IMPEDANCE ANALYSIS OF THICKNESS-SHEAR MODE QUARTZ-CRYSTAL RESONATORS IN CONTACT WITH LINEAR VISCOELASTIC MEDIA

An electromechanical description of the impedance response of thicknes s-shear mode quartz crystal resonators in contact with linear viscoela stic media is presented. Explicit assignments for equivalent circuit p arameters (resistances, inductances, and capacitances), are derived in terms of the properties of the resonant piezoid and damping fluid med ium. The calculation shows that the effect of fluid elasticity is a re duction in both the equivalent resistance and inductance relative to a corresponding viscous bulk. The lower inductance is due to a reduced decay envelope for shear wave propagation into the liquid; in effect, a smaller mass of liquid is ''dragged'' by the crystal. The lower equi valent resistance is due to the combined effect of lower energy dissip ation and enhanced recoverable energy storage within the mechanically active fluid layer near the crystal surface. Comparison of model predi ctions with published results on a variety of undamped, viscously damp ed, and viscoelastically damped crystals shows very good agreement. (C ) 1998 American Institute of Physics. [S0034-6748(98)02906-2]