Clad-modified with nanocrystalline metal oxide fiber optic gas sensors have been proposed for ambient temperature operation. The sensor output light intensity either increases or decreases when the gas concentration is increased. Study shows that optical properties of metal-oxides with air medium influence the gas sensing. Absorption characteristics of nanocrystalline metal oxides ( ZnO, Sm2O3 and Ce doped ZnO etc., ) in air, methanol, ethanol and ammonia are analyzed as well as their effect on gas sensing.
Successful isolation of single layer of graphene from graphite by mechanical exfoliation method, attracted a great
attention due to its unique structural, optical, mechanical and electronic properties. This makes the graphene as a
promising material in many possible applications such as energy-storage, sensing, electronic, optical devices and
polymer composite materials. High quality of reduced graphene oxide (rGO) material was prepared by chemical
reduction method at 100°C. The structural and optical properties of the rGO sheets were characterized by FT-IR,
micro Raman, powder XRD and UV-vis-NIR techniques. FT-IR reveals the absence of oxygen functional groups on
rGO due to the reduction process. Powder XRD shows the broad peak at 2θ=24.3° corresponding to interlayer
spacing 3.66Å which is smaller than the graphene oxide (GO). UV-vis-NIR of rGO displays the absorption peak at
271 nm indicates the reduction of GO and the restoration of C=C bonds in the rGO sheets. The cladding removed
and rGO coated poly-methyl methacrylate (PMMA) optical fiber is used for methanol and ethanol vapors detection
in the concentration ranging from 0 to 500 ppm at room temperature. The spectral characteristics along with output
intensity modulation of cladding removed and rGO coated fiber optic sensor reveal the potential of methanol and
ethanol vapor sensing properties.
We report, intrinsic fiber optic carbon nanotubes coated sensor for the detection of ammonia gas at room temperature.
Multimode step index polymethyl methacrylate (PMMA) optical fiber passive cladding is partly replaced by an active
coating of single and multi-walled carbon nanotubes following the dip coating technique and the reaction with ammonia
is studied by measuring the change in output intensity from the optical fiber under various ammonia gas concentrations
in the range 0-500 ppm in step of 50 ppm. The sensitivity is calculated for different wavelengths in the range 200-1100
nm both for single and multi-walled carbon nanotubes coated fiber. Higher sensitivities are obtained as 0.26 counts/ppm
and 0.31 counts/ppm for single-walled (average diameter 1.3 nm, 30 wt.% purity) and multi-walled (average diameter
10-15 nm, 95 wt.% purity) carbon nanotubes respectively. The role of diameter and purity of carbon nanotubes towards
the ammonia sensing is studied and the results are discussed.
Fiber optic sensor is proposed based on cladding modification method for detecting ammonia emissions. Nanocrystalline titanium dioxide is used as a sensing material and spectral characteristics of the
sensor are studied for different concentrations (50-500 ppm) of ammonia, methanol and ethanol. The sensor
shows a linear variation in the output light intensity with the concentration. The light intensity increases for
ammonia whereas it decreases for methanol and ethanol. Gas selectivity of the sensor is discussed.
Al2O3/ZrO2 multilayers have been deposited on Si(100) substrates by reactive pulsed laser deposition
technique. The experiments were performed at an optimized oxygen partial pressure of 3x10-2 mbar at room
temperature. A nanolaminate structure consisting of alternate layers of ZrO2 and Al2O3 with 40 bi-layers were
fabricated with thickness of each layer of zirconia and alumina of 15 nm and 5 nm, respectively. The cross-sectional
transmission electron microscope (XTEM) investigations were carried out on a multilayer thin film deposited at room
temperature. The XTEM study shows the formation of uniform thickness, higher fraction of monoclinic and small
fraction of tetragonal phases of zirconia and amorphous alumina. The ZrO2 /Al2O3 multilayer film was characterized
using high temperature x-ray diffraction (HTXRD) in the temperature range RT-1473 K. The ZrO2 /Al2O3 multilayer
shows a crystallization temperature of 673 K for the formation of tetragonal and monoclinic phases with significant
amount of tetragonal phase over the latter. From the HTXRD profiles, crystallite size, lattice parameters, and thermal
expansion coefficient of the tetragonal phase were calculated.
A fiber optic sensor for measuring thickness of transparent plates (1 to 2.5 mm) is proposed based on reflective type
displacement fiber optic sensor. The peak position in the output of the receiving fiber, which various linearly, is related
to the thickness of the transparent plate. Theoretical model is proposed and compared with the experimental results. The
output characteristics of the sensor are studied in terms of fiber optic parameters such as numerical aperture and
This paper deals with the study of Al-Si alloy laser melted with variable constituents of TiC and Fe coatings to generate
TiC reinforced with Fe-Al matrix composite layer on it. This experimentation deals with the investigation of the quality
of the composite layer generated by varying the process parameters and the coating composition. A superior composite
layer is established when the variable processing parameters were of 2.5kW laser power and 1.5 m/min. scan speed for
the coating composition of 25Fe-75TiC wt.%. This layer which consists of TiC reinforcement with Al-Fe matrix shows
an average microhardness of about 750 HV and also exhibits pore and crack free surface. Bonding strength of the
composite layer is also examined by the hardness test.
This paper presents an optical approach to estimate the thickness of biofilms on metals in natural aqueous environment.
An in-situ fibre optic sensor is held above the sample surface, to offer real time information continuously by measuring
the spatially resolved profiles of scattered light in biofilms. The optical results correlate well with the biofilm thickness
which is measured using a microscope and a microcapillary with a protruding thin, long flexible wire from the top of the
microcapillary. The biofilm thickness is less than 120 &mgr;m on test material after 20 days. Microscopic image analysis also
provides the evidence to confirm micro colony formation by rod and cocci bacterial species. The species Klebsiella are
found to be dominant on carbon steel. It is observed that measured optical intensity is proportional to the concentration
We have developed high power transverse flow (TF) CW CO2 lasers up to 15kW, a high repetition rate TEA CO2 laser of 500Hz, 500W average power and a RF excited fast axial flow CO2 laser at the Centre for Advanced Technology and have carried out various material processing applications with these lasers. We observed very little variation of discharge voltage with electrode gap in TF CO2 lasers. With optimally modulated laser beam we obtained better results in laser piercing and cutting of titanium and resolidification of 3 16L stainless steel weld-metal for improving intergranular corrosion resistance. We carried out microstructure and phase analysis of laser bent 304 stainless steel sheet and optimum process zones were obtained. We carried out laser cladding of 316L stainless steel and Al-alloy substrates with Mo, WC, and Cr2C3 powder to improve their wear characteristics. We developed a laser rapid manufacturing facility and fabricated components of various geometries with minimum surface roughness of 5-7 microns Ra and surface waviness of 45 microns between overlapped layers using Colmonoy-6, 3 16L stainless steel and
Inconel powders. Cutting of thick concrete blocks by repeated laser glazing followed by mechanical scrubbing process and drilling holes on a vertical concrete with laser beam incident at an optimum angle allowing molten material to flow out under gravity were also done. Some of these studies are briefly presented here.
The laser dye LD 473 exhibits in certain solvents largely red shifted ASE band from the fluorescence band maximum. The study on this behavior shows that the emitting species observed under conventional spectrofluorimeter measurements are different from those observed under high power pulsed laser excitation in these solvents.
A simple technique is described to measure the diameters of thin electrical wires using laser with microprocessor. A wire is moved across the laser beam. This results in change in the photodetector output for a finite time duration which is determined using a microprocessor. The product of the time duration and the velocity with which the wire is moved gives the diameter of the wire. This technique can be used to measure the size of the large objects. This technique is also a noncontact method and can be used in hostile environments.