QCM-D with At-cut Quartz First Spurious Mode: Experimental Characterization under Different Mechanical Loads

Quartz Crystal Microbalance with Dissipation monitoring (QCM-D) is a widely used technique for studying interfacial phenomena, particularly in tribology, thin-film characterization, and biosensing. While conventional QCM-D measurements focus on the fundamental thickness-shear mode, quartz crystals also exhibit spurious resonances that respond differently to external loads. In this work, we propose a novel approach to excite and analyze the first spurious mode of a QCM sensor to assess its sensitivity to mechanical loading. Our results show that, unlike the fundamental mode, the spurious resonance exhibits a non-linear relationship between equivalent inductance and resistance, with its frequency shift increasing significantly under higher loads. This suggests a stronger sensitivity to dissipation and viscoelastic effects at the solidliquid interface. Furthermore, we demonstrate that the proposed method achieves sufficient accuracy (tone estimation standard deviation lower than 1 ppm and resistance estimation standard deviation lower than 1%) using simple signal processing techniques, providing a practical alternative to impedance spectroscopy. These findings highlight the potential of spurious resonances to complement standard QCM-D measurements, offering enhanced capabilities for characterizing thin films, lubricants, and viscoelastic materials.