Date of Award

2011

Level of Access

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Interdisciplinary Program

Advisor

John Vetelino

Second Committee Member

Douglas Bousfield

Third Committee Member

Fabien Josse

Abstract

The lateral-field excited (LFE) acoustic wave sensor element has been shown to be more sensitive to mass, viscous, and electrical loading than the quartz crystal microbalance. Despite this, no equivalent circuit exists to model the LFE sensor element under simultaneous mechanical and electrical loading by a liquid. In this work an equivalent circuit model of the LFE sensor element loaded with a Newtonian liquid is developed. This equivalent circuit model is the first to model an LFE sensor under liquid loads with lumped elements that relate to the piezoelectric crystal and the material properties of the contacting liquid. The LFE sensor element is examined by solving the coupled-wave equations for the thickness-shear mode in the multi-layered LFE sensor structure, resulting in an expression for the admittance of the LFE sensor element. The effects of liquid perturbations to the admittance of the LFE sensor element are modeled as discrete circuit elements in an equivalent circuit. The model is verified independently by measuring the sensor response of LFE sensor elements with a variety of electrode gap separations, (0.5, 1.0, and 2.0 mm), to changes in liquid viscosity, permittivity, and conductivity. The equivalent circuit model developed is accurate, within ±5%, admittance near the resonant frequency for LFE sensor elements in deionized water. The model predicts the frequency shift of the LFE sensor element to perturbations in the density, viscosity, permittivity, and conductivity of the contacting liquid.

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