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The paper presents a new contribution to the design of quartz crystal oscillators for high sensitivity microbalance sensors used in liquid media. The oscillation condition for the Miller configuration was studied in order to optimize the values of the components to obtain oscillators for use in extreme conditions of damping. The equations relating the value of the active and passive components with the maximum supported damping and detected mass were obtained. A CAD tool was developed to help users in the design of microbalances adapted to the application requirements. To increase the mass sensitivity, four optimized microbalance circuits at augmenting frequencies were developed. The components of the circuits were optimized in order to maintain the oscillations in a wide dynamic range of resonator losses. A calibration of the sensors was made. To determine the real sensitivity of the mass sensors, the frequency noise was studied.