An integrated electromagnetic micro-turbo-generator supported on encapsulated microball bearings

Abstract

This dissertation presents the development of an integrated electromagnetic microturbo-generator supported on encapsulated microball bearings for electromechanical power conversion in MEMS (Microelectromechanical Systems) scale. The device is composed of a silicon turbine rotor with magnetic materials that is supported by microballs over a stator with planar, multi-turn, three-phase copper coils. The microturbo-generator design exhibits a novel integration of three key technologies and components, namely encapsulated microball bearings, incorporated thick magnetic materials, and wafer-thick stator coils. Encapsulated microball bearings provide a robust supporting mechanism that enables a simple operation and actuation scheme with high mechanical stability. The integration of thick magnetic materials allows for a high magnetic flux density within the stator. The wafer-thick coil design optimizes the flux linkage and decreases the internal impedance of the stator for a higher output power. Geometrical design and device parameters are optimized based on theoretical analysis and finite element simulations. A microfabrication process flow was designed using 15 optical masks and 110 process steps to fabricate the micro-turbogenerators, which demonstrates the complexity in device manufacturing. Two 10 pole devices with 2 and 3 turns per pole were fabricated. Single phase resistances of 46Ω and 220Ω were measured for the two stators, respectively. The device was actuated using pressurized nitrogen flowing through a silicon plumbing layer. A test setup was built to simultaneously measure the gas flow rate, pressure, rotor speed, and output voltage and power. Friction torques in the range of 5.5-33µNm were measured over a speed range of 0-16krpm (kilo rotations per minute) within the microball bearings using spin-down testing methodology. A maximum per-phase sinusoidal open circuit voltage of 0.1V was measured at 23krpm, and a maximum per-phase AC power of 10µW was delivered on a matched load at 10krpm, which are in full-agreement with the estimations based on theoretical analysis and simulations. The micro-turbogenerator presented in this work is capable of converting gas flow into electricity, and can potentially be coupled to a same-scale combustion engine to convert high-density hydrocarbon energy into electrical power to realize a high-density power source for portable electronic systems.

An investigation on the electromagnetic design optimization of rotary micromachines with double-layer permanent magnets

“…The parameter values used in the simulations have been selected considering previously reported designs in , as well as commercial availability and microfabrication limitations for our device design, and are listed in Table 1. Note that (i) the rotor-to-stator air gap is desired to be as small as possible for higher B avg , and is set to 50 m, which is an achievably small gap considering the manufacturing and testing constraints [11][12][13][14][15][16][17][18], (ii) the spacing between top and bottom magnet layers on the rotor is set to be equal to magnet thickness. The material parameters (magnetic permeability and remanent flux density) are set in the model according to the vendor specifications.…”

“…The same design with four pole NdFeB magnets was miniaturized down to a diameter of 2 mm in [15], resulting in a total AC output power of 6.6 mW. The author of this work presented the first integrated microgenerator using novel microball bearings in [16][17][18][19]. Using 10 pole NdFeB magnets, 5.6 W was demonstrated at relatively lower speeds [16].…”

Integrated sensing of mechanical parameters in a micro-turbo-generator

“…The stator is composed of three-phase planar Cu coils embedded in a thermally-oxidized silicon substrate ( Figure 1d). The thickness of the substrate was selected to be 400 µm for performance optimization [8]. The radial coil sections are connected together over a dielectric KMPR layer having vias at the connection sites on the stator backside ( Figure 1e).…”

“…Significant research efforts have been dedicated in this direction to develop rotary microgenerators with various actuation mechanisms [1][2][3][4][5][6][7][8]. Depending on the device design and required power output, these devices were shown to operate under a wide range of mechanical conditions.…”

“…The rotor was levitated and spun at a maximum speed of 40krpm. Recently, the authors of this work have reported the development of a microball bearing supported micro-turbo-generator, and presented detailed characterization of electrical power generation at operating conditions up to 23 krpm, 12.6 slm, and 1.2 psi [8].…”