measurements with an Epstein frame, are presented and discussed. The magnetic flux density influence on hysteretic strain behavior of magnetostriction was evaluated, as well as the effect of a clamping load on core joints. Nowadays, optical interrogators for Bragg gratings have a high acquisition frequencies and wavelength sensitivity when compared to former optical interrogation systems, allowing to evaluate physical phenomena without electromagnetic interference and with equivalent resolution of conventional strain gauges. © 2019 Cassiano C. Linhares et al.

2019

High sensitivity strain sensor based on twin hollow microspheres

Autores
Monteiro, CS; Kobelke, J; Schuster, K; Bierlich, J; Silva, SO; Frazao, O;

Publicação
MICROWAVE AND OPTICAL TECHNOLOGY LETTERS

Abstract
A sensor based on 2 hollow core microspheres is proposed. Each microsphere was produced separately through fusion splicing and then joined. The resultant structure is a Fabry-Perot interferometer with multiple interferences that can be approximated to a 4-wave interferometer. Strain characterization was attained for a maximum of 1350 mu epsilon, achieving a linear response with a sensitivity of 3.39 +/- 0.04 pm/mu epsilon. The fabrication technique, fast and with no chemical hazards, as opposed to other fabrication techniques, makes the proposed sensor a compelling solution for strain measurements in hash environments.

2019

Graphene oxide as a tunable platform for microsphere-based optical fiber sensors

Autores
Monteiro, CS; Raposo, M; Ribeiro, P; Silva, S; Frazao, O;

Publicação
Proceedings of SPIE - The International Society for Optical Engineering

Abstract
Hollow microsphere fiber sensors are Fabry-Perot interferometers (FPI) that can be used for lateral loading, temperature, and refractive index sensing. In this work, graphene oxide (GO) is explored as a tunable platform for enhancing the spectral properties of hollow microsphere fiber sensors. GO offers similar mechanical and optical properties as graphene, with the advantage of a wider range of deposition methods and a lower cost. The influence of multilayer coatings of polyethylenimine (PEI) and GO, achieved with the layer-by-layer technique, on the reflectivity of the outer surface, and hence, on the spectrum of the FPI for maximum of 30 bilayers was studied. The obtained results revealed a change of the microsphere outer surface reflectivity and also of visibility of the reflected spectrum when varying the number of bilayers. A maximum signal amplitude of 3.9 dB was attained for the 13th bilayer, allowing to conclude that PEI/GO multilayer coatings can be used for enhancing desired properties of the three-wave FPI for different sensing applications. © 2019 SPIE.

2019

3D prototyping of a fiber Bragg grating vibration sensor for power transformers

Autores
Monteiro, CS; Viveiros, D; Linhares, C; Tavares, SMO; Mendes, H; Silva, SO; Marques, PVS; Frazao, O;

Publicação
Proceedings of SPIE - The International Society for Optical Engineering

Abstract
In this work, 3D printing is explored as a solution for fast prototyping of optical fiber sensors with applications in power transformers. Two different sensing structures were evaluated using finite element method (FEM) analysis and were fabricated using 3D printing. The printed structures are composed by acrylonitrile butadiene styrene (ABS), a common thermoplastic polymer used in 3D printing. Attaching a fiber Bragg grating (FBG) to each structure, frequency measurements were successfully obtained for values between 20 and 250 Hz. © 2019 SPIE.