Table Of ContentAcoustic Wave Sensors
Acoustic Wave Sensors
This is a volume in
APPLICATIONS OF MODERN ACOUSTICS
Series Editors:
Richard Stem Moises Levy
Applied Research Laboratory Department of Physics
Pennsylvania State University University of Wisconsin at Milwaukee
State College, Pennsylvania Milwaukee, Wisconsin
Acoustic Wave Sensors
Theory, Design, and Physico-Chemical
Applications
D. S. Ballantine, Jr. R. M. White
Chemistry Department Department of Electrical Engineering
Northern Illinois University and Computer Science
De Kalb, Illinois Berkeley Sensor & Actuator Center
University of California
Berkeley, California
S. J. Martin
A. J. Ricco
G. C. Frye E. T. Zellers
Microsensor R&D Department of Environmental
Sandia National Laboratories and Industrial Health
Albuquerque, New Mexico Department of Chemistry
University of Michigan
Ann Arbor, Michigan
H. Wohltjen
Microsensor Systems, Inc.
Bowling Green, Kentucky
ACADEMIC PRESS
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Acknowledgments
We thank Barb Wampler and Kathy Rice of Sandia National
Laboratories for assistance with graphics and proof reading of
many sections of this book, and Stuart Wenzel and Ben Costello
of Berkeley Microlnstruments for providing many of the illus-
trations in Chapter 3.
This book is printed on acid free paper. O
Copyright (cid:14)9 1997 by Academic Press
All rights reserved.
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Library of Congress Cataloging-in-Publication Data
Acoustic wave sensors ' theory, design, and physico-chemical
applications / D.S. Ballantine, Jr. ... [et al.].
p. cm.---(Applications of modern acoustics)
Includes bibliographical references and index.
ISBN 0-12-077460-7 (alk. paper)
1. Acoustic surface wave devices. 2. Detectors. 3. Chemical de-
tectors. 4. Biosensors. I. BaUantine, David Stephen. II. Series.
TK5984.A38 1996 96-21931
681 ' .2---dc20 CIP
Printed in the United States of America
96 97 98 99 00 MV 9 8 7 6 5 4 3 2 1
Table of Contents
Series Preface xi
Chapter 1 Why Acoustic Sensors?
1.1 What Is a Sensor?
1.2 The Microsensor Revolution and the Role of Acoustics
1.3 Where They Fit and How They Are Used
1.4 About the Authors and the Rest of the Book
References
Chapter 2 Fundamentals of Acoustic Waves 10
2.1 Wave Propagation in an Elastic Medium 10
2.1.1 Displacement, Stress, and Strain 12
2.1.2 Equation of Motion 15
2.1.3 Reduced Notation (Engineering Notation) 16
2.1.4 The Wave Equation 18
2.1.5 Bulk-wave Damping 21
2.2 Piezoelectricity 22
2.2.1 The Wave Equation for Piezoelectric Materials 25
2.2.2 Energy Density and Power Flow 28
2.3 Perturbations in Acoustic Wave Propagation 31
References 35
vi Contents
Chapter 3 Acoustic Wave Sensors and Responses 36
3.1 Thickness-Shear Mode (TSM) Resonator 38
3.1.1 TSM Resonator Mass Sensitivity 43
3.1.2 Electrical Characteristics of an Unperturbed TSM Resonato 45
3.1.3 Electrical Characteristics of the TSM Resonator with an Arbitrary Surface
Perturbation 48
3.1.4 Electrical Characteristics of TSM Resonator with an
Ideal Mass Layer 52
3.1.5 Electrical Characteristics of the TSM Resonator Contacted by Liquid 54
3.1.6 Effect of Surface Roughness on TSM Resonator Liquid Loading 59
3.1.7 Solid/Liquid Boundary Conditions and Wetting of Textured Surfaces 62
3.1.8 Dynamics of a TSM Resonator with a Viscoelastic Film 66
3.1.9 Electrical Characteristics of a TSM Resonator Coated with a Viscoelastic Film 68
3.2 Surface Acoustic Wave (SAW) Devices 70
3.2.1 SAW Excitation and Detection 72
3.2.2 lnterdigital Transducer Frequency Response 74
3.2.3 SAW Perturbation Mechanisms 78
3.2.4 SAW Mass Loading 80
3.2.5 SAW Acoustoelectric Response 83
3.2.6 Parametric Representation of the SAW Acoustoelectric Response 89
3.2.7 Elastic and Viscoelastic Films on a SAW Device 89
3.2.8 SAW Response from Acoustically Thin Films 93
3.2.9 SAW Response from Acoustically Thick Films 96
3.3 Acoustic Plate Mode (APM) Devices 99
3.3.1 APM/Liquid Interactions 103
3.3.2 Mass Sensitivity of the APM 104
3.3.3 APM Liquid Loading 106
3.3.4 APM Acoustoelectric Coupling 109
3.4 Flexural Plate-Wave (FPW) Devices 111
3.4.1 Flexural Plate Waves 113
3.4.1.1 Behavior of the FPW Velocities and Particle Motions
3.4.2 FPW Perturbation Mechanisms 119
3.4.2.1 Effects of Increasing the Mass/Area of the Plate 3.4.2.2E ffects of Loading
with a Non-Viscous Fluid 3.4.2.3G ravimetdc Detection of an Added Mass in a Liquid
3.4.2.4 Effects of Loading with a Viscous Liquid 3.4.2.5O ther Perturbations
3.4.3 FPW Kinetic Effects: Pumping and Mixing 134
3.4.3.1 Experimental Observations 3.4.3.2P henomena Involved 3.4.3.3 Applications
3.5 Comparisono f Acoustic Sensing Devices 140
3.5.1 Recently Introduced Acoustic Sensors 140
Contents vii
3.5.1.1 Thin-Film Compressional Bulk-Wave Sensor 3.5.1.2S urface Transverse Wave
(STW) Sensor 3.5.1.3 Love Wave Sensor 3.5.1.4T hin-Rod Flexural-WaveS ensor
3.5.2 Comparison of Gravimetric Acoustic Sensors 141
3.5.3 Qualitative Comparison of Acoustic Sensors 145
References 145
Chapter 4: Materials Characterization 150
4.1 Overview of Applications 151
4.1.1 Characterization of Thin Film Materials 151
4.1.2 Characterization of Fluid Properties 153
4.2 Characterization of Polymers 154
4.2.1 Viscoelastic Properties 155
4.2.1.1 Determination of Transition Temperatures 4.2.1.2 Extraction of Storage
and Loss Moduli 4.2.1.3 Absorption Phenomena and Plasticization
4.2.2 Diffusion and Permeation 167
4.2.2.1 Real-Time Monitoring 4.2.2.2 Fickian Diffusion 4.2.2.3 Non-Fickian Diffusion
4.2.2.4 Permeation Rate Evaluation
4.3 Surface Adsorption and Characterization of Porous Films 179
4.3.1 Physisorption: Characterizing Surfaces and Pores 179
4.3.1.1 Characterizing Surfaces and Adsorbed Layers 4.3.1.2 Characterizing Film
Surface Area and Pore Size Distribution 4.3.1.3 AW Device Results with Porous Films
4.3.2 Chemisorption 191
4.3.2.1 Overview of Chemisorption 4.3.2.2 Self-Assembling Films
4.3.3 Adsorption at Solid-Liquid Interfaces 193
4.4 Real-Time Monitoring of Chemical and Materials Processes 197
4.4.1 Monitoring Film and Particle Deposition and Removal 197
4.4.2 Polymerization Reactions 200
4.4.3 Corrosion Monitoring 205
4.4.4 Electrochemical Studies 207
4.4.5 Miscellaneous Materials/Process Characterization 209
4.5 Summary 210
References 212
Chapter 5: Chemical and Biological Sensors 222
5.1 Introduction 222
5.2 Detection Mechanisms 223
5.2.1 Mass Loading 225
viii Contents
5.2.2 Mechanical Properties 228
5.2.3 Rheological Properties 233
5.2.4 Electrical Properties 234
5.2.5 Thermal Effects 238
5.3 Performance Criteria 238
5.3.1 Selectivity 239
5.3.2 Reversibility: Sensors and Dosimeters 241
5.3.3 Sensitivity 243
5.3.4 Dynamic Range 244
5.3.5 Stability, Repeatability, Reliability, and Reproducibility 245
5.3.6 Response Time 246
5.3.7 Environmental Effects 247
5.4 Coating-Analyte Interactions and Acoustic-Wave Chemical Sensors 248
5.4.1 Physical and Chemical Interactions 251
5.4.2 Thermodynamics of Adsorption: Adsorption Isotherms 256
5.4.2.1 Langmuir Isotherm 5.4.2.2 Freundlich Adsorption Isotherm
5.4.2.3 BET Adsorption Model 5.4.2.4 Capillary Condensation; Other Models
5.4.3 Kinetics of Adsorption 266
5.4.3.1 Rate Expressions 5.4.3.2 Transport through Films
5.4.4 Adsorption-Based Acoustic-Wave Sensors 272
5.4.4.1 Common Materials for Physical Adsorption 5.4.4.2 Physisorption-Based Sensors
5.4.4.3 Chemisorption-BasedS ensors
5.4.5 Absorption and Polymer Sorption 288
5.4.5.1 Overview of Polymer Sorption Isotherms 5.4.5.2 Normal Boiling Point Model
5.4.5.3 Regular Solution Theory (Hildebrand Solubility Parameter) 5.4.5.4 Linear Solva-
tion Energy Relationships (Solvatochromatic Parameters) 5.4.5.5 Empirical Methods
5.4.6 Absorption-Based Sensors 300
5.4.7 Biochemical Interactions and Acoustic-Wave Sensors 306
5.5 Selectivity Revisited: Sensor Arrays and Pattern Recognition 313
5.5.1 Coating Selection 314
5.5.2 Sensor Array Data Interpretation 315
5.6 Summary 320
References 320
Chapter 6: Practical Aspects of Acoustic-Wave Sensors 331
6.1 Introduction 331
6.2 Basics of Acoustic-Wave Sensor Design and Fabrication 332
6.2.1 Device Configurations 332
Contents ix
6.2.1.1 One-Port: Bulk and SAW Resonators 6.2.1.2T wo-Ports: SAW, APM
and FPW Delay Lines and Resonators
6.2.2 Substrate Materials 337
6.2.3 Interdigital Transducer Design 339
6.2.4 Microfabrication Technology 342
6.2.4.1 Metal Selection and Deposition 6.2.4.2P hotolithographic Patterning
6.2.4.3 Preparation for Packaging
6.2.5 Chemically Selective Coatings: Requirements and Methods of Application 347
6.2.5.1 General Coating Requirements 6.2.5.2 Solution-Phase Methods of Application
6.2.5.3 Vapor-Phase Methods of Application
6.3 Acoustic-Wave Measurement Technology 355
6.3.1 Instrumentation and Components 355
6.3.2 Measurement of Acoustic-Wave Device Frequency Response 357
6.3.2.1 One-Port Devices 6.3.2.2T wo-Port Devices
6.3.3 Real-Time Monitoring of Acoustic-Wave Devices for Sensing
and Characterization Applications 361
6.3.3.1 Simultaneous Measurement of Acoustic-Wave Velocity and Attenuation
6.3.3.2 One-Port Devices 6.3.3.3 Two-Port Devices: Oscillator Circuits 6.3.3.4T wo-
Port Devices: Propagation Measurements 6.3.3.5 Two-Port Devices: Phase-Locked Loops
6.4 Controlling the Sensor Environment 375
6.4.1 Temperature Effects and the Need for Temperature Control 375
6.4.2 Pressure Effects 378
6.4.3 Flow-Rate Effects 378
6.4.4 Sensor Packaging Considerations 379
6.4.5 Remote Sensor Location Schemes 382
6.5 Enhancing Sensor Performance by System Design 384
6.5.1 Baseline Drift Compensation Strategies 384
6.5.2 Vapor Concentration Enrichment 386
6.5.3 Array Sensors and Pattern Recognition 390
6.6 System Design Challenges 393
References 394
Appendix A: Lists of Symbols by Chapter 396
Appendix B" Glossary of Terms 408
Appendix C: Polymeric Materials 421
Appendix D: Commercial Sources for Acoustic-Wave Substrates,
Devices,and Systems 428
Index 430
