Fiber-optic evanescent wave sensor for gas detection

Abstract

A novel fiber-optic evanescent wave sensor is presented. The sensor, composed of a lead salt tunable infrared laser and a multimode uncladded silver halide infrared optic fiber, was used for rapid measurement of sulfur hexafluoride pressures at a few-percent detection limit. High-precision detection and identification of a large variety of gases are possible.

Theory of fiber-optic, evanescent-wave spectroscopy and sensors

“…Three different apparatuses, A-C in our nomenclature, were considered, and parameters were taken from experimental data. 10,15,18 The integration of Eq. 112 was carried out along the following lines with an eight-point Gauss-Legendre integration scheme.…”

“…This method has the advantages of fast, real-time, in situ, selective, nondestructive, and safe detection. It has been successfully employed in a variety of configurations for studies of solid-liquid interfaces, 3 chemical reaction rates, 4 complex material curing, 5 organometallic thin films, 6 liquid 7-10 and gas [11][12][13][14][15] detection and monitoring, concentration measurements, [16][17][18][19] and biological applications. 20,21 Usually the sensing elements are installed in a Fourier-transform IR 1FTIR2 spectrometer system, but recently tunable lasers were incorporated into FEWS systems 10,22 instead of conventional blackbody sources.…”

A fiber-optic methane gas sensor system with improved accuracy using absorption-spectrum matched comb filter

“…Among those fiber-optic gas sensors, the infrared (IR) absorption spectroscopy is the most promising one [3,4], as it has many advantages including high sensitivity and gas selectivity, fast response time, robust to the environment disturbance, simple structure and reliable gas cell, and easily to form a sensor network by spatial division multiplexing (SDM) [4], time division multiplexing (TDM) [5], or wavelength division multiplexing (WDM) [6], etc. Fiber-optic evanescent wave spectroscopy based on the attenuated total-internal-reflection effect has also become a popular choice in IR absorbance spectroscopy for the environment monitoring [7]. Though they can achieve fast measurement response, they suffered from low system sensitivity and had poor mechanical stability.…”

An Infrared Evanescent Wave Sensing System Coupled with a Hollow Fiber Membrane for Detection of Volatile Organic Compounds in Aqueous Solutions

“…[1][2][3][4][5] Applying evanescent waves to FT-IR spectrometers offers the advantages of ease of operation and simple handling of aqueous samples. This technique is suited to the analysis of aqueous samples because the evanescent field penetrates only a very short distance (dp), which can be estimated 1 by the equation dp = λ/{2πn1[sin 2 θ -(n2/n1) 2 ] 1/2 }…”