A Compact Photoacoustic Detector for Trace Acetylene Based on 3-D-Printed Differential Helmholtz Resonators

Photoacoustic cell is an essential core component in a photoacoustic spectroscopy (PAS) gas sensing system, which is used to enhance and measure the absorption-induced acoustic signal. For certain applications, miniaturized photoacoustic cells with tiny inner volumes are preferred to reduce gas consumption. In this article, a photoacoustic cell with inner volume of only 0.5 mL is designed based on differential Helmholtz resonators (DHRs). After an initial simulation stage by the finite element analysis (FEA) based on COMSOL software, the photoacoustic cell is fabricated by 3-D printing. To facilitate laser power coupling, a micro fiber collimator is customized and integrated with photoacoustic cell to guide the laser beam. New concept of photoacoustic detector is proposed and integrated to a PAS system for trace acetylene detection. As a result, an excellent linearity of 0.99999 is achieved in the concentration range of 0-5000 ppm. A 1\sigma sensitivity of 0.13 ppm is measured within a response time of 10 s, the minimum detection limit (MDL) is evaluated to be 0.3 ppm. Allan deviation analysis indicate that the detection sensitivity can be improved to 16.6 ppb at an integration time of 910 s.