Optical sensing elements for nitrogen dioxide (NO2) gas detection, a sol-gel method for making the sensing elements and fiber optic sensors incorporating nitrogen dioxide gas optical sensing elements
First Claim
1. A nitrogen oxide sensor comprising:
- a nitrogen oxide sensing element made by a method comprising;
incorporating a diazotizing reagent which reacts with nitrous ions to produce a diazo compound and a coupling reagent which couples with the diazo compound to produce an azo dye into a sol; and
allowing the sol to gel;
wherein the gel comprises a microporous optically transparent inorganic matrix comprising immobilized diazotizing reagent and immobilized coupling reagent;
a light source; and
an optical detector;
wherein the sensing element is coupled to the light source by one or more transmitting optical fibers and wherein the sensing element is coupled to the detector by one or more receiving optical fibers such that light from the light source is transmitted through the one or more transmitting optical fibers and impinges on the sensing element and light impinging on the sensing element is transmitted through the one or more receiving optical fibers to the detector;
wherein the sensing element is in the form of a film;
wherein ends of the transmitting and receiving fibers adjacent the sensing element are bundled into an optical fiber cable having a planar cable end adjacent the sensing element, and wherein the planar surface of the film sensing element is oriented at an angle to the planar cable end adjacent the sensing element; and
wherein the angle of orientation of the film sensing element to the planar cable end is the Brewster'"'"'s angle (β
B) as calculated from the refractive index of the sensing element (n2) and the refractive index of the medium through which the light travels before impinging on the sensing element (n1) as set forth below;
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Abstract
A sensing element, a method of making a sensing element, and a fiber optic sensor incorporating the sensing element are described. The sensor can be used for the quantitative detection of NO2 in a mixture of gases. The sensing element can be made by incorporating a diazotizing reagent which reacts with nitrous ions to produce a diazo compound and a coupling reagent which couples with the diazo compound to produce an azo dye into a sol and allowing the sol to form an optically transparent gel. The sensing element changes color in the presence of NO2 gas. The temporal response of the absorption spectrum at various NO2 concentrations has also been recorded and analyzed. Sensors having different design configurations are described. The sensing element can detect NO2 gas at levels of parts per billion.
12 Citations
21 Claims
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1. A nitrogen oxide sensor comprising:
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a nitrogen oxide sensing element made by a method comprising; incorporating a diazotizing reagent which reacts with nitrous ions to produce a diazo compound and a coupling reagent which couples with the diazo compound to produce an azo dye into a sol; and allowing the sol to gel; wherein the gel comprises a microporous optically transparent inorganic matrix comprising immobilized diazotizing reagent and immobilized coupling reagent; a light source; and an optical detector; wherein the sensing element is coupled to the light source by one or more transmitting optical fibers and wherein the sensing element is coupled to the detector by one or more receiving optical fibers such that light from the light source is transmitted through the one or more transmitting optical fibers and impinges on the sensing element and light impinging on the sensing element is transmitted through the one or more receiving optical fibers to the detector; wherein the sensing element is in the form of a film; wherein ends of the transmitting and receiving fibers adjacent the sensing element are bundled into an optical fiber cable having a planar cable end adjacent the sensing element, and wherein the planar surface of the film sensing element is oriented at an angle to the planar cable end adjacent the sensing element; and wherein the angle of orientation of the film sensing element to the planar cable end is the Brewster'"'"'s angle (β
B) as calculated from the refractive index of the sensing element (n2) and the refractive index of the medium through which the light travels before impinging on the sensing element (n1) as set forth below; - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A nitrogen oxide sensor comprising:
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a film sensing element comprising a microporous matrix of an optically transparent material, a diazotizing reagent which reacts with nitrous ions to produce a diazo compound and a coupling reagent which couples with the diazo compound to produce an azo dye; a light source; and an optical detector; wherein the sensing element is coupled to the light source by one or more transmitting optical fibers and wherein the sensing element is coupled to the detector by one or more receiving optical fibers such that light from the light source is transmitted through the one or more transmitting optical fibers and impinges on the sensing element and light impinging on the sensing element is transmitted through the one or more receiving optical fibers to the detector; wherein ends of the transmitting and receiving fibers adjacent the sensing element are positioned on the same side of the film sensing element; wherein the film sensing element is positioned such that light impinging on the sensing element is reflected by the sensing element into one or more receiving fiber ends; wherein ends of the transmitting and receiving fibers adjacent the sensing element are bundled into an optical fiber cable having a planar cable end adjacent the film sensing element, and wherein the planar surface of the film sensing element is oriented at an angle to the planar cable end adjacent the sensing element; and wherein the angle of orientation of the film sensing element to the planar cable end is the Brewster'"'"'s angle (β
B) as calculated from the refractive index of the sensing element (n2) and the refractive index of a medium through which the light travels before impinging on the sensing element (n1) as set forth below; - View Dependent Claims (21)
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Specification