Abstract
One of the major issues in the use of the resonant photoacoustic cell is the resonance frequency of the cell. The frequency is not stable, and its changes depend mostly on temperature and gas mixture. This paper presents a new method for tracking resonance frequency, where both the amplitude and phase are calculated from the input samples. The stimulating frequency can be adjusted to the resonance frequency of the cell based on the phase. This method was implemented using a digital measurement system with an analog to digital converter, field programmable gate array (FPGA) and a microcontroller. The resonance frequency was changed by the injection of carbon dioxide into the cell. A theoretical description and experimental results are also presented.
Highlights
Photoacoustic (PA) spectroscopy is widely used for tracing gas analysis [1,2]
The resonance frequency is affected by the environmental parameters and the chemical composition of the gas mixture
The input signal from the converter is mixed with the signal generated by the numerical control oscillator (NCO)
Summary
Photoacoustic (PA) spectroscopy is widely used for tracing gas analysis [1,2]. The influence of noise becomes more significant when the concentration of target gas decreases. Any acoustic fluctuation picked up by the acoustic sensor (typical microphone) might be recognized as a PA signal. It can be a signal either from the measured. Selected papers from Third Conference on Photoacoustic and Photothermal Theory and Applications
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