Synapse-Inspired Magneto-Responsive Material
Open Access
- Author:
- Badri, Amal
- Graduate Program:
- Mechanical Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 01, 2021
- Committee Members:
- Karen Thole, Program Head/Chair
Zoubeida Ounaies, Thesis Advisor/Co-Advisor
Paris R Vonlockette, Committee Member
Joseph Najem, Thesis Advisor/Co-Advisor - Keywords:
- magneto-responsive material
artificial synapses
iron oxide
sedimentation
learning
memory
chain formation
viscosity
synapses
conductance
cyclic magnetic field
continuous magnetic field - Abstract:
- Learning and memory have inspired the research and discovery of materials that can mimic brain synapses, with applications in signal processing and computing. Synapses are junctions that allow neurons to transfer chemical and electrical signals among each other and are integral to the function of the brain. This study aims to fabricate and characterize artificial synapses using magneto-responsive materials, consisting of oleic acid-coated magnetic iron oxide microparticles dispersed in an organic solvent matrix. The broad goal is to design these materials so that they can emulate short-term synaptic plasticity via voltage-dependent changes in conductance. An optimum iron oxide to oleic acid weight ratio of 0.45 and mechanical stirring was employed to enhance dispersion and control the sedimentation rate of the material. Effects of other parameters such as volume fraction and carrier fluid viscosity were also investigated. In general, it was found that an increase in volume fraction of the particle and increase in viscosity of the carrier fluid resulted in a reduction in sedimentation rate, due to the higher drag forces experienced by the particles. Once the fabrication method was determined, the next step focused on the effect of the external magnetic field on the particle assembly. Application of a low-strength continuous and cyclic magnetic field leads to the formation of chain-like assemblies of iron oxide microparticles within the insulating matrix, which results in analog and hysteretic changes in conductance. Our work demonstrates that the application of a magnetic field increases the viscosity of the insulating matrix, which impacts the rates of chain formation and decay. Low, medium and high viscosities of the material were fabricated and characterized to understand the impact of viscosity on electrical conductance changes. Under the application of a continuous magnetic field, as viscosity increases, chain formation and changes in conductance with time slow down. Further, we find that a cyclic application of the magnetic field leads to changes in electrical conductance dependent on the viscosity of the carrier fluid. The resulting changes in conductance are driven by the interplay between drag and magnetic dipole-dipole forces acting on the material. Both low and high viscosity samples exhibited the synaptic plasticity state of facilitation, while medium viscosity samples displayed depression. The results of this research demonstrate promise and potential in terms of enabling artificial synapses and their functions using magneto-responsive material. By conducting further theoretical and experimental work such as using a larger viscosity range, different cycle times, and focusing on the fluids mechanics of the system, the material can be tailored to mimic artificial synapses.