M.Sc Thesis

M.Sc StudentBenhaim Alon
SubjectSelf Aligment Using Electromagnetic Induction for Mass
Fabrication of Micro-Coils
DepartmentDepartment of Mechanical Engineering
Supervisor PROF. David Elata
Full Thesis textFull thesis text - English Version


The importance of micro coils as passive electronic circuit components is increasingly growing. Recently, the interest in micro electromagnetic transducers is rising in MEMS and they are used as near-field antennas, as sensors, and as flux generators. Electromagnetic actuators have advantages compared to electrostatic actuators. These advantages include higher energy density, higher actuation force and displacement and the fact that they are less sensitive to environment and encapsulation conditions.

Coils with a relative small volume enable induction of a uniform high intensity magnetic field, however, currently there is no simple method for parallel fabrication of micro-coils in MEMS. Known techniques for the fabrication of micro-coils in MEMS include: fabrication of planar (2D) coils, stacking several layers of planar coils to form 3D coils or using wire bonding machines to form 3D coils. These methods lack the advantages of full parallel fabrication process or produce poor performance with low inductances and quality factors.

In my research, I considered a novel method for parallel fabrication of 3D micro-coils. My method requires a means of self-aligning of individual layers with planar 2D coils (rings) so that 3D structures may be produced in a parallel mass-fabrication process. The issue of self-alignment of two rings became a focal point of my research. The (horizontal) aligning force between two non-coaxial circular rings was investigated in a paper from 1996. It was suggested in the paper that at a critical vertical separation between the rings, the aligning force vanishes for any given eccentricity. The physical nature of the interaction forces (horizontal alignment and vertical levitation) between two rings was at first difficult to comprehend. Also, the notion of a neutral plane was difficult to explain physically or derive analytically. This is not only because of the rather complex geometry but also because the interaction forces are of an integrated nature. As a result, it is not easy to deduce the nature of the interaction forces from their functional form.

Therefore, I proposed a simpler model of the 3D problem associated with two conducting rings. My simplified model considers a 2D problem composed of two semi-infinite rectangular loops. In my simplified 2D model, it is easy to understand the physics behind the interaction forces from their functional form. My new model provides new insight to the alignment and levitation forces and sheds new light on the notion of a neutral plane.