DUAL-HARMONIC OSCILLATOR FOR ENHANCED SENSING WITH QUARTZ RESONATOR SENSORS

An oscillator circuit is proposed that simultaneously excites and tracks two harmonic resonances in a quartz crystal resonator (QCR) sensor. By probing the resonator at two harmonic modes at the same time, enhanced sensing capabilities can be conveniently achieved because a larger set of parameters can be measured with a single sensor. The circuit also provides compensation of the sensor parallel capacitance for increased accuracy. The oscillator was tested with 5-MHz AT-cut crystals simultaneously operated at the fundamental and third harmonic in contact with solutions of different density-viscosity products. The results show an excellent agreement between the oscillator readings and reference measurements taken with an impedance analyzer.