Ganesan A R

We propose a waveguide configuration with a plasmonic grating for tailoring dispersion characteristics. The unit-cell of the plasmonic grating encompasses the subwavelength distribution of metal nanowires forming a highly resonant effective medium. The configuration enables independent control of the coupling between the plasmonic and waveguide modes via the resonant strength of the effective medium. Numerical simulations show that the line shapes of the coupled modes can be varied from Fano to electromagnetically induced transparency-like. Furthermore, we use the structure to enhance the group index from 250 to 850 and to broaden the associated band from 40 to 180 meV.

Alignment of optical components is one of the important requirements in any optical system. Decentration of a component, like a lens, in the path of the beam, would introduce aberrations of various types. This would affect the measurement accuracy in the optical system such as an interferometer. In this work, we have analyzed the influence of decentration of an optical component on the wavefront in an optical system. The various aberrations caused due to the shifting of the axis of a lens in the path of an optical wavefront have been measured using a Shack Hartmann Wavefront Sensor and their influence studied. One of the lenses in the optical system is moved or decentered in transverse direction by 500 μm in steps of 50 μm. Decentration was done for all four quadrants. For each step, wavefront data is been taken and data was analyzed. Defocus, horizontal coma, vertical coma and spherical aberration were analyzed, apart from peak-to-valley and RMS values. Results showed that the error introduced is minimal up to 300 μm decentration, above which the aberrations were quite large. The experimental results and analyses are presented.

Gamma irradiated MTB has been explored as a chemical gas sensor. For this purpose, MTB is used as the cladding in the sensing area of a multimode optical fiber in a home made fiber optic gas sensor. Solid state sintering and melting-quenching methods were followed for the synthesis of polycrystalline and glassy magnesium tetraborate (MTB). The structural and morphological studies were carried out using powder XRD and FESEM analysis. XRD peaks matched well with the Joint committee on powder diffraction standards(JCPDS) data. From EDAX analysis, the elemental composition of the sample showed the presence of cerium in MTB. Samples were irradiated in a 60Co gamma chamber and the dose of 20 Gy was given to the samples. UV–vis spectra of the as-prepared and gamma irradiated MTBs showed a marked variation in the absorbance. The sensor was used for the detection of ammonia gas at various concentrations. The gamma irradiated MTB showed a highly improved response for gas detection compared to as prepared MTB. In this paper, the experimental results and analysis are presented for ammonia detection.

Poly(o-phenylenediamine) ferrite nanocomposites (PoPD/NiFe2O4) with different ratios of NiFe2O4 nanoparticles (10%, 20% and 30%) were synthesized by in-situ chemical oxidative polymerization method. NiFe2O4 nanoparticles were prepared by auto-combustion method using urea as fuel. The PoPD/NiFe2O4 nanocomposites were characterized by FTIR and XRD, SEM, TEM and thermogravimetric analysis. The FTIR and XRD pattern ascertain the interaction of PoPD with NiFe2O4 nanoparticles. The spherical morphology of PoPD is affected by the incorporation of NiFe2O4 nanoparticles. Magnetic properties of PoPD/NiFe2O4 nanocomposites were analyzed by using vibrating sample magnetometer. The hysteresis loops of NiFe2O4 and PoPD/NiFe2O4 nanocomposites exhibited ferromagnetic nature at room temperature. Dielectric properties of PoPD/NiFe2O4 nanocomposites at different temperatures have been carried in the frequency range from 50 Hz to 5 MHz. The ethanol gas sensing property of PoPD/NiFe2O4 nanocomposites was studied at room temperature using PMMA fiber optic method.

The wavefront aberrations induced by misalignments due to decentration and tilt of an optical component in an optical measurement system are presented. A ShackHartmann wavefront sensor is used to measure various aberrations caused due to the shifting of the axis and tilt of a lens in the path of an optical wavefront. One of the lenses in an optical system is decentered in the transverse direction and is tilted by using a rotational stage. For each step, wavefront data have been taken and data were analyzed up to the fourth order consisting of 14 Zernike terms along with peak-to-valley and root mean square values. Theoretical simulations using ray tracing have been carried out and compared with experimental values. The results are presented along with the discussion on tolerance limits for both decentration and tilt.

This paper discusses the performance evaluation of anidolic concentrators in an overcast sky condition. The concentrators were designed, with acceptance angles of 60°, 70° and 80°, first by maintaining the profile of the concentrator's uniform and secondly by keeping the height uniform. Studies were done using these concentrators with a model light pipe and the performance was compared with that of an acrylic dome and a profiled Fresnel collector. For a given condition, the illuminance ratio (ratio of illuminance measured at the base of the pipe to external illumination) increased with the acceptance angle. For a given acceptance angle, the concentrator with uniform height and variation of entrance aperture, performed better than a concentrator having a uniform profile.

The falling film evaporators are a class of heat exchanger that is widely studied. The research for improving the efficiency is still of prime importance because of its widespread applications in many industries such as desalination, food processing, nuclear energy, refrigeration etc. Our motive in this work is to investigate the potential use of heat and mass transfer enhanced surfaces for horizontal tube falling film evaporator to scale up its effectiveness. Four different tube surfaces viz. bare copper tube, Al2O3 thermal spray coated tube, Al2O3 + TiO2 thermal spray coated tube and open cell copper metal foam wrapped tube were taken for the study. Scanning electron microscope, 3D surface profilometer, contact angle metre and energy-dispersive X-ray spectroscopy were utilized to study the surface texture, surface roughness, wettability and composition, respectively. Out of these four surfaces, a total of eight configurations were realized by varying the coating thickness, surface roughness and porosity. A new prototype of horizontal tube falling film evaporator was designed and fabricated with fully wetted flow. An in house developed novel method based on laser interferometry was utilized for the experimental investigation. This non-invasive technique was capable of measuring falling film thickness and falling film interface temperature simultaneously with unprecedented circumferential span. For the film thickness evaluation, an optical shadow method incorporating Otsu's algorithm with precise interface tracking features was used. Mach–Zehnder Interferometer was employed to visualize the isotherm formation and to quantitatively infer the interface temperature. A 2D CFD study based on VOF model was carried out and found to be in good agreement with experimental as well as theoretical results. Further, the effect of flow rate, feed inlet water and body temperature were explored in detail and analysed statistically.

A Plastic PMMA optical fiber with a small portion of the clad being replaced by Gadolinium (Gd) doped CeO2 sensing material has been proposed in this work for VOC gas sensing. Gadolinium doped CeO2 has superior sensitivity, descent response, and recovery rate towards ammonia gas at room temperature than methanol and ethanol test gases. The number of oxygen species present on the surface after adsorption was found to be responsible for the enhanced sensitivity of Gadolinium doped CeO2 towards the VOC gases.

(MnNi)Fe2O4 nanoparticle was prepared by auto-combustion method and its composites with poly(o-phenylenediamine) (PoPD) were synthesized through in-situ oxidative polymerization method. FTIR and XRD studies confirmed the formation of PoPD/(MnNi)Fe2O4 nanocomposites. The crystalline size of PM1, PM2 and PM3 are 44 nm, 45 nm and 16 nm respectively. The dispersion of (MnNi)Fe2O4 nanoparticles in PoPD reduces their crystalline size. In PoPD/(MnNi)Fe2O4 nanocomposites, spherical morphology of PoPD is modified by (MnNi)Fe2O4 nanoparticles. TEM images showed that (MnNi)Fe2O4 nanoparticles are dispersed in PoPD matrix. The hysteresis loops of (MnNi)Fe2O4 nanoparticles and PoPD/(MnNi)Fe2O4 nanocomposites indicated that they are ferrimagnetic in nature. The saturation magnetization value of (MnNi)Fe2O4, PM1, PM2 and PM3 are 29.871 emu/g, 3.342 emu/g, 4.298 emu/g and 7.877 emu/g respectively. The thermal stability and saturation magnetization value of PoPD/(MnNi)Fe2O4 nanocomposites increases with increase in concentration of (MnNi)Fe2O4 nanoparticles. Dielectric properties of PoPD/(MnNi)Fe2O4 nanocomposites were studied at different frequencies and temperature. The Mn2+ substitution in NiFe2O4 has improved the ethanol sensitivity of PoPD/(MnNi)Fe2O4 nanocomposites. The dielectric constant of PoPD/(MnNi)Fe2O4 nanocomposites increases with increase in frequency, temperature and concentration of nanoparticles. Theoretical investigations of the metal oxide complex were done by utilizing a DFT/ B3LYP/LANL2DZ basis set. The optimized bond parameters (bond lengths, bond angles and dihedral angles) were determined using identical level of basis set. The NLO properties of the title compound was calculated using first-order hyperpolarizability calculation. The HOMO-LUMO, which clarifies the possible charge transfer, happens inside the molecule.

A Michelson interferometer has been developed which uses a right-angled prism mirrored on the sides containing the right angle, to measure small tilt angles with double sensitivity compared to the classical Michelson interferometer. The design of the interferometer, theory, relative sensitivity as well as experimental results are presented. With this setup, we could measure tilt angle up to 1 μrad .