Specifically designed lateral field excited (LFE) quartz crystal resonator sensors have been applied to liquids with systematically varied acoustic and electrical properties. Dramatic changes in the conductance spectrum including an extraordinary shift of the resonance frequency have been found when the bare sensing surface of the crystal is exposed to water [1]. It will be shown that the sensitivity to electrical properties of the liquid becomes effective via changes in the acoustic properties of the crystal and therefore appears in the complete admittance spectrum. Finite element simulations supporting this conclusion are presented in [2]. Here we report about the contributions of liquid density/viscosity and liquid permittivity to the sensor signal. Since the contributions superimpose, an empirical scheme could be developed to separate the mechanical from the electrical properties of the liquid.
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