The Lever oscillator for use in high resistance resonator applications

A series resonator oscillator design that operates over a wide dynamic range of resonator resistance is presented. This resistance range is compatible with in situ resonator sensors used in liquid environments. The Lever oscillator is useful for these applications because of its ability to measure the f₂ and R_m of the resonator. The oscillator´s variable leveraging effect has been shown to be useful for increasing the dynamic range of resonator resistance while maintaining sensitivity at lower resistances. The oscillator´s ability to servo a resonator-impedance phase has been demonstrated, and this phase can be made close to zero degrees by selection of transistor type and/or circuit resistance values. The relationship between the resonator frequency at a given phase with respect to true f_s is discussed along with correction methods. Currently this design is being implemented in a jet-fuel contamination sensory system and in a viscosity-density sensor using bulk wave resonators