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Publications

Publications by Orlando Frazão

2014

Fluid evaporation monitoring with suspended-core fibers

Authors
Mouraa, JP; Baierl, H; Auguste, JL; Jamier, R; Roy, P; Santos, JL; Frazao, O;

Publication
SECOND INTERNATIONAL CONFERENCE ON APPLICATIONS OF OPTICS AND PHOTONICS

Abstract
A new configuration for volatile organic compound sensing is proposed. A sub-milimiter four-hole suspended core optical fiber tip, spliced to a standard single mode fiber, is dipped in a liquid volatile compound and the reflected signal is continuously interrogated. When the fiber is immersed in acetone it suffers a 1 4 dB signal drop. Different menisci form in each cladding cavity, with different evaporation times and rates. The signal restores its initial state not when the evaporation process is complete but after the collapse of a dominant meniscus.

2014

Focused ion beam post-processing of optical fiber Fabry-Perot cavities for sensing applications

Authors
Andre, RM; Pevec, S; Becker, M; Dellith, J; Rothhardt, M; Marques, MB; Donlagic, D; Bartelt, H; Frazao, O;

Publication
OPTICS EXPRESS

Abstract
Focused ion beam technology is combined with chemical etching of specifically designed fibers to create Fabry-Perot interferometers. Hydrofluoric acid is used to etch special fibers and create microwires with diameters of 15 mu m. These microwires are then milled with a focused ion beam to create two different structures: an indented Fabry-Perot structure and a cantilever Fabry-Perot structure that are characterized in terms of temperature. The cantilever structure is also sensitive to vibrations and is capable of measuring frequencies in the range 1 Hz - 40 kHz. (C) 2014 Optical Society of America

2014

From conventional sensors to fibre optic sensors for strain and force measurements in biomechanics applications: A review

Authors
Roriz, P; Carvalho, L; Frazao, O; Santos, JL; Simoes, JA;

Publication
JOURNAL OF BIOMECHANICS

Abstract
In vivo measurement, not only in animals but also in humans, is a demanding task and is the ultimate goal in experimental biomechanics. For that purpose, measurements in vivo must be performed, under physiological conditions, to obtain a database and contribute for the development of analytical models, used to describe human biomechanics. The knowledge and control of the mechanisms involved in biomechanics will allow the optimization of the performance in different topics like in clinical procedures and rehabilitation, medical devices and sports, among others. Strain gages were first applied to bone in a live animal in 40's and in 80's for the first time were applied fibre optic sensors to perform in vivo measurements of Achilles tendon forces in man. Fibre optic sensors proven to have advantages compare to conventional sensors and a great potential for biomechanical and biomedical applications. Compared to them, they are smaller, easier to implement minimally invasive, with lower risk of infection, highly accurate, well correlated, inexpensive and multiplexable. The aim of this review article is to give an overview about the evolution of the experimental techniques applied in biomechanics, from conventional to fibre optic sensors. In the next sections the most relevant contributions of these sensors, for strain and force in biomechanical applications, will be presented. Emphasis was given to report of in vivo experiments and clinical applications.

2014

Gas sensing using wavelength modulation spectroscopy

Authors
Viveiros, D; Ribeiro, J; Flores, D; Ferreira, J; Frazao, O; Santos, JL; Baptista, JM;

Publication
SECOND INTERNATIONAL CONFERENCE ON APPLICATIONS OF OPTICS AND PHOTONICS

Abstract
An experimental setup has been developed for different gas species sensing based on the Wavelength Modulation Spectroscopy (WMS) principle. The target is the measurement of ammonia, carbon dioxide and methane concentrations. The WMS is a rather sensitive technique for detecting atomic/molecular species presenting the advantage that it can be used in the near-infrared region using optical telecommunications technology. In this technique, the laser wavelength and intensity are modulated applying a sine wave signal through the injection current, which allows the shift of the detection bandwidth to higher frequencies where laser intensity noise is reduced. The wavelength modulated laser light is tuned to the absorption line of the target gas and the absorption information can be retrieved by means of synchronous detection using a lock-in amplifier, where the amplitude of the second harmonic of the laser modulation frequency is proportional to the gas concentration. The amplitude of the second harmonic is normalised by the average laser intensity and detector gain through a LabVIEW (R) application, where the main advantage of normalising is that the effects of laser output power fluctuations and any variations in laser transmission, or optical-electrical detector gain are eliminated. Two types of sensing heads based on free space light propagation with different optical path length were used, permitting redundancy operation and technology validation.

2013

H-2 Sensing Based on a Pd-Coated Tapered-FBG Fabricated by DUV Femtosecond Laser Technique

Authors
Silva, S; Coelho, L; Almeida, JM; Frazao, O; Santos, JL; Malcata, FX; Becker, M; Rothhardt, M; Bartelt, H;

Publication
IEEE PHOTONICS TECHNOLOGY LETTERS

Abstract
An optical fiber probe sensor based on a tapered-fiber Bragg grating (FBG) coated with 150-nm-thick Pd film is proposed for hydrogen detection. The FBG was written in a 50-mu m-diameter tapered fiber by deep ultraviolet femtosecond laser technology. A second FBG was inscribed in the 125 mu m-fiber section for temperature compensation. The sensing head was able to detect H-2 concentration in the range 0%-1% (v/v) H-2 at room temperature; a maximum sensitivity of 81.8 pm/%(v/v) H-2 was attained with temperature compensation. The influence of the Pd coating over temperature sensitivity of standard and tapered-FBGs is also presented.

2013

HiBi Triangular Optical Nanowire in Suspended-Core Fiber for Sensing Applications

Authors
Andre, RM; Becker, M; Schuster, K; Rothhardt, M; Bartelt, H; Marques, MB; Frazao, O;

Publication
FIFTH EUROPEAN WORKSHOP ON OPTICAL FIBRE SENSORS

Abstract
A triangular nanowire is fabricated by tapering a suspended-core fiber and reducing the core size below one micrometer. The triangular nanowire has a high birefringence with an order of magnitude of 10-3 and when introduced in a fiber loop mirror presents a sinusoidal interference pattern generated by the fast and slow modes of the nanowire. The suspended nanowires were characterized in temperature and strain and enhanced sensitivities were found for both parameters when compared with untapered structures.

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