Evanescent wave fiber-optic CH4/CO2 gas sensing based on porous materials (Conference Presentation)

Methane is a major composition of natural gas and considered as a primary greenhouse gas of high global warming potential. In addition, it is also a hazardous flammable gas turns out to be highly explosive if its concentration level reaches 5 to 15 percent by volume. Carbon dioxide is another significant gas since CO2 corrosion is the most common cause of corrosion in natural gas pipelines. Long distance cost-effective CH4 and CO2 distributed sensing technologies for monitoring natural gas infrastructure are not yet readily available, and early corrosion on-set and low-level methane leak detection is highly desirable that can strengthen the integrity and operational reliability, improve the efficiency, and reduce pipeline emissions, which all advance the economics of natural gas delivery. In this work, two types of gas sensing materials, porous silica and hybrid polymer/metal-organic framework (MOF), are investigated based on evanescent wave absorption sensors consisting of a coreless fiber spliced between two single-mode fibers. The low-loss, low refractive index porous silica and the polymer/MOF material with an improved gas adsorption capability and CH4/CO2 selectivity prepared by the sol-gel dip-coating method are respectively used as coating applied to the surface of the coreless fiber. The effects of optical and morphological properties on the repeatability and sensitivity of fiber-optic evanescent wave sensors are studied from transmittance and reflectance measurements by utilizing laser diodes operating at CH4 and CO2 absorption lines. Distributed fiber gas sensing can benefit from the enhanced evanescent wave light scattering in the porous materials.