Table Of ContentMicrowave N on-Destructive
Testing and Evaluation
NON-DESTRUCTIVE EVALUATION SERIES
Volume 4
Non-destructive evaluation now has a central place in modem technology both
as a means of evaluating materials and products as they are manufactured and
for confirmation of fitness for purpose while they are in use.
This series provides in-depth coverage of the wide range of techniques that are
now available for the non-destructive evaluation of materials. Each volume will
contain material that is relevant to final year undergraduates in Engineering,
Materials Science and Physics in addition to post graduate students,
experienced research workers, and practising engineers. In some cases they will
be written with taught courses in mind, while other texts will be for the
qualified engineer or scientist who wishes to become familiar with a new topic
at research level.
Series editor
Professor W Lord
Department of Electrical and Computer Engineering
Iowa State University
Iowa
USA
Volume 1: Halmshaw: Industrial Radiology: Theory and Practice
ISBN: 0-412-62780-9
Volume 2: Blitz/Simpson: Ultrasonic Methods of Non-destructive Testing
ISBN: 0-412-60470-1
Volume 3: Blitz: Electrical and Magnetic Methods of Non-destructive Testing
ISBN: 0-412-79150-1
Microwave Non-Destructive
Testing and Evaluation
by
REZAZOUGHI
Applied Microwave Nondestructive Testing Laboratory (amntl)
Electrical and Computer Engineering Department
Colorado State University
Ft. Collins, Colorado
U.S.A.
KLUWER ACADEMIC PUBLISHERS
DORDRECHTI BOSTON I LONDON
A C.l.P. Catalogue record for this book is available from the Library of Congress.
ISBN 978-90-481-4015-2 ISBN 978-94-015-1303-6 (eBook)
DOI 10.1007/978-94-015-1303-6
Published by Kluwer Academic Publishcrs,
P.O. Box 17, 3300 AA Dordrecht, The Netherlands.
Sold and distributed in North, Central and South America
by Kluwer Academic Publishers,
101 Philip Drive, Norwell, MA 02061, U.S.A.
In all other countries, sold and distributed
by Kluwer Academic Publishers,
P.O. Box 322, 3300 AH Dordrecht, The Netherlands.
Prill ted Oil acid~fi·ee pap('/"
All Rights Reserved
© 2000 Kluwcr Academic Publishers
Softcover reprint of the hardcover 1s t edition 2000
and copyrightholders as specified on appropriatc pages within.
No part of the material protected by this copyright notice may be reproduced or
utilized in any form or by any means, clectronic or mechanical,
including photocopying, recording or by any information storage and
retrieval system, without written permission from the copyright owner.
To Molouk and Valiollah
Contents
Foreword
Xl
Colour Plates
Xlll
1 Introduction 1
1.1 General remarks 1
1.2 Microwave frequency bands 6
1.3 Required prior knowledge 7
1.4 Organization of chapters 8
1.5 Acknowledgment 10
References 1 1
2 Material characterization 12
2.1 Introduction 12
2.2 Dielectric properties 13
2.3 Carbon black loaded rubber 18
2.3.1 Measurement procedure 19
2.3.2 Dielectric properties of rubber compound 23
constituents
2.3.3 Cured rubber dielectric property dependence 24
on carbon black
2.3.4 Detection of curatives in uncured rubber 25
2.3.5 Measurement accuracy 30
2.4 Resin binder 32
2.4.1 Dielectric properties of fresh and 12-day old 32
resin binder
2.4.2 Resin loaded fiberglass 35
2.5 Porosity estimation in polymer composites 38
2.5.1 Sample preparation 39
2.6 Rust dielectric properties 43
2.6.1 Measurement procedure 44
2.6.2 Rust specimen description and measured 45
dielectric properties
2.7 Dielectric mixing models 46
2.7.1 Empirical dielectric mixing model for 48
cured carbon black loaded rubber
2.7.2 Empirical dielectric mixing model for 49
microballoon-filled epoxy resin
2.8 Summary 49
References 53
Contents
Yill
3 Layered dielectric composite evaluation 57
3.1 Introduction 57
3.2 What may be accomplished 58
3.3 Field regions 59
3.3.1 Far-field approach 60
3.3.2 Near-field approach 60
3.4 Electromagnetic modeling of the interaction of an 62
open-ended rectangular waveguide with multi-layered
dielectric composites
3.4.1 Theoretical formulation 63
3.4.2 Verification of derivations 70
3.4.3 Thickness determination of dielectric sheets 71
backed by conducting plates
3.4.4 Stratified dielectric composite inspection 82
3.4.5 Measurement optimization of frequency 90
and standoff distance
3.4.6 Detection of rust under dielectric coatings 105
3.4.7 Influence of backgap distance on 105
measurement sensitivity
3.5 Summary 118
References 120
4 Surface crack detection 123
4.1 Introduction 123
4.2 Open-ended waveguide approach 124
4.3 Theoretical analysis for exposed cracks 129
4.3.1 Formulation of the generalized 131
scattering matrix
4.3.2 Application of the boundary conditions 133
4.3.3 Application of the method of moments 134
4.3.4 Generalized scattering matrix 136
4.3.5 Convergence 137
4.3.6 Choice of higher-order modes 140
4.3.7 Results 141
4.4 Higher-order mode approach 143
4.4. 1 Results 147
4.5 Typical measurement results 154
4.5.1 Influence of crack width and depth 155
on characteristic signal
4.5.2 Influence of detector location on 158
characteristic signal
4.5.3 Influence of frequency on characteristic signal 160
4.5.4 Filled cracks 162
4.5.5 Covered cracks 168
4.5.6 Remote crack detection (influence of liftoff) 175
4.6 Crack sizing 179
4.6.1 Crack width or opening estimation 179
Contents IX
4.6.2 Crack depth estimation 183
4.6.3 Swept frequency technique 183
4.6.4 Influence of crack length on the phase 187
of reflection coefficient
4.6.5 Crack length estimation 189
4.6.6 Experimental results 189
4.7 Tip location detennination 193
4.8 Detection of stress-induced fatigue cracks 200
4.9 Summary 202
References 206
5 Near-field measurement techniques and applications 209
5.1 Introduction 209
5.2 Measurement techniques 210
5.2.1 Calibrated microwave measurement techniques 210
5.2.2 Uncalibrated microwave measurement techniques 213
5.3 Measurement procedures 21 7
5.3.1 Frequency and standoff distance optimization 217
5.4 Near-field imaging 220
5.4.1 Inclusions in glass reinforced polymer 221
epoxy
5.4.2 Flat bottom holes in glass reinforced 224
polymer epoxy
5.4.3 Disbond in thick sandwich composite 225
5.4.4 Impact damage in thick sandwich composite 228
5.4.5 Localized porosity 230
5.4.6 Resin variation in low-density fiberglass 232
composites
5.4.7 Rust under paint 233
5.4.8 Rust under laminate composites 236
5.5 Issues associated with near-field measurements 238
and imaging
References 242
6 Other developments and future 246
6.1 Introduction 246
6.2 Testing and evaluation of cement based materials 246
6.3 Open-ended coaxial probes for layered 252
composite inspection
6.4 Fatigue surface crack detection and evaluation 253
in metals using open-ended coaxial probes
6.5 Surface inspection of rolled steel 253
6.6 Barriers and future 254
References 255
Index 258
Foreword
Microwave and millimeter-wave non-destructive testing and evaluation
(NDT&E) is generally understood to mean using high-frequency
electromagnetic energy to inspect and characterize materials and structures.
In spite of possessing some distinct advantages in certain applications
compared to other NDT&E techniques, microwave NDT&E has only found
limited practical application during the past 45 years. These advantages
include lack of a need for contact between the sensor and the object being
inspected, the ability to penetrate dielectric materials, and superior
sensitivity to certain material constituents and flaws.
One factor contributing to this minimal acceptance by the NDT &E
community has been a generally poor understanding in this community of
the theory and practice that underlie the technology. This situation exists
partly because of a paucity of microwave NDT&E textbook and reference
material. Some chapters, reviews, and books aimed at filling this need have
been published in the past but, for the most part, this material is based on
the use of older microwave technology. However, during the past ten years
great strides have been made in ternlS of the cost, size, and ease of use of
microwave components. In addition, recent advances in modeling and
measurement techniques have expanded the range of applications for
microwave NDT&E. Such applications include inspecting modern
materials such as composites, detecting and characterizing surface flaws,
and evaluating the compressive strength of cement structures. These
advances have created an urgent need for up-to-date textbook material on
this subject.
Professor Zoughi, his colleagues, and his students have been at the
forefront of these recent advances in microwave NDT &E. Therefore, I
believe that this textbook will become a primary reference in the field and it
should be exceedingly useful to those who wish to learn more about current
theory and practice in microwave NDT&E. I strongly recommend it to
both students and practitioners.
Alfred J. Bahr, Ph.D.
Principal Scientist
SRI International
Menlo Park. California
USA
Colour Plates
