A High Sensitivity Gas Sensing Mechanism Based on Mode Localization and Adsorption Expansion

In this article, combining adsorption expansion and mode localization within the linear region, a double sensitivity amplification scheme is proposed for the first time. The gas sensor FEM model adopts a coupled micro clamped–clamped (c-c) beams, in which the sensing beam has center slits embedded with gas sensing film. The gas molecules adsorbed onto the sensing film embedded in center slits will generate an axis compressive stress on the sensing beam to decrease the bending stiffness by expanding the slits, and increase the effective mass of it. Compared to resonant structure without slits, the frequency shift is first amplified by the superposition of the sensing beam’s mass and stiffness changing. Furthermore, by mode localization, the frequency shift can be converted into the modal amplitude variation to achieve the second gas sensitivity amplification. Theoretically, dynamics of the coupled resonator model have been explored using the Galerkin discretization and multiscale method, and the expression of gas sensitivity has been derived. Theoretical results show that a larger absorption expansion coefficient of the functional film results in greater sensitivity amplification. Furthermore, numerical simulations and equivalent experiments have been implemented, which are consistent with the theoretical prediction. In equivalent experiments with 105 mg masses, the amplitude ratio sensitivity is 0.0202 per mg, while the relative frequency change sensitivity is 0.000976 per mg. Thus, a significant improvement in sensitivity is realized. This work not only opens a new avenue in applications of mode localization, but also provides a new metrological scheme for ppb level gas detection.