Date of Award
Fall 1992
Document Type
Thesis - Restricted
Degree Name
Master of Science (MS)
Department
Electrical Engineering
First Advisor
Josse, Fabien
Second Advisor
Shana, Zack
Third Advisor
Heinen, James A.
Abstract
It is well established that the application of a voltage to an interdigital transducer (IDT) on a piezoelectric substrate generates acoustic waves. The generated waves and the IDT electrical characteristics are a function of the piezoelectric material, orientation, IDT parameters and the adjacent medium. If the adjacent medium is coated with a viscoelastic dielectric film, a change in the IDT transduction characteristics will occur. By measuring the characteristics of the IDT, it may then be possible to quantify the film properties. This property could be used to develop a gas or liquidphase sensor utilizing a single-IDT configuration rather than an acoustic wave sensor utilizing two IDTs in a delay line configuration. In this thesis, the generation of an acoustic wave by an IDT at the interface between a piezoelectric substrate and an isotropic dielectric film is theoretically analyzed. Analytical expressions are obtained for the IDT electrical characteristics which include the radiation resistance, Ra, and the electrostatic capacitance, CT, in terms of the piezoelectric material constants, the IDT parameters, the film dielectric constant, viscoelastic properties and thickness, and wave frequency. It is shown that a single acoustic wave IDT on a piezoelectric substrate can be used to design a detector which could sense the variation of film dielectric constant, viscoelastic properties and thickness. Such variation may occur as the coated IDT is subjected to environmental change and as the film properties change due to a specific absorption. The variation in the IDT electrostatic capacitance, CT, can be used to monitor changes in the film dielectric constant and thickness while the radiation resistance, Ra, can be used to monitor changes in the viscoelastic properties and/or dielectric constant. The piezoelectric material and orientation selected for the study consists of the rotated Y-cut quartz which supports the shear horizontally polarized surface skimming bulk waves. Both the 2F-IDT and 4F-IDT structures were analyzed. The selected range of the film dielectric constant, "formula" and elastic constant, c44, used in the simulation represents typical values and variation of polyimide coating under fluid absorption.
Recommended Citation
Sethupathi, Raja Vel, "A Single-IDT Acoustic Wave Sensor for Viscoelastic Dielectric Film Media" (1992). Master's Theses (1922-2009) Access restricted to Marquette Campus. 4126.
https://epublications.marquette.edu/theses/4126