INTRODUCTION

This chapter on vibration transducers is the first in a group of seven chapters on the measurement of shock and vibration. Chapter 13 describes typical instrumentation used in making measurements with such devices; Chap. 15 covers the mounting of vibration transducers and how they may be calibrated under field conditions; more precise calibration under laboratory conditions is described in detail in Chap. 18. The selection of vibration transducers is treated in Chaps. 15 and 16. This chapter defines the terms and describes the general principles of piezoelectric and piezoresistive transducers; it also sets forth the mathematical basis for the use of shock and vibration transducers and includes a brief description of piezoelectric accelerometers, piezoresistive accelerometers, piezoelectric force and impedance gages, and piezoelectric drivers, along with a review of their performance and characteristics. Finally, the following various special types of transducers are considered: optical-electronic transducers, including laser Doppler vibrometers, displacement measurement systems, fiber-optic reflective displacement sensors, electrodynamic (velocity coil) pickups, differential-transformer pickups, servo accelerometers, and capacitance-type transducers.

Certain solid-state materials are electrically responsive to mechanical force; they often are used as the mechanical-to-electrical transduction elements in shock and vibration transducers. Generally exhibiting high elastic stiffness, these materials can be divided into two categories: the self-generating type, in which electric charge is generated as a direct result of applied force, and the passive-circuit type, in which applied force causes a change in the electrical characteristics of the material.

A piezoelectric material is one which produces...