“Foil Winding Inductors with Quasidistributed Gaps and Microfabricated Magnetic Components”
Charles R. Sullivan, Ph.D. (Chair)
Christopher G. Levey, Ph.D.
Jason T. Stauth, Ph.D.
Quasidistributed gap inductors with thin foil windings intended for high frequency (HF) current and thick foil windings intended for low frequency (LF) current are investigated. A new foil structure is designed to make low loss terminations for inductors. One prototype with a quasidistributed gap is designed and tested. At 250 kHz, the ESR of the prototype is 148.5 mΩ and the inductance is 35.7 μH. Compared to the same inductor with only the thick foil winding, the HF ESR of the inductor is reduced by a factor of 3.5, and the LF ESR is reduced by 8.5% at 60 Hz. Compared to the same inductor made with the thin foil windings only, the resistance of the composite structure is about 20% higher at HF, but at frequency lower than 20 kHz, the composite structure has lower ESR. To further improve this inductor, a new bobbin and a revised air gap structure are designed and tested. Based on two-dimensional finite element simulations and measurements, more improvements are discussed.
Microfabricated racetrack inductors targeted to operate between 5 MHz and 30 MHz are fabricated and tested. The fabrication process is based on Daniel Harburg’s Ph.D thesis, and some modifications are made to adjust the inductance and improve the microfabrication process. Small-signal measurements of the inductors show reduced inductance caused by thinner magnetic material, higher resistance caused by thinner coils and defective magnetic material structures, and smaller quality factors.
A "mushroom" structure made with NR-21, SU-8, and a thin layer of Ti is designed to work as a shadow mask to sputter toroidal cores, which can be used for toroidal inductors.
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