Abstract
Photoacoustic gas sensing is a method suited for the detection of radiation absorbing molecular species in the gas phase. Due to the backgroand-free detection, it has considerable benefits in the measurement of very low concentrations down to the parts-per-trillion range. Yet in resonant systems, the resonance frequency depends on several parameters like temperature or gas composition and therefore must be continuously determined. In the present work, we propose a new method of tracking the resonance frequency using a photoacoustic signal generated at the walls of the resonant cell. The method has been evaluated with two different photoacoustic setups intended for the detection of NO(2). We further propose an algorithm for finding the resonance frequency and evaluated the performance thereof. With this method, it is possible to detect the resonance frequency of a cylindrical and a dumbbell-shaped cell in less than two seconds and with an accuracy < 0.06% and < 0.2%, respectively.