An Introduction to Acoustical Holography

Transcription

1 An Introduction to Acoustical Holography

2 An Introduction to Acoustical Holography B. P. Hildebrand BatteUe Memorlaiinstitute Paelfle Northwest Laboratories Rlehland, Washington and B. B. Brenden Holosonies, Ine. Rlehland, Washington 9:' Springer Science+Business Media, LLC 1972

3 L1brary of Congress Catalog Card Number ISBN ISBN (ebook) DOI 1972 Springer Science+Business Media New York Originally published by Plenum Press, New York in Softcover reprint ofthe hardcover 1st edition 1972 All rights reserved No part of this publication may be reproduced in any form without written permission from the publisher

4 This book is dedicated with great affection to our wives, Thelma Hildebrand and Lavelle Brenden, for their unquestioning loyalty and support.

5 OBJECT RECON STRUCTED IMAGE Pipe wrench-this acoustical image of the pipe wrench was produced from a source-receiver scanned hologram having an aperture of 15 x 15 cm and a line density of 33 linesl cm. The pipe wrench was insonified with 5.1 MHz sound produced by a l-in.-diameter focused transducer.

6 Preface Since the first papers by E. N. Leith and J. Upatnieks on the subject of holography appeared in 1961, there has been a virtual explosion of research activity in the field. More than SOO papers and articles on holography have appeared in the last ten years. Many applications of holography have been proposed, and some of these are beginning to enter the realm of usefulness. One of the applications that appears to hold great promise is acoustic imaging by means of holography. The first papers on this subject appeared in but already research activity in the field is burgeoning. Tbree symposia whouy devoted to acoustical holography have been held and tbe papers published in book form. The purpose of this book is to bring together the results of research in acoustical holography, some of it as yet unpublished, under one cover so that workers in holography, nondestructive testing, medical imaging, underwater imaging, and seismic exploration can decide whether this new technique can be useful to them. The treatment of the book requires some knowledge of differential equations and diffraction theory, but is kept as simple as possible. The first chapter includes an historical sketch of the development of holography since its invention in 1948 by Gabor. The second chapter is devoted to the development of the holographie imaging equations using the approach first used by Meier. The third chapter serves as an introduction to acoustics for those readers unfamiliar with these concepts. The following three chapters describe the various methods for obtaining and reconstructing acoustical holograms with particular emphasis on the two most-developed methods; liquid-surface and scanning. Chapter seven provides brief descriptions of other techniques that have appeared in the literature with experimental vii

7 viii Preface results, where available. The last chapter describes possible applications of acoustical holography to ocean surveillance, medicine, nondestructive testing, seismic exploration, and nuclear technology. Wherever possible, experimental results are shown. We realize that a book published while research is still going on at a frantic pace is often obsolete by the time it comes out in print. Therefore, we have endeavored to use experimental results that were obtaided concurrently with the writing in order that at publication it be as up-to-date as possible. All such results, even for chapters discussing holography in general, were obtained with acoustical radiation at a frequency of 3 MHz unless otherwise noted. Much of the research reported in this book was performed at the Pacific Northwest Laboratories of the BatteUe Memorial Institute, under the sponsorship of tbe Holotron Corporation of Wilmington, Delaware. We thank our many colleagues for allowing us to draw upon their work, in particular R. B. Smith, D. R. Hoegger, T. J. Bander, V. I. Neeley, S. C. Keeton, F. V. Richard, G. Langlois, H. Toffer, K. A. Haines, and D. S. St. John. Special thanks is due H. D. Collins and R. P. Gribble who provided a majority of the experimental results. In addition, one of us (B. P. H.) wishes to thank E. N. Leith for introducing him to this fascinating field while a student at the University of Michigan. Thanks is due to Battelle Memorial Institute for providing the creative atmosphere and support of the Battelle Seattle Research Center during the writing ofthis monograph. Battelle Northwest has also supported this effort significantly. We wish to thank G. J. Dau for bis personal interest in this work and Mrs. Janice Sletager for editing the manuscript and coordinating the graphics and reproduction requirements. Finally, we acknowledge the largesse of the University of British Columbia in the person of Miss Kathy Hardwiek who typed the final manuscript and Holosonics Ine., for supplying some of the photographs for the liquid-surface holography results. B. P. HILDEBRAND B. B. BRENDEN December 1971

8 Contents Chapter 1. Introduction Fundamental Concepts 1.2. Historical Development. References Chapter 2. Holography Recording Process Reconstruction Process 2.3. Gabor Holography Leith-Upatnieks Holography 2.5. Hologram Classification Fresnel Holograms Fraunhofer Holograms Side-Band Fresnel or Fraunhofer Holograms Fourier Transform Holograms Focused-Image Holograms 2.6. Image Location 2.7. Magnification 2.8. Aberrations 2.9. Distortion Resolution References ix

9 x Contents Chapter 3. Acoustics Introduction Mechanical Vibrations Propagation of Sound in Liquids The Force Equation Description of the Wave Compressibility The Wave Description in Terms of Pressure Velocity of Propagation Radiation Pressure Energy and Intensity Velocity Potential Propagation of Sound in Solids Refraction and Reflection at Liquid-Solid Interfaces Interaction of an Acoustic Wave with a Liquid Interface Interaction at a Free-Liquid Surface Summary 65 References 66 Chapter 4. Scanned Acoustical Holography Scanned Receiver Acoustical Reference Electronic Reference Scanned Source Scanned Object Simultaneous Scanning Image Location Resolution Image Location Revisited Magnification Aberrations Distortion Recording and Reconstruction Time Gating 95 References 96

10 Contents xi Chapter S. Sampled Holograms Sampling Theory One-Dimensional Sampling Theory Two-Dimensional Sampling Theory Scanned Holography as a Sampling Process Effects of Sampling Information Content of Holograms Number of Degrees of Freedom in a Scanned Receiver Hologram Number of Degrees of Freedom in a Scanned Source Hologram Number of Degrees of Freedom in a Scanned Source and Receiver Hologram Special Sampling Schemes A Rotationally Symmetrie Sampling Theorem Circular Scanning 131 References 136 Chapter 6. Liquid-Surface Holography Introduction Description of the Acoustical Field Acoustical Transfer Functions for a Continuous Wave Hologram Interaction of Light with the Liquid Surface Effects Produced by Pulsing the Sound Waves Transfer Function Relating Liquid-Surface Ripple Displacement to Acoustic Radiation Pressure 153 References 158 Chapter 7. Other AcousticaI Holography Methods Photographie Film Ultrasound Camera 7.3. Particle Cell Bragg Diffraction Imaging Bragg Reftection Bragg Imaging

11 xii 7.5. Thermoplastie Film 7.6. Optieal and Eleetronie Readout Methods Optieal Heterodyne Teehnique Optieal Homodyne Teehnique Temporal Referenee Referenees Contents Chapter 8. Applications 8.1. Underwater Viewing Short-Range, High-Resolution Seareh System Medium-Range System Long-Range Systems Geophysieal Applieations Subsurfaee Cavity Mapping Distortion Correetion Nuclear Reaetor Surveillanee Ultrasonic Holographie Periseope External Surveillance System 8.4. Medical Imaging Liquid-Surfaee Holography Seanning Holography Nondestruetive Testing Liquid-Surfaee Holography Scanning Holography Interferometry Summary References Index