Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
9 results
Search Results
Item Active contours technique for fringe evaluation of complicated fringe patterns(2010) Joishi, R.; Reddy, K.P.J.; Hegde, G.M.An improved technique based on active contours approach is presented for the analysis of non-uniform finite fringe interferograms. The technique is validated by demonstrating its application in analyzing the interferomertic image having non-uniform fringe pattern generated by a supersonic flow in front of a blunt body. A filtering method for identifying the flow parameters is presented as an extension of this technique. Proposed technique also provides an estimate of the heterodyning spatial frequency. © 2010 SPIE.Item Quantitative density imaging of subsonic jet using planar laser induced fluorescence of MEK(2012) Shelar, M.S.; Umesh, G.; Hegde, G.M.; Jagadeesh, G.; Reddy, K.P.J.Quantitative molecular density distribution of Methyl ethyl ketone (MEK) in turbulent nitrogen jet (Re≈2-3×103) was measured using PLIF technique. The tracer (MEK) was seeded in the nitrogen jet by purging through the liquid MEK at ambient temperature. Planar laser sheet from frequency quadrupled, Q-switched, Nd: YAG laser (266 nm) was used as an excitation source. Emitted fluorescence images of jet flow field were recorded on CMOS camera. To obtain quantitative density profile, the dependence of PLIF intensity on MEK partial pressure was employed. Thus an instantaneous quantitative density image of nitrogen jet, seeded with MEK was obtained. © 2012 IEEE.Item Electronic band structure and photoemission spectra of graphene on silicon substrate(SPIE spie@spie.org, 2014) Javvaji, B.; Ravikumar, A.; Shenoy, B.M.; Roy Mahapatra, D.; Rahman, M.R.; Hegde, G.M.Synergizing graphene on silicon based nanostructures is pivotal in advancing nano-electronic device technology. A combination of molecular dynamics and density functional theory has been used to predict the electronic energy band structure and photo-emission spectrum for graphene-Si system with silicon as a substrate for graphene. The equilibrium geometry of the system after energy minimization is obtained from molecular dynamics simulations. For the stable geometry obtained, density functional theory calculations are employed to determine the energy band structure and dielectric constant of the system. Further the work function of the system which is a direct consequence of photoemission spectrum is calculated from the energy band structure using random phase approximations. © 2014 SPIE.Item Optoelectronic properties of graphene silicon nano-texture(Institute of Electrical and Electronics Engineers Inc., 2014) Brahmanandam, J.; Ajmalghan, M.; Abhilash, R.K.; Roy Mahapatra, D.; Rahman, M.R.; Hegde, G.M.Graphene on silicon with silicon dioxide quantum dots is a promising opto-electronic material. The optical band gap and the corresponding optical conductivity are estimated using the density functional approach with the combination of molecular dynamics. The regular repeating unit cell of graphene silicon nano-texture is identified using the classical molecular dynamics simulations. Electronic calculations predict the optical band gap is around 0.2 eV and the optical conductivity is identified to be 0.3 times the quantum conductance. © 2014 IEEE.Item Optoelectronic properties of graphene on silicon substrate: Effect of defects in graphene(SPIE spie@spie.org, 2015) Javvaji, B.; Ajmalghan, M.; Roy Mahapatra, D.; Rahman, M.R.; Hegde, G.M.Engineering of electronic energy band structure in graphene based nanostructures has several potential applications. Substrate induced bandgap opening in graphene results several optoelectronic properties due to the inter-band transitions. Various defects like structures, including Stone-Walls and higher-order defects are observed when a graphene sheet is exfoliated from graphite and in many other growth conditions. Existence of defect in graphene based nanostructures may cause changes in optoelectronic properties. Defect engineered graphene on silicon system are considered in this paper to study the tunability of optoelectronic properties. Graphene on silicon atomic system is equilibrated using molecular dynamics simulation scheme. Based on this study, we confirm the existence of a stable super-lattice. Density functional calculations are employed to determine the energy band structure for the super-lattice. Increase in the optical energy bandgap is observed with increasing of order of the complexity in the defect structure. Optical conductivity is computed as a function of incident electromagnetic energy which is also increasing with increase in the defect order. Tunability in optoelectronic properties will be useful in understanding graphene based design of photodetectors, photodiodes and tunnelling transistors. © 2015 SPIE.Item Photonic crystal ring resonator: A promising device for a multitude applications(SPIE spie@spie.org, 2017) Yadunath, T.R.; Kumar, R.R.; Tupakula, T.; Kandoth, A.; John, K.; Ramakrishnan, R.K.; Das, P.P.; Badrinarayana, T.; Mohan, S.; Hegde, G.M.; Srinivas, T.In this paper a 2D Photonic Crystal array in SOI platform having hexagonal periodicity with a ring defect incorporated along with two bus waveguides is conceptualized and realized for various applications of optical communication, sensing etc. The ring structure filters out a resonant wavelength from the spectrum carried to it through the line defect where the resonated peak is determined by the effective ring radius. The hexagonal architecture enables more coupling length than an ideal ring structure which helps in better intensity accumulation. The resonant peak exhibited at 1554nm in simulation, which is observed in the optical characterization at 1543nm. This is attributed to the fabrication tolerance. © 2017 SPIE.Item Visualization of coherent structures in turbulent subsonic jet using planar laser induced fluorescence of acetone(2013) Shelar, V.M.; Hegde, G.M.; Umesh, G.; Jagadeesh, G.; Reddy, K.P.J.In this paper, we present the molecular density distribution measurement in turbulent nitrogen jet (Re ? 3×103), using acetone as molecular tracer. The tracer was seeded in the nitrogen jet by purging through the liquid acetone at ambient temperature. Planar laser sheet of 266 nm wavelength from frequency quadrupled, Q-switched, Nd:YAG laser was used as an excitation source. Emitted fluorescence images of jet flow field were recorded on CMOS camera. The dependence of planar laser induced fluorescence (PLIF) intensity on acetone vapor density was used to convert PLIF image of nitrogen jet into the density image on pixel-by-pixel basis. Instantaneous quantitative density image of nitrogen jet, seeded with acetone, was obtained. The arrowhead-shaped coherent turbulent structures were observed in the present work. It was found that coherent structures were non-overlapping with separate boundaries. Breaking of coherent structures into turbulence was clearly observed above four times jet width. © EDP Sciences, 2013.Item Gas phase oxygen quenching studies of ketone tracers for laser-induced fluorescence applications in nitrogen bath gas(2014) Shelar, V.M.; Hegde, G.M.; Umesh, G.; Jagadeesh, G.; Reddy, K.P.J.In this paper we report the quantitative oxygen quenching effect on laser-induced fluorescence of acetone, methyl ethyl ketone, and 3-pentanone at low pressures (?700 torr) with oxygen partial pressures up to 450 torr. Nitrogen was used as a bath gas in which these molecular tracers were added in different quantities according to their vapor pressure at room temperature. These tracers were excited by using a frequency-quadrupled, Q-switched, Nd:YAG laser (266 nm). Stern-Volmer plots were found to be linear for all the tracers, suggesting that quenching is collisional in nature. Stern-Volmer coefficients (ksv) and quenching rate constants (kq) were calculated from Stern-Volmer plots. The effects of oxygen on the laser-induced fluorescence of acetone, methyl ethyl ketone, and 3-pentanone were compared with each other. Further, the Smoluchowski theory was used to calculate the quenching parameters and compared with the experimental results. Copyright © Taylor & Francis Group, LLC.Item Acetone planar laser-induced fluorescence for supersonic flow visualization in air and nitrogen jet(University of Malaya, 2014) Shelar, V.M.; Shrisha Rao, M.V.; Hegde, G.M.; Umesh, G.; Jagadeesh, G.; Reddy, P.J.Background: Laser based flow visualization techniques are indispensable tools for flow visualization in fluid dynamics and combustion diagnostics. Among these, PLIF is very popular because of its capability to give quantitative information about the flow. This paper reports the acetone tracer-based PLIF imaging of supersonic jet with air and nitrogen as bath gases. Methods: The tracer was seeded in the flow by purging bath gas through the liquid acetone at ambient temperature. Planar laser sheet from frequency quadrupled, Q-switched, Nd:YAG laser (266 nm) was used as an excitation source. Emitted PLIF images of a jet flow field were recorded on ICCD camera. Results: In this study, the dependence of PLIF images intensity on oxygen by comparing nitrogen jet with air in supersonic regime was presented. A lower temperature at the exit of the supersonic jet condenses the tracer which in turn forms droplets. Conclusions: There was a significant decrease in the PLIF image intensity in the case of air. This may be attributed to the oxygen present in the air. It is shown that image adding and Gaussian image processing of PLIF images for steadystate jet improve the quality of images. © 2014 Shelar et al.; licensee Springer.