Date of Award

Spring 5-13-2017

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science in Electrical Engineering (MSEE)

Department

Electrical and Computer Engineering

Advisor

John F. Vetelino

Second Committee Member

Mauricio Pereira da Cunha

Third Committee Member

Nuri Emanetoglu

Additional Committee Members

Jan H. Kuypers

Abstract

One of the most popular acoustic sensing platforms used for applications related to the environment, human health, agriculture, and homeland security is the quartz crystal monitor (QCM) which employs a piezoelectric resonator upon which a target selective film is deposited. These target selective films are designed to interact with a target analyte to cause a change in the resonance characteristics of the piezoelectric device. The crystallographic orientation and substrate material used in the QCM is the AT-cut of quartz which possesses a temperature stable transverse shear mode (TSM). The acoustic mode displacements in a TSM are normal to the propagation direction and minimal energy is lost from the sensor platform when the sensor is placed in contact with a gas or liquid. While the QCM platform is well suited to gas and liquid sensing applications in liquid media it does have some significant drawbacks. These drawbacks include low electromechanical coupling and an insensitivity to electrical property changes in the target selective film. The QCM’s insensitivity to electrical property changes is due to the placement of the exciting electrodes which cause the exciting electric field to be perpendicular to the sensor faces and confined within the quartz sensor resulting in what is what is commonly called thickness excitation (TE). These aforementioned drawbacks have provided the motivation to investigate other common piezoelectric crystalline materials such as lithium tantalate (LiTaO3) and lithium niobate (LiNbO3) as well as an alternative electrode orientation called lateral excitation (LE). LiTaO3 and LiNbO3 are known to have significantly higher electromechanical coupling than quartz while utilization of LE enables the platform to be sensitive to electrical property changes in a target selective film. A numerical study as well as experimental measurements have been performed to determine orientations of LiTaO3, LiNbO3, and quartz that, under LE, have high electromechanical coupling to TSM modes.

Other practical concerns related to the development of a novel sensor platform have been considered. One concern addressed is the acoustic mode’s resonance frequency stability with respect to changes in the ambient temperature which is commonly referred to as the temperature coefficient of frequency (TCF). Finally, potential methods for the reduction or elimination of unwanted and interfering resonant acoustic modes adjacent to the primary acoustic mode have also been explored.

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