PROLOGUE

This chapter provides background material on an essential element of the targeted flow-control strategy to be detailed in Chapter 14. Manufacturing processes that can create extremely small machines have been developed in recent years. Microelectromechanical systems (MEMS) refer to devices that have characteristic length of less than 1 mm but more than 1 μm, that combine electrical and mechanical components, and that are fabricated using integrated circuit batch-processing techniques. Electrostatic, magnetic, electromagnetic, pneumatic, and thermal actuators, motors, valves, gears, cantilevers, diaphragms, and tweezers of less than 100-μm size have been fabricated. These have been used as sensors for pressure, temperature, mass flow, velocity, and sound; as actuators for linear and angular motions; and as simple components for complex systems such as microheat engines and microheat pumps. Many of these microsensors and microactuators are potentially very useful for futuristic distributed control systems that are particularly suited for turbulent flows, as will be discussed in the next chapter. In the present chapter, we review the status of our understanding of fluid-flow phenomena particular to microdevices. In terms of applications, this and the following chapter emphasize the use of MEMS as sensors and actuators for flow diagnosis and control.