Search

This letter presents a method of measuring the strain during rapid maxillary expansion (RME) using fiber Bragg grating (FBG) sensors. The activation of the central jackscrew of the Hyrax expander provides the forces required to expand the maxilla that are transmitted to the teeth by a metallic wire. The strain resulted from the opening forces was measured by a FBG sensor bonded to the posterior arm of the appliance. A proof of concept is shown using a 3D printed maxillary model of the biomechanical structure of a human maxilla, in which the appliance was mounted. The sensor was able to measure static and dynamic events, such as the strain accumulation and viscoelastic strain patterns. An increase in the strain is observed as the number of activations increases. A fast decrease in the strain between activations was also observed. In spite of using a plastic model with viscoelastic properties, this decrease may be related to limitations of the central jackscrew. The instrumentation of the Hyrax expanders using FBG sensors assists in clinical studies on the biomechanics and the efficiency of RME. Different expanders can be compared using the present sensor, and tests on their components, especially the central jackscrew, contributes to improvements or new procedures on such treatments. [ABSTRACT FROM AUTHOR]

This letter presents the development and application of a multimaterial polymer optical fiber (POF) for temperature and force sensing. The POF is fabricated from the well-known polymethyl methacrylate (PMMA) through a conventional extrusion method combined with the Polycaprolactone (PCL), a biodegradable material with low melting point, which is thermally molded into the PMMA. In this approach, the high customizability enables the development of two configurations: (i) one input, one output (configuration 1); (ii) one input, two outputs (configuration 2). An advantageous feature of the PCL is its transmittance increase as a function of the temperature, which is confirmed via spectrophotometry at different temperatures. In the experimental analysis, the configuration 1 is used in the temperature tests and demonstrates a high linearity (coefficient of determination of 0.981) and resolution below 1°C, whereas its temperature limit is around 55°C. Configuration 2 is tested in simultaneous variations of temperature and transverse force, resulting in relative force insensitivity in temperatures below 40°C, whereas an optical power attenuation as a function of the applied force is found in temperatures around 55°C. Thus, the proposed approach shows a novel, flexible and customized technique for POF multimaterial fabrication, which can be employed not only on sensors applications, but also in the development of optical components based in POFs. [ABSTRACT FROM AUTHOR]

This paper proposes an optical fiber sensor system based on the strain rosette strategy to monitor the stress-strain state on the surface of a robotic manipulator tool. Three Fiber Bragg Grating (FBG) sensors are positioned according to a deformation rosette configuration within a slot in two 3D printed claws. The equations based on elasticity theory to obtain the stress-strain state from the sensors data are developed and a methodology using an auxiliary temperature sensor to prevent cross-sensitivity and to avoid measurement errors is proposed. The characterization tests show a highly linear behavior in terms of sensitivity to strain (R2 = 0.996 for the linear regression of the means) and to temperature variation (lower R2 between FBGs equal to 0.9868). From the compression tests, it is possible to conclude that the dynamic range of the sensors is adequate to the load capacity of the claws. Grip tests with different objects were performed on the manipulator to verify the system’s feasibility in real-time applications. Finally, from the data processing of the experiments on the robot, it is possible to apply failure criteria and shows that the grip structure is not at risk during the tests. [ABSTRACT FROM AUTHOR]

In this paper, the experimental analysis of different assembly configurations for diaphragm-embedded optical fiber sensors is proposed. A fiber Bragg grating (FBG) is embedded in a nitrile rubber diaphragm, which is positioned in different front and back supports. The difference between such supports is their contact angles with the diaphragm, which leads to differences in the strain applied in the FBG prior to the sensor application. This prestrain condition in the diaphragm influences the sensor’s performance in terms of sensitivity, linearity and hysteresis. To that extent, there are 8 different configuration angles, namely 0°, 1.5°, 3.8°, 6.8°, 9.0°, 11.3°, 13.5° and 15°. The diaphragm-embedded FBG is positioned at each configuration and pressure is transversely applied on the diaphragm region (which transmits strain to the optical fiber) at constant temperature conditions. Results show a relation between the configuration angle and the sensor performance, where sensitivity and linearity presented opposite behaviors, i.e., lower angles (especially the 0° angle) lead to high linearity with a coefficient of determination (R2) of 0.992, whereas higher angles resulted in higher sensitivity with the highest sensitivity value of 13.26 pm/kPa. In contrast, the sensor hysteresis showed a peak value of 6.7% at 9.0° angle with hysteresis decrease in angles higher and lower than 9.0°. The smallest hysteresis of 0.2% is obtained at 1.5°. The obtained results can be used as a guideline on the development of diaphragm-embedded sensors with the additional degree of freedom from the possibility of customizing the diaphragm assembly configuration to achieve predefined performance parameters. [ABSTRACT FROM AUTHOR]

In this article, we thoroughly discuss many aspects of diaphragm-embedded optical fiber sensors covering industrial, robotics and medical applications: from the modeling to field applications, which also include sensor fabrication (such as interferometers, grating-based sensors, intensity variation sensors) in standard and specialty optical fibers, diaphragm and optical fiber materials thermal and mechanical characterizations. The operation limits of the sensors, interrogation techniques and the measurement possibilities that such sensors provide are also discussed. We expect that this review and tutorial provide valuable information regarding the optical fiber sensor approach, material selection and sensor assembly for the development of diaphragm-embedded optical fiber sensors. [ABSTRACT FROM AUTHOR]

Computing performance and hardware integrity are tightly linked to adequate thermal management in datacenters. In addition, a large share of its electricity bills comes from cooling systems, so there is a pressing need for enhanced thermal management systems. This paper proposes a fiber Bragg grating (FBG) quasi-distributed sensing device as an alternative to electronic sensors. The main focus is to demonstrate that a FBG-based solution allows thermal measurement at critical non-monitored regions (blind spots) within a server in an acquisition rate of 1 Hz, with thermal sensitivity of 8.757 pm/°C, a thermal resolution smaller than 1 °C and spatial resolution and multiplexing needed to monitoring diverse blind spots where there is virtually no room for adapting conventional sensors. In addition, we also monitor spots where there are already internal sensors next to them (referential spots), such as central processing unit (CPU) and graphics processing unit (GPU). As a result, a simple FBG sensor calibration technique is proposed using those referential spots. The technique proposed can be scaled out to monitor a large number of elements across large areas in a datacenter environment, since quasi-distributed FBG sensing signal can be transmitted over longer optical fibers than those employed in optical distributed temperature systems (DTS). [ABSTRACT FROM AUTHOR]

This paper presents the development of a thermal measurement system for density, specific heat capacity and thermal conductivity in fluids. Due to toxic and flammable environment often found in oil industry, Fiber Bragg Gratings (FBGs) were used in the sensor development, which consists in a diaphragm-embedded FBG, to estimate density, and a FBG temperature sensor, to estimate specific heat and thermal conductivity. The diaphragm system, with sensitivity of 0.025 nm/kPa, was employed for density measurements in water, diesel and crude oil, becoming a feasible option for density estimation in fluids. The temperature sensor, with sensitivity of 11.5 pm/°C, was used to propose a method to estimate specific heat and thermal conductivity. The method uses the quantity of heat equation to estimate specific heat, then, density and specific heat to estimate thermal conductivity. To validate the method, it was presented three setups based in an acrylic tank, a Becker and a test tube. The tests were performed with water, mineral oil and kryo 51 oil. In addition the proposed system can be integrated in order to realize simultaneous measurements of density, specific heat and thermal conductivity with the same structure. [ABSTRACT FROM AUTHOR]

This letter presents the development and characterization of a Fabry-Perot interferometer (FPI) for the detection of dissolved ammonia. The FPI cavity is obtained by the alignment of two single mode fibers (SMFs), where a mixture of ultraviolet (UV) curable resin and Oxazine 170 perchlorate is positioned in the gap between both SMFs. The sensor operation principle is based on the chemical reaction between the dissolved ammonia and the Oxazine 170 perchlorate. Such reaction leads to the refractive index variation in the FPI cavity, which results in a wavelength shift of the reflected spectrum. The water absorption and temperature effects in the sensor response are characterized. Such characterizations demonstrate that a good sensor performance is achieved when it is submerged in aqueous solutions for about one hour (to enable the water absorption) and at controlled temperature conditions. Then, the FPI sensor is submerged in ammonia solutions with concentrations ranging from 0 to 700 ppb (in 100 ppb steps). Results show a reversibility of the proposed sensor and a high sensitivity of 4.3 pm/ppb (4.3 nm/ppm). Thus, the proposed sensor can be used on the detection of low concentrations of ammonia (in a sub-ppm range) with one of the highest reported sensitivities of ammonia sensors, which makes it suitable for water quality monitoring.This letter presents the development and characterization of a Fabry-Perot interferometer (FPI) for the detection of dissolved ammonia. The FPI cavity is obtained by the alignment of two single mode fibers (SMFs), where a mixture of ultraviolet (UV) curable resin and Oxazine 170 perchlorate is positioned in the gap between both SMFs. The sensor operation principle is based on the chemical reaction between the dissolved ammonia and the Oxazine 170 perchlorate. Such reaction leads to the refractive index variation in the FPI cavity, which results in a wavelength shift of the reflected spectrum. The water absorption and temperature effects in the sensor response are characterized. Such characterizations demonstrate that a good sensor performance is achieved when it is submerged in aqueous solutions for about one hour (to enable the water absorption) and at controlled temperature conditions. Then, the FPI sensor is submerged in ammonia solutions with concentrations ranging from 0 to 700 ppb (in 100 ppb steps). Results show a reversibility of the proposed sensor and a high sensitivity of 4.3 pm/ppb (4.3 nm/ppm). Thus, the proposed sensor can be used on the detection of low concentrations of ammonia (in a sub-ppm range) with one of the highest reported sensitivities of ammonia sensors, which makes it suitable for water quality monitoring. [ABSTRACT FROM AUTHOR]

This letter presents the development and thermal and mechanical considerations of sensing elements using different diaphragm materials which are embedded in optical fiber Bragg gratings (FBGs). Diaphragms made of polyurethane, polydimethylsiloxane (PDMS) and nitrile rubber were fabricated, and all of them with embedded FBGs. Tensile tests were performed in each material, showing the lower Young’s modulus of the PDMS (0.8 MPa), which is orders of magnitude lower than the ones of polyurethane (2.0 MPa) and nitrile rubber (362.2 MPa). Moreover, the highest strain limit was obtained in the PDMS diaphragm (24.5%). These results indicated the potential for higher pressure sensitivity of the PDMS, which was confirmed in the pressure characterization tests (pressure sensitivity of 1.4 nm/kPa). In addition, temperature tests indicated a higher sensitivity of the nitrile rubber, which presented a sensitivity of 49.8 pm/°C. Considering applications in which there are simultaneous variation of pressure and temperature, the nitrile presented a cross-sensitivity of 0.01 nm kPa−1°C−1 which is the lowest among the materials tested, indicating the possibility of obtaining the mitigation of temperature influence in the pressure response. It is also worth noting that the highest measurement range was obtained in the nitrile rubber diaphragm with linear responses in the range of pressures up to 3 kPa. [ABSTRACT FROM AUTHOR]

The 3-D printing process is a flexible, automated, customizable, and low-cost fabrication process. Fiber Bragg grating (FBG) sensors can be embedded into 3-D printed elements to obtain customized and low-cost sensing elements. However, the material infill is an important printing parameter that may affect the FBG response on both temperature and strain. This paper investigates the material infill influence on FBG-embedded 3-D printed sensing pads by both numerical and experimental approaches. The obtained sensing pads are able to withstand a force of 1 kN with sensitivities of about 0.7 pm/N and linearity higher than 98%. Numerical results show that the fiber has an influence on the strain distribution of the 3-D printed structure. Experimental results show that the infill’s thermal expansion-induced temperature sensitivity of the embedded FBG reported in the literature can be reduced by simply setting the correct infill density. The results obtained enable the application of 3-D printed sensing pads for structural health monitoring, soft robotics application, and force detectors for teleoperation in harsh environments. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the influence of temperature on the transverse force response of polymer optical fiber Bragg gratings (POFBGs) inscribed in cyclic transparent fluoropolymers (CYTOPs). The gratings are imprinted in the fiber using the direct-write, plane-by-plane femtosecond laser inscription method. The temperature increase leads to a decrease in the polymer Young's modulus, which causes a sensitivity variation in the POFBG sensor for transverse force applications. The proposed technique is based on the characterization of both the sensor's response offset and the material's Young's modulus variation due to the temperature increase. Transverse force tests were performed at different temperatures (30 °C, 40 °C, 50 °C, and 60 °C) and the compensated and uncompensated responses are compared in terms of root mean squared error (RMSE). The compensated results show an RMSE lower than 3% (mean value between all tested temperatures), which is 6.7 times lower compared with the uncompensated response. In addition, the proposed compensation technique presents a maximum RMSE reduction of 16 times at 60 °C. [ABSTRACT FROM AUTHOR]

The influence of annealing under different humidity conditions on temperature, strain, and transverse force performance of polymer optical fiber Bragg gratings (POFBG) inscribed in cyclic transparent amorphous fluoropolymers is presented. The POFBG are imprinted using direct-write, plane-by-plane femtosecond laser inscription method. Further improvement to the sensor's performance, with respect to sensitivity, linearity, and hysteresis, is obtained with a simple technique based on polymer viscoelastic response applied to the annealed POFBGs. The sensors were characterized for temperature, strain, and transverse force after annealing and results show that sensors annealed under water have the lowest hysteresis. Additionally, the temperature sensitivity increased when the sensor was annealed in low humidity conditions. Finally, for strain and transverse force, the highest sensitivity was obtained in POFBG sensors annealed under water. The compensation technique did not show a substantial decrease in hysteresis response for applied strain tests; however, for temperature and transverse force tests, the hysteresis decreased by more than two and four times, respectively. [ABSTRACT FROM AUTHOR]

Curvature sensors based on polymer optical fibers (POFs) present some advantages over the conventional technologies for joint angle assessment such as compactness, electromagnetic field immunity, and multiplexing capabilities. However, the polymer is a viscoelastic material, which does not have a constant response with stress or strain. In order to understand and model this effect, this paper presents the dynamic characterization of a POF. The effects of temperature, frequency, and loads on the fiber are analyzed for obtaining the influence of these parameters on the polymer dynamic Young modulus and time constant. Results show that a temperature on the range between 24 °C and 45 °C does not lead to considerable variations on the sensor output. Moreover, it is possible to estimate the storage modulus and loss factor from the frequency and temperature. The polymer time constant is defined on creep recovery experiments. Since the viscoelastic parameters are evaluated in different conditions of temperature, frequency, and load, a model for the stress behavior of the fiber is proposed. Such model leads to a root mean squared error between the modeled and measured results over 15 times lower than the one obtained with the model for bending stress without account the POF viscoelastic behavior. [ABSTRACT FROM PUBLISHER]

This paper presents a system capable of measuring temperature and relative humidity with polymer optical fiber (POF) sensors. The sensors are based on variations of the Young’s and shear moduli of the POF with variations in temperature and relative humidity. The system comprises two POFs, each with a predefined torsion stress that resulted in a variation in the fiber refractive index due to the stress-optic effect. Because there is a correlation between stress and material properties, the variation in temperature and humidity causes a variation in the fiber’s stress, which leads to variations in the fiber refractive index. Only two photodiodes comprise the sensor interrogation, resulting in a simple and low-cost system capable of measuring humidity in the range of 5–97% and temperature in the range of 21–46 °C. The root mean squared errors (RMSEs) between the proposed sensors and the reference were 1.12 °C and 1.36% for the measurements of temperature and relative humidity, respectively. In addition, fiber etching resulted in a sensor with a 2 s response time for a relative humidity variation of 10%, which is one of the lowest recorded response times for intrinsic POF humidity sensors. [ABSTRACT FROM AUTHOR]

This paper presents a polymer optical fiber (POF)-based temperature sensor. The operation principle of the sensor is the variation in the POF mechanical properties with the temperature variation. Such mechanical property variation leads to a variation in the POF output power when a constant stress is applied to the fiber due to the stress-optical effect. The fiber mechanical properties are characterized through a dynamic mechanical analysis, and the output power variation with different temperatures is measured. The stress is applied to the fiber by means of a 180° curvature, and supports are positioned on the fiber to inhibit the variation in its curvature with the temperature variation. Results show that the sensor proposed has a sensitivity of 1.04 × 10-3 °C-1, a linearity of 0.994, and a root mean squared error of 1.48 °C, which indicates a relative error of below 2%, which is lower than the ones obtained for intensity-variation-based temperature sensors. Furthermore, the sensor is able to operate at temperatures up to 110 °C, which is higher than the ones obtained for similar POF sensors in the literature. [ABSTRACT FROM AUTHOR]

This paper proposes a fiber optic liquid level sensor system based on a silica fiber Bragg grating embedded into an epoxy resin diaphragm coupled to a temperature reference sensor, used to compensate the temperature cross-sensitivity for improving the liquid level measurement accuracy. The proposed system was tested in an industrial water tank with heating and recirculation. The results demonstrated a temperature cross-sensitivity reduction, enhancing the liquid level measurement thermal stability by a factor of nine, when compared with some single head sensor configurations reported in literature. Our system presents high linearity ( $R>0.999$ ), superior sensitivity (2.8 pm/mm), and much lower temperature related error (1.04 mm/°C), when compared with the other diaphragm-based sensors recently reported in the literature. [ABSTRACT FROM PUBLISHER]

This paper proposed a liquid level measurement and classification system based on a fiber Bragg grating (FBG) temperature sensor array. For the oil classification, the fluids were dichotomized into oil and nonoil, i.e., water and emulsion. Due to the low variability of the classes, the random forest (RF) algorithm was chosen for the classification. Three different fluids, namely water, mineral oil, and silicone oil (Kryo 51), were identified by three FBGs located at 21.5 cm, 10.5 cm, and 3 cm from the bottom. The fluids were heated by a Peltier device placed at the bottom of the beaker and maintained at a temperature of 318.15 K during the entire experiment. The fluid identification by the RF algorithm achieved an accuracy of 100%. An average root mean squared error (RMSE) of 0.2603 cm, with a maximum RMSE lower than 0.4 cm, was obtained in the fluid level measurement also using the RF algorithm. Thus, the proposed method is a feasible tool for fluid identification and level estimation under temperature variation conditions and provides important benefits in practical applications due to its easy assembly and straightforward operation. [ABSTRACT FROM AUTHOR]

• The usage of a Polarization Maintaining Fiber (PMF) as a passive sensing element inside a Sagnac interferometer for temperature measurement is experimentally demonstrated. • A comparison between the numerical simulation and the experimental data is addressed. • A highly linear response and a sensitivity of −1.59 nm/°C for the 18–42 °C temperature range is presented. • The feasibility of using an all-fiber device as a temperature sensor for applications that demands very precise and reliable measurements are demonstrated. The usage of a 1 m Polarization Maintaining Fiber (PMF) as a passive sensing element for the experimental demonstration of a highly sensitive all-fiber temperature sensor based on a Sagnac interferometer configuration is presented here. Using a simple interrogation method tracing the wavelength shift of the obtained interference peaks, we were able to detect variations in a water bath temperature with a highly linear response with coefficient of determination ( R 2 ) of 0.9999 and a sensitivity of −1.59 nm/°C for the 18–42°C temperature range. This result demonstrates the feasibility of using this all-fiber device as a temperature sensor for many applications that demands very precise and reliable measurements. [ABSTRACT FROM AUTHOR]

• Estimation of the level using FBG temperature sensors array. • Machine learning to identify at which fluid each FBG is submerged with 89.54% accuracy. • Proposed Mixed Model (MM) uses combination of regression algorithms to level estimation. • MM has a RMSE of 3.58 cm, resulting 57.93% improvement compared to other algorithms. This paper proposes the use of the fiber Bragg grating (FBG) temperature sensors array to estimate the fluid level. The tank is 100 cm in height and 30 cm in width, with 9 FBG sensors distributed along with the tank height. This work proposes level estimation in two steps: level detection (classification) and level estimation (regression). The level detection consists of finding under which FBG the level is. We dichotomize the classes in water and not water: air. For the detection, we use the following Machine Learning (ML) algorithms: Logistic Regression (LogR), Decision Tree (DT), and Support Vector Machine (SVM). We chose the algorithms based on their usability in literature and theoretical consolidation. The algorithm with the best results among the ones tested is DT, resulting in an average accuracy of 89.54%. For the level estimation, we use the wavelength shift in conjunction with the classification obtained via DT. The level estimation consists of estimating in cm the location of the level. The algorithms chosen are Weighted Linear Regression (WLR), Support Vector Regression (SVR), SVR with kernel selection minimize cost (SVRmin). Each of the applied algorithms presented better results in different level intervals. Thus, we propose the Mixed Model (MM), which selects the lowest Root Mean Square Error (RMSE) among the tested regression algorithms at each level and associates it with it. The MM has a RMSE of 3.56 cm, which is approximately four times smaller than when using WLR. The SVM and SVMmin have RMSE of 6.28 cm and 6.14 cm, respectively. [ABSTRACT FROM AUTHOR]

• A large range displacement sensor using polymer optical fiber. • The LED-Belt is used as the light source. • A Side-coupling technique in which light is launched from the side of the fiber. We present a method for large displacement measurement based on light rays interference. Instead of fiber's end-face, we launched the light from the side of fiber using a LED-Belt (LB) as a light source. The relative movement between the LB and optical fiber corresponds to displacement change, and associated intensity variation is detected through a power meter. The linear-displacement has been achieved up to 1 m with a sensitivity of about 1.532 nW/mm, which results in a resolution of 0.653 mm. The range can be further enlarged by increasing the length of fiber and LED-Belt depending on the application requirements. The proposed sensor method is simple, cost-effective, and easy to manufacture. The design structure also has significant potential for strain, pressure, and liquid level sensing as well as shape sensing. [ABSTRACT FROM AUTHOR]