Date of Award

Spring 5-4-2018

Level of Access

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical and Computer Engineering

Advisor

Mauricio Pereira da Cunha

Second Committee Member

Nuri Emanetoglu

Third Committee Member

Donald Hummels

Additional Committee Members

Robert Lad
John Vetelino

Abstract

High-temperature, harsh-environment static and dynamic strain sensors are needed for industrial process monitoring and control, fault detection, structural health monitoring in power plant environments, steel and refractory material manufacturing, aerospace, and defense applications. Sensor operation in the aforementioned extreme environments require robust devices capable of sustaining the targeted high temperatures, while maintaining a stable sensor response. Current technologies face challenges regarding device or system size, complexity, operational temperature, or stability.

Surface acoustic wave (SAW) sensor technology using high temperature capable piezoelectric substrates and thin film technology has favorable properties such as robustness; miniature size; capability of mass production; reduced installation costs; battery-free operation; maintenance-free; and offer the potential for wireless, multi-sensor interrogation. These characteristics are very attractive for static and dynamic strain sensors targeted to operate in high-temperature harsh-environment conditions. The investigation of harsh-environment static and dynamic SAW strain sensors requires addressing the issues of: (i) sensor platform endurance and stability; (ii) development of durable packaging and attachment techniques; (iii) temperature compensation techniques, to mitigate temperature cross-sensing; and (iv) methods of sensor interrogation and calibration at high temperatures.

In this work, langasite-based SAW resonator (SAWR) sensors have been investigated. A stable sensor platform was verified for two types of thin-film electrode configurations, namely: co-deposited Pt/Al2O3 (up to 750oC) and multilayered PtNi|PtZr (up to 1000oC). High-temperature sensor attachment solutions for strain sensor applications were developed for temperatures up to 500oC. The developed SAWR sensors were tested and calibrated for both static and dynamic strain up to 400oC. A temperature compensation technique and a novel finite element analysis was used to perform high-temperature static strain calibration. A high-temperature dynamic strain test rig using a constant stress beam was designed, implemented and used to characterize the SAWR strain sensor performance in measuring dynamic strain. Using the in-phase and quadrature strain sensor signal analysis technique proposed and developed in this study, the existence of both amplitude and frequency modulations of the SAWR RF signal by the dynamic strain signal was confirmed, and the two types of modulations separated and quantified.

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