An Integrated Permanent-Magnet Microturbogenerator Supported on Microball Bearings

This paper presents the design, fabrication, and testing of an integrated microturbogenerator utilizing permanent magnets and microball bearings. The key components of this generator are the following: 1) a silicon microturbine rotor housing thick magnetic components; 2) encapsulated microball bearings providing a simple actuation scheme and a robust support structure; and 3) wafer-thick stator coils. The microturbogenerator was designed and fabricated to have a ten-pole rotor and a ten-pole three-turns-per-pole stator. The impedance of the stator coils was shown to be a purely resistive 220 Ω up to 10 kHz. The spin-down characterization of the rotor revealed a dynamic friction torque of 33 μN·m at a rotational speed of 16 kilo rotations per minute (krpm), corresponding to 6% turbine efficiency. The maximum per-phase ac open-circuit voltage and power were measured to be 0.1 V and 5.6 μW on a matched load at 23 krpm, respectively, in full agreement with theoretical analysis and performance estimations. The microturbogenerator presented in this paper provides a flexible design platform for further improvement and will lead to the development of next-generation integrated microturbogenerators offering high power, simple operation, and robust mechanics.