Novel magnetic–acoustic resonator sensors for remote liquid phase measurement and mass detection

Electromagnetic excitation of miniaturized acoustic resonator sensors is a novel approach with distinct advantages over piezoelectric resonators. A much wider range of transducer materials can be utilized, and remote excitation of resonant vibrations in a wide variety of different mode shapes is possible. These resonant modes display similar quality factors and characteristics as those in piezoelectric transducers and can be applied for mass detection as well as liquid phase sensing. In this contribution, we focus on the electromagnetic excitation of acoustic face shear mode (FSM) resonators for liquid property sensing. A variety of non-piezoelectric transducer materials has been investigated. For liquid phase sensing, we have found circular face shear mode resonators to be most sensitive to fluid properties, e.g., density and viscosity, while radial flexural plate modes excite compressional waves and are thus most sensitive to fluid volume, or rather the distance to the liquid surface, i.e. liquid level. Experimental results have been compared with an FEM eigenmode analysis and equivalent circuit models providing a better understanding of the generation and detection mechanisms.