Tuning fork-cantilever coupled dual-resonance fiber-optic photoacoustic sensor for simultaneous dual-gas detection

We report a fiber-optic tuning-fork-cantilever coupled photoacoustic (TFCC-PA) sensor for the simultaneous detection of methane (CH₄) and acetylene (C₂H₂). The sensor integrates a custom square-head 6063 aluminum-alloy tuning fork (ATF) and a laser-cut polyethylene terephthalate cantilever within a single nonresonant photoacoustic cell. Synchronous dual-channel readout is achieved using two Fabry-Perot (F-P) white-light interferometers combined with frequency-division-multiplexed demodulation. The low-frequency cantilever is suited to slowly relaxing CH₄, whereas the higher-frequency tuning fork is used to detect rapidly relaxing C₂H₂. Following structural optimization using COMSOL Multiphysics, experiments confirmed well-separated operating frequencies with negligible interchannel crosstalk. Both gases exhibited linear concentration responses with R² values of 0.99. At an integration time of 1 s, the detection limits were 6.54 ppm for CH₄ and 1.06 ppm for C₂H₂. Allan-Werle analysis yielded minimum detection limits of 167 ppb and 96.5 ppb, respectively. The proposed TFCC-PA sensor provides a robust and intrinsically safe solution for high-sensitivity multicomponent gas sensing applications.