Design and characterization of an active bridge oscillator as a QCM sensor for the measurement of liquid properties and mass films in damping media

This work presents the design and characterization of a 9MHz active bridge oscillator circuit for use as a high resolution quartz crystal microbalance sensor for liquid applications. During the design process, several simulations were run with a general-purpose circuit simulation program (PSpice) in order to predict the behavior of the sensor in different operating conditions such as mass film deposition on the quartz electrode or immersion of the sensor in a Newtonian liquid. Sensitivity coefficients of the oscillation frequency to mass changes on the surface of the resonator and changes in the density and viscosity of the liquid are obtained from the Pspice simulations and compared with the experimental ones obtained from calibration trials. To complete its characterization, the frequency stability in the time domain is determined and the resolution of the sensor is obtained. Finally, the performance of the oscillator is compared with that of a 9MHz Miller oscillator sensor, a topology previously studied by this group.