FIELD DEPLOYABLE GUIDED WAVE TRANSDUCERS FOR HIGH-TEMPERATURE APPLICATIONS
Open Access
- Author:
- Trivedi, Yamankumar Premalbhai
- Graduate Program:
- Engineering Science and Mechanics
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- April 18, 2019
- Committee Members:
- Clifford Jesse Lissenden III, Thesis Advisor/Co-Advisor
Andrea Paola Arguelles, Committee Member
Parisa Shokouhi, Committee Member - Keywords:
- Bismuth Titanate
Spray-on Transducers
Film Transducers
SHM
NDE
High-Temperature
Lithium Niobate
Lamb Wave generation
Guided Waves
Excitation Frequency
Dispersion Curves - Abstract:
- Degradation is a natural phenomenon that can occur in all materials, if undetected it can lead to structural failure. Thus, there is a crucial need to monitor structures exposed to some external stimuli. This lays the foundation for Nondestructive Evaluation and Structural Health Monitoring. Both approaches provide the means and information needed to detect the advance of damage. Of the multitude of techniques used in NDE or SHM, ultrasonic testing is perhaps the most common. The wide range of excitation methods and the ability to control the waves through various means account for its popularity. Transducers, which convert the energy from one form to another, facilitate the generation and detection of ultrasonic waves. However, the field-testing of structures at high-temperature is a challenge, as commercial transducers are often not suitable for such high-temperatures. Deposition and processing techniques for temperature-tolerant piezoelectric film transducers that are appropriate for field installation on metal structures with minimal need for heating the substrate are developed and tested. The direct bond of the film to the structure precludes the use of couplants. Film coatings have served various NDE purposes, where previous work investigated the use of sol-gel, potato starch and single crystal films. Herein, the ferroelectrics Bismuth Titanate and Lithium Niobate are investigated. The film consists of a piezoelectric powder, a lithium-silicate based high-temperature inorganic binding agent and water. Electrodes are installed on the top of the film and then it is poled. To show the viability of these films, pulse-echo, temperature testing and capacitance measurements are performed to characterize the films. Bismuth titanate films are also processed as comb transducers to send and receive guided waves, and for the first time Lamb waves are generated and received from this type of air-sprayed transducer.