Faculty Publications
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Publications by NITK Faculty
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Item Ion dynamics of a laser produced aluminium plasma at different ambient pressures(Springer Verlag service@springer.de, 2018) Sankar, P.; Shashikala, H.D.; Philip, R.Plasma is generated by pulsed laser ablation of an Aluminium target using 1064 nm, 7 ns Nd:YAG laser pulses. The spatial and temporal evolution of the whole plasma plume, as well as that of the ionic (Al2+) component present in the plume, are investigated using spectrally resolved time-gated imaging. The influence of ambient gas pressure on the expansion dynamics of Al2+ is studied in particular. In vacuum (10?5 Torr, 10?2 Torr) the whole plume expands adiabatically and diffuses into the ambient. For higher pressures in the range of 1–10 Torr plume expansion is in accordance with the shock wave model, while at 760 Torr the expansion follows the drag model. On the other hand, the expansion dynamics of the Al2+ component, measured by introducing a band pass optical filter in the detection system, fits to the shock wave model for the entire pressure range of 10?2 Torr to 760 Torr. The expansion velocities of the whole plume and the Al2+ component have been measured in vacuum. These dynamics studies are of potential importance for applications such as laser-driven plasma accelerators, ion acceleration, pulsed laser deposition, micromachining, laser-assisted mass spectrometry, ion implantation, and light source generation. © 2017, Springer-Verlag GmbH Germany, part of Springer Nature.Item Exploring the synergistic interactions of TiO2, rGO, and g-C3N4 catalyst admixtures in a polystyrene nanocomposite photocatalytic film for wastewater treatment: Unary, binary and ternary systems(Elsevier Ltd, 2019) Das, S.; Mahalingam, H.Reduced graphene oxide (rGO) as well as graphitic carbon nitride (g-C3N4) were synthesised and blended along with TiO2 at specific ratios in polystyrene photocatalytic films to find out the optimum efficiency. The prepared photocatalysts were characterised by scanning electron microscopy (SEM-EDX), X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR) and contact angle analyser. The SEM, XRD, and FTIR analysis indicated that the nanoparticles were evenly distributed on the surface of the polystyrene film. The stability of the polymer film with respect to possible leaching of the embedded catalyst particles was evaluated by ICP-OES analysis. The photocatalytic activity of the admixture was evaluated using remazol turquoise blue dye as a model organic pollutant, and it was found that the photocatalytic ternary admixtures displayed much higher photocatalytic activity (99%) than the unary (89%) or binary (94%) mixtures indicating the synergistic effect of these catalysts. The effect of catalyst ratio, immobilisation, pH, initial dye concentration, irradiated light source, the presence of H2O2 and reusability of the film were also evaluated. The degradation of the dye is confirmed by TOC analysis (40% reduction), and HPLC/MS was used to identify the final degraded compounds. © 2019 Elsevier Ltd.Item Photomechanical actuation of polydimethylsiloxane/carbon black nanocomposite(Institution of Engineering and Technology jbristow@theiet.org, 2020) Hiremath, S.; Kulkarni, S.M.Materials such as carbon black (CB), carbon nanotube, graphene, etc. have been found to deform on exposure to the light source. Introducing these materials into polymers could convert them to photo-responsive composites. This is demonstrated by the experiment in which polydimethylsiloxane (PDMS) polymer containing CB nanofiller composites is prepared, and its photomechanical actuation from exposure to IR light source is recorded using a laser displacement sensor. The particle size analysis reveals the size of the CB, which is verified by the dynamic light scattering method. The UV-vis-IR spectrophotometer study shows that an increase in the light absorbance capacity of nanocomposites compared to the plain polymer. The PDMS/CB nanocomposite beam exhibited a significant deformation compared to plain PDMS. Deformation of the order of 10-11 mm is observed for a given IR source. The deformation found to have good repeatability but with some thermal hysteresis in cyclic actuation and de-actuation. © 2020 Institution of Engineering and Technology. All rights reserved.Item Numerical analysis of polymer composites for actuation(International Information and Engineering Technology Association, 2020) Hiremath, S.; Sangappa, V.; Rajole, S.; Kulkarni, S.M.The design of a polymer composite actuator is essential for micro and nano applications. Thus, the composite material may deform or deflects as specific stimuli are applied, such as heat, electrical, light source, etc. The deformation of the composite material is caused by the type of stimulus applied. Hence, while it is heated, the expansion takes place quickly, and the heating is shut down, the material shrinks very slowly. In the present investigation, this phenomenon is mainly studied in the actuation of composite beams. Numerical analysis of carbon black filled polymer composite beam expansion, and contraction is being analyzed in this research. The structure of the beam has been created, and the composite properties are incorporated into the beam, and the uniform heat source is applied on to the surface of the beam. The heating and cooling of the composite material predict the increase and decrease in the temperature of the beam. The numerical analysis of the temperature-dependent expansion and contraction of the composite beam has been carried out successfully. An increase in temperature is observed to signify the slight expansion in the composite beam, whereas the contraction of the composite beam takes a longer time to reach room temperature. Also, the increase in the content of the filler leads to a decrease in the expansion of the composite beam. The numerical simulation of the polymer composite thus provides a solid platform for the experimental study of thermal actuators. © 2020 Lavoisier. All rights reserved.Item Progression and characterization of polydimethylsiloxane-carbon black nanocomposites for photothermal actuator applications(Elsevier B.V., 2021) Hiremath, S.; H, S.M.; Kulkarni, S.M.The new development of polymer-based actuators triggers the progress of nanocomposites. Polymer materials are currently used in sensors, microfluidic devices, electrical and thermal actuators, and energy harvesting applications due to ease of availability, excellent tolerable properties, and customizable properties. The polymer-based nanocomposite can be driven by various stimuli, which is the actuator's emerging field. Thus, photothermal actuation is a thurst area of research transforming light energy into mechanical energy through the polymer material. The photo-responsive material can be prepared and tested for photo-actuation by incorporating the nanoparticles into the polymer. The present work focuses on developing polydimethylsiloxane (PDMS) and carbon black (CB) nanocomposite. The objective here is to investigate the photothermal actuator's performance by illuminating the infrared (IR) light source and studying its most influential characteristics, such as absorbance, thermal conductivity, and the thermal expansion coefficient. The PDMS / CB nanocomposite absorbs the IR light and then increases temperature, which is finally transformed into a beam deflection. Responses are measured as a result of time deflection using the Laser displacement sensor. It is noted that the deflection of the nanocomposite beam is linearly increased during illumination with light while it is exponentially decreasing when the light is turned off. The proposed polymer nanocomposite is approximately deflected by 9 mm in the duration of 16 s duration. Furthermore, the experimental deflection of the photothermal actuator is very close to theoretical results. The nanocomposite PDMS / CB reveals that there is an increase in absorbance by increasing the filler content. The nanocomposite conductivity is 35.2 % higher than the base material. As well, the thermal expansion coefficient decreases with an increase in carbon black content. The photothermal actuator's development is an ongoing process in which the material parameter, actuator geometry, and many more are modified. As a result, the photothermal bending performed can provide a means for various light-driven applications. © 2020 Elsevier B.V.Item Dual emissive water-based flexo ink from tapioca-derived carbon dots for anti-counterfeiting applications(Elsevier B.V., 2022) Ullal, N.; Lewis, P.M.; Dhanya, D.; Kulkarni, S.D.; P.j, A.; K, U.B.Counterfeiting of high-value items is a challenging menace worldwide, and luminescent nanoparticles-based security inks have promising applications while addressing this global issue. As Carbon dots (CDs) show attractive functional properties, hydrophilic CDs were prepared through hydrothermal approach from tapioca starch as an eco-friendly precursor. CDs with bluish-green fluorescence emission under 365 nm UV light illumination was obtained using column chromatography technique. TCSPC studies indicated the presence of blue and green emitters with average lifetimes of 1.12 and 1.61 ns, respectively. The graphitic and polycrystalline nature of CDs (~9 nm) with negatively charged surface groups was confirmed through ATR-IR, XPS, RS, XRD, SAED, DLS and TEM. An eco-friendly water-based security ink for flexography printing was formulated, and the influence of the ink components on the fluorescence of CDs were studied. The prints on UV dull paper displayed good abrasion resistance, densitometry and colorimetric values. The letters written using the invisible ink exhibited good security features including excellent covertness under daylight, and a bluish-green emission under 365 nm UV light. Moreover, a yellow emission was perceived using a yellow-orange pass filter under the same light source. The surface morphology and electrical property investigations suggested the use of flexo-ink in flexible printed electronics for anti-counterfeiting. These results propose that Tapioca-derived CDs can enable unique optical features in its eco-friendly ink formulation to demonstrate promising security applications. © 2022 Elsevier B.V.Item BER analysis of a full-duplex relay-assisted BPSK-SIM based VLC system for indoor applications(Optica Publishing Group (formerly OSA), 2023) Bhargava Kumar, L.B.; Naik, R.P.; Choudhari, D.; Krishnan, P.; G.D., G.D.G.; Jagadeesh, V.K.This paper contemplates a relay-assisted visible light communication (VLC) system, where the light source (table lamp) acts as a relay node and cooperates with the main light source. Following the IEEE 802.15.7r1 VLC reference channel model, we assume that there are two different light sources present in an office room. The first one is the source terminal present on the ceiling and another one is the desk lamp that serves as the relay station, which works in a full-duplex method. Because of the loop interference channel, we model the VLC relay terminal using ray tracing simulations. We have analyzed the bit error rate (BER) performance of the relay-assisted VLC system using a binary phase shift keying–subcarrier intensity modulation (BPSK-SIM) technique. The proposed method outperforms existing phase shift keying (PSK) and square M-quadrature amplitude modulation (M-QAM) techniques. The proposed VLC system using the BPSK-SIM technique achieves a BER performance of 10−12 for an SNR of 20 dB. The results of the proposed full-duplex and half-duplex relayed VLC systems are evaluated using equal power allocation (EPA) and optimum power allocation (OPA) techniques over three different modulation schemes, which are 2-PSK, square M-QAM, and BPSK-SIM. © 2023 Optica Publishing Group.