Non-dispersive infrared multi-gas measurements in challenging environments
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URL
Journal Title
Journal ISSN
Volume Title
Sähkötekniikan korkeakoulu |
Master's thesis
Authors
Date
2019-05-06
Department
Major/Subject
Advanced Materials and Photonics
Mcode
ELEC3035
Degree programme
NanoRad - Master’s Programme in Nano and Radio Sciences (TS2013)
Language
en
Pages
111+7
Series
Abstract
This research examined the performance of a prototype optical gas measurement device utilizing non-dispersive infrared (NDIR) measurement principle. It was compared to several of its competitor devices. Parameters such as response time, accuracy, cross-sensitivity and spectral width of infrared bandpass filters were measured. The prototype has tunable optical filters that are electrostatically controlled Fabry-Perot interferometers (FPI). They are primarily designed for DC drive that restricts the maximum physical and spectral tuning distance. It was examined how much spectral range increase can be gained by driving certain FPIs with AC signal instead of DC signal. Finally, three wide band thin film infrared bandpass filters were designed, simulated and optimized. They are intended to cover the longer spectral range that a possible future AC driven FPI might use. Compared to its competitors, the prototype device was found to have a good measurement accuracy in gas mixtures. It was also found to have the lowest cross-sensitivity between two main application gases compared to the other devices. The response time of prototype device was slower compared to some of the competitors. It was found possible to control the FPIs designed for DC operation with AC driving signal. The best attained spectral range increase was some 18% but required excessively large control voltages. The performance increase was relatively good but AC drive with high voltages is impractical to incorporate into current products. It was deemed that the parasitic capacitance of the current FPI microstructure is too large to effectively utilize the range extension benefit of AC drive. Three theoretical bandpass filters were designed from different material combinations. After optimization, the first and the third filters were able to meet the requirements while the second could mostly meet them.Description
Supervisor
Sun, ZhipeiThesis advisor
Heikkilä, AnttiKeywords
infrared technology, optical gas measurement, Fabry-Perot interferometer, ATEX, optical filter design