Piotr Kisała

Method of simultaneous measurement of two direction force and temperature using FBG sensor head

This paper presents a method for measuring two components of bending force and temperature using one sensor head. Indirect inference based on the spectra of two fiber Bragg gratings (FBGs) placed on a cantilever beam is used. The method was developed during work on the inverse problem of determining a nonuniform stress distribution based on FBG spectra. A gradient in the FBG stress profile results in a characteristic shape of its reflective spectrum. The simultaneous measurements of force and temperature were possible through the use of an appropriate layout of the sensor head. The spectral characteristics of the sensors gratings do not retain full symmetry, which is due to the geometry of the sensors head and the related difference in the distribution of the axial stress of the gratings. In the proposed approach, the change in width of the sum of the normalized transmission spectra was used to determine the value of the applied force. In the presented method, an increase in the sensitivity of this change to the force is obtained relative to the other known systems. A change in the spectral width was observed for an increase in bending forces from 0 to 150 N. The sensitivity coefficient of the spectral width to force, defined as the ratio of the change of the spectral half-width to the change in force was 2.6e-3  nm/N for the first grating and 1.2e-3  nm/N for the second grating. However, the sensitivity of the whole sensor system was 5.8e-3  nm/N, which is greater than the sum of the sensitivities of the individual gratings. For the purpose of this work, a station with a thermal chamber has been designed with a bracket on which fiber optic transducers have been mounted for use in further measurements. The sensor head in this experiment is considered to be a universal device with potential applications in other types of optical sensors, and it can be treated as a module for development through its multiplication on a single optical fiber.

Application of inverse analysis to determine the strain distribution with optoelectronic method insensitive to temperature changes

This paper presents the application of inverse analysis to determine the stress distribution in a way that is insensitive to changes in temperature. For this purpose, a sensor with a fiber Bragg grating (FBG) was used. The paper discusses the direct solution of the task and presents the development and validation of a mathematical model of the Bragg grating sensor. Computer simulations were performed to apply numerical algorithms that completed the calculations according to the mathematical structure of the model and considered the values of all other elements of the FBG sensor. An experimental study was also conducted using a constructed measuring post.

Inverse problem of determining periodic surface profile oscillation defects of steel materials with a fiber Bragg grating sensor

We propose and experimentally demonstrate a method for the detection of steel material defects utilizing a fiber Bragg grating sensor. The considered defects are periodic grooves along the length of the tested steel profile. Direct measurement of the spectral reflectance characteristics of the fiber is performed, and the related inverse problem of indirect defect shape determination is solved. It has been demonstrated that the defect periodicity estimation is 2.5 mm, with an error of less than 0.1. Furthermore, it has been shown that for periodic intervals of the order of 5 mm, the difference between the strain amplitude calculated using our method and the amplitude obtained via the finite element method was 1.4 mϵ.

Temperature-insensitive simultaneous rotation and displacement (bending) sensor based on tilted fiber Bragg grating

In this paper, we present a method for the simultaneous measurement of rotation and displacement or rotation and bending using single tilted fiber Bragg grating (TFBG). The insensitivity of the proposed system to temperature changes and the stretching direction of the fiber section in the sensing structure have been demonstrated. The experimentally determined sensitivities for rotation, displacement and bending are as follows: -0.0018 1/deg., 0.0054 nm/mm, and -0.055 1/mm over the measurement ranges of approximately 25-80 degrees, 34-74 mm, and 26.4-20 mm, respectively. The presented measurement system is versatile due to the ability to tune the measurement range by changing the fiber-loop radius.

Overhead Transmission Line Sag Estimation Using a Simple Optomechanical System with Chirped Fiber Bragg Gratings. Part 1: Preliminary Measurements

A method of measuring the power line wire sag using optical sensors that are insensitive to high electromagnetic fields was proposed. The advantage of this technique is that it is a non-invasive measurement of power line wire elongation using a unique optomechanical system. The proposed method replaces the sag of the power line wire with an extension of the control sample and then an expansion of the attached chirped fiber Bragg grating. This paper presents the results of the first measurements made on real aluminum-conducting steel-reinforced wire, frequently used for power line construction. It has been shown that the proper selection of the CFBG (chirped fiber Bragg grating) transducer and the appropriate choice of optical parameters of such a sensor will allow for high sensitivity of the line wire elongation and sag while reducing the sensitivity to the temperature. It has been shown that with a simple optomechanical system, a non-invasive measurement of the power line wire sag that is insensitive to temperature changes and the influence of high electromagnetic fields can be achieved.

A Novel Simple TFBG Spectrum Demodulation Method for RI Quantification

This letter presents a novel method for the analysis of tilted fiber Bragg grating (TFBG) transmission spectra. The processing method is based on the transmission spectrum contour length, which is calculated in the wavelength range where cladding modes appear. The proposed algorithm is based on a modified analysis method that is used in spectrometric surveys of gas spectra in cases with unknown or fluctuating baselines. Experimental results obtained using the proposed method are compared with results from the most commonly used TFBG spectral analysis methods that utilize global monitoring of cladding modes.

Application of a modified evolutionary algorithm for the optimization of data acquisition to improve the accuracy of a video-polarimetric system

The use of the polarimetry techniques for display and study of biological tissues has gained increasing interest in recent years. This interest is related mainly to the non-invasiveness, relatively low cost, and ease of application among other characteristics. However, for full use of these advantages, the calibration methods must ensure the minimization of the effects of uncertainties related to the optical element positioning and the noise in intensities measurements.

Method of simultaneous measurement of bending forces and temperature using Bragg gratings

This paper presents the method of bending force and temperature measurement. For this purpose, a station with a thermal chamber has been designed and a bracket used in further measurements on which Bragg gratings have been mounted. The performance of simultaneous measurements of force and temperature was possible through the use of an appropriate layout of the sensor. The method of indirect measurements was used, using information deriving from the spectrum of the uniform Bragg gratings, placed on the cantilevers. The measuring system scheme was proposed for measuring sizes measured in the form of bending force, acting in two directions, perpendicular to the grating axis. The increase in the sensitivity of the change on the force is obtained in relation to the system, in which only information on the width of the spectrum of one of the gratings would be used. A change in the spectral width value was observed along with the increase in bending forces from 0 to 10N for two cantilever beams schemes. The head of the sensor can reach larger physical sizes, in exchange enabling a measurement of force and temperature in many places, thus determine the distribution of force and temperature.

Optical switching method based on two diffraction gratings bistable system

This paper presents properties of all-optical bistable fibre switch using two fibre Bragg gratings and rare earth elements doped optical fiber. It is not possible to obtain bistable properties at low switching power level in case of a single fibre grating. In this article the method of optical switching that uses all-optical switch has been proposed. It has been achieved by varying the refractive index of nonlinear optical material as a result of light signal amplitude changes. Presented optical bistable device can be used both in contemporary optically switched networks as well as in optoelectronic sensors, owing to their high achievable resolution.

A study and modeling of Fabry-Perot cavities with rare earth doped fiber

This paper presents properties of all-optical bistable fibre switch using two fibre Bragg gratings and rare earth elements doped optical fiber. It is not possible to obtain bistable properties at low switching power level in case of a single fibre grating. In this article the method of optical switching that uses all-optical switch has been proposed. It has been achieved by varying the refractive index of nonlinear optical material as a result of light signal amplitude changes. Presented optical bistable device can be used both in contemporary optically switched networks as well as in optoelectronic sensors, owing to their high achievable resolution.