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.
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.
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
diameter.
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