Focused Practice

I. Answer the following questions:

1. What word-combinations do the letters CAD and BPM stand for?

2. What are large size reductions due to?

3. How can the improvements be gained?

4. How has the thermal performance of a new motor design traditionally been estimated?

5. What is the problem with traditional design methods?

6. What can one of the thermal modules of a new available motor design package be used for?

II. Analyse the grammar structures underlined in the above text.

III. Speak on: The revolution in compact BMP motors.

Unit 25 Grammar: The Infinitive Word List:

1. micro-electro-mechanical systems (MEMS)	электромеханические микросистемы
2. the microbearing device	устройство, опирающееся на микроподшипники
3. power MEMS applications	устройства MEMS большой мощности
4. rig	оснастка
5. microbiaricated rotor	микроротор
6. LIGA=lithography	литография, нанесение металлического слоя
7. induced stresses	обусловленные воздействия
8. rpm=revolutions per minute	об/мин
9. two orders	два порядка, т.е. в 100 раз
10. aircraft propulsion	двигатель летательного аппарата
11. circumferential tip speed	окружная скорость
12. pin bearing	шарнирно-неподвижная опора
13. turbomachinery	турбины
14. viscous drag	вязкостное торможение

Demonstration of a Microfabricated High-Speed Turbine Supported on Gas Bearings

To achieve high power and efficiency from a rotating device, high circumferential tip speed is a necessity. Conventional scale turbomachinery typically run with tip speeds of order 500 m/s, enabling high-power density applications such as gas turbines for aircraft propulsion and power generation. In order to achieve high levels of power density, microfabricated rotors will need to run at comparable tip speeds. Typical rotating micromachines, such as gears and micromotors, are formed either by surface micromachining or LIGA, supported by solid contact on a pin bearing, and entrained by electrical or contact forces acting on the edges of the rotor. These micro-rotors have reached of order 2 m/s tip speed, which is two orders of magnitude lower than desired for Power MEMS applications.

An effort has been undertaken to develop high-speed rotating devices to enable high-power density MEMS. A single-crystal silicon air turbine supported on gas lubricated bearings has been operated in a controlled and sustained manner at rotational speeds greater than 1 million rpm and power levels approaching 5 W. The device is a second-generation version of the microbearing rig first reported in 1999, and is the first micromachine to operate at circumferential tip speeds of hundreds of meters per second, comparable to conventional scale turbomachinery. To achieve this level of peripheral speed, microfabricated rotors must withstand large induced stresses, need a sufficient power source to drive them, and require stable, low friction bearings for support. The successful operation of the microbearing device motivates the use of this technology for high-power density MEMS.

The turbine was designed to provide sufficient power to overcome the viscous drag in the bearings and on the back side of the rotor. While viscous drag is relatively large in microsystems due to the small length scale, it is still quite small compared to the capabilities of high-speed turbomachinery. The turbine for the microbearing device had to be intentionally designed to match the relatively low power requirements of the viscous drag. Alternative turbine designs, compatible with the current process and geometric constraints, that produce tens of watts of power (beyond the drag requirements) have been designed for Power MEMS applications.