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Signal processor for optical fiber sensors based on MEMS Fabry-Perot interferometer
Nikola Uremović, 2020, master's thesis

Abstract: In the master thesis, we have created an interrogation system for measuring the change of the optical path in the Fabry-Perot interferometer caused by the strain of the surface at which it was attached to. The change of strain can be calculated via a change in optical path length which is visible as a shift in phase angle. The system will be used as a system for measuring strain, although it can be used for measuring various physical parameters that can cause a change in optical path length, such as pressure, force, temperature, etc. Initially, the theoretical background of the system and project components are represented and explained, following the building process of the electronic and optical part of the project. Lastly, the working principle and programming algorithms of a system are presented and explained. Measurement results are shown at the end, as well as the conclusion that is drawn from the thesis.
Keywords: optical fibers, sensors, interferometer, signal processing
Published: 04.11.2020; Views: 130; Downloads: 33
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Fiber-optic sensors for measurements of torsion, twist and rotation
Vedran Budinski, Denis Đonlagić, 2017, review article

Abstract: Optical measurement of mechanical parameters is gaining significant commercial interest in different industry sectors. Torsion, twist and rotation are among the very frequently measured mechanical parameters. Recently, twist/torsion/rotation sensors have become a topic of intense fiber-optic sensor research. Various sensing concepts have been reported. Many of those have different properties and performances, and many of them still need to be proven in out-of-the laboratory use. This paper provides an overview of basic approaches and a review of current state-of-the-art in fiber optic sensors for measurements of torsion, twist and/or rotation.
Keywords: fiber optic sensors, twist sensors, rotation sensors, circular birefringence, linear birefringence, FBG, polarization, optical fibers, Fiber Bragg Gratings
Published: 22.06.2017; Views: 695; Downloads: 163
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Structure-mechanical properties relationship of poly(ethylene terephthalate) fibers
Milena Žiberna-Šujica, Majda Sfiligoj-Smole, 2003, original scientific article

Abstract: The correlation between the fiber structure and mechanical properties of two different poly(ethylene terephthalate) fiber types, that is, wool and cotton types produced by three producers, was studied. Fiber structure was determinedusing different analytical methods. Significant differences in the suprastructure of both types of conventional textile fibers were observed, although some slight variations in the structure existed between those fibers of the same type provided by different producers. A better-developed crystalline structure composed of bigger, more perfect, and more axially oriented crystallites was characterized for the cotton types of PET fibers. Crystallinity is higher, long periods are longer, and amorphous domains inside the long period cover bigger parts in this fiber type in comparison with the wool types of fibers. In addition, amorphous and average molecular orientation is higher. The better mechanical properties of cotton PET fiber types, as demonstrated by a higher breaking tenacity and modulus accompanied by a lower breaking elongation, are due to the observed structural characteristics.
Keywords: textile industry, fibers, mechanical properties, polyethyleneterephthalate
Published: 01.06.2012; Views: 1342; Downloads: 91
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Mild oxidation of cellulose fibers using dioxygen as ultimate oxidizing agent
Gabriela Biliuta, Lidija Fras Zemljič, Valeria Harabagiu, Sergiu Coseri, 2011, original scientific article

Abstract: Two types of regenerate cellulose fibres were oxidized under mild conditions, by using N-hydroxyphthalimide as catalyst and molecular oxygen as ultimate oxidizing agent. The amounts of negatively charged groups introduced were determined by means of potentiometric titration. The degree of polymerization and molar mass of the oxidized fibres determined viscosimetrically, has been found to be almost unaffected during oxidation.
Keywords: viscose fibers, modal fibers, oxidation, N-hydroxyphthalimide, NHPI, phthalimide-N-oxyl radical, PINO
Published: 01.06.2012; Views: 1268; Downloads: 39
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The interaction ability of cellulosic materials as a function of fine structure and Helmholtz surface energy
Tatjana Kreže, Karin Stana-Kleinschek, Volker Ribitsch, Zdenka Peršin, Majda Sfiligoj-Smole, 2005, original scientific article

Abstract: Many chemical or physical modification processes significantly influence the accessibility of fiber forming polymers by causing structural changes. The wettability and sorption ability improvements of polymeric materials are major tasks during finishing processes. Different pre-treatment processes are used in order to improve the accessibility of dissociable groups, hydrophilicity, dyeability, and whiteness. These are usually alkaline purification, chemical bleaching and mercerization. In a previous paper we presented the data for structural characteristics (density, crystallinity index, molecular orientation, void volume, diameter and the specific inner surface of void, etc.) of untreated regenerated cellulose fibers (viscose, modal and lyocell) [41]. We now compare the influence of different pre-treatment processes on fiber structure and the accessibility of the chemical groups of these fibers. In order to improve the accessibility, two pre-treatment processes were used: chemical bleaching of fibers and tensionless alkali treatment. The influence of these pre-treatment processes on the structure parameters was evaluated using viscosity measurements (determination of polymerization degree (DIN 54 270)) and iodine sorption ability measurements according to the Schwertassek method (determination of crystallinity index) [13, 16]. The reactivity and accessibility in a polar environment was determined using tensiometry. Contact angles between the fibers and liquids of different polarities were determined using the powder contact angle method and calculated from a modified Washburn equation [26, 28]. The surface free (Helmholtz) energy of differently treated fibers was determined from the contact angle data using the Owens-Wendt-Raeble-Kaelble approximation [30, 33, 35]. The differences in the accessibility of raw and pre-treated regenerated cellulose fibers obtained using tensiometry are compared with the results of the conventional method used to determine moisture adsorption (DIN 54 351, DIN 53 802). In regard to raw fibers, viscose shows the most hydrophilic characteristic: adsorbs the highest amount of moisture, has the fastest penetration velocities (Fig. 6), the smallest contact angle, and the highest SFE (Fig. 8). Modal fibers have the largest contact angle, the lowest SFE, and they adsorb the smallest amount of water vapor. Pre-treatments increase the sorption ability and the surface free (Helmholtz) energy while they decrease the contact angle. This makes the material more accessible to water and chemicals used in the finishing processes although the crystallinity index increases. The main modification in polymer properties caused by the treatments is an increase in the fiber SFE caused by an increase of the fiber surfaces because of swelling in the alkaline medium (washing, slack-mercerization), and due to an increase of accessible OH- and COOH-groups (bleaching). This enables the formation of an increased number of hydrogen bridges between the water molecules and the OH- and COOH-groups. Our investigations confirm the results published earlier thatthe main property necessary for the proper sorption behavior of cellulose materials are the accessible, less ordered regions and not the degree of crystallinity.
Keywords: regenerated cellulose fibers, fiber pre-treatment, iodine sorption, cristallinity, tensiometry, contact angle, Helmholtz surface energy, water adsorption
Published: 01.06.2012; Views: 2020; Downloads: 55
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Cellulose fibres functionalised by chitosan : characterization and application
Simona Strnad, Olivera Šauperl, Lidija Fras Zemljič, 2010, independent scientific component part or a chapter in a monograph

Keywords: cellulose fibers, medical applications, chitosan, antimicrobic properties
Published: 31.05.2012; Views: 1270; Downloads: 20
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Bond improvement in cementitious mortars reinforced with continuous carbon filaments
Andrej Ivanič, Samo Lubej, Milan Radosavljević, 2009, published scientific conference contribution

Abstract: Among various parameters that influence the properties of the composite, the bond between the cementitious matrix and the fibres is the most important one. This paper investigates the influence of admixtures - silica fume, superplasticizer and air entraining agent - on the improvement of the bond between bundled carbon filaments and cementitious mortars. An overall microstructural analysis has shown that the addition of silica fume strengthen the interfacial transition zone by both the reduction of its porosity and the consumption of CH crystals. The addition of a superplasticizer increased the workability of fresh mortars, but the bond improvement was insignificant. The application of the air entraining agent caused the formation of air bubbles inside the mortar matrix. Air bubbles formed in the vicinity of the multifilament yarn were found to provide mechanical anchoring for fibres leading to a significant increase in interface friction. Fibre-bundle pullout tests were carried out to confirm the effectiveness of the admixtures to improve the interface bonding. Based on the resulting load-displacement curves, air entraining agent was found to be most effective in enhancing the bonding characteristics of the cementitious composite.
Keywords: carbon fibers, cementitious composites, bond properties
Published: 31.05.2012; Views: 1025; Downloads: 29
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Tyrosinase catalysed coupling of functional molecules onto protein fibres
Suzana Jus, Vanja Kokol, Georg M. Gübitz, 2008, original scientific article

Abstract: Grafting, using oxidative enzymes shows a high potential for wool fibres funktionalisation. In this work we attempt to graft on wool fibres with phenolic antioxidants order to introduce and improve the properties of the fibre. The approach of tyrosinase to oxidize tyrosine residues in wool proteins to quinones, which can further react with free sulfhydryl (thiol), amino or phenolic groups of different substrates was exploited to couple different phenolic antioxidants (caffeic acid and chlorogenic acid) onto the wool fibre proteins. Tyrosinase catalysed reactions were followed by different analytical methods like oxygen consumption, FT-NIR Raman and UV/VIS spectroscopy. It was proved that phenolic compounds used are strongly cross-linked on the wool fibre resulting to an improved antioxidant activity.
Keywords: textile fibres, wool fibers, tyrosinase, caffeic acid, chlorogenic acid, grafting, chemical modification of fibres
Published: 31.05.2012; Views: 1267; Downloads: 79
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