Novel readout electronics for TSM viscosity sensors

In this contribution, we describe a novel electronic readout circuit for TSM resonators, which can be used, e.g., for viscosity sensing in liquids. 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 synchronous detector. The sensor is externally fed by a voltage controlled oscillator, which is tuned to the fundamental resonance 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 can be used as output signals providing a measure for the viscosity.