Equivalent Circuit Models for Magnetoelastic Resonance Sensors With Various Surface Loadings

Sensors based on the magnetoelastic (ME) effect have been developed for various applications, such as food safety, immunoassays, and health monitoring. A major obstacle to the widespread adoption of ME sensors is the poor understanding of the electrical impedances that constitute the system and how these impedances are influenced by surface loadings. Here, we derive a lumped-element model to approximately predict the near-resonance electrical behavior of an ME sensor simultaneously loaded with a mass layer and a semi-infinite Newtonian liquid. For more extensive applicability, a hybrid model, combining a modified Butterworth–Van Dyke (mBVD) model and a transmission line model, is derived for the first time to predict the response of the ME sensor under various surface conditions, including rigid solids, fluids, viscoelastic media, or any combinations thereof. The theoretical models are experimentally verified for accuracy and used to quantitatively analyze the mass, viscosity, and modulus of loadings by extracting the electrical parameters. This modeling work is crucial for the development of ME sensors in various applications and for providing insights into the physical mechanisms of advanced devices.