The paper describes an optical fiber based sensor (FOS) for the detection of the pollutant gas, NO2, in a mixture of gases.
The design comprises of a fiber optic transflection probe with a sensor element placed at one end. In the present FOS, the transducing component is prepared by sol-gel process. An equal quantity of a diazotizing reagent together with a coupling reagent is immobilized in the sol-gel matrix, which forms an azo dye in the presence of NO2. The sensor relies on the coloration reaction occurring at the micropores of this sol-gel film in the NO2 environment and offers a consequent variation in the optical absorption at a specific wavelength. The current sensor design gives more than 85% of variation in the output intensity at a NO2 concentration of few parts per million in air sample.
Since fiber reinforced polymer composites are becoming increasingly popular, nondestructive damage detection in these materials has become an important issue. Real time structural health monitoring using Fiber Optic Polarimetric Sensors (FOPS) in an interesting field of research in recent years. This paper presents the performance of FOPS using three different optical sensing fibers: low birefringence (low-bi), high birefringence (high-bi) and an ordinary single mode polarization maintaining fiber. The static and dynamic response of these fibers are experimentally evaluated under different conditions. The experiments were conducted on composite structures by embedding the optical fibers into specimen. Composite materials are extensively used in aerospace applications. The sensitivity of all fibers under different conditions is discussed for static and dynamic loading.
Dynamic analysis of structures and machines provide valuable information on the performance and reliability of structures. In this paper, we present the development of a Fiber Optic Polarimetric Sensor (FOPS*) for dynamic and impact loading. The sensor monitors the change in the state of polarization of the light beam traversing the fiber under dynamic loading. The dynamic response of three different sensing optical fibers - high birefringence (bow-tie) fiber, low birefringence fiber and an ordinary communication grade single mode fiber are evaluated. The studies were carried out by embedding the optical fibers in a glass fiber reinforced plastic (GFRP) specimen and the performances of the three different systems were compared.
In this work a new approach based on the fiber Optic Evanescent Wave (FOEW) Spectroscopy is developed for the effective determination of dental caries activity in human saliva. The biosensor design utilized the exponentially decaying wave that extends to the lower index region of the optical fiber's core-cladding interface. In order to achieve this, a short length of the cladding is removed and the fiber core surface is coated with a porous glass medium using sol-gel technique. The acidogenic profile resulting from the Streptococcus mutans activity in the human saliva is monitored using an indicator, which was encapsulated within the porous coating. These investigations display the potential benefits of FOEW based microbial sensor to monitor caries activity in human saliva.
The design and fabrication of a fiber optic pH sensor working on the basis of evanescent wave absorption is presented. A pH sensitive dye is immobilized on the uncladed portion of the optic fiber by sol-gel route. The sensitivity of the device is found to increase when multiple sol-gel coatings are used as the cladding in the sensing region. The sensor response and its dynamic range are reported for two pH indicator dyes, viz. bromocresol purple and bromocresol green.
A novel approach for the detection of nitrogen dioxide gas is described. This optical fiber based sensor (FOS) works on the principal of evanescent wave (EW) absorption phenomenon. EWs at the uncladded portion of a multimode fiber is utilized for the senor development by replacing this region with a coating of Metallophthalocyanine, which is thermally deposited at a reduced pressure. MPcs are very sensitive to NO2 gas and there is a change in the EW absorption in the NO2 environment. Compared to other gas sensing devices, this is highly sensitive technique. The attraction of this FOS is its simple architecture and the easiness to implement.
A new sensing technique for the in situ monitoring of the rate of pulsed laser deposition of metal thin films has been developed. This optical fiber based sensor utilizes the evanescent wave penetration of waveguide modes into the uncladded portion of a multimode fiber. The utility of this optical fiber sensor is demonstrated in the case of pulsed laser deposition (PLD) of silver thin films obtained by a Q- switched Nd:YAG laser which is used to irradiate a silver target at the required conditions for the preparation of thin films. In the present paper we describe the performance and characteristics of this sensor and show how this device can be an effective tool for the monitoring of the deposition rate of silver thin films.
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