Date of Award

2017

Document Type

Open Access Dissertation

Department

Mechanical Engineering

Sub-Department

College of Engineering and Computing

First Advisor

Victor Giurgiutiu

Abstract

Risks and costs associated with aging infrastructure have been mounting, presenting a clear need for innovative damage monitoring solutions. One of the more powerful damage monitoring approaches involves using ultrasonic guided waves which propagate through a structure and carry damage-related information to permanently bonded sensors. Ultrasonic fiber-optic sensors are one of the most promising technologies for this application: they are immune to electromagnetic interference, present no ignition hazard, and transmit their data over tens of kilometers. However, before they can be widely employed, several limitations need to be overcome: poor sensitivity, unidirectional sensing, and loss of ultrasonic functionality due to static loading.

In this dissertation, these limitations were addressed using a mechanical design approach, combining a mechanical resonator with a fiber-optic sensing element. Based on this principle, two fiber-optic sensors were developed: a ring sensor and a wave-absorbing acoustic black hole sensor. Sensitivity improvements up to 28 dB were achieved through mechanical resonance. Prototypes were shown to be insensitive to static loads and detected waves omnidirectionally. The sensors were also miniaturized and designed to be sensitive to different types of wave motion; the ring sensor was sensitive to out-of-plane motion only, and the acoustic black hole sensor was sensitive to both in-plane and out-of-plane motion. The sensor development process is presented from concept sketch to modeling, design, verification, optimization, and calibration.

Rights

© 2017, Erik Frankforter

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