Localised heating effects on AT-cut Quartz Crystal Microbalances: Experimental characterisation through admittance measurements

The research focuses on the experimental characterisation of the effect of localised heating on the sensing area for 5 MHz AT-cut Quartz Crystal Microbalances (QCMs). Through contactless temperature and admittance measurements, the work explores the performance of the QCMs under challenging conditions, up to about 300 °C, and analyses the trends and magnitudes of the admittance modulus and phase changes with respect to temperature. Experimental results show that all tested QCMs experienced irreversible oscillation loss well below the Curie temperature, providing weak oscillation amplitudes beyond 250 °C and a permanent failure before 305 °C, despite maintaining their mechanical integrity; furthermore, it is found that the oscillation loss is independent of any ageing effects. Infrared imaging confirms that surface temperatures never exceed 300 °C, indicating that oscillation loss is driven by thermal gradients rather than intrinsic material limitations. Localised heating also induces sharper resonance frequency shifts at high temperatures and steep thermal gradients, resulting in shifts of the oscillation frequency about 50% higher than what is measured under uniform heating. These findings highlight the impact of non-uniform temperature fields on AT-cut QCMs operation, leading to signal loss that should be overcome by proper accommodation strategies aiming to minimise the thermal gradient during operative conditions.