A Fast Resonance Frequency Tracking Method for Photoacoustic Cell Based on the Hybrid Single-Frequency Excitation and FFT

Abstract

The resonance photoacoustic (PA) cell has a resonance enhancement effect and higher resonance frequency. It can significantly improve the signal-to-noise ratio of PA gas detection. However, in resonance PA gas detection, the resonance frequency of the PA cell mainly depends on the gas composition, temperature, and pressure and therefore must be continuously tracked and measured. A fast resonance frequency tracking method for PA cell based on the hybrid single-frequency excitation and the fast fourier transform (FFT) is proposed. The hybrid single-frequency serves as the excitation signal. The FFT is used to collect the spectral data of all frequencies within a certain bandwidth. Under the same conditions, the resonance frequency is measured by sweep frequency and hybrid single-frequency. The experiments show that the resonance frequency tracking time in the 200?Hz bandwidth is 200?s by sweep method. The hybrid single-frequency takes only 1.1?s, which is only 0.55% of the sine sweep tracking time. The accuracy of frequency tracking can reach 1?Hz. In the long-term stability test, the resonance frequency fluctuation is less than?±?1?Hz, and its standard deviation (1 \(\sigma\)) is 0.5681?Hz. This method provides a quick and accurate method for determining the resonance frequency of the resonance PA cell.