Results

Main results for sensor system S1 (grain size discrimination)

The team proposed two different methods for the discrimination of the dust grain size: method 1 consisted in an array of different QCMs driven by different currents (or voltage) to modulate the amplitude of the oscillation; method 2 consisted in the implementation of resonant microstructures on the sensor surface (i.e. the electrode).

For Method 1, an optimised mixture of ethanol and deionised water was identified as the best medium for dispersing the micro particles during laboratory testing, to ensure uniform layers. The results show that for each sensor in the array, the sensitivity to microparticles size is modulated by both resonating frequency and oscillation amplitude. In particular for the 2 um: using 20 MHz QCM at driven voltage > 1 V the sensitivity is negative (the sensor response is negative).  In the case of 10 um: the response of 20 MHz is closed to zero. While in the case of 10 MHz if a driven voltage > 2 V the response is negative but in a driven voltage < 1.5 V it shows a good response. In conclusion, it is possible to achieve the discrimination of the particulate size by using an array of crystals operating at different frequencies by properly tuning the oscillation amplitude.

For Method 2, the team studied by FEM analysis the behaviour of the SU8 (that is the resin) microstructures on the sensor surface to improve the adhesion of larger particles. Different analytical models were developed to identify the optimal geometries to ensure that these structures do not interfere with the crystal main vibration frequency.

Main results for sensor system S2 (high temperature TGA)

The team originally identified GaPO4 for the sensor system S2 because of its exceptional thermal stability and high electromechanical coupling, which offers superior sensitivity in comparison to quartz. However, due to the extreme fragility of the GaPO4 crystals bought from one of the few suppliers and the lack of availability of GaPO4 raw crystals worldwide, the team has studied a different strategy, exploiting quartz to higher temperatures with respect to current use (up to 100-120°C).

The new quartz crystals (IT-cut) were tested in laboratory environment up to 250°C, showing their suitability for higher temperature applications compared to standard AT-cut crystals. IT-cut crystals provide a smoother frequency response and a stable plateau around 100°C.

More detailed results will be shared after the publication of the articles.