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Publicações

Publicações por CAP

2011

DESIGN AND EXPERIMENTAL EVALUATION OF A COMPOSITE STRAIN ROSETTE USING FIBER BRAGG GRATING

Autores
Ramos, CA; de Oliveira, R; Marques, AT; Frazao, O;

Publicação
MICROWAVE AND OPTICAL TECHNOLOGY LETTERS

Abstract
The purpose of this study is to design a composite strain rosette using embedded fiber Bragg grating (FBG) sensors. Those strain rosettes are meant to be used as alternative to the conventional electric rosettes in structural health monitoring applications being glued at the structure surface. A thin (400 mu m) and flexible weaved carbon fiber reinforced plastic (CFRP) composite rosette is proposed. The three FBG sensors were written in a single optical fiber. Special care was devoted to the embedding process of the optical fiber sensors in the weaved composite plate in order to avoid significant alteration of the light reflected back by the FBG. The strain response of the composite rosette was compared to electrical strain gage's when applied at the surface of an aluminium sample submitted to tension, flexion and to dynamic strain. (C) 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53: 1853-1857, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26098

2011

Chirped Bragg Grating Fabry-Perot Interferometer for Nanostrain Measurement

Autores
Silva, RM; Ferreira, MS; Frazao, O;

Publicação
INTERNATIONAL CONFERENCE ON APPLICATIONS OF OPTICS AND PHOTONICS

Abstract
In this work, a simple real-static nanostrain sensor based on a Bragg grating structure is presented. The setup is constituted by a narrow linewidth laser as light source, an optical circulator and a photodetector. The sensing head is formed by a chirped Bragg grating inscribed in a standard single mode fiber (SMF-28) by the phase technique. The fiber face end is cleaved and coated with a silver mirror, obtaining a Fabry-Perot interferometer. It is observable that the fringes period increases along the grating, due to the chirp spectrum (0.4 nm/cm) characteristics. The laser is fixed in one slope region of the fringe pattern. When strain is applied, the optical power changes linearly. A sensitivity of 5.72 mu W/mu epsilon in a range of 2 mu epsilon. The sensing head resolution is 70 n epsilon for a measurement step of 875 n epsilon.

2011

Brillouin Stokes comb generated in a distributed fiber Raman amplifier

Autores
Martins, HF; Marques, MB; Frazao, O;

Publicação
INTERNATIONAL CONFERENCE ON APPLICATIONS OF OPTICS AND PHOTONICS

Abstract
A Brillouin Stokes comb laser with increased flatness is reported. The feedback for the laser is provided by a distributed mirror combined with a narrowband seed laser. The Brillouin seed power and wavelength optimization is crucial in order to obtain a uniform power level between Stokes lines. The Brillouin seed must have a relatively large power and its wavelength must be located close to the Raman peak gain region. The flat-amplitude bandwidth is also determined by the choice of Raman pump wavelength. A flat-amplitude bandwidth of 34 nm from 1538 nm to 1572 nm is measured when Raman pump wavelength is set to 1455 nm. 425 uniform Brillouin Stokes lines with 0.08 nm spacing are generated across the wavelength range. The average signal-to-noise ratio of 15 dB is obtained for all the Brillouin Stokes lines. This type of laser can be used in optical communications as a multiwavelength source and also in metrology as a frequency ruler.

2011

Torsion sensor based on a high-birefringent Sagnac loop interferometer

Autores
Ferreira, MS; Silva, RM; Frazao, O;

Publicação
INTERNATIONAL CONFERENCE ON APPLICATIONS OF OPTICS AND PHOTONICS

Abstract
In this work, a high-birefringent Sagnac loop interferometer torsion sensor is presented. The sensing head is inserted between the output ports of a high-birefringent coupler and it is formed by a section of standard single mode fiber. The sensing head characterization is done for torsion, temperature and strain measurements. The spectral response of this sensing head presents two interferometers, which are dependent on the light polarization states. Interference occurs due to the different lengths of the coupler output arms. This configuration allows the exclusion of a polarization controller, since it is possible to manipulate directly the polarization of light that travels inside the coupler. When the sensing head is subjected to torsion, it is possible to observe a beat between the two interferometers. In this case, there is a simultaneous pi/4 excitation of the two polarization states in the splices region. The torsion sensitivity is related to the sensing head length. The sensor response is periodic and the twist range can be from -2 pi to 2 pi. The sensor is unaffected by temperature and strain variations. This configuration is simple and when compared to the conventional configuration, the polarization controller is suppressed. The setup can be used in specific applications, such as in mechanical engineering.

2011

Measurement of dynamic strain using an optic fibre system in adaptive composite laminates with an integrated piezoelectric sensor/actuator

Autores
Ramos, CA; de Oliveira, R; Marques, AT; Frazao, O;

Publicação
OPTICA APPLICATA

Abstract
This study seeks the development of adaptive composites capable to monitor and actively damp vibrations. In the proposed material, vibrations measurements are performed by an embedded low finesse optical fibre extrinsic Fabry-Perot interferometer, while active damping will be performed by embedded piezoelectric ceramics. This paper focuses on the development of the monitoring procedure. The proposed interrogation procedure for the low finesse optical fibre extrinsic Fabry-Perot interferometer was successfully used to monitor the composite plate when submitted to four-point bending dynamic tests at different frequencies. The embedding of both sensing and actuating components in carbon-fibre reinforced composite laminates is also presented. In the case of the actuator, the efficiency of the embedding process was merely analysed from the capability of the piezoelectric ceramic to monitor dynamic strain of the composite using the PZT piezoelectric inverse effect.

2011

Highly-Birefringent Photonic Bandgap Bragg Fiber Loop Mirror for Sensing Applications

Autores
Ferreira, MS; Baptista, JM; Roy, P; Jamier, R; Fevrier, S; Frazao, O;

Publicação
21ST INTERNATIONAL CONFERENCE ON OPTICAL FIBER SENSORS

Abstract
A highly-birefringent photonic bandgap Bragg fiber loop mirror sensor is proposed. Thanks to the Bragg fiber geometry, one can observe the group birefringence and the bandgap fiber in the transfer function. The sensing head presented different sensitivities for strain and temperature measurements. Using the matrix method, both the physical parameters can be discriminated. It is important to highlight that this Bragg fiber presents sensitivity to temperature of similar to 5.75 nm/degrees C, for the group birefringence measurand.

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