This work shows preliminary results of the detection of Glyphosate in water by using optical fiber spectroscopy. A colloid with citrate-caped silver nanoparticles was employed as substrate for the measurements. A cross analysis between optical absorption and inelastic scattering evidenced a controlled aggregation of the sample constituents, leading to the possibility of quantitative detection of the analyte. The estimate limit of detection for Glyphosate in water for the proposed sensing scheme was about 1.7 mg/L.
This work describes two approaches for refractometric sensors based on cascaded long period gratings for evaluating
substances with refractive indices equal to or higher than the fiber cladding at room temperature. The devices are
experimented on the assessment of fuel quality regarding the presence of remaining vegetable oil in biodiesel, as well as
to determine the concentration of biodiesel in the biodiesel-petrodiesel blends.
This paper describes an approach to identify, quantify and express uncertainties in optical fiber grating sensor
measurements, based on the International Standard Organization's Guide to the Expression of Uncertainty in
Measurement. The proposed approach was used to evaluate the uncertainties in the measurements performed with both a
fiber Bragg temperature sensor and a long period grating refractometric sensor.
Experimental and numerical demonstration of the acousto-optic effect applied in long period grating by means of
flexural waves is presented. The interaction between acoustic and optical waves is modeled with help of the method of
assumed modes, which delivers the strain field inside the grating and the transfer matrix method, which, given the strain
field as input, calculate the resultant grating spectrum. The experimental and theoretical results are found to be in good
agreement. The main effect of the bends in the grating is the break of degeneracy of the circular cladding modes, leading
the attenuation band to be changed. Among all the applications of this methodology, it is important to mention the
possibility of use as a tunable filter, laser cavity gain controller, switching device and transducer in sensing systems.
This work presents a sensing system based on an etched fiber Bragg grating, applied to the refractometric analysis of
water-ethanol mixtures. The system configuration employs one etched-FBG operating at two temperatures, (20.0 ± 0.5)
°C and (3.0 ± 0.5) °C. The sensing system performance in measuring the ethanol-water proportions is evaluated in the
concentration range between 0.0 and 100.0 % v/v of water in ethanol, resulting in uncertainties less than 3.9 % v/v. The
sensor capability to determine the ethanol concentration is shown, even for the range of concentrations where the
correlation between refractive index and ethanol proportion in the sample presents an ambiguous behavior.
In this work is reported the bending sensing characteristics of a long-period grating produced point-by-point with a
266 nm Nd:YAG laser. Spectral changes of the transducer subjected to bends with curvatures from 0 to 3.13 m-1 were
investigated. The magnitude of the bend-induced wavelength shift is nonlinear and dependent on the rotation of the
cylindrical fibre relative to the bending plane. For each constant bending applied to the grating, the fibre was rotated
around its axis in angular steps of 15º, within the angular range from 0 to 180º. An artificial neural network model was
applied for identifying the curvatures, resulting in a root-mean-square error of 0.028 m-1.
In this work we studied the behavior of an in fiber Mach-Zehnder interferometer for salinity measurements. The salt
species used are KCl, NaCl e NaCOOH (organic salt) within the concentration range from 3 g.L-1 to 150 g.L-1. The
results are compared with traditional salinity measurement methods (conductivity and refractive index) and show that the
device can distinguish and identify the concentration of each species saline.
This work shows the use of long period gratings in the petroleum sector, in two specific applications. The proposed
sensors are employed both to identify substances in a simulated flow inside a pipeline, and to assess the gasoline
conformity commercialized in gas stations. The gratings responses for each specific case were employed to train and to
validate two different topologies of artificial neural networks: perceptron multilayer and radial base function. The
obtained results show that fiber optic sensors supervised by artificial neural networks can constitute systems for smart
measurement with high applicability in the petrochemical field.
The influence of temperature in the measurements of surrounding refractive index using long-period fiber gratings is
studied for room temperature variations. For temperature changes close to 2°C it is verified wavelength shifts lower than
0.1 nm for the grating immersed in air and as high as 1.1 nm for a hydrocarbon sample whose refractive index is 1.4530.
Sensitivity evaluations of long-period fiber gratings and evanescent fiber sensors require a temperature system control
that keeps the temperature constant. Otherwise, it should be considered compensation systems that consider not only the
temperature changes but also the refractive index and the thermal-optical coefficient of the materials under analysis.
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