Asymmetric Tongs Induced Frequency Splitting Achieving Simultaneous Two-Component Gas Sensing with a Single Quartz Tuning Fork in Two Independent Resonant Modes

In this paper, a highly sensitive light-induced thermoelastic spectroscopy (LITES)-based dual-gas simultaneous sensor by utilizing an asymmetric quartz tuning fork (AQTF) was reported for the first time. Using a standard commercial QTF as the substrate, the AQTF was constructed through a mechanical assembly-based tuning method. The resonant frequency of the AQTF was theoretically derived, and its resonance characteristics and modal behavior were investigated via finite-element analysis. The results indicate that by introducing an asymmetric configuration, the standard commercial QTF achieves clear resonance frequency splitting into two separate peaks. The corresponding vibration modes are both of the in-plane symmetric type, while the two are mutually independent and exert no interference on each other. This therefore lays a foundation for achieving simultaneous dual-gas sensing with a single QTF. Methane (CH4) and acetylene (C2H2) were chosen as the target to investigate the sensor performance. To enhance the detection sensitivity, a multipass cell with an absorption path length of 40 m was employed, and a transimpedance amplifier was used to amplify the electrical signal generated by the AQTF. When the integration time of the LITES system was increased to 200 s, the minimum detection limits for simultaneous CH4 and C2H2 detection were obtained to be 65.72 and 19.85 ppb, respectively.