Date of Award

August 2019

Degree Type

Thesis

Degree Name

Master of Science

Department

Engineering

First Advisor

Chiu Law

Abstract

Fiber optic current sensors (FOCSs) have unique advantages in electromagnetic interference

immunity and direct current measurements. Here, magnetostrictive composites and

their interactions with embedded ber Bragg gratings (FBG) were explored to form novel

FOCSs with predictable and temperature-independent sensitivity. Magnetostrictive, particularly

Terfenol-D/epoxy, composites maintain the mangetostrictive expansion under an

external magnetic eld while gaining

exibility in engineering. In contrast to ordinary strain

gauges, an embedded FBG can provide an optical signal inferring simultaneously a strain

and its gradient inside a composite. In principle, the sensing of strain gradient is thermally

independent. Creating appropriate geometries for magnetostrictive composites enables the

conversion of a uniform external magnetic eld into an internal one with a certain eld gradient

that enacts a strain distribution inside the composite transferred to the FBG. Hence,

the strain gradient sensing with the FBG can be exploited for temperature independent

measurement of the external magnetic eld. Such a strain gradient will alter the spectral

properties of the FBG, such as the power and bandwidth of the returned optical signal. The

experimental results from two separate sensors have conrmed the trend that is predicted

by the theory and simulations. They will substantiate the claim of sensitivity tuning solely

with geometry. These FOCSs will provide reliable reading for wide operating temperatures

if the underlying materials allow.

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