Mechanica1 Engineering Series

Frederick F. Ling Series Editor

Springer-Science+ Business Media, LLC

Mechanical Engineering Series

Introductory Attitude Dynamics F.P. Rimrott

Balancing of Bigh-Speed Machinery M.S. Darlow

Theory of Wire Rope, 2nd ed. G.A. Costello

Theory of Vibration: An Introduction, 2nd ed. A.A. Shabana

Theory of Vibration: Discrete and Continuous Systems, 2nd ed. A.A. Shabana

Laser Machining: Theory and Practice G. Chryssolouris

Underconstrained Structural Systems E.N. Kuznetsov

Principles of Beat Transfer in Porous Media, 2nd ed. M. Kaviany

Mechatronics: Electromechanics and Contromechanics D.K. Miu

Structural Analysis of Printed Circuit Board Systems P.A. Engel

Kinematic and Dynamic Simulation of Multibody Systems: The Real-Time Challenge J. Gareia de Jal6n and E. Bayo

Bigh Sensitivity Moire: Experimental Analysis for Mechanics and Materials D. Post, B. Han, and P. Ifju

Principles of Convective Beat Transfer M. Kaviany

Laminar Viscous Flow V.N. Constantinescu

(continued after index)

Ilene J. Busch-Vishniac

Electromechanical Sensors and Actuators

With 378 Figures

, Springer

Ilene J. Busch-Vishniac Dean, Whiting School of Engineering Johns Hopkins University 3400 N. Charles Street Baltimore, MD 21218-2681, USA

Series Editor Frederick F. Ling Emest F. Gloyna Regents Chair in Engineering Department of Mechanical Engineering The University of Texas at Austin Austin, TX 78712-1063, USA

and William Howard Hart Professor Emeritus Department of Mechanical Engineering,

Aeronautical Engineering and Mechanics Rensselaer Polytechnic Institute Troy, NY 12180-3590, USA

Library of Congress Cataloging-in-Publication Data Busch-Vishniac. Hene 1.

Eleetromechanical sensors and actuators I Hene 1. Busch-Vishniae. p. em. - (Meehanical engineering series)

IncJudes bibliographieal references and index. ISBN 978-1-4612-7142-0 ISBN 978-1-4612-1434-2 (eBook) DOI 10.1007/978-1-4612-1434-2

1. Transdueers. 2. Deteetors. 3. Aetuators. 1. Tide. II. Series: Mechanical engineering series (Berlin, Germany) TK7872.T6B87 1998 681' .2--dc21 98-11966

Printed on acid-free paper.

II;:) 1999 Springer Science+Business Media New York Originally published by Springer-Verlag New York Berlin Heidelberg in 1999 Softcover reprint of the hardcover 1 st edition 1999

All rights reserved. This work may not be translated or eopied in whole or in part without the written permission of the publisher (Springer Science+Business Media, LLC), except for brief excerpts in connection with reviews or scholarly analysis. U se in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use of general descriptive names, trade names, trademarks, etc., in this publication, even if the former are not especially identified, is not to be taken as a sign that such names, as understood by the Trade Marks and Merchandise Marks Act, may accordingly be used freely by anyone.

Production managed by Timothy Taylor; manufacturing supervised by Jacqui Ashri. Photoeomposed eopy prepared using the eompositor's TEX files.

987 6 5 4 3 2 1

SPIN 10658156

For Ethan, Cady, and Miriam, the lights on my journey.

Mechanical Engineering Series

Frederick F. Ling Series Editor

Advisory Board

Applied Mechanics

Biomechanics

Computational Mechanics

Dynamical Systems and Control

Energetics

Mechanics of Materials

Processing

Production Systems

Thermal Science

Tribology

FA Leckie University of California, Santa Barbara

v.c. Mow Columbia University

H.T. Yang University of California, Santa Barbara

K.M. Marshek University of Texas, Austin

J.R. Welty University of Oregon, Eugene

I. Finnie University of California, Berkeley

K.K. Wang Cornell University

G.-A. Klutke Texas A&M University

A.E. Bergles Rensselaer Polytechnic Institute

W.O. Winer Georgia Institute of Technology

Series Preface

Mechanical engineering, an engineering discipline borne of the needs of the industrial revolution, is once again asked to do its substantial share in the call for industrial renewal. The general call is urgent as we face profound issues of productivity and competitiveness that require engineering solutions, among oth­ers. The Mechanical Engineering Series features graduate texts and research monographs intended to address the need for information in contemporary areas of mechanical engineering.

The series is conceived as a comprehensive one that covers a broad range of concentrations important to mechanical engineering graduate education and research. We are fortunate to have a distinguished roster of consulting editors on the advisory board, each an expert in one of the areas of concentration. The names of the consulting editors are listed on the facing page of this volume. The areas of concentration are: applied mechanics; biomechanics; computational mechanics; dynamic systems and control; energetics; mechanics of materials; processing; thermal science; and tribology.

I am pleased to present this volume in the Series: Electromechanical Sensors and Actuators, by Ilene Busch-Vishniac. The selection of this volume under­scores again the interest of the Mechanical Engineering series to provide our readers with topical monographs as well as graduate texts in a wide variety of fields.

Austin, Texas Frederick F. Ling

Vll

Preface

In the past few decades improvements in electronics have outpaced improve­ments in sensors and actuators so significantly that in virtually all measurement and control systems it is the sensors and actuators which account for the bulk of the expense, the majority of the size, and the lion's share of the system failures. For improvements to be forthcoming, it clearly is necessary to under­stand how sensors and actuators work. The aim of this book is to provide a detailed description of the various mechanisms that can be exploited in the de­sign of electromechanical sensors and actuators.

There are a number of books available on sensors and measurements, but this book is a significant departure from the norm. The typical book on sensors or on measurements is either a compendium of commercially available devices, or a discussion of techniques used in sensing various parameters (e.g., acceleration, force, displacement, etc.). What these approaches obscure is that different sorts of devices might well use the same fundamental coupling mechanism to link electrical and mechanical behavior. For instance, an ultrasonic cleaner and an accelerometer might be nearly identical, despite their seemingly disparate appli­cations. In this book, the focus is on the fundamental coupling mechanisms. As each mechanism is presented, commercially available sensors and actuators from a wide a range of applications are given.

The standard treatment of measurement also draws a strong distinction be­tween sensing and actuation, although the devices used might be nearly identical in means of operation. For instance, a solenoid can be used either to sense a

ix

x Preface

position (sensor) or to impose a position (actuator). While the optimal geometric design and choice of materials might well depend on which of these two opera­tions the transducer is aimed to perform, the fundamental means by which the electrical and mechanical domains are coupled are identical. In this book, both sensors and actuators are treated, and the analysis developed applies uniformly to both unless otherwise stated.

By focusing on the fundamental coupling between electrical and mechanical energy domains, this book arms the reader with an arsenal that is appropriate for transducer design. Because the book grew out of notes used in a graduate course on electromechanical sensors and actuators at The University of Texas, the analytical developments are the sort we would find in a textbook rather than a handbook. Additionally, a large number of examples of commercially avail­able transducers are presented. These examples serve to define the state-of-the­art electromechanical transduction, and provide a vehicle for discussion of some of the more practical issues associated with transducer design and use. A signifi­cant amount of the material contained within has never been previously pub­lished, so this book is a combination of a textbook and a research monograph, appropriate for both students and practitioners with an interest in the measure­ment and control of mechanical systems.

This book is divided into three parts. Chapters 1 and 2 form the introductory part of the book, entitled Basic Tools for Transducer Modeling. Chapters 3 to 8 constitute the Transduction Mechanisms part of the book. Each chapter dis­cusses a particular class of transduction mechanisms. For example, Chapter 3 deals with transduction based on changes in the energy stored in an electric field. Each chapter in this part of the book provides an analytical description of the transduction mechanisms and examples of devices using that method. These examples incorporate a wide variety of applications, sizes, scales, and sophisti­cation. Chapters 9 to 11 form the Transducer Theory and Description part of the book. This section deals with 2-port theory, which applies generally to trans­ducers, and with the meaning of various specifications associated with trans­ducers.

Baltimore, Maryland Ilene J. Busch-Vishniac

Acknowledgments

This manuscript is the culmination of years of conversations with leading au­thorities in the field of transduction. Without the help of my colleagues this text would never have appeared. I am particularly indebted to Elmer Hixson for introducing me to his way of thinking about sensors and actuators, and to David Blackstock and Mark Hamilton for their encouragement while I labored over this book. I am also grateful to my students, who inspired the writing and helped me find errors.

Most of this book was written while I was on the faculty of The University of Texas at Austin. The final stages were completed at Boston University, where I spent a year on sabbatical thanks to the generosity of Allan Pierce.

A great deal of the painstaking work for this book required the careful atten­tion of Cindy Pflughoft, the world's greatest secretary. Without her willingness to track down sources and organize my files of catalogs and papers, this book would not have been possible.

Baltimore, MD Ilene J. Busch-Vishniac

Xl

Contents

Series Preface vii

Preface Ix

Acknowledgments xi

I Basic Tools for Transducer Modeling 1

1 Introduction 3 1.1 What Is a Transducer? . . . . . . . . . . . . . . . . 3 1.2 Why Study Transducers? .............. 7 1.3 Division of Transducers into Sensors and Actuators 8 1.4 Transducers as Part of a Measurement or Control System 11 1.5 Historical Perspective . . 13 1.6 Organization of this Book . . . . . . . . . . . . . . . . . 14

2 System Models 17 2.1 System Analogies . . . . . . . . . . . . . . . . . . . 18 2.2 Ideal I-Port Elements . . . . . . . . . . . . . . . . . 22

2.2.1 Comments on Modeling and I-Port Elements 27 2.3 Circuit Models . . . . . . . . 29 2.4 Bond Graph Models . . . . . 34 2.5 Nonenergic 2-Port Elements. 43 2.6 Multiport Energic Elements . 45

XIV Contents

2.7 Model Analysis 2.8 References...

II Transduction Mechanisms

3 Transduction Based on Changes in the Energy Stored in an Electric

50 52

55

Field 59 3.1 Electric Fields and Forces . . . . . . . . . . . . . . . . . . .. 59 3.2 Transducers Made with a Variable Gap Parallel Plate Capacitor. 63

3.2.1 Relating Displacement and Voltage. 66 3.2.2 Relating Force and Voltage . . . . . . . . . . . . . .. 74 3.2.3 Relating Force and Charge . . . . . . . . . . . . . .. 78

3.3 Transducers Using Other Means of Varying the Capacitance in a Parallel Plate Capacitor . . 79 3.3.1 Variable Area . . . . . . . . . . 79 3.3.2 Varying Permittivity. . . . . . . 85

3.4 Transducers with Cylindrical Geometry. 89 3.5 Gradient Transduction Using Two Dielectrics 92 3.6 Electrostrictive Transduction 96 3.7 Summary. 97 3.8 References.......... 98

4 Transduction Based on Changes in the Energy Stored in a Magnetic Field 100 4.1 Magnetic Systems . . . . . 100

4.1.1 Magnetic Materials 105 4.1.2 Magnetic Circuits . 106

4.2 Variable Reluctance Transducers with Varying Gap 107 4.2.1 Relating Displacement and MAGNETOMOTANCE 110 4.2.2 Relating Force and Magnetomotance . . . . . . 116 4.2.3 Relating Force and Flux. . . . . . . . . . . . . 117

4.3 Variable Reluctance Transducers with Varying Permeability and Area . . . . . . . . . . . 121 4.3.1 Variable Area . . . . . . . . . . . . . . . . . . . 122 4.3.2 Variable Permeability . . . . . . . . . . . . . . . 123

4.4 Gradient Transduction with Two Ferromagnetic Materials 129 4.5 Magnetostrictive Transduction 131 4.6 Eddy Current Transducers. 134 4.7 Summary.. 137 4.8 References......... 138

5 Piezoelectricity and Pyroelectricity 140 5.1 Piezoelectric Relations. 142 5.2 Piezoelectric Materials ..... 147

Contents xv

5.3 Piezoelectric Structures in Transducers 154 5.4 Models of Piezoelectricity . . . . . . . 159 5.5 Examples of Piezoelectric Transducers 163

5.5.1 Examples of Broadband Transducers Using One Piezoelectric Element or a Stack of Parallel Piezoelectric Elements ... . . . . . . . . . . . 164

5.5.2 Examples of Resonant Transducers Using a Single Piezoelectric Element or Element Stack ..... . 170

5.5.3 Example ofa Transducer Using Multiple Nonparallel Piezoelectric Elements ...... . . . . . . . . .. 172

5.5.4 Examples of Transducers which Are Unconventional 173 5.6 Pyroelectricity 177 5.7 Summary. 179 5.8 References.. 181

6 Linear Inductive Transduction Mechanisms 184 6.1 Piezomagnetism....... 185 6.2 Pyromagnetism............. 187 6.3 Charged Particle Interactions . . . . . . 188

6.3.1 Examples of Transducers Based on the Motion of Charged Particles in a Magnetic Field 190

6.4 Hall Effect Transducers . . . . . . . 195 6.4.1 Example Hall Effect Sensors 200

6.5 Summary. 203 6.6 References.............. 206

7 Transduction Based on Changes in the Energy Dissipated 207 7.1 Conductive Switches. . . . . . . . . . . . . . . . 208 7.2 Continuously Variable Conductivity Transducers. 210 7.3 Potentiometric Devices ... 213 7.4 Piezoresistivity.......... 216

7.4.1 Material Description .. 217 7.4.2 Strain Gauge Structures . 219 7.4.3 ElectricalOperation. 225

7.5 Thermoresistivity... 228 7.6 Thermoelectricity...... 234

7.6.1 Seebeck Effect ... 234 7.6.2 Peltier and Thomson Effects 240

7.7 Magnetoresistivity.......... 242 7.8 Shape Memory Alloys in Transduction 243 7.9 Summary. 247 7.10 References............... 247

8 Optomechanical Sensors 8.1 Quantum Detectors

250 252

xvi Contents

8.1.1 Photoconductive Sensors . . . . 8.2 Fiber Optic Waveguide Fundamentals . . 8.3 Intensity-Modulated Fiber Optic Sensors 8.4 Phase-Modulated Sensors 8.5 Photostriction 8.6 Summary.. 8.7 References..

III Analysis of Transducers

9 2-port Theory 9.1 Basic 2-Port Equations 9.2 Reciprocity ...... . 9.3 Connected 2-Ports . . . 9.4 Transfer Matrix and Sensitivity . 9.5 Wave Matrix Representation and Efficiency 9.6 Summary .. 9.7 References..................

10 Response Characteristics 10.1 Response Characteristics Defined . . . . . . . . . . .

10.1.1 Example of Transducer Selection Based on Specifications . . . .

10.2 Calibration.......... 10.3 Frequency and Time Scaling 10.4 Summary.. 10.5 References .....

11 Practical Considerations 11.1 Digitization of Analog Signals 11.2 Signal Conditioning

11.2.1 Filtering . . . . . . . . 11.2.2 Amplifying . . . . . .

11.3 Novel Sensing/Actuation Techniques 11.3.1 Frequency Detection Schemes 11.3.2 Lapsed Time Detection .

11.4 Spatially Distributed Transducers 11.5 Summary.. 11.6 References............

Index

253 256 262 271 273 274 275

277

279 279 285 288 291 293 299 299

300 300

308 310 316 318 318

320 321 325 325 330 331 331 334 335 337 337

339