Hollow-waveguide-based carbon dioxide sensor for capnography

Abstract

A CO 2 sensor for capnography, based on a hollow waveguide (HWG) and tunable diode laser absorption spectroscopy (TDLAS), is presented; the sensor uses direct absorption spectroscopy and requires neither frequent calibration nor optical filters, giving it a significant advantage over existing techniques. Because of the HWG, the CO 2 measurement achieved a concentration resolution of 60 ppm at a measurement rate of 25 Hz, as characterized by Allan variance. The length of the HWG was selected to efficiently suppress the optical fringes. This setup is perfectly suited for the detection of CO 2 by capnography, and shows promise for the potential detection of other breath gases.

Mid-Infrared Tunable Laser-Based Broadband Fingerprint Absorption Spectroscopy for Trace Gas Sensing: A Review

“…Recently, new types of gas cells have been developed to achieve long optical path in a smaller volume, including modified MPCs [111][112][113][114][115][116], circular multi-reflection (CMR) cells [117][118][119][120][121][122][123][124], and HWG [32,63,69,[125][126][127][128]. Guo and Sun reviewed the progress in modified MPCs and CMR cells and compared them in terms of optical pathlength (OPL), volume, and path-to-volume ratio (PVR) [116].…”

Compact Hollow Waveguide Mid-Infrared Gas Sensor For Simultaneous Measurements of Ambient CO2 and Water Vapor

“…Detection limit of the HWG based sensor may be improved significantly by increasing the length of optical path via increasing length of the HWG or placing two dielectric mirrors with modest reflectivity at the two ends of the HWG to build a multi pass cavity. [14] 3337 nm WMS 2f 5 m 164 s 7.4×10 -6 (CH3SCH3) [15] 3392 nm WMS 2f 5 m 295 s 3.6×10 -5 (CH3SH) [16] 3392 nm WMS 2f/1f 75 cm 9 s 5.2×10 -6 (CH4) [17] 2003 nm DAS 12 cm 3 s 1.2×10 -5 (CO2) [18] 3393 nm DAS 5 m 1.84 s 1. To evaluate the response time of the HWG gas sensor, the dynamic measurements of about 30 minutes with an average time of 1 s for different diluted CO 2 concentrations are shown in Fig.…”

“…The HWG was first proposed by Garmire et al [9] in 1976. It has been continuously evolved and spread to numerous applications [10][11][12][13][14][15][16][17], and is generally defined as a capillary tube whose core is air and surrounding has a refractive index higher than 1.0. In order to reduce the light propagation loss, the HWG is usually coated with a metallic layer of Ag on the inner wall of the silica glass tubing [18] and then a dielectric layer of AgI over the metal film [19].…”

“…The hollow waveguide (HWG), serving as light guides and gas transmission cell simultaneously, are an elegant alternative to address both requirements, hence has been regarded as a valuable gas absorption cell for TDLAS based measurements. Compared with traditional folded gas cell, a HWG cell has a low internal volume (several milliliters) and the extended optical path (several meters) with low cost [15], which causes faster response times (several seconds) [16] and high sensitivity. Furthermore, the HWG can be coiled into relatively small spaces to save gas cell space [20].…”

Simultaneous measurement of gas distribution in a premixed flame using adaptive algebraic reconstruction technique based on the absorption spectrum

“…In combustion research, the distributions of temperature and concentration are quite important for on-line measurement. However, traditional line-of-sight TDLAS can only get the average values of temperature and concentration along a direction of the laser path [5][6][7] . Recently, many computerized tomography (CT) methods combined with TDLAS have been used to reconstruct the spatial distributions of temperature and gas concentrations in combustion research.…”