A fully-integrated multi-watt permanent-magnet turbine generator

Abstract

The energy density available from batteries is increasingly becoming a limiting factor in the capabilities of portable electronics. As a result, there is a growing need for compact, high energy density sources. This thesis presents the design, fabrication, and testing of a fully-integrated permanent-magnet turbine generator based on silicon MEMS technology envisioned to replace batteries. The air-driven device, supported on gas bearings, has been experimentally shown to deliver 19 mW to matched resistive loads of 0.33 [omega] while operating at a rotational speed of 40 krpm. With an active volume of 41 mm³, this translates to a power density of 0.46 mW/mm³. By extrapolating the experimental data up to the design speed of 360 krpm, it is expected that the integrated generator can deliver 1.5 W of output power.This research represents the first batch-fabricated permanent-magnet generator shown to generate milliwatt-level power, with a further potential to deliver watt-level power. To achieve full integration, a broad range of topics are examined, including the design of gas bearings, high-speed mechanical analysis using non-ideal material interfaces, magnetic rotor balancing, and novel fabrication techniques.A major challenge unique to the integrated device is the need for both silicon and non-silicon components on the same die. While the silicon components are precision micromachined using DRIE and can withstand high temperatures, the permanent magnets are laser-machined separately and rapidly demagnetize when exposed to heat. Similar problems exist for the copper surface windings. The differences are reconciled with the use of a novel drop-in technique, which involves placing nonsilicon components into the die after all the silicon fabrication is complete.