Small-Volume Hollow Cell-Based High-Sensitivity Cantilever-Enhanced Photoacoustic Gas Analyzer

A small-volume hollow cell-based fiber-optic photoacoustic gas analyzer is proposed for high-sensitivity gas detection. The cell has overall dimensions of 54 × 54 × 148 mm, making it much shorter than conventional H-type photoacoustic cells with the same resonant tube length. Its internal air domain accounts for 91% of the volume of the minimum bounding box, while the equivalent ratio for traditional H-type cells is only approximately 50%. The hollow configuration not only maximizes the internal space utilization of the gas cell but also enhances the photoacoustic excitation efficiency. Finite element simulation results verify that the optimized hollow structure improves the photoacoustic signal amplitude by 39% compared with the conventional H-type cell under the same external dimensions. To further improve the performance of the gas analyzer, a fiber-optic cantilever microphone and a multipass cell are integrated into the photoacoustic cell. The performance has been verified via the detection of CH4. The response time of the gas analyzer with different gas inlets and outlets is analyzed using a finite element method and determined experimentally. The shortest response time reaches 17 s. The system achieves a minimum detection limit (MDL) of 6.5 ppb at 1 s averaging time, with a normalized noise equivalent absorption (NNEA) coefficient (NNEA) of 6.7 × 10-11 cm-1 W Hz-1/2. This work presents a feasible and effective strategy for developing a compact, high-sensitivity gas analyzer by synergistically optimizing the photoacoustic cell geometry.