An Investigation on Observed Positive Frequency Shifts during Gas Uptake for Coupled Resonators

This work reports positive frequency shift behavior of zeolitic imidazolate framework-8 (ZIF-8)-coated coupled resonators during gas uptake, contrary to the expected negative frequency shift behavior. A hypothesis that the gas uptake induced both mass and stiffness perturbations to the coupled resonators is proposed. The mutual effect of simultaneous mass and stiffness perturbations on a coupled resonator system is explored. A new scheme combining frequency difference and out-of-phase amplitude ratio with a dual in-phase drive is proposed to effectively decouple the influence of mass perturbation from simultaneous stiffness perturbation. The measured results of the ZIF-8-coated coupled resonators agreed with the theoretical analysis based on the hypothesis, which verified the hypothesis and explained the positive frequency shift behavior.