Improved Electronic Interfaces for Heavy Loaded AT Cut Quartz Crystal Microbalance Sensors

A new configuration of an automatic capacitance compensation (ACC) technique based on an oscillator-like working interface, which permits the tracking of the series resonant frequency, the monitoring of the motional resistance and the parallel capacitance of a thickness-shear mode (TSM) quartz crystal microbalance (QCM) sensor, is introduced. The new configuration permits an easier calibration of the system which, in principle, improves the accuracy. Experimental results are reported with 9 and 10 MHz crystals in liquid with different parallel capacitances which demonstrate the effectiveness of the capacitance compensation. Some frequency deviations from the exact series resonant frequency, measured by an impedance analyzer, are explained by the specific non idealities of the circuit. A tentative approach is proposed to solve this problem that is also common to previous ACC systems.