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ACOUSTICAL IMAGING

ACOUSTICAL IMAGING

TECHNIQUES AND APPLICATIONS FOR ENGINEERS

Woon Siong Gan

Acoustical Technologies Singapore Pte Ltd

A John Wiley & Sons, Ltd., Publication

This edition first published 2012C 2012 John Wiley & Sons, Ltd

Registered office

John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, United Kingdom

For details of our global editorial offices, for customer services and for information about how to apply for permission to reuse the copyright material in this book please see our website at www.wiley.com.

The right of the author to be identified as the author of this work has been asserted in accordance with the Copyright, Designs and Patents Act 1988.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior permission of the publisher.

Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books.

Designations used by companies to distinguish their products are often claimed as trademarks. All brand names and product names used in this book are trade names, service marks, trademarks or registered trademarks of their respective owners. The publisher is not associated with any product or vendor mentioned in this book. This publication is designed to provide accurate and authoritative information in regard to the subject matter covered. It is sold on the understanding that the publisher is not engaged in rendering professional services. If professional advice or other expert assistance is required, the services of a competent professional should be sought.

Library of Congress Cataloging-in-Publication Data

Gan, Woon Siong.

Acoustical imaging : techniques and applications for engineers / Woon Siong Gan. p. cm.

Includes bibliographical references and index. ISBN 978-0-470-66160-4 (hardback)

1.Acoustic imaging. 2. Sound-waves–Scattering. I. Title.

TA1770.G36 2012 620.2 8–dc23

2011052023

A catalogue record for this book is available from the British Library.

ISBN: 978-0-470-66160-4

Typeset in 10/12pt Times by Aptara Inc., New Delhi, India

Contents

About the Author

xv

Foreword

 

xvii

1

Introduction

1

 

References

4

2

Physics of Acoustics and Acoustical Imaging

5

2.1

Introduction

5

2.2

Sound Propagation in Solids

5

 

2.2.1

Derivation of Linear Wave Equation of Motion and

 

 

 

its Solutions

5

2.2.2Symmetries in Linear Acoustic Wave Equations and the

 

 

New Stress Field Equation

6

2.3

Use of Gauge Potential Theory to Solve Acoustic Wave Equations

7

2.4

Propagation of Finite Wave Amplitude Sound Wave in Solids

8

 

2.4.1

Higher-Order Elasticity Theory

9

 

2.4.2

Nonlinear Effects

9

 

2.4.3

Derivation of the Nonlinear Acoustic Equation of Motion

9

 

2.4.4

Solutions of the Higher-Order Acoustics Equations of Motion

10

2.5

Nonlinear Effects Due to Energy Absorption

11

 

2.5.1

Energy Absorption Due to Thermal Conductivity

11

 

2.5.2

Energy Absorption Due to Dislocation

11

2.6

Gauge Theory Formulation of Sound Propagation in Solids

12

2.6.1Introduction of a Covariant Derivative in the Infinitesimal

Amplitude Sound Wave Equation

13

2.6.2Introduction of Covariant Derivative to the Large Amplitude

 

 

Sound Wave Equation

13

 

References

14

3

Signal Processing

15

3.1

Mathematical Tools in Signal Processing and Image Processing

15

 

3.1.1

Matrix Theory

15

3.1.2

Some Properties of Matrices

16

vi

 

 

Contents

 

3.1.3

Fourier Transformation

17

 

3.1.4

The Z-Transform

22

3.2

Image Enhancement

23

 

3.2.1

Spatial Low-Pass, High-Pass and Band-Pass Filtering

23

 

3.2.2

Magnification and Interpolation (Zooming)

24

 

3.2.3

Replication

24

 

3.2.4

Linear Interpolation

24

 

3.2.5

Transform Operation

24

3.3

Image Sampling and Quantization

24

 

3.3.1

Sampling versus Replication

26

 

3.3.2

Reconstruction of the Image from its Samples

26

 

3.3.3

Nyquist Rate

27

 

3.3.4

Sampling Theorem

27

3.3.5Examples of Application of Two-Dimensional

 

 

Sampling Theory

27

 

3.3.6

Sampling Theorem for Radom Fields

28

 

3.3.7

Practical Limitation in Sampling and Reconstruction

28

 

3.3.8

Image Quantization

28

3.4

Stochastic Modelling of Images

28

 

3.4.1

Autoregressive Models

29

 

3.4.2

Properties of AR Models

30

 

3.4.3

Moving Average Model

30

3.5

Beamforming

30

 

3.5.1

Principles of Beamforming

30

 

3.5.2

Sonar Beamforming Requirements

32

3.6

Finite-Element Method

32

 

3.6.1

Introduction

32

 

3.6.2

Applications

33

3.7

Boundary Element Method

34

 

3.7.1

Comparison to Other Methods

35

 

References

36

4

Common Methodologies of Acoustical Imaging

37

4.1

Introduction

37

4.2

Tomography

37

 

4.2.1

The Born Approximation

42

 

4.2.2

The Rytov Approximation

42

 

4.2.3

The Fourier Diffraction Theorem

43

 

4.2.4

Reconstruction and Backpropagation Algorithm

44

4.3

Holography

50

 

4.3.1

Liquid Surface Method

50

4.4

Pulse–Echo and Transmission Modes

53

 

4.4.1

C-Scan Method

53

 

4.4.2

B-Scan Method

55

4.5

Acoustic Microscopy

59

 

References

60

Contents

 

vii

5

Time-Reversal Acoustics and Superresolution

63

5.1

Introduction

63

5.2

Theory of Time-Reversal Acoustics

63

 

5.2.1

Time-Reversal Acoustics and Superresolution

68

5.3

Application of TR to Medical Ultrasound Imaging

69

5.4Application of Time-Reversal Acoustics to Ultrasonic

Nondestructive Testing

70

5.4.1

Theory of Time-Reversal Acoustics for Liquid–Solid Interface

72

5.4.2Experimental Implementation of the TRM for Nondestructive

 

 

Testing Works

73

 

5.4.3

Incoherent Summation

75

 

5.4.4

Time Record of Signals Coming from a Speckle Noise Zone

76

 

5.4.5

The Iterative Technique

77

 

5.4.6

Iterative Process for a Zone Containing a Hard-Alpha

77

 

5.4.7

Iterative Process as a Pure Speckle Noise Zone

77

5.5

Application of TRA to Landmine or Buried Object Detection

80

 

5.5.1

Introduction

80

 

5.5.2

Theory

81

 

5.5.3

Experimental Procedure

82

 

5.5.4

Experimental Setup

83

 

5.5.5

Wiener Filter

84

 

5.5.6

Experimental Results

84

5.6

Application of Time-Reversal Acoustics to Underwater Acoustics

86

 

References

86

6

Nonlinear Acoustical Imaging

89

6.1

Application of Chaos Theory to Acoustical Imaging

89

 

6.1.1

Nonlinear Problem Encountered in Diffraction Tomography

89

 

6.1.2

Definition and History of Chaos

89

 

6.1.3

Definition of Fractal

90

 

6.1.4

The Link between Chaos and Fractals

91

 

6.1.5

The Fractal Nature of Breast Cancer

92

 

6.1.6

Types of Fractals

93

 

6.1.7

Fractal Approximation

96

 

6.1.8

Diffusion Limited Aggregation

96

 

6.1.9

Growth Site Probability Distribution

96

 

6.1.10

Approximating the Scattered Field Using GSPD

98

 

6.1.11

Discrete Helmholtz Wave Equation

99

 

6.1.12

Kaczmarz Algorithm

100

 

6.1.13

Hounsfield Method

101

 

6.1.14

Applying GSPD into Kaczmarz Algorithm

102

 

6.1.15

Fractal Algorithm Using Frequency Domain Interpolation

103

6.1.16Derivation of Fractal Algorithm’s Final Equation Using

 

Frequency Domain Interpolation

103

6.1.17

Simulation Results

104

6.1.18

Comparison between Born and Fractal Approximations

106

viii

 

 

Contents

6.2

Nonclassical Nonlinear Acoustical Imaging

107

 

6.2.1

Introduction

107

 

6.2.2

Mechanisms of Harmonic Generation via CAN

108

 

6.2.3

Nonlinear Resonance Modes

111

 

6.2.4

Experimental Studies on Nonclassical CAN Spectra

112

6.2.5CAN Application for Nonlinear Acoustical Imaging

 

 

and NDE

113

 

6.2.6

Conclusion

115

6.3

Modulation Method of Nonlinear Acoustical Imaging

116

 

6.3.1

Introduction

116

 

6.3.2

Principles of Modulation Acoustic Method

117

 

6.3.3

The Modulation Mode Method of Crack Location

117

 

6.3.4

Experimental Procedure of the Modulation Method for NDT

118

 

6.3.5

Experimental Procedures for the Modulation Mode System

118

 

6.3.6

Conclusions

121

6.4

Harmonic Imaging

121

 

References

122

7

High-Frequencies Acoustical Imaging

125

7.1

Introduction

125

7.2

Transducers

125

7.3

Electronic Circuitry

126

7.4

Software

 

127

7.5Applications of High-Frequencies In Vivo Ultrasound

 

Imaging System

127

7.6

System of 150 MHz Ultrasound Imaging of the Skin and the Eye

128

7.7

Signal Processing for the 150 MHz System

129

7.8

Electronic Circuits of Acoustical Microscope

135

 

7.8.1

Gated Signal and Its Use in Acoustical Microscope

135

 

7.8.2

Quasi-Monochromatic Systems

137

 

7.8.3

Very Short Pulse Technique

138

 

References

138

8

Statistical Treatment of Acoustical Imaging

141

8.1

Introduction

141

8.2

Scattering by Inhomogeneities

142

8.3

Study of the Statistical Properties of the Wavefield

143

 

8.3.1

Fresnal Approximation or Near-Field Approximation

146

 

8.3.2

Farfield Imaging Condition (Fraunhofer Approximation)

147

 

8.3.3

Correlation of Fluctuations

152

 

8.3.4

Quasi-static Condition

156

 

8.3.5

The Time Autocorrelation of the Amplitude Fluctuations

157

 

8.3.6

Experimental Verification

160

8.3.7Application of Fluctuation Theory to the Diffraction Image

 

of a Focusing System

162

8.3.8

Conclusion

163

Contents

 

ix

8.4

Continuum Medium Approach of Statistical Treatment

163

 

8.4.1

Introduction

163

 

8.4.2

Parabolic Equation Theory

163

 

8.4.3

Assumption for the Refractive Index Fluctuation

164

 

8.4.4

Equation for the Average Field and General Solution

165

 

References

168

9

Nondestructive Testing

169

9.1

Defects Characterization

169

9.2

Automated Ultrasonic Testing

171

 

9.2.1

Introduction

171

 

9.2.2

Testing Procedure

172

 

9.2.3

Example of an AUT System

173

9.2.4Signal Processing and Automatic Defects and Features

 

 

Clarification in AUT

174

9.3

Guided Waves Used in Acoustical Imaging for NDT

176

9.4

Ultrasonic Technologies for Stress Measurement and Material Studies

178

 

9.4.1

Introduction

178

 

9.4.2

Internal Stress Measurements

180

 

9.4.3

V(z) Curve Technique in the Characterization of Kissing Bond

183

9.5

Dry Contact or Noncontact Transducers

185

 

9.5.1

Defect Depth, Sizing and Characterization

185

 

9.5.2

Pitch/Catch Swept Method

185

 

9.5.3

Pitch/Catch Impulse Method

185

 

9.5.4

MIA Test Method

185

9.6

Phased Array Transducers

186

 

9.6.1

Introduction

186

 

9.6.2

Meaning of Phased Array

187

 

9.6.3

Principle of Phased Array Ultrasonic Technology

188

 

9.6.4

Focal Laws

191

 

9.6.5

Basic Scanning and Imaging

191

9.6.6Advantages of Phased Array Testing as Compared with

 

 

Conventional UT

192

 

References

193

10

Medical Ultrasound Imaging

195

10.1

Introduction

195

10.2

Physical Principles of Sound Propagation

196

 

10.2.1

Propagation of Sound Wave in Solids

196

 

10.2.2

Contrast

197

10.3

Imaging Modes

198

 

10.3.1

B-Scan

198

 

10.3.2

C-Scan

205

10.4

B-scan Instrumentation

207

 

10.4.1

Manual Systems

207

 

10.4.2

Real-Time System

210

x

 

 

Contents

 

10.4.3

Mechanical Scan

210

 

10.4.4

Electronic Scan

211

10.5

C-scan Instrumentation

217

 

10.5.1

Sokolov Tube

217

 

10.5.2

Ultrasonic Holography

218

10.6

Tissue Harmonic Imaging

220

 

10.6.1

Introduction

220

 

10.6.2

Principles of Tissue Harmonic Imaging

221

 

10.6.3

Image Formation in Tissue Harmonics

224

 

10.6.4

Tissue Harmonic Image Characteristics

226

 

10.6.5

Some Examples of Commercial Systems

228

10.7

Elasticity Imaging

228

 

10.7.1

Introduction

228

 

10.7.2

Comparison of Human Palpation and Elasticity Imaging

229

 

10.7.3

Choice of Force Stimulus and Imaging Modality

231

 

10.7.4

Physics of Elasticity Imaging

233

 

10.7.5

Image Formation Algorithm

236

 

10.7.6

Some Examples of Commercial Systems

238

10.8

Colour Doppler Imaging

244

 

10.8.1

Doppler Ultrasound

244

 

10.8.2

Pulsed (Gated) and Spectral Doppler

245

 

10.8.3

Quantitative Doppler Techniques

246

 

10.8.4

Velocity Measurements

247

 

10.8.5

Spectral Doppler Waveform Measurements

247

 

10.8.6

Volume Blood Flow Measurements

248

 

10.8.7

Colour Doppler

248

 

10.8.8

Newer Techniques

250

10.9

Contrast-Enhanced Ultrasound

250

 

10.9.1

Introduction

250

 

10.9.2

Bubble Echocardiogram

251

 

10.9.3

Microbubble Contrast Agents

251

 

10.9.4

How it Works

253

 

10.9.5

Applications

253

10.10 3D Ultrasound Medical Imaging

254

 

10.10.1

Introduction

254

 

10.10.2

Elective 3D Ultrasound

255

 

10.10.3

Risk Reduction of 3D Ultrasounds

257

 

10.10.4

Future Developments

257

 

10.10.5

Regional Anaesthesia

258

10.11

Development Trends

258

 

References

 

259

11

Underwater Acoustical Imaging

263

11.1

Introduction

263

11.2 Principles of Underwater Acoustical Imaging Systems

264

 

11.2.1

Spreading Loss

264

11.2.2

Attenuation Loss

264

Contents

 

xi

 

11.2.3

Propagation Theory

265

 

11.2.4

Reflection and Scattering from the Sea Surface

266

 

11.2.5

Reflection and Scattering from the Sea Bottom

267

 

11.2.6

Sea Bottom – Reflection Loss

267

 

11.2.7

Sound Channel

269

11.3

Principles of Some Underwater Acoustical Imaging Systems

270

11.4

Characteristics of Underwater Acoustical Imaging Systems

273

11.5

Imaging Modalities

275

 

11.5.1

Sonar Acoustical Imaging

275

 

11.5.2

Orthoscopic Acoustical Imaging

277

11.6

A Few Representative Underwater Acoustical Imaging System

278

 

11.6.1

Focused Acoustical Imaging System

278

11.6.2Electronic Beam-Focused Underwater Acoustical

 

 

Imaging System

279

 

11.6.3

Holographic Acoustical Imaging

283

11.7

Application of Robotics to Underwater Acoustical Imaging

287

 

References

 

287

12

Geophysical Exploration

289

12.1

Introduction

289

12.2

Applications of Acoustical Holography to Seismic Imaging

290

12.3

Examples of Field Experiments

291

 

12.3.1

One-Dimensional Holographic Arrays

291

 

12.3.2

Two-Dimensional Holographic Arrays

292

12.4

Laboratory Modelling

297

12.5

Techniques of Image Processing and Enhancement

297

 

12.5.1

Weak Signal Enhancement

298

 

12.5.2

Phase Contrast Enhancement Technique

298

12.6

Computer Reconstruction

298

 

12.6.1

Removal of Conjugate Images

299

 

12.6.2

Fourier Transform Hologram

299

 

12.6.3

Examples of Computer Reconstruction

300

 

12.6.4

Backward Wave Propagation or Frequency Domain Migration

302

 

12.6.5

Correlation Holography

302

12.7

Other Applications of Seismic Holography

303

 

12.7.1

Monitoring Burning Fronts in Oil-Shale Retorts

303

12.8

Signal Processing in Seismic Holography

303

 

12.8.1

Velocity Filtering

303

 

12.8.2

Two-Dimensional Fourier Transform Techniques

304

 

12.8.3

Tau-p Transform (Slant Stack)

305

 

12.8.4

The Inverse Tau-p Transform

306

 

12.8.5

Examples of k-ω and Tau-p Transforms

308

12.9

Application of Diffraction Tomography to Seismic Imaging

310

 

12.9.1

Reconstruction Algorithms

317

 

12.9.2

Computer Simulations for the VSP Case

321

12.10

Conclusions

322

 

References

 

323