Optical fiber Bragg grating sensors (FBGs) were used to measure strain and the temperature field that develop during laser drilling of carbonate rock samples. The shear deformation and high temperature gradient measured are clearly correlated with traces of fractures observed. Beyond the volume directly evaporated by laser exposure, a greater volume around the drilling area was fractured. From the perforation process point of view, it results in an increase of efficiency.
In this paper we discuss results obtained with an in-line Fabry-Perot interferometer (FPI) built by splicing a small section of capillary fiber between two pieces of standard single mode fiber, resulting in a rectangular air cavity. The FPIs were characterized regarding sensitivity to temperature and longitudinal strain. The FPIs were bonded to pieces of Terfenol-D, a magnetostrictive alloy, to be used as magnetic field sensors. Fiber Bragg Gratings were also bonded to Terfenol-D for comparison. The FPI based on capillary optical fiber and Terfenol-D showed a higher sensitivity to an applied magnetic field when compared to an FBG.
The viability of a fiber optic reflection-based Localized Surface Plasmon Resonance (LSPR) sensor using layer-by-layer technique composed by PAMAM-AuNP with and without AuNP-citrate was investigated. The PAMAM-AuNPs and PAMAM-AuNPs/AuNP-citrate layers were deposited on the endface of an optical fiber and the reflected signal was acquired. Deposition time and number of layers were optimized viewing LSPR sensing applications. Results with and without AuNP-citrate were compared. The sensor is being characterized as a refractive index sensor.
In this paper we discuss the stability and effectiveness of an optical fiber sensor for CO2 phase monitoring that could be used inside pipelines, rock caverns and steel tanks for Carbon Capture and Storage (CCS) systems; in Enhanced Oil Recovery (EOR) processes; and in mapping of natural reservoirs. The sensor is an optical fiber refractometer and is shown to be capable of identifying phase changes and when two-phase systems co-exist, even near the phase transition line. When properly calibrated, the sensor can be used to obtain the refractive index and density (calculated with the Lorentz-Lorentz formula) of CO2.
The effects induced by low and high pressure ingression of hydrogen on UV-written germanium doped silica optical
fiber Bragg gratings-at room and high temperature-are studied and discussed. Results show that at elevated
temperatures (>150 °C), an immediate and permanent shift of the peak grating reflectivity is induced and proportional to
the hydrogen concentration (10 pm/AtmH2), whilst at room temperature most of the grating spectrum changes are
transient and mostly reversible.
A refractive index sensor based on the Fresnel reflection at the tip of a single mode optical fiber is used to study phase
changes of CO2 when cooled down from room to -50° C. The sensor system is compact and can be readily integrated into
other optical and electronic systems. The refractive index measurements present good agreement with the literature. The
use of the refractometer as a tool to determine the CO2 phase in oil fields is envisaged.
Previously, we developed an all-fiber reflection Localized Surface Plasmon Resonance (LSPR) sensor based on specular
reflection and LSPR from Au nanoparticles (NPs). The sensor was characterized with standard refractive index fluids.
We now demonstrate that this sensor can be used in chemical sensing applications by using it to monitor the refractive
index of Carbon dioxide (CO2) with refractive index from n=1.04 to n=1.36. In this experiment, the sensor presented a
resolution of approximately 0.02RIU and a sensitivity of at least -45nm/RIU. These results show that the all-fiber
reflection LSPR sensor is a viable method for chemical sensing.
The application of optical fiber sensors in hydrogen rich atmospheres and temperatures as high as 300 °C is presented
and discussed. Two well known optical fiber sensor technologies are evaluated: (1) distributed temperature sensing,
based on Raman scattering, and (2) fiber Bragg gratings. Results show that a new generation of gratings and possibly of
fibers that are more hydrogen resistant, both optically and mechanically, are needed.
A magnetic field sensor comprised of a high birefringence photonic crystal fiber coated by a Terfenol-D/Epoxy
composite layer is proposed. Magnetic fields induce strains in the magnetostrictive composite that are transferred to the
fiber interfering with light propagation. The sensitivity of the developed sensor with magnetic fields is measured to be 6
pm mT-1.
A high sensitivity optical fiber pressure sensor based on a modal interferometer with high birefringence photonic fiber is
proposed and demonstrated. The sensor dependence with hydrostatic pressure is evaluated both numerically and
experimentally. The measured pressure sensitivity at room temperature is found to be 3.36 nmMPa-1.
The development of new techniques for writing and tailoring the properties of Bragg gratings has generated a suite of
distinct grating types that are optimised for performance within different temperature windows. These cover gratings
produced by recipes such as hypersensitisation, thermal processing and single and multiphoton writing. In this paper, we
review four types of high temperature gratings that offer comprehensive coverage of temperature space for most
applications of interest. Up to 1200°C novel processing methods allow standard silica-based optical fibres to be used.
However, beyond these temperatures, optical fibres made from other materials, such as sapphire, need consideration.
A simple interrogation system for semi-distributed fiber Bragg grating (FBG) sensor array with a tunable pulsed laser is
demonstrated. The pulsed light source is used to discriminate, in space or in time, the FBG position. The sensor array can
then be constituted with low reflectivity FBG (<5%) and with the same wavelength (the FBGs have to be spatially
separated). This improvement increases the capacity of the tunable pulsed laser system interrogation, which can reach up
to 1000 sensors in one single fiber. The signals are measured with only one photodetection system, which makes
detection less dependent of intensity variations and minimizes external influences on the circuit, such as variations in the
environment temperature. A test approach has been assembled for the interrogation of five sensors in the same fiber,
varying its reflectivity from 0.8% to 1.6% and with the same nominal wavelength.
Thorough the last two decades, oil and gas reservoirs discovered and developed in deep and ultra deep waters have
continuously posed challenges to petroleum exploration and production activities in offshore basins. Maintaining
optimum flow rates of oil and gas from subsea wellheads to surface processing facilities demands new technological
solutions for petroleum companies operating in such frontiers. Integrity assurance of structures, equipment, and
flow lines plays a major role in maximizing offshore production systems availability while at the same time keeping
safety, operational, and environmental risks at minimum levels. In this scenario, implementation of permanent
health monitoring solutions must take into account the environment of oil and gas production facilities, where
installations in hazardous classified areas require explosion and fire-proof instrumentation. In this context, optical
fiber sensors offer an attractive alternative to electrical sensing technologies, which, until now, have been the
primary choice by maintenance personnel at offshore production units.
This work presents a system for the interrogation of optical fiber Bragg grating sensors based on time domain reflectometry and fixed filters. In this system, filtering is accomplished by fiber Bragg gratings, and a pulsed broadband light source is employed to illuminate the gratings. The spectral informations from the sensors are related to the ratio of two pulse intensities, each from a different filter. The signals are measured with a unique photodetection system, which makes detection independent of intensity variations and minimizes external influences on the circuit, such as variations in the environment temperature. Also, a small number of optical couplers and circulators are needed, so the interrogation system costs per sensor is considerably reduced. A test approach has been assembled for the interrogation of six sensors. Comparisons between experimental results and simulations show a good agreement. Extrapolations indicate that it would be possible to interrogate sensors with spectral variations up to 2 nm, providing uncertainties smaller than 5 pm, which is adequate for multiplexed sensing of temperature in a range of 200°C.
An analysis of the Bragg wavelength deviation generated by TDM/WDM multiplexing of large number of fiber Bragg grating (FBG) sensors has been proposed. Demodulation technique based on Fixed Spectrum Filters is compared with peak position of full wavelength spectrum. Results indicate that the fixed filter approach is less sensitive to wavelength distortion due to shadow of other sensors operating at the same nominal wavelength, allowing much larger number of FBG sensors. A simulated result show less than 1 pm deviation with up to 100 sensors at same wavelength, with 1% peak reflectivity for each sensor.
Fiber Bragg grating (FBG) sensors offer many advantages for monitoring strain and temperature, other physical parameters can be measured through the use of mechanical transducers. However, FBGs are sensitive to strain and temperature and, in many cases, it is difficult to discrminate both measurements. To overcome this problem several techniques have been proposed, most of them employing more than one grating. This work demonstrates the possibility to discriminate temperature and pressure measurements using only one FBG sensor and a low cost demodulation technique based on two fixed filters. A pressure transducer has been used to transfer a lateral force to the fiber, proportional to the applied pressure, generating birefringence in the Bragg grating. The system allowed to measure pressure in the range of 0 to 400 psi with uncertainty of 4 psi and, simultaneously, measure temperature in a range of 22°C with uncertainty of 0.1°C.
Corrosion control in pipelines and wells is a critical issue in the oil industry. In this paper, we present an optical fiber sensing technique devoted to monitor one of the parameters involved in corrosion: the environment acidity. In the proposed technique, a transducer mechanically couples a fiber Bragg grating to a pH sensitive hydrogel. The possibility of determining pH values with resolution of 10-2 in a range from 3 to 6 is evaluated and discussed.
This paper reports results of the application of a simple technique that explores the use of piezoelectric actuators and sensors to monitor the growth of surface breaking defects in beams. The method consists in exciting the structure with piezoelectric actuators, subjected to either a single frequency or broad-band signal, while recording the electromechanical response of sensors placed close to the defect. Piezoelectric sensors detect the damage growth by monitoring changes in the dynamic strain field induced by the actuator near the defect. The performance of this methodology was assessed through experiments in beams containing surface breaking fatigue cracks or machined slots. Results have shown that the choice of adequate parameters, such as sensor size and its distance to the crack edge, allows the detection of small changes in defect depth. Finite element simulations were also performed to determine a correlation between sensor response, sensor location, and damage size. Results from tests performed in a three-dimensional framed structure are also presented.
Fiber Bragg Gratings (FBG) have been applied to a wide range of systems both in telecommunication and sensors systems. For sensors the main advantages in using FBG are the ease of multiplexing and the reliability of measurements due to spectral encoding. Although many different ways of analyzing the spectral response of a FBG have been proposed and demonstrated, most of them involve sophisticated electronics and do not take into account practical problems. We describe a simple, robust and low cost technique in which a reference grating is used as a spectral filter for the sensing grating. In our prototype a 1550 nm pig-tailed LED is used as broad band source. As the system is proposed for strain measurements, special attention is paid to field calibration and long term measurements. Two calibration methods are demonstrated. One uses the digitalized reflection spectra of sensor and filter grating and numerically predicts the sensor output. The other method is based on the application of a controlled opposite strain on the filter grating. Both methods were compared with conventional resistance strain gage and the measuring accuracy is estimated. We also point out applications where FBG strain sensor can have significant advantages over conventional electric counterparts.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.