The paper presents the analysis of the influence of elongation of stainless steel and aluminium samples on the response of uniform fiber Bragg gratings used as measuring transducers. Research indicates the possibility of material type and material thicknessing on the basis of transmission spectra obtained with the use of a periodic structure. During the research, deformations of transmission spectra were noticed. These defects may be the result of the glue connection used for assemble the periodic structure to the sample. The results of the research were presented in the form of charts obtained on the basis of transmission spectra.
The article presents the possibilities of detecting defects in steel material using the fiber Bragg gratings (FBG). Measurement of sensitivity to force change is ensured by shifting the FBG. Steel samples were used for the tests: one standard sample and the others were incised. The incisions were at right angles and sharp to the axis of the fiber. The FBG was glued to the sample along its entire length and then lengthened by force. The transmission spectrum was being obtained on the Optical Spectrum Analyzer (OSA). It was used to determine the processing characteristics: the main minimum on the transmission characteristics and the full width at half maximum (FWHM) depending on the force transferred. On the first characteristic, the quantity of incisions can be detected (for a larger amount of incisions the main minimum changes significantly), and on the second characteristic, both the quantity of incisions (the greater the number of incisions the FWHM change is greater) and the approximate angle of incision relative to the fiber axis, FWHM decreased during increasing forces in the case of a right angle, while it increased in the case of an acute angle.
The article presents the possibilities of defects detection in the form of welds of leading steel elements, using the fiber Bragg gratings (FBG). Measurement of sensitivity to force change is ensured by shifting the FBG spectrum. Two steel samples of the same dimensions were used for the tests. The first one lacking significant defects in its structure, while the second one has been cut in the middle and it has been welded. FBG has been glued to the sample over its entire length. The results of measurements in the form of basic characteristics of the described stress sensor are presented below.
The paper presents a fiber optic force sensor with reduced temperature sensitivity. The sensor operates in the configuration of a birefringent fiber based Sagnac interferometer, where the measured quantity induces a change of the birefringence and in consequence a shift of the interferometer spectrum. In order to reduce the temperature sensitivity of the sensor, the fiber was attached to the cantilever beam acting as the force transducer only in two points (or in one point) and not along the whole length of the sensing segment of the fiber as in the previous design. Several versions of attaching the fiber to the beam were investigated, which make it possible to change the sensitivity of the sensor in a wide range. The transfer curve of the sensor was calculated analytically and then measured for the different versions of the sensor. The temperature sensitivity of the sensor was also measured and compared to the temperature sensitivity of the original design.
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