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.
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.
This paper demonstrates the use of low-cost off-the-shelf (OTS) microelectromechanical system (MEMS) technology to perform vibration-based in situ monitoring, diagnostics, and characterization of a MEMS microball bearing supported radial air turbine platform. A multimodal software suite for platform automation and sensor monitoring is demonstrated using a three-level heuristic software suite and sensor network. The vibration diagnostic methods used in the platform have applications in rotary microsystems for the early detection of failure, fault diagnosis, and integrated diagnostic systems for feedbackbased optimization to increase device performance, reliability, and operational lifetimes. The studied rotary microdevice used a dual OTS accelerometer configuration for dual range parallel redundant vibration analysis. The sensor suite has been used to monitor and detect multiple operational parameters measured optimally in time or frequency domains such as rotor instability, imbalance, wobble, and system resonance. This paper will lay the framework for active diagnostics in future MEMS devices through integrated systems.[2014-0236]
This work demonstrates the utilization of an Off-TheShelf (OTS) MEMS accelerometer to accurately and repeatedly determine the onset of instability and perform in situ diagnostics of a high-performance rotary MEMS device. The accelerometer is shown to provide high sensitivity, wide bandwidth vibration measurements when bonded to the stator of a MEMS device. Vibration sensing is augmented with optical displacement sensors to create a multi-modal sensor platform. The sensor suite has been used to characterize the rotor instability for rotor speeds from 10-20 krpm, diagnose imbalance acceleration with sensitivity down to 0.001 g, determine rotor wobble of with an accuracy of <500 nm, and monitor system resonances through the speed range of 5-20 krpm. The data provided by the on-chip accelerometer can be used in feedback systems to optimize device performance and increase operational lifetimes.
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