QCM-Micropillar-based coupled resonators in the detection of gas mass flow rates

We report the discovery of a micropillar-based quartz crystal microbalance (QCM) coupled resonator sensor (CRS) in detecting flow rates of gases with different densities. The fabricated QCM CRS was housed in a stainless steel chamber and the resonance frequency changes associated with gas flow at small values of mass flow rates inside the chamber were measured. Argon and helium were used as the test gases. The results obtained revealed an extraordinary sensitivity to mass flow rate changes under room temperature and flow rates as low as 20 sccm. Moreover, the QCM-CRS system was able to differentiate the densities of the two gases. Identical experiments conducted using a bare QCM showed that the mass flow rates had negligible effects on the QCM resonance frequency response. Thus, it is evident that a coupled resonance phenomenon plays a significant role in enabling the QCM to be sensitive to small mass changes caused by differences in flow rates. We propose that the QCM-CRS system can be used as a new class of mass flow sensing element, especially for flow measurement in vacuum processing systems.