ACC oscillator for in-liquid quartz microbalance sensors

An oscillator design is presented that provides accurate tracking of the series resonant frequency of liquid-loaded thickness-shear mode (TSM) quartz microbalance sensors. This is obtained by means of the automatic capacitance compensation (ACC) of the sensor parallel capacitance, without any manual adjustment required The oscillator advantageously outputs three signals respectively related to the sensor series resonant frequency, quality factor, and compensated parallel capacitance. Experimental results are reported that were obtained with 10-MHz crystals double-side immersed into several liquids with different acoustic and dielectric loading levels.