A quartz-crystal-sensor oscillator appropriate for highly viscous liquid measurements

This paper describes a sensor oscillator appropriate for quartz crystal microbalance (QCM) based measurements in highly viscous liquids. The oscillator is stabilized by a recently developed impedance transformation QCM filter network which greatly reduces electrical load by the sustaining amplifier. In addition, it provides 0 phase and a well behaved symmetric resonance at the QCM series resonant frequency f_s over three orders of magnitude variation range of the motional resistance R_m. The sustaining amplifier has a constant pure resistive input and output impedance to eliminate phase shifts due to QCM impedance changes with liquid load. Also it allows precise gain and phase control for accurate adjustment of the oscillator frequency at f_s and extraction of R_mmiddot information at the measured liquid load. The oscillator was tested with different water based glycerol solutions in the 40 wt% to 100 wt% range. The worst- case frequency error was within 5 % in this viscosity range.