This article describes the design, development and characterization of an evanescent wave fiber optic sensor (EWFS) for the detection of toxic ammonia gas. Sol-gel technology is employed for immobilizing a reversible ammonia sensitive dye on the middle unclad region of a multimode fiber. Ammonia gas permeating into the immobilized dye, the
color of the dye changes reversibly from yellow to blue with increasing concentration of ammonia gas. The concentration of ammonia gas can be determined by measuring the absorption at a given wavelength. The response of the sensor to different concentrations of ammonia, recovery time, reusability, etc of the developed sensor is also discussed. The techniques described here is also relevant to the detection of a wide range of other gases.
This article describes the design, development and characterization of a fiber optic sensor based on evanescent wave absorption in Long Period Grating (LPG) on multimode optical fibers, for the detection of toxic ammonia gas. The sensing length of the sensing element is only 10mm, but the dynamic range is as good as that of the conventional evanescent wave sensors. Sol-gel technology is employed for immobilizing a reversible ammonia sensitive dye on the
grating region of a multimode fiber. Ammonia gas permeating into the immobilized dye, the color of the dye changes reversibly from yellow to blue with increasing concentration of ammonia gas. The concentration of ammonia gas can be determined by measuring the absorption at a given wavelength. The dynamic range of the sensor is from 0.027 to 2.04 mM/Ltr.
In the present study, we report the design and development of a cost-effective, simple, sensitive LED - based fiber optic sensor for detecting trace amounts of chloride ions in water. A multimode plastic clad silica (PCS) fiber with the cladding removed and long period grating (LPG) written on its middle region acts as the sensing element. Exposure of the sensing region to water samples containing spectroscopic reagents for the detection of chloride ions causes evanescent wave absorption, which increases with increase in concentration. The limit of detection of the sensor is found to be a few parts per billion and the operational range covers more than five orders of magnitude.
In this paper, we present the details of a optical fiber sensor, based on evanescent wave absorption in Long periodic grating (LPG) in multimode optical fibers, for measuring trace amounts of chromium concentration in water. The detection limit of the sensor is a few parts per billion (ppb) and the operating range is more than 3 orders of magnitude. The sensing length of the sensing element is only 10mm, but the dynamic range is as good as that of the conventional unclad evanescent wave sensors. A plastic clad silica core (PCS) fiber with LPGs on its middle region acts as the sensing element. Exposure of this sensing region to water samples containing spectroscopic reagents for the detection of chromium causes evanescent wave absorption, which increases with increasing concentration of chromium. The use of a super-bright green light emitting diode (LED) as light source reduces the size and cost of the system considerably. In order to reduce the effect of power supply fluctuations or ambient variations of the LED, a reference arm and ratio detector are employed.
An open photoacoustic cell under heat transmission configuration has been employed to evaluate the thermal and transport properties of n-type Si doped GaAs epitaxial layer and p-type Be doped GaAs epitaxial layer grown on GaAs substrate by molecular beam epitaxial method. The variation of the characteristics of the photoacoustic signal with chopping frequency clearly indicate the different heat generation mechanisms occurring in the sample under optical excitation at 2.54eV with laser beam. The values of thermal diffusivity, diffusion coefficient, surface recombination velocity and nonradiative recombination time have been evaluated for the sample by fitting the experimentally obtained phase of the photoacoustic signal with the theoretical model. It has been observed that the nature of dopant influences the values of thermal and transport properties of the semiconductor samples.
In this paper, we present the details of a simple, sensitive, low cost and portable optical fiber sensor, based on evanescent wave absorption, for measuring chromium concentration in water ranging from 10ppb to 2000ppb. A plastic clad silica core (PCS) fiber with unclad middle region acts as the sensing element. The use of a super-bright green light emitting diode (LED) as light source reduces the size and cost of the system considerably. The use of a reference arm and ratio detector significantly reduces the effect of power supply fluctuations or ambient variations of the LED. The conventional methods used for the determination of chromium in water are spectrophotometric and colorimetric methods. Hence a comparative study between the present sensor and the spectrophotometric method has also been carried out. The response time of the sensor is also studied.
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