Piezoelectric Sensorics: Force Strain Pressure Acceleration and Acoustic Emission Sensors Materials and Amplifiers

271 Pages·2002·6.49 MB·English

by  Dip.-Ing.ETH Gustav Gautschi (auth.)

G.Gautschi
Piezoelectric Sensorics
Springer-Verlag Berlin Heidelberg GmbH
G. Gautschi
Piezoeleetrie Sensories
Force
Strain
Pressure
Acceleration and Acoustic Emission Sensors
Materials and Amplifiers
With 175 Figures
Springer
Dipl.-Ing. ETH Gustav Gautschi
Oetlisbergstr. 25
CH-8053 Zürich
Switzerland
e-mail: [email protected]
ISBN 978-3-642-07600-8 ISBN 978-3-662-04732-3 (eBook)
DOI 10.1007/978-3-662-04732-3
Library of Congress Cataloging -in -Publieation -Data
Gautsehi, G. (Gustav), 1936-
Piezoelectrie sensories : force, strain, pressure, acceleration and acoustie emission sensors, materials and
amplifiers / G. Gautschi.
p.em.
Rev. and enlarged translation of chapters 6 -12 of German text by Jan Tiehy and Gustav Gautsehi.
Includes bibliographieal references and index.
1. Piezoelectrie transducers.1. Title.
TK7872.P54 G38 2002
681'.2-dc21
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Preface
Sensors are the key to life and survival - and to the success of modern technology.
Nature has provided living creatures with a wealth of sensors for a variety of
measurands, such as light, sound, temperature, speed, motion, distance, force,
pressure, acceleration, odor and so on - sensors, whose performance and
specifications have often not been matched yet by man-made devices. Even at
today's high level of electronics and information technology, sensors remain the
crucial and decisive interface needed to reliably relate phenomena occurring in the
environment to corresponding electric signals that can be processed to obtain the
desired information and subsequent correct reaction of systems.
Although the literature on sensors is extremely vast, there is one type of sensors
which so far has received little attention: the piezoelectric sensor. Certainly, most
handbooks on measurement mention briefly this type of sensor yet there is not a
single book in the English language dedicated entirelyto piezoelectric sensors and
giving a reasonably complete overview. There are only the books by [Gohlke 1955
and 1959] and [Tichy and Gautschi 1980], all in German.
The information and explanation given on piezoelectric sensors in
measurement handbooks is - regrettably - rather terse and often quite limited. In
particular there are certain prejudices and even misconceptions about
piezoelectric sensors that have been perpetuated over many years and still persist
today, such as: "piezoelectric sensors can only be used for dynamic measurements
and are usually limited to measuring vibration". My practical experience of over
30 years in the field and elose contact with countless users of sensors worldwide,
has confirmed again and again that there is indeed a widespread lack of full
understanding of the nature of piezoelectric sensors and their applications, both
in academia and industry.
Therefore the goal of this book is to give a comprehensive overview of
piezoelectric sensors, their characteristics and their proven practical applications.
The book is not intended to be an instruction on how to build piezoelectric
sensors. Rather, their properties and their "behavior" as sensing devices are
presented with the aim to enable the reader to make a better and more objective
choice when looking for a suitable sensor to fulfill a given measuring task. For each
type of sensor, some exemplary applications are described to illustrate the
possibilities offered and to give the reader ideas for his own work.
In chapter 1, abrief comparison of the piezoelectric sensing principle with other
types of sensors illustrates the possibilities offered. The historic background
VI Preface
highlighted in chapter 2 describes a number of interesting facts whieh are not so
weIl known generally. The piezoelectric materials and their physical properties
currently used in sensors are presented in chapter 3. An important but often
neglected subject is the terminology for correctly defining and comparing the
characteristies (specifications) of sensors, the topic of chapter 4. Chapter 5 gives
an overview of the parts and the basie design of sensors. Sensors for the
measurands force, strain, pressure, acceleration and acoustic emission are presented
in chapters 6 to 10. These chapters are intentionally weIl illustrated to show the
reader the great variety of applications existing for piezoelectrie sensors.
Chapter 11 treats the amplifiers used with piezoelectrie sensors and their
partieular nature. Here again there are still widespread misconceptions about
these amplifiers because the output signal of piezoelectric sensors - electrie charge
- is not so often encountered in other fields of measuring electronies.
The number of references cited had to be kept within reasonable limits and is
far from exhaustive. Readers may also refer to the included list of manufacturers
of piezoelectrie sensors from whom more information can be obtained.
The first book written together with Jan Tiehy [Tiehy and Gautschi 1980]
covered both, the theory of the physics of crystals, and the piezoelectrie sensors
and their applications. Practieal considerations prompted us to split the book into
two volumes. This book corresponds to the second part (chapters 6 ... 12) ofthe
previous book, considerably enlarged and brought up to date. The chapters on the
measurands strain and acoustic emission are new. The first part of the previous
book authored by Jan Tichy (chapters 1 ... 6) has also been rewritten, enlarged and
updated by Jid Erhart, Jan Fousek, Vaclav Janovec, Jana Privratska and Jan Tichy
[Erhard et al 2002]. Therefore, the two new volumes are complementary, but can
be used separately, too.
I am highly indebted to a number of friends and colleagues who significantly
contributed to the manuscript. Claudio Cavalloni reviewed the manuscript and
wrote the chapter 3.5 on the new materials of the CGG group while Roland Sommer
contributed to the chapter 3.7 on piezoelectrie ceramies and thin films. Wolfgang
Wallnöfer and Peter Worsch provided the chapter 3.4 on gallium orthophosphate.
The manuscript was also critieally reviewed and commented on by Christoph
Gossweiler, Karl-Heinz Martini and Jan Tiehy, co-author of our first book in German.
My thanks go to a number of sensor manufacturers who generously contributed
material that serves to exemplify the vast range and variety of applications.
Throughout the project, the staff of the Springer-Verlag offered an excellent
co operation and continuous support for which I am especially grateful.
Although this book is based on the previous German edition and has been
enlarged, it is a first attempt to cover the entire field of piezoelectric sensors in a
single volume. There is certainly room for improvement and I greatly welcome
comments, criticism and suggestions ([email protected]) to
consider for further enhancing a next edition.
Zurich, November 2001
Gustav H. Gautschi
Contents
Symbols, Quantities and Units ...................................... XI
1 Introduction ............................................. 1
2 Background of Piezoelectric Sensors ........................ 5
2.1 Direct and Converse Piezoelectric Effect ..................... 5
2.2 Discovery of the Piezoelectric Effect ........................ 6
2.3 Applications of the Converse Piezoelectric Effect ............. 8
2.4 History of Piezoelectric Sensors ............................ 9
3 Piezoelectric Materials for Sensors ......................... 13
3.1 Requirements of Piezoelectric Materials for Sensors ........... 13
3.2 Quartz .................................................. 14
3.2.1 Choice of Co ordinate System ............................... 15
3.2.2 Physical Properties ....................................... 17
3.2.3 Synthetic Quartz Crystals .................................. 20
3.2.4 Twinning ................................................ 21
3.2.5 Suppressing Secondary Twinning ........................... 26
3.2.6 Temperature Dependence of Piezoelectric Constants .......... 27
3.2.7 Nonlinear Electromechanical Properties of a-Quartz .......... 29
3.2.8 Piezoelectric Properties of ß-Quartz ........................ 30
3.3 Tourmaline .............................................. 31
3.4 Gallium Orthophosphate .................................. 35
3.5 Crystals of the CGG Group ................................. 37
3.6 Other Piezoelectric Single Crystals .......................... 40
3.7 Piezoelectric Textures ..................................... 43
3.7.1 Piezoelectric Ceramics .................................... 43
3.7.2 Piezoelectricity in Thin Films .............................. 50
4 Piezoelectric Sensor Terminology .......................... 51
4.1 Definition of a Sensor ..................................... 52
4.2 Properties of Sensors ..................................... 53
4.2.1 Static Characteristics ..................................... 53
4.2.1.1 Properties Relating to the Measurand ....................... 53
4.2.1.2 Properties of the Relationship Between Measurand
and Output .............................................. 55
VIII Contents
4.2.1.3 Influence of Temperature on the Relationship Between
Measurand and Output .................................... 60
4.2.1.4 Influence of Acceleration and Vibration on the Relationship
Between Measurand and Output ............................ 65
4.2.1.5 Drift, Stability and Repeatability ............................ 65
4.2.2 Dynamic Characteristics .................................. 66
4.2.3 Electrical Characteristics .................................. 70
4.2.4 Effects of Sensor Mounting ................................ 70
4.2.5 Lifetime of a Sensor ....................................... 71
4.2.6 Cross Talk ............................................... 72
5 Piezoelectric Sensors ..................................... 73
5.1 Introduction ............................................. 73
5.2 Fundamental Observations on Measuring Force .............. 74
5.3 Basic Design of a Sensor ................................... 76
5.4 General Review of Practical Sensor Designs .................. 81
5.5 Components of a Sensor ................................... 85
5.5.1 Transduction Elements .................................... 85
5.5.1.1 Quartz .................................................. 85
5.5.1.2 Tourmaline .............................................. 87
5.5.1.3 Crystals of the CGG-Group and Gallium Orthophosphate ...... 87
5.5.1.4 Piezoelectric Ceramics .................................... 87
5.5.2 Electrodes ............................................... 88
5.5.3 Insulating Materials ...................................... 89
5.5.4 Preloading Elements ...................................... 89
5.5.5 Sensor Housings ......................................... 90
5.5.6 Connectors .............................................. 90
6 Force and Torque Sensors ................................. 93
6.1 Quantity, Units of Measurement, and Co ordinate Systems ...... 93
6.2 Force Sensors ............................................ 94
6.2.1 Sensors for Compression Force ............................. 94
6.2.2 Linear Compression Force Sensors .......................... 95
6.2.3 Measuring Tension Force with Preloaded Force Sensors ....... 97
6.3 Multicomponent Force Sensors ............................. 102
6.4 Torque Sensors ........................................... 105
6.5 Cross Talk in Single-and Multicomponent Force Sensors ...... 106
6.6 Mounting Force Sensors ................................... 109
6.7 Measuring 3 Forces and 3 Moments (6 Components) .......... 112
6.8 Calibration of Force Sensors ............................... 123
7 Strain Sensors ........................................... 127
7.1 Quantity and Units of Measurement ........................ 127
7.2 Working Principle of Piezoelectric Strain Sensors ............. 127
Contents IX
7.3 Surface Strain Sensors .................................... 128
7.4 Strain Pins for Internal Strain .............................. 130
7.4.1 Longitudinal Strain Pins ................................... 130
7.4.1.1 Measuring Tie Bar Loading ................................ 131
7.4.1.2 Measuring Pressure Variations in Thick-Walled Pipes ......... 132
7.4.2 Transverse Strain Pins ..................................... 134
7.5 Omnidirectional Strain Sensors ............................ 136
7.6 Piezoelectric "Strain Gage" ................................. 137
7.7 Multiaxial Strain Sensors .................................. 138
7.8 Calibration of Piezoelectric Strain Sensors ................... 139
8 Pressure Sensors ......................................... 141
8.1 Quantity and Units of Measurement ........................ 141
8.2 Design of Piezoelectric Pressure Sensors ..................... 142
8.3 Low-Pressure Sensors ..................................... 144
8.4 Pressure Sensors for General Applications ................... 146
8.5 High-Pressure Sensors .................................... 148
8.6 Pressure Sensors with Acceleration Compensation ............ 150
8.7 Pressure Sensors for High Temperature ...................... 155
8.8 Sensors for Cylinder Pressure in Internal Combustion Engines .. 156
8.9 Sensors for Cavity Pressure in Plastics Processing and in
Die Casting of Metals ..................................... 159
8.10 Calibration of Pressure Sensors ............................. 161
9 Acceleration Sensors ...................................... 167
9.1 Quantity and Units of Measurement ........................ 167
9.2 Basic Properties of Acceleration Sensors ..................... 167
9.3 Designs of Piezoelectric Acceleration Sensors ................ 177
9.4 Characteristics of Sensors with Piezoelectric Ceramic or
Tourmaline Elements ..................................... 181
9.5 Acceleration Sensors with High Sensitivity ................... 183
9.6 Acceleration Sensors for General Applications ................ 184
9.7 Acceleration Sensors for Measuring Shock ................... 186
9.8 Acceleration Sensors for High Temperature .................. 188
9.9 Acceleration Sensors for Low Temperature ................... 190
9.10 Acceleration Sensors for Modal Analysis ..................... 190
9.11 Triaxial Acceleration Sensors ............................... 193
9.12 Calibration of Acceleration Sensors ......................... 194
10 Acoustic Emission Sensors ................................ 199
10.1 Quantity and Units of Measurement ........................ 199
10.2 Background of AE as Process Parameter ..................... 200
10.3 Design of AE Sensors ..................................... 201
10.4 AE Sensors for Process Monitoring ......................... 203