A transverse shear model of a piezoelectric chemical sensor

This model of a transverse shear-mode piezoelectric quartz-crystal chemical sensor is based on the fundamental equations of motion and piezoelectricity. The geometry includes the crystal as well as a metal electrode and a polymeric sensing layer immersed in a fluid medium. All of these are considered to be viscoelastic materials, and slip at the three interfaces is included. The model is shown to agree well with both experimental data and published correlations of the series resonant frequency and equivalent series resistance under both mass and liquid loading. In addition, the mechanical resonant behavior is also calculated. The interfacial slip parameter and the complex shear viscosity are shown to be mathematically interchangeable but not physically equivalent. Negative elastic coefficients obtained from the slip parameters for less viscous fluids suggests that interfacial slip is an important process, which dominates viscoelastic effects for these fluids. (C) 1998 American Institute of Physics.