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Microwave Auditory Effects
And Applications
By
JAMES C. LIN, Ph.D.
A ssociate Professor of Electrical Engineering
Adjunct Associate Professor of Physical Medicine and Rehabilitation
Wayne State University
Former Assistant Professor of Rehabilitation Medicine
and Assistant Director, Bioelectromagnetics Research Laboratory
University of Washington School of Medicine
CHARLES
C
THOMAS
•
Illinois
•
•
PUBLISHER
U.S.A.
Springfield
Published and Distributed Throughout the World by
CHARLES C THOMAS • PUBLISHER
Bannerstone House
301-327 East Lawrence Avenue, Springfield, Illinois, U.S.A.
,/
Preface
This book is protected by copyright. No part of it
may be reproduced in any manner without written
permission from the publisher.
T
©
1978,
by
CHARLES C THOMAS • PUBLISHER
ISBN 0-398-03704-3
Library of Congress Catalog Card Number: 77-21499
With THOMAS BOOKS careful attention is given to all details of
manufacturing and design. It is the Publisher's desire to present books that
are satisfactory as to their physical qualities and artistic possibilities and
appropriate for their particular use. THOMAS BOOKS will be true to those
laws of quality that assure a Rood name and good will.
Library of Congress Cataloging in Publication Data
Lin, James C.
Microwave auditory effects and applications.
Bibliography: p.
Includes index.
1. Auditory perception. 2. Microwaves-
Physiological effect.
I.
Title. [DNLM:
1. Microwaves. 2. Hearing. WV270 L735m]
QP461.L46
612'.01445
77-21499
ISBN 0-398-03704-3
Printed ill the United States of America
C-l
interaction with biological sys-
tems is drawing the attention of many scientists and engineers
in life and physical sciences. While microwave radiation with
su~­
ficiently high power densities and sufficiently long exposure pen-
ods is known to produce hyperthermia and its associated adverse
as well as beneficial effects, other effects especially those occurring
at low average power densities with negligible, measurable tissue
temperature rise remain distressingly out of focus. This mono-
graph presents one of the most interesting and widely recognized
phenomenon: microwave-induced hearing.
The purpose of the book is to bring a body of research litera-
ture, scattered in a large number of journals and
repor~s,
into
some compact form for the convenience of students and research-
ers. It will deal with selected experimental and theoretical topics
in an interdisciplinary field which is 'undergoing explosive growth.
A few suggestions for research and potential applications are also
included.
For the reader who is not familiar with the subject, some rele-
vant information about microwave radiation and biological effects
of microwaves is provided in Chapter 1. A brief description of the
auditory system is outlined in Chapter 2 as a place of reference
for the subsequent discussion of microwave effects on this system.
Major experimental evidence of pulse-modulated microwave-in-
duced auditory effects are presented in Chapters 3 and 4. The
speculations and hypotheses regarding mechanisms are treated
next. Chapter 6 examines in detail the implications of induced
thermoelastic theory using a spherical head-model. The use of
pulse-modulated microwave radiation as a tool in clinical medi-
cine and laboratory investigations has been given special atten-
tion in Chapter 7. The reader who is less mathematically inclined
may wish to skip some of the material of Chapter 5 and 6; how-
~ver,
the reader will probably be rewarded by a better understand-
mg of the models if he or she elects to read at least the narrative
HE SUBJECT OF MICROWAVE
v
--_
..............
-
William
D.
Mcintyre Library
(1.
f
~(~ ~#]. ~t7:
/i.
VI
Microwave Auditory Effects and Applications
portions of these sections.
Statements regarding microwave exposure parameters were left
in the terms used in the originating report. No attempt was made
to standardize these terms since assumptions concerning omitted
details could easily lead to erroneous interpretation. The Interna-
tional System (SI) of units is used exclusively; conversion factors
for selected quantities can be found in Appendix A.
It should be mentioned that some of the material, especially
many of the hypotheses regarding the mechanisms involved, may
become obsolete more rapidly than other; however, this represents
current views on the subject. It is hoped that the information
contained here will not only impart to the reader some basic
knowledge of the subject but will also show that the subject area
is relatively undeveloped at the present time and that further re-
search is needed.
This book evolved from a set of notes prepared for a sequence
of lectures at the University of Washington Center for Bioengi-
neering. Subsequently, these notes were enlarged and used for a
one-quarter special topics course offered as a part of the bioengi-
neering program in the Department of Electrical and Computer
Engineering at Wayne State University. The students were, for the
most part, in their first or second year of graduate study.
The author would like to express his appreciation to Drs.
Arthur W. Guy and Justus F. Lehmann of the University of Wash-
ington School of Medicine, who through their publications and
personal contacts stimulated his interest in the use of microwaves
in medicine and greatly influenced his point of view. He has also
benefited from the casual encounters with his friends and col-
leagues from many parts of the country, and the manuscript prof-
ited from corrections and clarifications suggested by many stu-
dents. The author would like to thank Ms. Joanne Juhl, Mai Hsu,
and Anne Matthews for their assistance in the preparation of the
manuscript and to acknowledge the National Science Foundation
for their support of his research covered in this book. Finally, he
would like to thank his wife, Mei Fei, without whose patience and
understanding this monograph would not have materialized.
Contents
Page
Preface
Chapter
v
1.
Introduction
Microwave Radiation
A Comparison of Electromagnetic Radiation
- Biological Effects of Microwave Radiation
2.
The.
Auditory System .
E~temaf
and Middle Ears .
The
Inner Ear .
Action- 'Potentials of the Auditory Nerve
Central Auditory Pathways
Transmission of Sound
Loudness and Pitch
Sound Localization
Deafness.
Audiometry .
3.
Psychophysical Observations
Experimental Human Exposures
Detection in Laboratory Animals
4.
Neurophysiological Correlations
Electrophysiological Recordings
"Threshold" Determination
Effect of Masking .
5.
The Interactive Mechanism
Site of Interaction .
Mechanism of Interaction
Physical Properties of Biological Materials
A Quantitative Comparison
A Summary .
6. The Spherical Model
Microwave Absorption
Temperature Rise
3
3
7
10
19
19
23
31
33
34
36
37
39
40
45
45
57
68
68
88
95
99
99
100
106
111
122
135
136
144
C.
LIN
Detroit, Michigan
JAMES
vii
viii
Chapter
Microwave
Auditory
Effects .and Applications
Page
Thermoelastic Equation of Motion
Sound Wave Generation in a Stress-Free Sphere
Sound Wave Generation in a Sphere with Constrained
Boundary .
A Summary .
7. Applied Aspects
Potential Applications
Maximum Permissible Exposure
Other Biological Effects .
Appendix A.
Units and Conversion Factors .
Appendix B.
Publications of Pertinent Conferences and Symposia
Author Index
Subject Index
.
145
146
157
168
173
173
178
179
193
195
197
201
Microwave Auditory Effects
And Applications
Chapter 1
Introduction
T
o
with a consideration of microwave ra-
diation and its relationship to other types of electromagnetic
radiation. A brief historical introduction to the field of biological
effects of microwave radiation is included to give an overview of
early contributions.
A
variety of references to more comprehensive
treatment of the general subject area will be found in the material
that follows.
MICROWAVE RADIATION
H IS
CHAPTER BEGINS
Microwave radiation is a form of electromagnetic radiation
which falls within the frequency range of
300
MHz to
300,000
MHz (megahertz
==
10
6
Hz). It exists naturally as a part of the
radiant energy given off by the sun; it is also produced by vacuum
tubes and semiconductor devices. Man-made microwave energy
may be conducted from the source by coaxial transmission lines
or waveguides and emitted from transmitting antennas as a wave
with oscillating electric and magnetic fields which pass into free
space or material media. Microwave may be received by a receiv-
ing antenna and detected by diodes or similar devices. It propa-
gates at the speed of light, which in free space is approximately
3
x
10
8
m/ sec. The speed of propagation, v, is equal to the
product of microwave frequency, f, and the wavelength,
A.
That
is
v
=
fA
( 1.1 )
where the units of f and
A
are, respectively, hertz (Hz) and me-
ters (m).
At distances far from the transmitting antenna (usually ten
wavelengths or more), microwaves may be considered as plane
waves whose electric and magnetic fields are perpendicular to each
other and both are perpendicular to the direction of propagation.
Moreover, the electric and magnetic field maxima occur at the
same location in space at any given moment, as depicted in Fig-
3

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