UDC 621.373.826
EXHALED AIR ANALYZER: NOISE AND INTERFERENCE REDUCTION
E. Y. Khadzhiyskaya, post-graduate student, RTU MIREA, Basic Department No. 343 Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russia;
orcid.org/0000-0002-9115-9871, e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
E. V. Stepanov, Dr. in physics and mathematics, Professor, Head of Department, Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russia;
orcid.org/0000-0002-9297-4093, e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
This study presents the method for enhancing the sensitivity of weak resonant absorption detection in exhaled air using tunable diode lasers (TDLAS) operated in a pulse-periodic mode. The aim of the work is to minimize the influence of white noise and interference effects in the process of measuring carbon dioxide isotopic ratio (δ13CO2) in breath samples. The characteristics of distributed feedback TDL being used in the experiments are described along with the techniques for noise suppression and measurement accuracy im provement including hardware approaches (signal averaging, differentiation, integration, laser selection, and optical alignment) and software methods (Fourier filtering and numerical differentiation). Experimental studies to evaluate the dependence of signal-to-noise ratio on the number of optical reflections and accumu lation cycles were conducted. Six reflections and 200 accumulations are established to provide the optimal balance between extended optical path length and minimized interference distortions. The results confirm the effectiveness of proposed approach and demonstrate the potential of TDL-based systems for non-invasive, high-precision, and highly sensitive analysis of isotopic composition of exhaled carbon dioxide.
Key words: : tunable diode laser, pulse-periodic mode, δ13CO2, exhaled breath, noise, Fourier filtering, gas analysis.