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.

Fiber Bragg Grating (FBG) sensors are strain and temperature sensors with advantages such as small diameter, multiplexing capability, intrinsic safety and biocompatibility. In dentistry, FBG sensors were tested in appliances, implants and splints. In addition to the study of dental biomechanics, these sensors are used in the development of new techniques and products or in the comparison of established treatments. The working principle of measurement of bite forces applied to occlusal splints and the distributed sensing capability along the Chirped FBG (CFBG) are demonstrated in the present proof-of-concept using a PDMS silicone splint. The CFBG exhibits different spectral shapes for each of the four positions of the one-point force application. The average wavelength and the full width at half maximum (FWHM) of the spectra reflected by the CFBG are able to estimate the intensities and the positions, respectively, of the compression forces of the tooth. The instrumentation of occlusal splints with CFBG sensors can help in the distinction between different bite patterns in occlusal stabilization splints during bruxism episodes, along with the understanding of the effects and efficacy of these appliances in treatments and the comparison of different 3D-printed and traditional occlusal splints.

The control of tendon-driven actuators is mainly affected by the tendon behavior under stress or strain. The measurement of these parameters on artificial tendons brings benefits on the control and novel approaches for soft robotics actuators. This paper presents the development of polymer optical fiber sensors fabricated through the light spinning polymerization process (LPS-POF) in artificial tendons. This fiber has exceptionally low Young’s modulus and high strain limits, suitable for sensing applications in soft structures. Two different configurations are tested, indicating the possibility of measuring strain and stress applied in the tendon with determination coefficients of 0.996 and 0.994, respectively.

This paper 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.

This study presents the development and validation of a fibre Bragg gratings (FBGs)‐based sensor system for the assessment of strain in the midpalatal suture in subjects using rapid palatal expanders (RPEs). The ex‐vivo experiments were made by means of positioning two RPEs in a porcine palatal region. The RPEs used were the Hyrax, a tooth‐borne expander and MARPE (microimplant‐assisted rapid palatal expansion), a bone‐borne expander. In order to define the regions in the palatal region for the sensors positioning, a finite‐element analysis was performed in a porcine head subjected to the loadings caused by an RPE. In addition, a strain transfer model was used to obtain a correction coefficient that approximates the strain estimated by the FBG to the actual strain in the structure under shear and normal stress. Results show high linearity in the sensors characterisation tests with the advantages of compactness, intrinsic safe operation and multiplexing capabilities of FBGs. In the RPE analysis, a higher strain was estimated in the anterior region, which is in accordance with the simulation and previously reported results, where MARPE showed a higher strain (with an exponential pattern) than Hyrax as the number of activations increase.

Water–oil separation is important in the oil industry, as the incorrect classification of oil can lead to losses in the production and have an environmental impact. This paper proposes the use of fiber Bragg grating (FBG) temperature sensor array to identify the oil in water–emulsion–oil systems, using only the temperature responses for oil classification results in operational and economic benefits. To demonstrate the possibility of using the FBG temperature sensor to classify oil level, the temperature distribution of an oil storage tank, with 2 m height and 0.8 m in diameter, is simulated using thermal distribution models. Then, the temperature effect in a 2 m long FBG array with a different number and distribution of FBGs is simulated using the transfer matrix method. In each case, we extract the wavelength shift ($\Delta \lambda$), total width at half the maximum (FWHM) and the location of the FBG in the fiber. For the oil classification, we dichotomized the fluids into oil and non-oil (water and emulsion). Due to the low separability of the classes, the random forest algorithm was chosen for classification, starting with 200 FBG equidistant sensors and decreasing to 6, with different distributions along the fiber. As expected, the highest accuracy occurs with the 200 FBGs array (96%). However, it was possible to classify the oil with an accuracy of 94.89% with only 8 FBGs, using tests for two proportions (with a significance of 5%); the accuracy of 8 FBGs is the same as of 50 FBGs.