Emerald Group Publishing Limited
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Multi-Wafer Rotating MEMS Machines – Turbines, Generators and Engines
Article Type: Book review From: Assembly Automation, Volume 31, Issue 1
Jeffrey H. Lang,Springer,2010,$169.00,454,ISBN: 978-0-387-77746-7,www.springer.com/engineering/electronics/book/978-0-387-77746-7
This research reference book gathers all presently available information related to MEMS turbines, generators and engines, collected and written by the most active researchers in the field. The material presented within the 452 pp. of the book is distributed in nine chapters and the subject is covered by 12 authors, eight of whom are from MIT.
General design considerations associated with the miniaturization, thermodynamic scaling, bearings and rotor dynamics, materials and turbo-machinery-related issues, are presented in Chapter 2, right after an introduction into the subject. In the same second chapter, brief considerations that will be further detailed, are given to materials selection – to satisfy the system requirements and the micro-fabrication constraints, to combustion, to controls and sensing, as well as to the integration. Chapter 3 covers materials selection in relation with the micro-fabrication limitations and the specific requirements associated with the high-operating temperature. Packaging is discussed here mainly from the material selection perspective. SiC/Si hybrid structures appear to be at the present time, the suitable choice to satisfy both the strength at high temperatures, as well as machinability. Chapter 4 addresses in detail, the configurational design based on bonding layers of patterned wafers. Six wafers for bearing rig and turbo-charger structures, and ten wafers in a self-sustained engine, are discussed in detail as examples. The level of detailing goes to the extent that someone with a MEMS background and access to micro-fabrication facilities may reproduce the structure after completion of the device and mask designs. Special attention is given to rotor-releasing methods. Three methods are presented in the chapter: mechanical fuse method, bonded oxide pad rotor releasing method, and free rotor method. A significant part of the chapter is dedicated to the journal bearing and blades, both processed by DRIE. Bonding is further addressed using as an example, a self-sustained ten-layer engine. Chapter 5 presents the fundamental principles and the fabrication technologies associated with micro-scale rotating magnetic machines. Although some of the challenges such as the supporting and release of the rotor are similar to those of MEMS turbines, specific aspects such as magnetic material assembly or multi-level coil fabrication are briefly addressed in this chapter. Electro-deposition and sputtering are the two technologies of choice for the above fabrication challenges. Integration is further discussed through two examples: the induction machine and the permanent magnet machine. Chapter 6 addresses one of the most significant challenges associated with MEMS rotating machines: bearings and seals design for four mm diameter rotors in MEMS turbines, where rpm of 2.5 million revolutions per minute are desired. The subject presented in this chapter may not be familiar to MEMS trained researchers, but is essential in the design of miniature rotating systems that require ultra-short bearings and ultra-high rpm. Ultra-high speed revolution of rotors, the stability of the motion, scaling laws, and whirl instability are topics discussed in detail in this chapter. Axial bearings and damping associated with tilting of the blades disk are discussed in detail. Pressure drop in the labyrinth seals, which is the typical seal configuration of such structures, is also presented in detail. Chapter 7 deals with the thermo fluidics and turbo machinery in MEMS turbo machines. The polytrophic efficiency of miniature structures is discussed based on the classic turbo machinery theory. Heat transfer issues as well as the fabrication constraints on the efficiency of the compact configuration machine are discussed. In this chapter, a macro-compressor test rig design (scale 75:1) is detailed. Instrumentation aspects are discussed in conjunction with performance measurements and performance measures. Chapter 8 presents, from the system perspective, a detailed analysis of the MEMS generators and motors from the performance point of view. Modeling and assumptions in the electric induction micro-machine as well as in permanent magnet synchronous machine are presented in great detail. Design hints are given such that one could get acquitted with the field quite fast. Experimental data are presented for selected built configurations. Chapter 9 presents aspects related to micro-combustion in MEMS turbo-machines. Starting with combustion strategy and chemistry, the authors present results of simulations based on experiments carried out, to understand this phenomenon at a small scale. Flame stability for two types of combustion chambers is discussed and some design methodologies are recommended.
This reference work is extremely useful to those who wish to commence work in this exciting area. The material presented by the authors leave many open doors to research topics.
Dr Ion StiharuProfessor of Mechanical and Industrial Engineering, Concordia University, Montreal, Canada