Date of Award

Winter 12-16-2022

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Electrical Engineering (MEE)

Department

Electrical and Computer Engineering

Advisor

Mauricio Pereira da Cunha

Second Committee Member

Robert Lad

Third Committee Member

Donald Hummels

Additional Committee Members

Senthil Vel

Abstract

Static and dynamic strain sensing is needed in high-temperature, harsh environment applications for structural health monitoring, condition-based maintenance, process efficiency monitoring, and operator safety in power plants, oil wells, metallurgy, aerospace, and automotive industries. Some challenges for sensors in these environments include device integrity, stability, mounting, packaging, and data acquisition techniques. In addition, it is desirable for sensors in high-temperature harsh-environments to be compact, operate without a battery, and have wireless interrogation capabilities so that they can be installed in small, hard-to-reach locations that otherwise could not be monitored.

Surface acoustic wave resonator (SAWR) sensors can respond to the demands of high-temperature, harsh-environment applications due to: (i) the existence of piezoelectric substrates and thin film electrode technology capable of operating at high temperatures (above 1000°C); (ii) sensor response to static and dynamic strain components; (iii) small sensor size; (iv) wireless interrogation capability; (v) and battery-free operation. SAWR strain sensing for harsh-environment applications needs to address some of the issues inherent to these environments, such as: (i) sensor mounting techniques to metal parts, (ii) stability of the sensor and sensor mounting technique, (iii) packaging of the sensor, and (iv) cross-sensitivity between strain and temperature.

In this work, langasite (LGS) SAWR sensors were used, due to the proven performance of these devices at high temperature at UMaine, for static and dynamic strain measurements. Simulation of the strain due to thermal expansion and mechanical loads was performed to determine where there were concentrations of high strain at the adhesive/LGS and adhesive/metal interfaces as well as adhesive shaping designs aimed at minimizing this strain. Wireless interrogation of SAWR static and dynamic strain sensors using inductive coupling techniques was achieved up to 400°C. After temperature cycling, it was determined that cracking was taking place within the ceramic adhesive layer and along the borders of the SAWR sensor chip that causes degradation and inconsistency in the SAWR strain response. Based on these results, further investigation of static and dynamic strain sensors using alternative adhesives was done limited to 200°C. Two polymer epoxy adhesives showed stability after temperature cycling between 50°C and 250°C. Using the polymer epoxy that showed greater stability for the static strain, dynamic strain was measured. The test setup implementation was investigated towards improving the stability of dynamic strain sensor measurements after temperature cycling. Finally, a method for extracting temperature and the dynamic strain magnitude and spectral components was devised and implemented using a single SAWR sensor.

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