Faculty Publications

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Publications by NITK Faculty

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    Magnetic domain studies of cobalt nanostructures
    (2012) Nagaraja, H.S.; Nagaraja, K.K.; Rossignol, F.; Dumas-Bouchiat, F.; Champeaux, C.; Catherinot, A.
    The pulsed laser deposition technique associated with a low energy cluster beam is used to deposit cobalt thin films with a thickness 100-200 nm and cobalt dots of a diameter 100-200 nm on silicon substrates. The deposited thin films of Co are composed of clusters of a size 10- 50 nm, with very few large grains as revealed by atomic force microscopy. The observations performed by magnetic force microscopy on as-grown thin films reveal randomly distributed out-of-plane magnetic domain structures. These magnetic domains are aligned linearly by applying an external magnetic field either perpendicular or parallel to the substrate during the deposition. In addition, the effect of film thickness and roughness on multidomains is reported. The increase of roughness resulted in the decrease of magnetic domain width from 200 to 100 nm. This decrease is accompanied by the appearance of instability in the stripe domain pattern. Well separated cobalt dots of diameter in the range of 100-200 nm are also deposited on silicon substrates, which show arc-like multidomains. The domains seem to be oriented along the long axis of the dots. The domain structure of Co nanodots is similar to that of Co thin films indicating strong magnetic coupling of clusters. © Springer Science+Business Media, LLC 2012.
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    Magnetic-field tuning of whispering gallery mode lasing from ferromagnetic nematic liquid crystal microdroplets
    (OSA - The Optical Society info@osa.org, 2017) Mur, M.; Sofi, J.A.; Kvasi?, I.; Mertelj, A.; Lisjak, D.; Niranjan, V.; Mus?evic?, I.; Dhara, S.
    We report magnetic field tuning of the structure and Whispering Gallery Mode lasing from ferromagnetic nematic liquid crystal micro-droplets. Microlasers were prepared by dispersing a nematic liquid crystal, containing magnetic nanoparticles and fluorescent dye, in a glycerol-lecithin matrix. The droplets exhibit radial director structure, which shows elastic distortion at a very low external magnetic field. The fluorescent dye doped ferromagnetic nematic droplets show Whispering Gallery Mode lasing, which is tunable by the external magnetic field. The tuning of the WGM lasing modes is linear in magnetic field with a wavelength-shift of the order of 1 nm/100 mT. Depending on the lasing geometry, the WGMs are red- or blue-shifted. © 2017 Optical Society of America.
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    Experimental investigation of 3D-printed polymer-based MR sandwich beam under discretized magnetic field
    (Springer Verlag service@springer.de, 2018) Rajpal, R.; Lijesh, K.P.; Gangadharan, K.V.
    Smart materials are being employed in dynamic systems to tune the stiffness and damping of the structure by using external stimuli. Magnetorheological elastomers (MREs) are considered to be as one of the smart materials because of their characteristics of altering the dynamic properties under the external magnetic field. So far, MRE sandwich beams have been developed by embedding them between two parent structures. In the present work, a novel technique of embedding MR materials is presented to create complex sandwich structures. This technique will replace the conventional embedding technique which uses adhesives to bind the MR materials with the parent structure. The vibration characteristics of the developed sandwich beams are estimated by conducting harmonic analysis to a predefined band of frequency range under the different directions of magnetic field. Sinusoidal signals of desired frequency and amplitude were proffered using NI educational laboratory virtual instrumentation suite to an amplified piezoactuator for exciting the MR sandwich beam. A non-contact-type laser displacement sensor is used in this study to avoid the additional mass of the sensor on the beam. The results indicate that the smart materials can be efficiently embedded with the sandwich beam without using the adhesives. It is also found that by changing the direction of magnetic field, the range of the variation in stiffness of MR sandwich beam can be increased to enhance the isolation effect at fundamental natural frequency. © 2018, The Brazilian Society of Mechanical Sciences and Engineering.
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    Influence of Magneto-combustion on regulated emissions of an automotive engine under variable speed operation
    (MechAero Found. for Techn. Res. and Educ. Excellence office@mechaero.org, 2020) Oommen, L.P.; Kumar, G.N.
    The present study investigates the influence of magneto-combustion on the macro pollutants emitted from a multi point fuel injection (MPFI) automotive engine. The regulated emissions of an auto engine include carbon monoxide, un-burnt hydrocarbon (UBHC)and oxides of nitrogen (NOx) which are the by-products of internal combustion of the hydrocarbon fuel used. Depending upon the physiochemical characteristics of pollutants and their concentrations, these pollutants result in numerous physical ailments and mortality. Magneto-combustion is an under investigated technology which effectively reduces the emission of toxic vehicular exhaust. The exposure to an external magnetic field realigns the hydrocarbon structure and alters its combustion properties. The tests conducted on a Maruthi Zen MPFI engine under two different patterns of magnetisation resulted in a maximum reduction of carbon monoxide by 23.97%, UBHC by 13.1% and NOx by 5.23%, thereby reduced the cumulative negative impact on the environment. © 2020. MechAero Foundation for Technical Research & Education Excellence.
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    Torque generation in lightweight four rotor magnetorheological brake
    (Springer, 2024) Kadam, S.; Kariganaur, A.K.; Kumar, H.
    Non-Newtonian behaviour of the Magnetorheological (MR) fluid under the influence of external magnetic field can be commissioned to design various applications such as MR brake, damper, and clutches, etc. Better design strategies, material selection and characterization led to realize the potential of MR brakes to replace conventional brakes. The present study emphasises on developing lightweight (1.8 kg) multi-rotor MR brake (MMRB). Finite element method magnetics (FEMM) software is utilized to determine the material required for a single-rotor MRB. FEMM material selection analysis is incorporated into the modeled MMRB, and the nature of magnetic flux density throughout the MR gap was obtained. Magnetic circuit analysis of the proposed brake is carried out to find torque estimation using analytical equations and Bingham plastic model. The proposed brake is fabricated and characterized using commercial MRF (132 DG, Lord Corporation). The study compares the torque outputs obtained experimentally with finite element analysis (FEA) and analytical approach. The average maximum magnetic flux density through FE analysis is found to be 0.45 T @ 3 A current. The average error between FE obtained and experimentally obtained torque output of the brake is around 5%. Further, an alternate design is proposed by utilizing same rotor diameter and number of electromagnetic coils. The new design is lighter in weight (0.8 kg) and exhibits enhancement in the torque output and torque to weight ratio by around 31% and 55%, respectively than the present design. © Indian Academy of Sciences 2024.