In this conducted research, optical fiber sensors are used to measure low strength alternating magnetic fields. Various fiber sensor configurations are tested and investigated to demonstrate sensing capabilities at different field magnitudes and frequencies. Distributed acoustic sensing fibers (DAS) have been largely studied and documented across a variety of applications and sensing systems. This research uses the DAS technology in tandem with magnetostrictive materials to create a distributed multi-material optical fiber magnetic sensor.
Magnetic sensing has high demand across different fields and often runs into challenges of extreme environments including high temperature, corrosion, and areas with poor accessibility. The robust and distributed nature of optical fiber sensors which can be cheaply produced for long lengths is an attractive option over other single point magnetic sensors. In down hole applications specifically, having a distributed sensor able to be deployed easily and over long distances for magnetic sensing would be a large improvement to bulkier traditional magnetometers.
In the conducted study, different magnetostrictive materials are implemented in distributed optical fiber sensors to analyze and compare the effective sensitivity and potential commercial viability. Nickel, galfenol alloy, and MetGlas alloy inclusions are drawn into fused silica optical fibers with Bragg gratings inscribed later on for DAS capability. Each was investigated for its response to varying AC magnetic fields to determine relative sensitivity and resolution for distributed magnetic field sensing. / Master of Science / Magnetic sensing has high demand in biomedical applications as well as within the oil and energy industry. This research proposes a series of optical fiber-based sensors to overcome many of the challenges present amidst traditional magnetic sensors. Materials that respond to magnetic fields by either contracting or expanding are coined magnetostrictive. The proposed fiber-based sensors use magnetostrictive materials to create a change in the optical path length of the light being transmitted through the optical fiber. This path difference can be converted to a strain measurement and when compared with a standardized magnetometer, a calibration curve is established for the fiber sensor.
Different magnetostrictive materials are studied for measuring various alternating magnetic field amplitude strengths to look at improved sensitivity and/or resolution. This includes nickel, galfenol alloy, which is made up of iron and gallium, and MetGlas, which is composed of primarily of iron. Small wires of the respective materials are drawn out inside the silica fiber while the optical fiber is made so that continuous lengths run the course of the fiber. Different sizes were experimented with. Another simplified tested setup used a ribbon of the MetGlas while a distributed acoustic fiber sensor was laid on top to pick up the strain response while exposed to an alternating magnetic field.
All of the mentioned test setups showed success in measuring alternating magnetic field strengths with a clear positive correlation of strain response to magnetic field amplitude. A calibration curve was established for each sensing system and analyzed to show an effective sensitivity range.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/118607 |
| Date | 28 March 2024 |
| Creators | Dejneka, Zachary Bryce |
| Contributors | Materials Science and Engineering, Pickrell, Gary R., Homa, Daniel S., Wang, Anbo |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf, application/pdf |
| Rights | Creative Commons Attribution 4.0 International, http://creativecommons.org/licenses/by/4.0/ |
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