Arnaldo G. Leal-Junior

POFBG-Embedded Cork Insole for Plantar Pressure Monitoring

We propose a novel polymer optical fiber (POF) sensing system based on fiber Bragg gratings (FBGs) to measure foot plantar pressure. The plantar pressure signals are detected by five FBGs, in the same piece of cyclic transparent optical polymer (CYTOP) fiber, which are embedded in a cork insole for the dynamic monitoring of gait. The calibration and measurements performed with the suggested system are presented, and the results obtained demonstrate the accuracy and reliability of the sensing platform to monitor the foot plantar pressure distribution during gait motion and the application of pressure. This architecture does not compromise the patient’s mobility nor interfere in their daily activities. The results using the CYTOP fiber showed a very good response when compared with solutions using silica optical fibers, resulting in a sensitivity almost twice as high, with excellent repeatability and ease of handling. The advantages of POF (e.g., high flexibility and robustness) proved that this is a viable solution for this type of application, since POF’s high fracture toughness enables its application in monitoring patients with higher body mass compared with similar systems based on silica fiber. This study has demonstrated the viability of the proposed system based on POF technology as a useful alternative for plantar pressure detection systems.

A Polymer Optical Fiber Temperature Sensor Based on Material Features

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.

Dynamic Compensation Technique for POF Curvature Sensors

Polymer optical fibers (POF) can be applied as curvature sensors due to its high strain limits, fracture toughness, and flexibility in bend. However, POFs present viscoelastic behavior, which leads to a phase lag between the stress and strain. The polymer viscoelasticity can be associated to the high hysteresis and the errors that curvature sensors based on POF may present. For this reason, this paper proposes a dynamic compensation technique based on the angular velocity of the sensor. The technique comprises of initial quasi-static tests and tests with different angular velocities for the reduction of the sensor root mean squared error (RMSE) and hysteresis. Results show a reduction of both hysteresis and RMSE in almost all angular velocities tested. The mean reduction of the hysteresis is 20%. Whereas a mean reduction of about 3 times of the RMSE was obtained. Furthermore, the compensation technique results on a calibration equation, which can be applied in real-time measurements.

Liquid Level Measurement Based on FBG-Embedded Diaphragms With Temperature Compensation

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 (

Polymethyl methacrylate (PMMA) recycling for the production of optical fiber sensor systems

R>0.999

Polymer-optical-fiber-based sensor system for simultaneous measurement of angle and temperature

), 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.

Measurement of Temperature and Relative Humidity with Polymer Optical Fiber Sensors Based on the Induced Stress-Optic Effect

This paper proposes the recycling of poly (methyl methacrylate) plates, formerly used in LCD monitors to produce polymer optical fibers without cladding for sensor systems and a discussion about the fabrication process of the fiber cladding is briefly presented. After disassembling LCD monitors the acrylic plate is cleaned and submitted to an extrusion process. Extrusion temperatures of 220°C, 230°C and 240°C were applied, and the produced polymer fibers were characterized by infrared and visible spectrometry, as well as evaluated for thermal analysis through differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Furthermore, a refractive index sensor was developed with the recycled fibers. Results show that the recycled fiber refractive index sensor is linear (R2 = 0.99) and presents a sensitivity of more than 4 times higher when compared to a sensor using a commercial POF.

Polymer Optical Fiber Sensors Approaches for Insole Instrumentation

This paper presents a polymer-optical-fiber (POF)-based sensor system for simultaneous measurement of angle and temperature. The main contribution is obtaining a sensor with higher temperature sensitivity and lower hysteresis on the angle measurements. The annealing was made on the fibers under the conditions of low relative humidity and under water, and a third set of samples without any heat treatment was applied for comparison with the annealed ones. Results of temperature and angle characterization show that the fibers annealed under water presented higher temperature sensitivity and lower errors when compared with the fibers annealed with low humidity or the fibers without annealing. Furthermore, the fibers annealed under water also presented lower hysteresis on the angle characterization. For these reasons, such fibers were employed for the temperature and angle measurements, which results in a sensor system capable of simultaneously measuring the angle and temperature with root-mean-squared error of 0.82°C for temperature and 2.20° for angle, which is further reduced to 1.20° after the application of a dynamic compensation technique for POF curvature sensors.

Fabrication and Characterization of Bragg Grating in CYTOP POF at 600-nm Wavelength

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.

Compensation technique for environmental and light source power variations applied in a polymer optical fiber curvature sensor for wearable devices

Advantages like electromagnetic field immunity, fracture toughness, high strain limits, flexibility in bending and impact resistance of polymer optical fibers (POFs) are beneficial for applications that involve embedment in flexible structures. Since insoles are one of these flexible structures that may be used in different wearable applications, POFs can be applied and this paper proposes the application of POF sensors in insole instrumentation with two different approaches: intensity variation-based and polymer optical fiber Bragg gratings (POFBGs). Results show that both approaches present low errors with root mean squared errors (RMSEs) of 45.17 kPa for the plantar pressure monitoring with the POFBG-based insole and 5.30 N for the ground reaction force measurement with the intensity variation sensors. These results demonstrate the feasibility of POF sensors applications in flexible structures and in wearable applications such as insoles and soft robotics instrumentation.