First Advisor

Jonathan Bird

Term of Graduation

Winter 2023

Date of Publication


Document Type


Degree Name

Doctor of Philosophy (Ph.D.) in Electrical and Computer Engineering


Electrical and Computer Engineering





Physical Description

1 online resource (xviii, 207 pages)


This dissertation is devoted to investigating the performance potential of coaxial radial flux modulating magnetic gears for use in propulsive thruster applications. The research has focused on studying magnetic gear designs suitable for use in electric aircraft drivetrains and electric boat thrusters. Consequent pole, flux concentration and Halbach rotor magnetic gear typologies have been analyzed and compared with respect to their torque density performance for the first time. It is shown that the Halbach rotor magnetic gear holds the greatest potential with respect to achieving volumetric and mass torque densities parity with an equivalent mechanical gear.

A high volumetric torque density Halbach rotor coaxial magnetic gear with a 1:5.67 gear ratio was designed, fabricated, and experimentally tested. The radial flux prototype achieved a volumetric torque density of 279 Nm/L at a torque of 190 Nm. This design validated the high torque density performance of a Halbach rotor coaxial magnetic gear.

A high mass torque density 1:12.4 gear ratio Halbach rotor radial flux coaxial magnetic gear was also designed for an electric vertical take-off and landing vehicle. The design was computed using 3-D finite element analysis to have a mass torque density of 53 Nm/kg at a torque of 240 Nm. The design was experimentally verified with a prototype. This design demonstrated the feasibility of a lightweight magnetic gear for the use in an electric aircraft. A thermal and electrical loss analysis was conducted by using 3-D finite element analysis, where the hysteresis loss and eddy current loss was used as heat source in the thermal model. It was shown that a magnetic gear efficiency greater than 99% at rated torque is feasible.

Prior research indicated that when using a high gear ratio (> 1:10), the torque density of coaxial magnetic gear is greatly reduced. This research used a comprehensive finite element analysis geometric sweep method to demonstrate for the first time that by increasing the magnetic gear diameter, a magnetic gear can simultaneously achieved a high torque density and a high gear ratio. Using 3-D finite element analysis, it was shown that a single-stage 1:33.3 gear ratio coaxial magnetic gear can operate with an active region volumetric torque density of 336 Nm/L or an active region mass torque density of 92 Nm/kg.

A magnetic equivalent circuit analytical modeling approach that allows the characterization of the spatial and temporal harmonic components in a magnetic gear was also developed and its accuracy was compared with an equivalent finite element analysis model.


©2023 Ho Yin Wong

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