Title: Characterization of Bending Magnetostriction in Iron Gallium Alloys for Nanowire Sensor Applications
M.Sc Thesis And Dissertation - Deparment Of Doctor of Philosophy on Aerospace Engineering
Abstract: This research explores the possibility of using electrochemically deposited nanowires of magnetostrictive iron-gallium (Galfenol) to mimic the sensing capabilities of biological cilia. Sensor design calls for incorporating Galfenol nanowires cantilevered from a membrane and attached to a conventional magnetic field sensor. As the wires deflect in response to acoustic, airflow, or tactile excitation, the resultant bending stresses induce changes in magnetization that due to the scale of the nanowires offer the potential for excellent spatial resolution and frequency bandwidth. In order to determine the suitability for using Galfenol nanowires in this role, the first task was experimentally characterizing magnetostrictive transduction in bending beam structures, as this means of operation has been unattainable in previous materials research due to low tensile strengths in conventional alloys such as Terfenol-D. Results show that there is an appreciable sensing response from cantilevered Galfenol beams and that this phenomenon can be accurately modeled with an energy based formulation. For progressing experiments to the nanowire scale, a nanomanipulation instrument was designed and constructed that interfaces within a scanning electron microscope and allows for real time characterization of individual wires with diameters near 100 nm. The results of mechanical tensile testing and dynamic resonance identification reveal that the Galfenol nanowires behave similarly to the bulk material with the exception of a large increase in ultimate tensile strength. The magnetic domain structure of the nanowires was theoretically predicted and verified with magnetic force microscopy. An experimental methodology was developed to observe the coupling between bending stress and magnetization that is critical for accurate sensing, and the key results indicate that specific structural modifications need to be made to reduce the anisotropy in the nanowires in order to improve the transduction capabilities. A solution to this problem is presented and final experiments are performed.
Project Intro: This research was only made possible by the nanowire fabrication e orts of our collaborators at the University of Minnesota, Professor Bethanie Stadler and her students Patrick McGary and Liwen Tan. Dr. Stadler has worked very closely with us on handling and manipulating the nanowire arrays, and I thank her for being understanding of the feedback that we have provided. She has always been very kind and supportive and I sincerely hope that she knows how much I appreciate the contributions of her and her team. Patrick and Liwen have overcome numerous obstacles in order to successfully fabricate magnetic nanowires in well ordered arrays, and without their diligence and creativity my research would never have gotten of the ground.The design, construction, and integration of the nanomanipulator instrument is a testament to the openness and generosity of Professor Rodney Ruo , formerly at Northwestern University, and his post-doctoral researcher Dmitriy Dikin. After a literature review identi ed their previous device as the perfect foundation for our intended machine, they were kind enough to host me for the day and answer every question that I had. We covered the key constraints to be wary of, the available means of data collection, some potential experimental pitfalls, even the most reliable iv part suppliers. In the end the design and implementation of our manipulator stage was made entirely possible by this visit. I thank them for going above and beyond expectations for sharing information with a fellow researcher.
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Keywords: Engineering, Aerospace, nanowire; magnetostriction; Galfenol, MFM, shape anisotropy; nanomanipulation.
