Novel analog readout electronics for microacoustic thickness shear-mode sensors

In this paper, a novel purely analog electronic readout circuit for sensors based on thickness shear-mode (TSM) resonators is introduced. This system can, e.g., be used for viscosity sensing of liquids, even if the liquid shows a comparatively high viscosity. In contrast to conventionally utilized oscillator circuits, the present circuit eliminates the disturbing influence of the static capacitance of the sensor by means of a dedicated synchronous detector circuit. The sensor is externally driven by a voltage-controlled oscillator (VCO), which is tuned to the resonator's fundamental frequency by means of a control circuit utilizing a frequency modulation of the VCO signal. When the control loop has settled, either the obtained resonance frequency or the damping of the sensor, which is indicated by means of a DC output voltage, can be used as the output signal providing a measure for the viscosity.