Electromagnetic and Piezoelectric Transducers

Introduction

Transducers are critical in active structures technology; they can play the role of actuator, sensor, or simply energy converter, depending on the applications. In many applications, the actuators are the most critical part of the system; however, the sensors become very important in precision engineering where sub-micron amplitudes must be detected.

Two broad categories of actuators can be distinguished: “grounded” and “structure borne” actuators. The former react on a fixed support; they include torque motors, force motors (electrodynamic shakers) or tendons. The second category, also called “space realizable”, include jets, reaction wheels, control moment gyros, proof-mass actuators, active members (capable of both structural functions and generating active control forces), piezo strips, etc... Active members and all actuating devices involving only internal, self-equilibrating forces, cannot influence the rigid body motion of a structure.

This chapter begins with a description of the voice-coil transducer and its application to the proof-mass actuator and the geophone (absolute velocity sensor). Follows a brief discussion of the single axis gyrostabilizer. The remaining of the chapter is devoted to the piezoelectric materials and the constitutive equations of a discrete piezoelectric transducer. Integrating piezoelectric elements in beams, plates and trusses will be considered in the following chapter.