Cantilever-Enhanced Photoacoustic Spectroscopy: Simultaneous Demodulation of Resonant and Nonresonant Signals for the Measurement of Dual SF₆ Decomposition Components

Photoacoustic spectroscopy (PAS) gas sensing systems are generally classified into resonant and nonresonant types. However, it remains unclear whether signals at both resonant and nonresonant frequencies can be demodulated by one demodulation channel and one pass cell to achieve the simultaneous detection of two target molecules. In this study, a cantilever-enhanced photoacoustic (PA) gas detection system was utilized to measure H₂S and CO₂, both of which have been identified as typical fault gases in SF₆ gas-insulated electrical equipment. The vibration modes of the cantilever beam at its first resonant and nonresonant frequencies were simulated and analyzed. Utilizing a laser interferometer, the vibration signals of a cantilever beam were measured. The results confirm that the resonant and nonresonant components of the vibration signal can be demodulated simultaneously. Gas detection experiments were conducted using a cantilever beam-based PAS gas sensing unit. Measurements in the ternary gas mixtures demonstrated the feasibility of simultaneously detecting H₂S and CO₂ by extracting components at 34 and 349 Hz. The PA signals exhibited a strong linear relationship with the gas concentrations, and the detection limits of H₂S and CO₂ are 2.55 and 84.69 ppm, respectively.