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. 2022 Feb 7;22(3):1251. doi: 10.3390/s22031251

Figure 12.

Figure 12

Physical origin of frequency-based humidity sensor using QCM. (a) Before and (b) after the adsorption of water molecules on QCM. The resonant frequency of the mechanical oscillating substrate is shifted by the adsorption. The advantage of this method is to evaluate the mass of adsorbed water molecules directly.