ABSTRACT
Electroactive and magnetoactive materials are materials that modify their shape in response to electric or magnetic stimuli. Such materials permit induced-strain actuation and strain sensing which are of considerable importance in micromechatronics. On one hand, induced-strain actuation allows us to create motion at the microscale without pistons, gears, or other mechanisms. Induced-strain actuation relies on the direct conversion of electric or magnetic energy into mechanical energy. Induced-strain actuation is a solid-state actuation, has much fewer parts than conventional actuation, and is much more reliable. Induced-strain actuation offers the opportunity for creating micromechatronics systems that are miniaturized, effective, and efficient. On the other hand, strain sensing with electroactive and magnetoactive materials creates direct conversion of mechanical energy into electric and magnetic energy. With piezoelectric strain sensors, strong and clear voltage signals are obtained directly from the sensor without the need for intermediate gauge bridges, signal conditioners, and signal amplifiers. These direct sensing properties are especially significant in dynamics, vibration, and audio applications in which alternating effects occur in rapid succession, thus preventing charge leakage. Other applications of active materials are in sonic and ultrasonic transduction, in which the transducer acts both as a sensor and an actuator, first transmitting a sonic or ultrasonic pulse, and then listening for the echoes received from the defect or target. In this chapter, we will discuss several types of active materials: piezoelectric ceramics,
electrostrictive ceramics, piezoelectric polymers, and magnetostrictive compounds. Various formulations of these materials are currently available commercially. The names PZT (a piezoelectric ceramic), PMN (an electrostrictive ceramic), Terfenol-D (a magnetostrictive compound), and PVDF (a piezoelectric polymer) have become widely used. In this chapter, we attempt a review of the principal active material types. We will treat each material type separately, will present their salient features, and introduce the modeling equations. In our discussion, we will start with a general perspective on the overall subject of piezoelectricity and ferroelectric ceramics, explaining some of the physical behavior underpinning their salient features, especially in relation to perovskite crystalline structures. Then, we will discuss manufacturing and quality control issues related to ferroelectric ceramics. We will continue by considering separately the piezoceramics and electrostrictive ceramics commonly used in current applications and commercially available to the interested user. The focus of the discussion is then switched toward piezoelectric polymers, such as PVDF, with their interesting properties, such as flexibility, resilience, and durability, which make them preferable to ferroelectric ceramics in certain applications. The discussion of
Analysis, and Design with
magnetostrictive materials, such as Terfenol-D, concludes our review of the active materials spectrum. This chapter paves way toward the next chapters, in which the use of active materials in the construction of induced-strain actuators and active sensors for micromechatronics applications will be discussed.
