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In this paper field measurements are carried out using a distributed acoustic sensing system (DAS) for the identification of horse gait. The DAS system has a spatial resolution of 1 m, frequency range of 1–5 kHz and the fiber length is of about 70 m. The optical fiber cable lays down into trench of 15 cm of depth. Several measurements are also carried out in order to fully understand the measuring capacity of the system, including a 2 kg calibrated impact hammer and a small controlled blast of 12.6 Pa of air pressure. Results demonstrate the capacity to measure soil mechanical waves speed of 171 m/s for the impact hammer tests and sound speeds in air of about 366 m/s for the controlled blast tests. The experiments involving horses allowed the identification of three distinct horse gait patterns: step, trot and gallop, as well the horse speed in each gait with SNR about 30 dB.

Cable fault characterization usually requires time-domain profiles to locate and quantify failures. These profiles may be obtained from S-Parameters measured in the frequency domain through inverse Fourier methods. The Chirp Z Transform is a common approach for obtaining time-domain parameters from measured S-parameters. Most existing methods employ the Inverse Chirp Z Transform by a minimum norm solution, which does not have strong physical support. In this paper, we propose a Sparse Inverse Chirp Z Transform approach, specially designed for sparse time-domain signals representing localized fault locations in cables. Two algorithms are proposed to perform the conversion: OMP and FISTA. Their performances are verified in comparison with reference values, showing good agreement for both simulated and experimental data.

The temperature on the busbars of electric generators in the end-winding region needs to be monitored continuously. High temperature is associated with curvatures, seams, and poor ventilation. However, this solution has limitations, such as the number of measurement points. This article presents a reconstruction algorithm to estimate high-resolution signals, from readings of a distributed temperature system for monitoring high-power generator bars. The purpose of this work is to measure the temperature in the end-winding region with optical sensors based on Raman distributed temperature sensing (RDTS). The ability of RDTS equipment to perform a measurement is limited by its spatial resolution of 1 m. The proposed algorithm reduces spatial resolution through signal processing without changing the equipment hardware. Through the experimental results, it was possible to perform accurate temperature measurements for lengths up to 15 cm using the sensor element. With this method, the final winding of a generator bar of a 355 MW hydroelectric plant was instrumented in the laboratory. The results show that it is possible to monitor the temperature over this region, which has a length of 45 cm. Therefore, the proposed method has the potential for the use of RDTS systems for temperature acquisition of small, medium, and large electrical machines.

This paper presents a new methodology for measuring vibration and temperature using fiber Bragg grating (FBG) sensors embedded in carbon fiber polymer attached directly on the iron core of a power transformer. The device has a quick-coupling clip design and is fabricated from a carbon fiber reinforced composite (CFRP) for robustness and flexibility. Temperature and vibration FBG sensors are embedded in the carbon fiber clip, which is easily and quickly coupled directly to the transformer iron core. In the low frequency ranges, from 0 to 500 Hz, vibrations are mainly generated in the core. Rigidity is controlled by clip thickness and geometry, since the system is designed to have a wide operating frequency range. The embedded strain FBG sensor sensitivity has been improved due to its spring-shaped design static and dynamic simulations applying the Finite Element Method (FEM) were performed to determine the optimal dimensions and structure of the part. The clip’s frequency response function (FRF) was assessed and tested by using three techniques: FEM harmonic analysis, mechanical impact testing, and optical FBG sensing. The results demonstrate a 3.94 % differential among the methods. A comparison was made of the power transformer’s FRF when fitted with a glued free FBG sensor and an embedded FBG sensor. In both cases, the transformer was subjected to varying electrical load conditions (no-load, linear, and nonlinear load). The results showed a 19 % average sensitivity improvement when the embedded sensor was compared to the free sensor.

This paper introduces a novel fiber-based sensor for dynamic strain and temperature measurements in the stator of rotating electrical machines. Fiber Bragg grating sensors were integrated into carbon fiber reinforced polymer. The encapsulation has appropriate mechanical energy transfer to measure dynamic strain and temperature. The proposed sensor is installed in the stator of the induction motor allowing to analyze the dynamic strain generated by the machine. The main failure in induction motors is attributed to bearing failures. In this work, the tests were performed operating at full load with new and defective bearings. The results show the main peaks of frequency caused by strain observed coincide with the electrical supply frequency (60 Hz) and mechanical bearing forces (30 Hz), with harmonic components at 120, 180, and 240 Hz. However, for the damaged bearings frequencies of 89.8, 116.5, 146.4, and 149.7 Hz were identified. These frequency components were generated by defects in the outer race, rolling element and inner race. The fundamental components of 30 and 60 Hz between the new and damaged bearings presents an increase of more than 75 %. Results show the potential of the proposed sensor in the monitoring of temperature and dynamic strain in electrical machines.

This paper presents the development and application of an electrical impedance sensor allied with an optical fiber Bragg grating (FBG) sensor whereby both are integrated in fiberglass composite material. The use of composite material allows the integration of the sensors according to the desired geometry. In the field of oil and gas production it is of great importance to monitor the formation of clathrate hydrates (crystalline structures) because such solids may disrupt the flow causing risks and increasing extraction costs. As there is no fully established method for this sensing application, impedance spectroscopy allied to temperature technique is explored for the purpose. Hence, impedance spectra from 1 kHz to 5 MHz along with temperature readings are obtained during an exemplary hydrates experiment, showing that the developed system is able to monitor the hydrates formation in pipes.

The use of optical fiber sensors to monitor electric machines is reviewed. A specific application of a new multiparametric transducer to measure dynamic strain and temperature directly in the stator core of an induction motor is presented.

The gauge length parameter selection affects the quality of data measured in Distributed Acoustic Sensing. This paper uses Fiber Bragg Grating's strain measurements in controlled experiments to promote optimization of gauge length in DAS measurements.

This paper presents the preliminary results of the Fiber Bragg Gratings sensors temperature/strain cross-sensitivity allied to a low sampling rate to distinguish Partial Discharge (PD) events in power cables.

© 2017 IEEE. This article reports a 3-D printing intelligent insole gait monitoring system based on an embedded fiber Bragg grating (FBG). The smart insole combines 3-D printing technology and FBG sensors providing high sensitivity and end-point low cost. Results using pressure points measured by four FBGs are sufficient to differentiate foot loads and gait types.

Two-phase flows of gas and liquid streams in pipes are used in various industries, such as the pharmaceutical, energy, petrochemical, and food industries. Therefore, monitoring and investigation of phenomena related to the flow are of significance for various applications. The construction and evaluation of an electrical and optical probe for the monitoring of two-phase flows in industrial environments are presented in this paper. The probe consists of two stainless-steel electrodes positioned transverse to the flow to measure the fluid electrical conductance. One of the electrodes is hollow. An optical fiber Bragg grating sensor is used to measure the strain. In order to verify the probe performance, two calibration techniques (static and dynamic) along with a mathematical model for strain measurement are employed. The experimental data from the two calibrations are in good agreement with the theoretical values. The developed probe is applied in a two-phase flow test bench to monitor different two-phase flows in the slug flow regime. The obtained results demonstrate its capability to monitor specific parameters of this flow regime. Therefore, the proposed sensor is very promising for flow monitoring.

This contribution reports the development and characterization of an optical system based on parallel Fiber Bragg Gratings (FBGs) to monitor the movements of the wrist and fingers of a hand. The system consisted of a reflective configuration made of FBGs detecting the movements of the fingers and one more located on the wrist as a reference. All FBGs were multiplexed in order to collect the basic movements of the hand. Fibers were embedded in polydimethylsiloxane for protection and to give flexibility to the optical detection setup. Measurements of strain, angle and torsion were performed during the experiments, obtaining sensitivities up to 1.29 pm/ \mu \varepsilon in strain and 64.23 pm/° in angle. Also, a study on the influence of a single sensor on the performance of the whole system was analyzed for a complete study of this proof of concept. The obtained results present a simple system that can be used to monitor the positions of the hand or for the rehabilitation of patients suffering from neuromotor or post-stroke diseases. This work was supported in part by the National Research Agency through the Project from Spanish under Grant TEC2016-78047-R, in part by the Government of Navarra Project from Spanish under Grant SENSMOV: 0011-1365-2017-000135, in part by the Brazilian Projects of Fundação Araucária, in part by the Secretaria de Estado da Ciência, Tecnologia e Ensino Superior do Paraná (SETI), in part by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), in part by Financiadora de Estudos e Projetos (FINEP), and in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Brazil, under Grant 001.

This paper presents the utilization of optical fiber Bragg gratings (FBGs) embedded into a carbon fiber reinforced polymer transtibial prosthesis to evaluate the user's gait, and its own performance. Static mechanical tests were performed to characterize the sensors. Vertically and horizontally positioned FBGs within the structure have been used for load and strain force evaluation during real-time experiments with a candidate at different speeds on a treadmill. For simplicity, one non-amputee candidate performed the experiments using a mechanical adaptation. Distinctive patterns of response of the FBGs located at different points within the prosthetic structure enabled the differentiation between slow and fast motion gait cycle and the force distribution during the tread. This optical instrumentation contributes to the development of a new tool for the evaluation of prosthesis design and amputee patients rehabilitation and to the assessment of the performance of athletes during training or competition.

In this paper, the dynamic strain measurement of a four-pole induction motor stator operating at 75% and 100% of the rated load is used to detect a broken rotor bar. Four fiber Bragg grating (FBG) strain sensors are installed inside the motor, between two stator teeth. Electromagnetic immunity and decreased size of the FBGs make them suitable for this application. When a broken bar is present, some characteristic frequencies in the stator strain spectrum appear. The values of these frequencies are proportional to the motor slip. Instrumentation allows the diagnosis of the broken bar in two different regions of the stator strain frequency spectrum: first, near the rotational frequency, and second, close to twice as much the supply frequency. Two different supply conditions are presented, feeding the motor from an electrical grid and by using a variable-frequency driver. The experimental results indicate that the broken rotor bar can be detected in all supply situations by using the two regions of the stator strain spectrum. By using the method presented in this paper, the broken rotor bar can be detected, even with a harmonic distortion in voltage. This is an advantage over the classic motor current signature analysis method.

Partial discharges are a type of electric discharge that cause localized breakdowns in a small portion of an insulating material without forming a complete rupture. In high power electric machines as well as in transmission lines, partial discharges are caused by the degradation and/or the presence of defects in the insulation. The damage caused by the partial discharges can be either thermal, mechanical or chemical and can cause progressive deterioration of the insulation and lead to catastrophic failure causing serious safety risks. In this work a Distributed Optical Fiber Sensor System (DOFS) for vibration measurements based on Sagnac interferometry is proposed. This system uses acoustic wave emission phenomena to detect and locate electric discharges in electric machines and insulated electrical cables. Two experiments were carried out evaluating the performance of the system. Electric discharges were measured firstly over a conductive board with an attached 10 m long flat-coiled optical fiber sensor and secondly, over a 1.20 m long electrical cable with an optical fiber sensor longitudinally attached to it. Results demonstrate that due to the high sensitivity of the system it is possible to detect partial discharges in both proposed experiments. This effect is observed even with a theoretical fiber optical sensing spatial resolution of approximately 50 m. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001.

This work presents preliminary results from a single FBG sensor used to recognize fingers movement pattern. Six subjects had their movements acquired to signal processing through Linear Discriminant Analysis (LDA) further. Firstly, the index and middle fingers movements are discriminated within a training group of four subjects. To apply the LDA result, a test group of two subjects is used. Despite the non-symmetrical Gaussian samples distribution, the LDA technique was able to differentiate between the two fingers within all the subjects.

In this work, a methodology to measure deformation directly in the iron core of a power transformer using optical sensors is presented. The vibration of a power transformer is mostly generated in the core. Therefore, a clip support of a carbon fiber reinforced polymer with embedded fiber Bragg gratings (FBG) sensors was manufactured. The optical clip sensor can be operated in a wide range of frequencies. The sensitivity can be controlled by varying the stiffness of the clip. The static and dynamic characteristics of this sensor embedded in the carbon fiber were verified and presented through the finite element method and experimental tests were conducted. Through a comparison of results with a non-encapsulated FBG sensor, the clip sensor achieved an average sensitivity of over 19 % and 10 % at the frequency peaks of 60 Hz and 240 Hz, respectively.

The diffusion of optical fibers has leveraged the development of several researches studies in the field of industrial applications. The sensing element is the fiber itself, and the reading is performed by commercial distributed temperature sensing (DTS) equipament based on Raman scattering. Most commercial DTS equipament has a spatial resolution of one meter, which makes it difficult to employ in small and medium structures or equipment. In addition to the advantage of having reduced dimensions, these sensors are immune to electromagnetic interference (EMI). These characteristics are fundamental for use in electric machines. This paper presents a scheme to reduce the spatial resolution through signal processing without changing the hardware of the equipament, thus aiming at new applications of this technology in small and medium-sized structures.

Mechanical and electrical forces of a three-phase induction motor (TIM), in operation, can cause strain in the stator, which may lead to frustrating vibration problems. These problems may greatly reduce reliability and ultimately lead to increased maintenance cost. This paper shows the method to overcome this problem by carrying out the dynamic strain measurement analysis in a TIM running at no-load condition, using an optical fiber sensor. The dynamic strain induced by mechanical and electrical forces was measured by using fiber Bragg gratings (FBGs), installed inside the motor, in between two stator teeth. The electromagnetic immunity and reduced size of the FBGs render them suitable for this application. The frequency components of the strain in TIM were predicted using a model of the forces present in the air gap, considering static and dynamic rotor eccentricities. Two TIM motors, one of 2-poles and the other of 4-poles, and each equipped with two FBGs strain sensors, were used. The sensors were positioned between two stator teeth, separated by 120° from each other in the 2-pole motor and 90° in the 4-pole motor. The experimental analysis shows that the frequency components of the dynamic force spectrum presented by the two motors are the same as those predicted theoretically. Rotor eccentricity was achieved by attaching an unbalanced load to the rotor shaft. The amplitude of vibration at rotor rotational frequency increased when the unbalanced load on the rotor shaft increased. The measurement presented in this paper can be used to determine some TIM parameters, such as the effect of the motor power supply on its vibration signal. It can also be used as a potential maintenance tool for the continuous monitoring of the TIM with high sensitivity.

Traditional Raman distributed optical sensor (DTS) exhibits a low-pass characteristic that causes sharp temperature changes to be over smoothed. This behavior can be modeled as the convolution of the real temperature profile with the DTS impulse response. This paper presents a deconvolution algorithm developed to improve the spatial resolution of a Raman DTS system. The algorithm is based on a linear DTS model and total variation regularization. The main advantage is the ability to correctly reconstruct hot regions with dimensions down to 15 cm, which represents a resolution gain of up to six times when compared with the DTS spatial resolution of 1 m. We present simulations and experimental results demonstrating the efficacy of the proposed method.

© 2013 IEEE. Top-down contact angle (CA) measurements are used to characterize the green leaves and purple flowers of both old and young the Cattleya warneri orchids. The top-down CA allows the characterization of large surfaces away from the leaf edge, avoiding traditional cutting required for side view CA measurement. This allows large area mapping without damaging leaves making the method amenable to fieldwork and useful in environmental diagnostics. Young leaves are found to be hydrophobic whilst old leaves become practically hydrophilic across their entirety, mostly as a result of continued exposure to changes in the environment over time. The flowers are hydrophobic because of their visual and tactile attractor function for pollinating animals and the self-cleaning of dirt and pathogens. Real-time measurement and mapping of CA of surfaces open a new tool to assess the long-term impact of plant aging, pollution, and more of organisms in the field. The method has clear applications elsewhere such as in industrial probing of surfaces and products.

This paper proposes an approach to process the response of a distributed temperature sensor using a nonlinear autoregressive with external input neural network. The developed model is composed of three steps: extraction of characteristics, regression, and reconstruction of the signal. Such an approach is robust because it does not require knowledge of the characteristics of the signal; it has a reduction of data to be processed, resulting in a low processing time, besides the simultaneous improvement of spatial resolution and temperature. We obtain total correction of the temperature resolution and spatial resolution of 5 cm of the sensor.

© 2001-2012 IEEE. This paper presents a method to measure the temperature of the fixed and mobile bearings of a crankshaft in a large diesel engine using optical fiber Bragg gratings (FBGs). The FBG sensor development and the encapsulation with stainless-steel tube are described. The sensors were tested in a large diesel engine in full operation and the results demonstrate the efficiency of the proposed temperature measurement method in monitoring the crankshaft bearings. It is possible to anticipate fault signals with proper processing of temperature data.

This paper presents a new method for thermal imaging of hydroelectric generators stators. The method is based on distributed temperature optical fiber sensing using Raman scattering. The thermal image is generated by combining the information of temperature and the spatial position of the sensor with the 3-D model of the structure. Regarding the use of conventional sensors, such as resistance temperature detector or PT100, the main advantage is the possibility to identify temperature variations over the entire stator surface. The results were obtained over a 22-h test with a 200-MW hydroelectric generator. The produced thermal images showed a great potential for monitoring the temperature distribution in the stator according to the generator load. The new method can contribute for identification of fault in the structure insulation, which when early identified can reduce damage caused by short circuit in the stator windings.