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Jacob Fraden
Handbook
of Modern
Sensors
Physics, Designs, and Applications
FifthEdition

Jacob Fraden
Handbook of Modern
Sensors
Physics, Designs, and Applications
Fifth Edition

Jacob Fraden
Fraden Corp.
San Diego, CA, USA
ISBN 978-3-319-19302-1 ISBN 978-3-319-19303-8 (eBook)
DOI 10.1007/978-3-319-19303-8
Library of Congress Control Number: 2015947779
Springer Cham Heidelberg New York Dordrecht London
# Springer International Publishing Switzerland 2004, 2010, 2016
# American Institute of Physics 1993, 1997
This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of
the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations,
recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission
or information storage and retrieval, electronic adaptation, computer software, or by similar or
dissimilar methodology now known or hereafter developed.
The use of general descriptive names, registered names, trademarks, service marks, etc. in this
publication does not imply, even in the absence of a specific statement, that such names are exempt
from the relevant protective laws and regulations and therefore free for general use.
The publisher, the authors and the editors are safe to assume that the advice and information in this
book are believed to be true and accurate at the date of publication. Neither the publisher nor the
authors or the editors give a warranty, express or implied, with respect to the material contained
herein or for any errors or omissions that may have been made.
Printed on acid-free paper
Springer International Publishing AG Switzerland is part of Springer Science+Business Media
(www.springer.com)

Preface
Numerous computerized appliances wash clothes, prepare coffee, play music,
guard homes, and perform endless useful functions. However, no electronic device
operates without receiving external information. Even if such information comes
from another electronic device, somewhere in the chain, there is at least one
component that perceives external input signals. This component is a sensor.
Modern signal processors are the devices that manipulate binary codes generally
represented by electric impulses. As we live in an analog world that mostly is not
digital or electrical (apart from the atomic level), sensors are the interface devices
between various physical values and the electronic circuits that “understand” only
the language of moving electrical charges. In other words, sensors are eyes, ears,
and noses of the silicon chips. This book is about the man-made sensors that are
very much different from the sensing organs of living organisms.
Since the publication of the previous edition of this book, sensing technologies
have made remarkable leaps. Sensitivities of sensors have become higher, their
dimensions smaller, selectivity better, and prices lower. A new, major field of
application for sensors—mobile communication devices—has been rapidly
evolving. Even though such devices employ sensors that operate on the same
fundamental principles as other sensors, their use in mobile devices demands
specific requirements. Among these are miniature dimensions and complete inte-
gration with the signal processing and communication components. Hence, in this
new edition, we address in greater detail the mobile trend in sensing technologies.
A sensor converts input signals of a physical nature into electrical output. Thus,
we will examine in detail the principles of such conversions and other relevant laws
of physics. Arguably one of the greatest geniuses who ever lived, Leonardo da
Vinci, had his own peculiar way of praying (according to a book I read many years
ago, by Akim Volinsky, published in Russian in 1900). Loosely, it may be trans-
lated into modern English as something like, “Oh Lord, thank you for following Thy
own laws.” It is comforting indeed that the laws of Nature do not change—it is our
appreciation of the laws that is continually refined. The sections of the book that
cover these laws have not changed much since the previous editions. Yet, the
sections that describe the practical designs have been revised substantially. Recent
ideas and developments have been added, while obsolete and less interesting
designs were dropped.
v

In the course of my engineering work, I often wished for a book which combined
practical information on the many subjects relating to the most important physical
principles, design, and use of various sensors. Of course, I could browse the Internet
or library bookshelves in search of texts on physics, chemistry, electronics, technical,
and scientific magazines, but the information is scattered over many publications and
websites, and almost every question I was pondering required substantial research.
Little by little, I gathered practical information on everything which is in any way
related to various sensors and their applications to scientific and engineering
measurements. I also spent endless hours at a lab bench, inventing and developing
numerous devices with various sensors. Soon, I realized that the information I had
collected would be quite useful to more than one plerson. This idea prompted me to
write this book, and this fifth updated edition is the proof that I was not mistaken.
The topics included in the book reflect the author’s own preferences and
interpretations. Some may find a description of a particular sensor either too
detailed or broad or perhaps too brief. In setting my criteria for selecting various
sensors for this new edition, I attempted to keep the scope of this book as broad as
possible, opting for many different designs described briefly (without being trivial,
I hope), rather than fewer treated in greater depth. This volume attempts (immod-
estly perhaps) to cover a very broad range of sensors and detectors. Many of them
are well known, but describing them is still useful for students and for those seeking
a convenient reference.
By no means this book is a replacement for specialized texts. It gives a bird’s-eye
view at a multitude of designs and possibilities, but does not dive in depth into
any particular topic. In most cases, I have tried to strike a balance between details
and simplicity of coverage; however simplicity and clarity were the most important
requirements I set for myself. My true goal was not to pile up a collection of informa-
tion but rather to entice the reader into a creative mindset. As Plutarch said nearly two
millennia ago, “The mind is not a vessel to be filled but a fire to be kindled. . .”
Even though this book is for scientists and engineers, as a rule, the technical
descriptions and mathematic treatments generally do not require a background
beyond a high school curriculum. This is a reference text which could be used by
students, researchers interested in modern instrumentation (applied physicists and
engineers), sensor designers, application engineers, and technicians whose job is to
understand, select, or design sensors for practical systems.
The previous editions of this book have been used quite extensively as desktop
references and textbooks for the related college courses. Comments and suggestions
from sensor designers, application engineers, professors, and students have
prompted me to implement several changes and to correct errors. I am deeply
grateful to those who helped me to make further improvements in this new edition.
I owe a debt of gratitude and many thanks to Drs. Ephraim Suhir and David Pintsov
for assisting me in mathematical treatment of transfer functions and to Dr. Sanjay
V. Patel for his further contributions to the chapter on chemical sensors.
San Diego, CA, USA Jacob Fraden
April 12, 2015
vi Preface

Contents
1 Data Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Sensors, Signals, and Systems . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Sensor Classiﬁcation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.3 Units of Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2 Transfer Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.1 Mathematical Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.1.1 Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1.2 Functional Approximations . . . . . . . . . . . . . . . . . . . 15
2.1.3 Linear Regression . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.1.4 Polynomial Approximations . . . . . . . . . . . . . . . . . . 19
2.1.5 Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.1.6 Linear Piecewise Approximation . . . . . . . . . . . . . . . 21
2.1.7 Spline Interpolation . . . . . . . . . . . . . . . . . . . . . . . . 22
2.1.8 Multidimensional Transfer Functions . . . . . . . . . . . . 23
2.2 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.3 Computation of Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.4 Computation of a Stimulus . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.4.1 Use of Analytical Equation . . . . . . . . . . . . . . . . . . . 29
2.4.2 Use of Linear Piecewise Approximation . . . . . . . . . 29
2.4.3 Iterative Computation of Stimulus
(Newton Method) . . . . . . . . . . . . . . . . . . . . . . . . . . 32
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3 Sensor Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.1 Sensors for Mobile Communication Devices . . . . . . . . . . . . . 35
3.1.1 Requirements to MCD Sensors . . . . . . . . . . . . . . . . 36
3.1.2 Integration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.2 Span (Full-Scale Input) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.3 Full-Scale Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.4 Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.5 Calibration Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.6 Hysteresis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.7 Nonlinearity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
vii

3.8 Saturation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
3.9 Repeatability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.10 Dead Band . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.11 Resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
3.12 Special Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
3.13 Output Impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
3.14 Output Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
3.15 Excitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.16 Dynamic Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.17 Dynamic Models of Sensor Elements . . . . . . . . . . . . . . . . . . . 54
3.17.1 Mechanical Elements . . . . . . . . . . . . . . . . . . . . . . . 54
3.17.2 Thermal Elements . . . . . . . . . . . . . . . . . . . . . . . . . 55
3.17.3 Electrical Elements . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.17.4 Analogies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
3.18 Environmental Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
3.19 Reliability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
3.19.1 MTTF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
3.19.2 Extreme Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
3.19.3 Accelerated Life Testing . . . . . . . . . . . . . . . . . . . . . 63
3.20 Application Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . 65
3.21 Uncertainty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
4 Physical Principles of Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.1 Electric Charges, Fields, and Potentials . . . . . . . . . . . . . . . . . 70
4.2 Capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
4.2.1 Capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
4.2.2 Dielectric Constant . . . . . . . . . . . . . . . . . . . . . . . . . 79
4.3 Magnetism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
4.3.1 Faraday Law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
4.3.2 Permanent Magnets . . . . . . . . . . . . . . . . . . . . . . . . 88
4.3.3 Coil and Solenoid . . . . . . . . . . . . . . . . . . . . . . . . . . 89
4.4 Induction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
4.4.1 Lenz Law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
4.4.2 Eddy Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
4.5 Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
4.5.1 Speciﬁc Resistivity . . . . . . . . . . . . . . . . . . . . . . . . . 98
4.5.2 Temperature Sensitivity of a Resistor . . . . . . . . . . . 99
4.5.3 Strain Sensitivity of a Resistor . . . . . . . . . . . . . . . . 102
4.5.4 Moisture Sensitivity of a Resistor . . . . . . . . . . . . . . 104
4.6 Piezoelectric Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
4.6.1 Ceramic Piezoelectric Materials . . . . . . . . . . . . . . . 108
4.6.2 Polymer Piezoelectric Films . . . . . . . . . . . . . . . . . . 112
4.7 Pyroelectric Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
4.8 Hall Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
viii Contents

4.9 Thermoelectric Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
4.9.1 Seebeck Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
4.9.2 Peltier Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
4.10 Sound Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
4.11 Temperature and Thermal Properties of Materials . . . . . . . . . . 132
4.11.1 Temperature Scales . . . . . . . . . . . . . . . . . . . . . . . . 133
4.11.2 Thermal Expansion . . . . . . . . . . . . . . . . . . . . . . . . 135
4.11.3 Heat Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
4.12 Heat Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
4.12.1 Thermal Conduction . . . . . . . . . . . . . . . . . . . . . . . . 139
4.12.2 Thermal Convection . . . . . . . . . . . . . . . . . . . . . . . . 141
4.12.3 Thermal Radiation . . . . . . . . . . . . . . . . . . . . . . . . . 142
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
5 Optical Components of Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
5.1 Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
5.1.1 Energy of Light Quanta . . . . . . . . . . . . . . . . . . . . . 155
5.1.2 Light Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . 157
5.2 Light Scattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
5.3 Geometrical Optics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
5.4 Radiometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
5.5 Photometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
5.6 Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
5.7 Mirrors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
5.7.1 Coated Mirrors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
5.7.2 Prismatic Mirrors . . . . . . . . . . . . . . . . . . . . . . . . . . 173
5.8 Lenses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
5.8.1 Curved Surface Lenses . . . . . . . . . . . . . . . . . . . . . . 174
5.8.2 Fresnel Lenses . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
5.8.3 Flat Nanolenses . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
5.9 Fiber Optics and Waveguides . . . . . . . . . . . . . . . . . . . . . . . . 179
5.10 Optical Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
5.10.1 Lensing Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
5.10.2 Concentrators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
5.10.3 Coatings for Thermal Absorption . . . . . . . . . . . . . . 186
5.10.4 Antireflective Coating (ARC) . . . . . . . . . . . . . . . . . 187
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
6 Interface Electronic Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
6.1 Signal Conditioners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
6.1.1 Input Characteristics . . . . . . . . . . . . . . . . . . . . . . . . 194
6.1.2 Amplifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
6.1.3 Operational Amplifiers . . . . . . . . . . . . . . . . . . . . . . 199
6.1.4 Voltage Follower . . . . . . . . . . . . . . . . . . . . . . . . . . 201
Contents ix

6.1.5 Charge- and Current-to-Voltage Converters . . . . . . . 201
6.1.6 Light-to-Voltage Converters . . . . . . . . . . . . . . . . . . 203
6.1.7 Capacitance-to-Voltage Converters . . . . . . . . . . . . . 205
6.1.8 Closed-Loop Capacitance-to-Voltage Converters . . . 207
6.2 Sensor Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
6.2.1 Ratiometric Circuits . . . . . . . . . . . . . . . . . . . . . . . . 209
6.2.2 Differential Circuits . . . . . . . . . . . . . . . . . . . . . . . . 212
6.2.3 Wheatstone Bridge . . . . . . . . . . . . . . . . . . . . . . . . . 212
6.2.4 Null-Balanced Bridge . . . . . . . . . . . . . . . . . . . . . . . 215
6.2.5 Bridge Ampliﬁers . . . . . . . . . . . . . . . . . . . . . . . . . . 216
6.3 Excitation Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
6.3.1 Current Generators . . . . . . . . . . . . . . . . . . . . . . . . . 220
6.3.2 Voltage Generators . . . . . . . . . . . . . . . . . . . . . . . . . 222
6.3.3 Voltage References . . . . . . . . . . . . . . . . . . . . . . . . 223
6.3.4 Oscillators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
6.4 Analog-to-Digital Converters . . . . . . . . . . . . . . . . . . . . . . . . . 225
6.4.1 Basic Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226
6.4.2 V/F Converters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
6.4.3 PWM Converters . . . . . . . . . . . . . . . . . . . . . . . . . . 231
6.4.4 R/F Converters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
6.4.5 Successive-Approximation Converter . . . . . . . . . . . 234
6.4.6 Resolution Extension . . . . . . . . . . . . . . . . . . . . . . . 235
6.4.7 ADC Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
6.5 Integrated Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
6.5.1 Voltage Processor . . . . . . . . . . . . . . . . . . . . . . . . . . 239
6.5.2 Inductance Processor . . . . . . . . . . . . . . . . . . . . . . . 240
6.6 Data Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
6.6.1 Two-Wire Transmission . . . . . . . . . . . . . . . . . . . . . 242
6.6.2 Four-Wire Transmission . . . . . . . . . . . . . . . . . . . . . 243
6.7 Noise in Sensors and Circuits . . . . . . . . . . . . . . . . . . . . . . . . 243
6.7.1 Inherent Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
6.7.2 Transmitted Noise . . . . . . . . . . . . . . . . . . . . . . . . . 247
6.7.3 Electric Shielding . . . . . . . . . . . . . . . . . . . . . . . . . . 252
6.7.4 Bypass Capacitors . . . . . . . . . . . . . . . . . . . . . . . . . 255
6.7.5 Magnetic Shielding . . . . . . . . . . . . . . . . . . . . . . . . 256
6.7.6 Mechanical Noise . . . . . . . . . . . . . . . . . . . . . . . . . . 258
6.7.7 Ground Planes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258
6.7.8 Ground Loops and Ground Isolation . . . . . . . . . . . . 259
6.7.9 Seebeck Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
6.8 Batteries for Low-Power Sensors . . . . . . . . . . . . . . . . . . . . . . 263
6.8.1 Primary Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
6.8.2 Secondary Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
6.8.3 Supercapacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
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6.9 Energy Harvesting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
6.9.1 Light Energy Harvesting . . . . . . . . . . . . . . . . . . . . . 267
6.9.2 Far-Field Energy Harvesting . . . . . . . . . . . . . . . . . . 268
6.9.3 Near-Field Energy Harvesting . . . . . . . . . . . . . . . . . 269
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
7 Detectors of Humans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
7.1 Ultrasonic Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
7.2 Microwave Motion Detectors . . . . . . . . . . . . . . . . . . . . . . . . 276
7.3 Micropower Impulse Radars . . . . . . . . . . . . . . . . . . . . . . . . . 281
7.4 Ground Penetrating Radars . . . . . . . . . . . . . . . . . . . . . . . . . . 284
7.5 Linear Optical Sensors (PSD) . . . . . . . . . . . . . . . . . . . . . . . . 285
7.6 Capacitive Occupancy Detectors . . . . . . . . . . . . . . . . . . . . . . 289
7.7 Triboelectric Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292
7.8 Optoelectronic Motion Detectors . . . . . . . . . . . . . . . . . . . . . . 294
7.8.1 Sensor Structures . . . . . . . . . . . . . . . . . . . . . . . . . . 295
7.8.2 Multiple Detecting Elements . . . . . . . . . . . . . . . . . . 297
7.8.3 Complex Sensor Shape . . . . . . . . . . . . . . . . . . . . . . 297
7.8.4 Image Distortion . . . . . . . . . . . . . . . . . . . . . . . . . . 297
7.8.5 Facet Focusing Elements . . . . . . . . . . . . . . . . . . . . 298
7.8.6 Visible and Near-IR Light Motion Detectors . . . . . . 299
7.8.7 Mid- and Far-IR Detectors . . . . . . . . . . . . . . . . . . . 301
7.8.8 Passive Infrared (PIR) Motion Detectors . . . . . . . . . 302
7.8.9 PIR Detector Efﬁciency Analysis . . . . . . . . . . . . . . 305
7.9 Optical Presence Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309
7.9.1 Photoelectric Beam . . . . . . . . . . . . . . . . . . . . . . . . 309
7.9.2 Light Reﬂection Detectors . . . . . . . . . . . . . . . . . . . 310
7.10 Pressure-Gradient Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
7.11 2-D Pointing Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
7.12 Gesture Sensing (3-D Pointing) . . . . . . . . . . . . . . . . . . . . . . . 314
7.12.1 Inertial and Gyroscopic Mice . . . . . . . . . . . . . . . . . 315
7.12.2 Optical Gesture Sensors . . . . . . . . . . . . . . . . . . . . . 315
7.12.3 Near-Field Gesture Sensors . . . . . . . . . . . . . . . . . . . 316
7.13 Tactile Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318
7.13.1 Switch Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319
7.13.2 Piezoelectric Tactile Sensors . . . . . . . . . . . . . . . . . . 320
7.13.3 Piezoresistive Tactile Sensors . . . . . . . . . . . . . . . . . 323
7.13.4 Tactile MEMS Sensors . . . . . . . . . . . . . . . . . . . . . . 326
7.13.5 Capacitive Touch Sensors . . . . . . . . . . . . . . . . . . . . 326
7.13.6 Optical Touch Sensors . . . . . . . . . . . . . . . . . . . . . . 330
7.13.7 Optical Fingerprint Sensors . . . . . . . . . . . . . . . . . . . 331
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332
Contents xi

8 Presence, Displacement, and Level . . . . . . . . . . . . . . . . . . . . . . . . . 335
8.1 Potentiometric Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336
8.2 Piezoresistive Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340
8.3 Capacitive Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342
8.4 Inductive and Magnetic Sensors . . . . . . . . . . . . . . . . . . . . . . . 345
8.4.1 LVDT and RVDT . . . . . . . . . . . . . . . . . . . . . . . . . 346
8.4.2 Transverse Inductive Sensor . . . . . . . . . . . . . . . . . . 348
8.4.3 Eddy Current Probes . . . . . . . . . . . . . . . . . . . . . . . 349
8.4.4 Pavement Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . 351
8.4.5 Metal Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . 352
8.4.6 Hall-Effect Sensors . . . . . . . . . . . . . . . . . . . . . . . . 353
8.4.7 Magnetoresistive Sensors . . . . . . . . . . . . . . . . . . . . 358
8.4.8 Magnetostrictive Detector . . . . . . . . . . . . . . . . . . . . 361
8.5 Optical Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362
8.5.1 Optical Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363
8.5.2 Proximity Detector with Polarized Light . . . . . . . . . 363
8.5.3 Prismatic and Reﬂective Sensors . . . . . . . . . . . . . . . 364
8.5.4 Fabry-Perot Sensors . . . . . . . . . . . . . . . . . . . . . . . . 366
8.5.5 Fiber Bragg Grating Sensors . . . . . . . . . . . . . . . . . . 368
8.5.6 Grating Photomodulators . . . . . . . . . . . . . . . . . . . . 370
8.6 Thickness and Level Sensors . . . . . . . . . . . . . . . . . . . . . . . . . 371
8.6.1 Ablation Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . 372
8.6.2 Film Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373
8.6.3 Cryogenic Liquid Level Sensors . . . . . . . . . . . . . . . 375
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376
9 Velocity and Acceleration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379
9.1 Stationary Velocity Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . 382
9.1.1 Linear Velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
9.1.2 Rotary Velocity Sensors (Tachometers) . . . . . . . . . . 384
9.2 Inertial Rotary Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
9.2.1 Rotor Gyroscope . . . . . . . . . . . . . . . . . . . . . . . . . . 386
9.2.2 Vibrating Gyroscopes . . . . . . . . . . . . . . . . . . . . . . . 387
9.2.3 Optical (Laser) Gyroscopes . . . . . . . . . . . . . . . . . . . 390
9.3 Inertial Linear Sensors (Accelerometers) . . . . . . . . . . . . . . . . 392
9.3.1 Transfer Function and Characteristics . . . . . . . . . . . 393
9.3.2 Inclinometers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397
9.3.3 Seismic Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . 400
9.3.4 Capacitive Accelerometers . . . . . . . . . . . . . . . . . . . 401
9.3.5 Piezoresistive Accelerometers . . . . . . . . . . . . . . . . . 404
9.3.6 Piezoelectric Accelerometers . . . . . . . . . . . . . . . . . 405
9.3.7 Thermal Accelerometers . . . . . . . . . . . . . . . . . . . . . 406
9.3.8 Closed-Loop Accelerometers . . . . . . . . . . . . . . . . . 410
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411
xii Contents

10 Force and Strain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413
10.1 Basic Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413
10.2 Strain Gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416
10.3 Pressure-Sensitive Films . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418
10.4 Piezoelectric Force Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . 420
10.5 Piezoelectric Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
10.6 Optical Force Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 428
11 Pressure Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429
11.1 Concept of Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429
11.2 Units of Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431
11.3 Mercury Pressure Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432
11.4 Bellows, Membranes, and Thin Plates . . . . . . . . . . . . . . . . . . 433
11.5 Piezoresistive Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435
11.6 Capacitive Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440
11.7 VRP Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
11.8 Optoelectronic Pressure Sensors . . . . . . . . . . . . . . . . . . . . . . 443
11.9 Indirect Pressure Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445
11.10 Vacuum Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447
11.10.1 Pirani Gauge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447
11.10.2 Ionization Gauges . . . . . . . . . . . . . . . . . . . . . . . . . 449
11.10.3 Gas Drag Gauge . . . . . . . . . . . . . . . . . . . . . . . . . . . 450
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
12 Flow Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453
12.1 Basics of Flow Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . 453
12.2 Pressure Gradient Technique . . . . . . . . . . . . . . . . . . . . . . . . . 456
12.3 Thermal Transport Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . 458
12.3.1 Hot-Wire Anemometers . . . . . . . . . . . . . . . . . . . . . 459
12.3.2 Three-Part Thermoanemometer . . . . . . . . . . . . . . . . 463
12.3.3 Two-Part Thermoanemometer . . . . . . . . . . . . . . . . . 465
12.3.4 Microﬂow Thermal Transport Sensors . . . . . . . . . . . 468
12.4 Ultrasonic Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 470
12.5 Electromagnetic Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472
12.6 Breeze Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474
12.7 Coriolis Mass Flow Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . 475
12.8 Drag Force Flowmeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477
12.9 Cantilever MEMS Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . 478
12.10 Dust and Smoke Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . 479
12.10.1 Ionization Detector . . . . . . . . . . . . . . . . . . . . . . . . . 479
12.10.2 Optical Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . 481
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483
Contents xiii

13 Microphones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485
13.1 Microphone Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . 487
13.1.1 Output Impedance . . . . . . . . . . . . . . . . . . . . . . . . . 487
13.1.2 Balanced Output . . . . . . . . . . . . . . . . . . . . . . . . . . 487
13.1.3 Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 487
13.1.4 Frequency Response . . . . . . . . . . . . . . . . . . . . . . . . 488
13.1.5 Intrinsic Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488
13.1.6 Directionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489
13.1.7 Proximity Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . 492
13.2 Resistive Microphones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493
13.3 Condenser Microphones . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493
13.4 Electret Microphones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495
13.5 Optical Microphones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 497
13.6 Piezoelectric Microphones . . . . . . . . . . . . . . . . . . . . . . . . . . . 500
13.6.1 Low-Frequency Range . . . . . . . . . . . . . . . . . . . . . . 500
13.6.2 Ultrasonic Range . . . . . . . . . . . . . . . . . . . . . . . . . . 501
13.7 Dynamic Microphones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 504
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505
14 Humidity and Moisture Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . 507
14.1 Concept of Humidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507
14.2 Sensor Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511
14.3 Capacitive Humidity Sensors . . . . . . . . . . . . . . . . . . . . . . . . . 512
14.4 Resistive Humidity Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . 515
14.5 Thermal Conductivity Sensor . . . . . . . . . . . . . . . . . . . . . . . . 516
14.6 Optical Hygrometers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 517
14.6.1 Chilled Mirror . . . . . . . . . . . . . . . . . . . . . . . . . . . . 517
14.6.2 Light RH Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . 518
14.7 Oscillating Hygrometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 519
14.8 Soil Moisture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 523
15 Light Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525
15.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525
15.1.1 Principle of Quantum Detectors . . . . . . . . . . . . . . . 526
15.2 Photodiode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 530
15.3 Phototransistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536
15.4 Photoresistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 538
15.5 Cooled Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 540
15.6 Imaging Sensors for Visible Range . . . . . . . . . . . . . . . . . . . . 543
15.6.1 CCD Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 544
15.6.2 CMOS Imaging Sensors . . . . . . . . . . . . . . . . . . . . . 545
15.7 UV Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 546
15.7.1 Materials and Designs . . . . . . . . . . . . . . . . . . . . . . 546
15.7.2 Avalanche UV Detectors . . . . . . . . . . . . . . . . . . . . 547
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15.8 Thermal Radiation Detectors . . . . . . . . . . . . . . . . . . . . . . . . . 549
15.8.1 General Considerations . . . . . . . . . . . . . . . . . . . . . . 549
15.8.2 Golay Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551
15.8.3 Thermopiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552
15.8.4 Pyroelectric Sensors . . . . . . . . . . . . . . . . . . . . . . . . 558
15.8.5 Microbolometers . . . . . . . . . . . . . . . . . . . . . . . . . . 564
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567
16 Detectors of Ionizing Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569
16.1 Scintillating Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 570
16.2 Ionization Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 574
16.2.1 Ionization Chambers . . . . . . . . . . . . . . . . . . . . . . . . 574
16.2.2 Proportional Chambers . . . . . . . . . . . . . . . . . . . . . . 575
16.2.3 Geiger–Müller (GM) Counters . . . . . . . . . . . . . . . . 576
16.2.4 Semiconductor Detectors . . . . . . . . . . . . . . . . . . . . 578
16.3 Cloud and Bubble Chambers . . . . . . . . . . . . . . . . . . . . . . . . . 582
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 583
17 Temperature Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585
17.1 Coupling with Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585
17.1.1 Static Heat Exchange . . . . . . . . . . . . . . . . . . . . . . . 585
17.1.2 Dynamic Heat Exchange . . . . . . . . . . . . . . . . . . . . . 589
17.1.3 Sensor Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . 592
17.1.4 Signal Processing of Sensor Response . . . . . . . . . . . 594
17.2 Temperature References . . . . . . . . . . . . . . . . . . . . . . . . . . . . 596
17.3 Resistance Temperature Detectors (RTD) . . . . . . . . . . . . . . . . 597
17.4 Ceramic Thermistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 599
17.4.1 Simple Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . 601
17.4.2 Fraden Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 602
17.4.3 Steinhart and Hart Model . . . . . . . . . . . . . . . . . . . . 604
17.4.4 Self-Heating Effect in NTC Thermistors . . . . . . . . . 607
17.4.5 Ceramic PTC Thermistors . . . . . . . . . . . . . . . . . . . . 611
17.4.6 Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 615
17.5 Silicon and Germanium Thermistors . . . . . . . . . . . . . . . . . . . 617
17.6 Semiconductor pn-Junction Sensors . . . . . . . . . . . . . . . . . . . . 620
17.7 Silicon PTC Temperature Sensors . . . . . . . . . . . . . . . . . . . . . 624
17.8 Thermoelectric Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 626
17.8.1 Thermoelectric Laws . . . . . . . . . . . . . . . . . . . . . . . 628
17.8.2 Thermocouple Circuits . . . . . . . . . . . . . . . . . . . . . . 630
17.8.3 Thermocouple Assemblies . . . . . . . . . . . . . . . . . . . 633
17.9 Optical Temperature Sensors . . . . . . . . . . . . . . . . . . . . . . . . . 635
17.9.1 Fluoroptic Sensors . . . . . . . . . . . . . . . . . . . . . . . . . 635
17.9.2 Interferometric Sensors . . . . . . . . . . . . . . . . . . . . . . 637
17.9.3 Super-High Resolution Sensing . . . . . . . . . . . . . . . . 637
17.9.4 Thermochromic Sensors . . . . . . . . . . . . . . . . . . . . . 638
17.9.5 Fiber-Optic Temperature Sensors (FBG) . . . . . . . . . 639
Contents xv

17.10 Acoustic Temperature Sensors . . . . . . . . . . . . . . . . . . . . . . . . 640
17.11 Piezoelectric Temperature Sensors . . . . . . . . . . . . . . . . . . . . . 641
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 642
18 Chemical and Biological Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . 645
18.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 646
18.1.1 Chemical Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . 646
18.1.2 Biochemical Sensors . . . . . . . . . . . . . . . . . . . . . . . 647
18.2 History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 647
18.3 Chemical Sensor Characteristics . . . . . . . . . . . . . . . . . . . . . . 648
18.3.1 Selectivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 648
18.3.2 Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 650
18.4 Electrical and Electrochemical Sensors . . . . . . . . . . . . . . . . . 651
18.4.1 Electrode Systems . . . . . . . . . . . . . . . . . . . . . . . . . 651
18.4.2 Potentiometric Sensors . . . . . . . . . . . . . . . . . . . . . . 655
18.4.3 Conductometric Sensors . . . . . . . . . . . . . . . . . . . . . 656
18.4.4 Metal Oxide Semiconductor (MOS)
Chemical Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . 661
18.4.5 Elastomer Chemiresistors . . . . . . . . . . . . . . . . . . . . 663
18.4.6 Chemicapacitive Sensors . . . . . . . . . . . . . . . . . . . . 666
18.4.7 ChemFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 668
18.5 Photoionization Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . 669
18.6 Physical Transducers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671
18.6.1 Acoustic Wave Devices . . . . . . . . . . . . . . . . . . . . . 671
18.6.2 Microcantilevers . . . . . . . . . . . . . . . . . . . . . . . . . . 674
18.7 Spectrometers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 676
18.7.1 Ion Mobility Spectrometry . . . . . . . . . . . . . . . . . . . 677
18.7.2 Quadrupole Mass Spectrometer . . . . . . . . . . . . . . . . 678
18.8 Thermal Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 679
18.8.1 Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 679
18.8.2 Pellister Catalytic Sensors . . . . . . . . . . . . . . . . . . . . 680
18.9 Optical Transducers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 681
18.9.1 Infrared Detection . . . . . . . . . . . . . . . . . . . . . . . . . 681
18.9.2 Fiber-Optic Transducers . . . . . . . . . . . . . . . . . . . . . 682
18.9.3 Ratiometric Selectivity (Pulse Oximeter) . . . . . . . . . 683
18.9.4 Color Change Sensors . . . . . . . . . . . . . . . . . . . . . . 686
18.10 Multi-sensor Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 688
18.10.1 General Considerations . . . . . . . . . . . . . . . . . . . . . . 688
18.10.2 Electronic Noses and Tongues . . . . . . . . . . . . . . . . 688
18.11 Speciﬁc Difﬁculties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 692
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 693
19 Materials and Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 699
19.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 699
19.1.1 Silicon as Sensing Material . . . . . . . . . . . . . . . . . . . 699
19.1.2 Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 703
xvi Contents

19.1.3 Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 708
19.1.4 Ceramics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 710
19.1.5 Structural Glasses . . . . . . . . . . . . . . . . . . . . . . . . . . 710
19.1.6 Optical Glasses . . . . . . . . . . . . . . . . . . . . . . . . . . . 711
19.2 Nano-materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 714
19.3 Surface Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 715
19.3.1 Spin Casting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 715
19.3.2 Vacuum Deposition . . . . . . . . . . . . . . . . . . . . . . . . 716
19.3.3 Sputtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 717
19.3.4 Chemical Vapor Deposition (CVD) . . . . . . . . . . . . . 718
19.3.5 Electroplating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 719
19.4 MEMS Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 721
19.4.1 Photolithography . . . . . . . . . . . . . . . . . . . . . . . . . . 722
19.4.2 Silicon Micromachining . . . . . . . . . . . . . . . . . . . . . 723
19.4.3 Micromachining of Bridges and Cantilevers . . . . . . . 727
19.4.4 Lift-Off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 728
19.4.5 Wafer Bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 729
19.4.6 LIGA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 730
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 731
Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 733
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 753
Contents xvii

About the Author
Jacob Fraden holds a Ph.D. in medical electronics and is President of Fraden Corp., a
technology company that develops sensors for consumer, medical, and industrial applications.
He has authored nearly 60 patents in the areas of sensing, medical instrumentation, security,
energy management, and others.
xix

Data Acquisition
1
“It’s as large as life, and twice as natural”
—Lewis Carroll, “Through the Looking Glass”
1.1 Sensors, Signals, and Systems
A sensor is often defined as a “device that receives and responds to a signal or
stimulus”. This definition is broad. In fact, it is so broad that it covers almost
everything from a human eye to a trigger in a pistol. Consider the level-control
system shown in Fig. 1.1 [1]. The operator adjusts the level of fluid in the tank by
manipulating its valve. Variations in the inlet flow rate, temperature changes (these
would alter the fluid’s viscosity and consequently the flow rate through the valve),
and similar disturbances must be compensated for by the operator. Without
control the tank is likely to flood, or run dry. To act appropriately, the operator
must on a timely basis obtain information about the level of fluid in the tank. In this
example, the information is generated by the sensor, which consists of two main
parts: the sight tube on the tank and the operator’s eye, which produces an electric
response in the optic nerve. The sight tube by itself is not a sensor, and in this
particular control system, the eye is not a sensor either. Only the combination of
these two components makes a narrow-purpose sensor (detector) that is selectively
sensitive to the fluid level. If a sight tube is designed properly, it will very
quickly reflect variations in the level, and it is said that the sensor has a fast
speed response. If the internal diameter of the tube is too small for a given fluid
viscosity, the level in the tube may lag behind the level in the tank. Then, we have to
consider a phase characteristic of such a sensor. In some cases, the lag may be
quite acceptable, while in other situations, a better sight tube design would be
required. Hence, the sensor’s performance must be assessed only as part of a data
acquisition system.
# Springer International Publishing Switzerland 2016
J. Fraden, Handbook of Modern Sensors, DOI 10.1007/978-3-319-19303-8_1
1

This world is divided into natural and man-made objects. The natural sensors, like
those found in living organisms, usually respond with signals having electrochemi-
cal character; that is, their physical nature is based on ion transport, like in the nerve
fibers (such as an optic nerve in the fluid tank operator). In man-made devices,
information is also transmitted and processed in electrical form, however, through
the transport of electrons. Sensors intended for the artificial systems must speak the
same language as the systems “speak”. This language is electrical in its nature and
the sensor shall be capable of responding with the output signals where information
is carried by displacement of electrons, rather than ions.1
Thus, it should be possible
to connect a sensor to an electronic system through electrical wires, rather than
through an electrochemical solution or a nerve fiber. Hence, in this book, we use a
somewhat narrower definition of a sensor, which may be phrased as
A sensor is a device that receives a stimulus and responds with an electrical signal.
The term stimulus is used throughout this book and needs to be clearly understood.
The stimulus is the quantity, property, or condition that is received and converted
into electrical signal. Examples of stimuli are light intensity and wavelength, sound,
force, acceleration, distance, rate of motion, and chemical composition. When we
say “electrical,” we mean a signal which can be channeled, amplified, and modified
by electronic devices. Some texts (for instance, [2]) use a different term,
measurand, which has the same meaning as stimulus, however with the stress on
quantitative characteristic of sensing.
We may say that a sensor is a translator of a generally nonelectrical value into an
electrical value. The sensor’s output signal may be in form of voltage, current, or
charge. These may be further described in terms of amplitude, polarity, frequency,
Fig. 1.1 Level-Control
System. Sight tube and
operator’s eye form a
sensor—device that converts
information into electrical
signal
1
There is a very exciting field of the optical computing and communications where information is
processed by a transport of photons. That field is beyond the scope of this book.
2 1 Data Acquisition

phase, or digital code. The set of output characteristics is called the output signal
format. Therefore, a sensor has input properties (of any kind) and electrical output
properties.
Any sensor is an energy converter. No matter what you try to measure, you
always deal with energy transfer between the object of measurement to the sensor.
The process of sensing is a particular case of information transfer, and any trans-
mission of information requires transmission of energy. One should not be confused
by the obvious fact that transmission of energy can flow both ways—it may be with
a positive sign as well as with a negative sign; that is, energy can flow either from
the object to the sensor or backward—from the sensor to the object. A special case
is when the net energy flow is zero, and that also carries information about existence
of that particular situation. For example, a thermopile infrared radiation sensor will
produce a positive voltage when the object is warmer than the sensor (infrared flux
is flowing to the sensor). The voltage becomes negative when the object is cooler
than the sensor (infrared flux flows from the sensor to the object). When both
the sensor and the object are at exactly the same temperature, the flux is zero and
the output voltage is zero. This carries a message that the temperatures are equal to
one another.
The terms sensor and term detector are synonyms, used interchangeably and
have the same meaning. However, detector is more often used to stress qualitative
rather than quantitative nature of measurement. For example, a PIR (passive
infrared) detector is employed to indicate just the existence of human movement
but generally cannot measure direction, speed, or acceleration.
The term sensor should be distinguished from transducer. The latter is a
converter of any one type of energy or property into another type of energy or
property, whereas the former converts it into electrical signal. An example of a
transducer is a loudspeaker which converts an electrical signal into a variable
magnetic field and, subsequently, into acoustic waves.2
This is nothing to do with
perception or sensing. Transducers may be used as actuators in various systems. An
actuator may be described as opposite to a sensor—it converts electrical signal into
generally nonelectrical energy. For example, an electric motor is an actuator—it
converts electric energy into mechanical action. Another example is a pneumatic
actuator that is enabled by an electric signal and converts air pressure into force.
Transducers may be parts of a hybrid or complex sensor (Fig. 1.2). For example,
a chemical sensor may comprise two parts: the first part converts energy of an
exothermal chemical reaction into heat (transducer) and another part, a thermopile,
converts heat into an electrical output signal. The combination of the two makes a
hybrid chemical sensor, a device which produces electrical signal in response to a
chemical reagent. Note that in the above example a chemical sensor is a complex
sensor—it is comprised of a nonelectrical transducer and a simple (direct) sensor
converting heat to electricity. This suggests that many sensors incorporate at least
2
It is interesting to note that a loudspeaker, when connected to an input of an amplifier, may
function as a microphone. In that case, it becomes an acoustical sensor.
1.1 Sensors, Signals, and Systems 3

one direct-type sensor and possibly a number of transducers. The direct sensors are
those that employ certain physical effects to make a direct energy conversion into a
generation or modulation of an electrical signal. Examples of such physical effects
are the photoeffect and Seebeck effect. These will be described in Chap. 4.
In summary, there are two types of sensors, direct and hybrid. A direct sensor
converts a stimulus into an electrical signal or modiﬁes an externally supplied
electrical signal, whereas a hybrid sensor (or simply—a sensor) in addition needs
one or more transducers before a direct sensor can be employed to generate an
electrical output.
A sensor does not function by itself; it is always part of a larger system that may
incorporate many other detectors, signal conditioners, processors, memory devices,
data recorders, and actuators. The sensor’s place in a device is either intrinsic or
extrinsic. It may be positioned at the input of a device to perceive the outside effects
and to inform the system about variations in the outside stimuli. Also, it may be an
internal part of a device that monitors the devices’ own state to cause the appropri-
ate performance. A sensor is always part of some kind of a data acquisition system.
In turn, such a system may be part of a larger control system that includes various
feedback mechanisms.
To illustrate the place of sensors in a larger system, Fig. 1.3 shows a block
diagram of a data acquisition and control device. An object can be anything: a car,
space ship, animal or human, liquid, or gas. Any material object may become a
subject of some kind of a measurement or control. Data are collected from an object
by a number of sensors. Some of them (2, 3, and 4) are positioned directly on or
inside the object. Sensor 1 perceives the object without a physical contact and,
therefore, is called a noncontact sensor. Examples of such a sensor is a radiation
detector and a TV camera. Even if we say “noncontact”, we remember that energy
transfer always occurs between a sensor and object.
Sensor 5 serves a different purpose. It monitors the internal conditions of the
data acquisition system itself. Some sensors (1 and 3) cannot be directly connected
to standard electronic circuits because of the inappropriate output signal
formats. They require the use of interface devices (signal conditioners) to produce
a speciﬁc output format.
Sensors 1, 2, 3, and 5 are passive. They generate electric signals without energy
consumption from the electronic circuits. Sensor 4 is active. It requires an operating
Fig. 1.2 Sensor may incorporate several transducers. Value s1, s2, etc. represent various types of
energy. Direct sensor produces electrical output e

signal that is provided by an excitation circuit. This signal is modified by the sensor
or modulated by the object’s stimulus. An example of an active sensor is a
thermistor that is a temperature-sensitive resistor. It needs a current source, which
is an excitation circuit. Depending on the complexity of the system, the total
number of sensors may vary from as little as one (a home thermostat) to many
thousands (a space station).
Electrical signals from the sensors are fed into a multiplexer (MUX), which is
a switch or a gate. Its function is to connect the sensors, one at a time, to an analog-
to-digital converter (A/D or ADC) if a sensor produces an analog signal, or directly
to a computer if a sensor produces signals in a digital format. The computer controls
a multiplexer and ADC for the appropriate timing. Also, it may send control signals
to an actuator that acts on the object. Examples of the actuators are an electric
motor, a solenoid, a relay, and a pneumatic valve. The system contains some
peripheral devices (for instance, a data recorder, display, alarm, etc.) and a number
of components that are not shown in the block diagram. These may be filters,
sample-and-hold circuits, amplifiers, and so forth.
To illustrate how such a system works, let us consider a simple car door
monitoring arrangement. Every door in a car is supplied with a sensor that detects
the door position (open or closed). In most cars, the sensor is a simple electric
switch. Signals from all door switches go to the car’s internal processor (no need for
an ADC as all door signals are in a digital format: ones or zeros). The processor
identifies which door is open (signal is zero) and sends an indicating message to the
peripheral devices (a dashboard display and an audible alarm). A car driver (the
actuator) gets the message and acts on the object (closes the door) and the sensor
outputs the signal “one”.
Fig. 1.3 Positions of sensors in data acquisition system. Sensor 1 is noncontact, sensors, 2 and
3 are passive, sensor 4 is active, and sensor 5 is internal to data acquisition system
1.1 Sensors, Signals, and Systems 5

An example of a more complex device is an anesthetic vapor delivery system. It is
intended for controlling the level of anesthetic drugs delivered to a patient through
inhalation during surgical procedures. The system employs several active and
passive sensors. The vapor concentration of anesthetic agents (such as halothane,
isoﬂurane, or enﬂurane) is selectively monitored by an active piezoelectric sensor
being installed into a ventilation tube. Molecules of anesthetic vapors add mass to
the oscillating crystal in the sensor and change its natural frequency, which is a
measure of the vapor concentration. Several other sensors monitor the concentration
of CO2, to distinguish exhale from inhale, and temperature and pressure, to compen-
sate for additional variables. All these data are multiplexed, digitized, and fed into
the digital signal processor (DSP) which calculates the actual vapor concentration.
An anesthesiologist presets a desired delivery level and the processor adjusts the
actuators (valves) to maintain anesthetics at the correct concentration.
Another example of a complex combination of various sensors, actuators, and
indicating signals is shown in Fig. 1.4. It is an Advanced Safety Vehicle (ASV) that
was developed by Nissan. The system is aimed at increasing safety of a car. Among
many others, it includes a drowsiness warning system and drowsiness relieving
system. This may include the eyeball movement sensor and the driver head
inclination detector. The microwave, ultrasonic, and infrared range measuring
sensors are incorporated into the emergency braking advanced advisory system to
illuminate the break lamps even before the driver brakes hard in an emergency, thus
advising the driver of a following vehicle to take evasive action. The obstacle
warning system includes both the radar and infrared (IR) detectors. The adaptive
cruise-control system works if the driver approaches too closely to a preceding
vehicle; the speed is automatically reduced to maintain a suitable safety distance.
The pedestrian monitoring system detects and alerts the driver to the presence of
pedestrians at night as well as in vehicle blind spots. The lane-control system helps
in the event the system detects and determines that incipient lane deviation is not
the driver’s intention. It issues a warning and automatically steers the vehicle, if
necessary, to prevent it from leaving its lane.
Fig. 1.4 Multiple sensors, actuators, and warning signals are parts of the Advanced Safety
Vehicle (Courtesy of Nissan Motor Company)

In the following chapters we focus on sensing methods, physical principles of
sensor operations, practical designs, and interface electronic circuits. Other essen-
tial parts of the control and monitoring systems, such as actuators, displays, data
recorders, data transmitters, and others are beyond the scope of this book and
mentioned only briefly.
The sensor’s packaging design may be of a general purpose. A special packaging
and housing should be built to adapt it for a particular application. For instance, a
micromachined piezoresistive pressure sensor may be housed into a watertight
enclosure for the invasive measurement of the aortic blood pressure through a
catheter. The same sensor will be given an entirely different packaging when
intended for measuring blood pressure by a noninvasive oscillometric method
with an inflatable cuff. Some sensors are specifically designed to be very selective
in a particular range of input stimulus and be quite immune to signals outside the
desirable limits. For instance, a motion detector for a security system should
be sensitive to movement of humans and not responsive to movement of smaller
animals, like dogs and cats.
1.2 Sensor Classification
Sensor classification schemes range from very simple to the complex. Depending
on the classification purpose, different classification criteria may be selected. Here
are several practical ways to look at sensors.
1. All sensors may be of two kinds: passive and active. A passive sensor does not
need any additional energy source. It generates an electric signal in response to
an external stimulus. That is, the input stimulus energy is converted by the sensor
into the output signal. The examples are a thermocouple, a photodiode, and a
piezoelectric sensor. Many passive sensors are direct sensors as we defined them
earlier.
The active sensors require external power for their operation, which is called
an excitation signal. That signal is modified (modulated) by the sensor to
produce the output signal. The active sensors sometimes are called parametric
because their own properties change in response to an external stimulus and
these properties can be subsequently converted into electric signals. It can be
stated that a sensor’s parameter modulates the excitation signal and that modu-
lation carries information of the measured value. For example, a thermistor is a
temperature-sensitive resistor. It does not generate any electric signal, but by
passing electric current (excitation signal) through it its resistance can be
measured by detecting variations in current and/or voltage across the thermistor.
These variations (presented in ohms) directly relate to temperature through a
known transfer function. Another example of an active sensor is a resistive strain
gauge in which electrical resistance relates to strain in the material. To measure
the resistance of a sensor, electric current must be applied to it from an external
power source.
1.2 Sensor Classification 7

2. Depending on the selected reference, sensors can be classiﬁed into absolute and
relative. An absolute sensor detects a stimulus in reference to an absolute
physical scale that is independent on the measurement conditions, whereas a
relative sensor produces a signal that relates to some special case. An example of
an absolute sensor is a thermistor—a temperature-sensitive resistor. Its electrical
resistance directly relates to the absolute temperature scale of Kelvin. Another
very popular temperature sensor—a thermocouple—is a relative sensor. It
produces an electric voltage that is function of a temperature gradient across
the thermocouple wires. Thus, a thermocouple output signal cannot be related to
any particular temperature without referencing to a selected baseline. Another
example of the absolute and relative sensors is a pressure sensor. An absolute
pressure sensor produces signal in reference to vacuum—an absolute zero on a
pressure scale. A relative pressure sensor produces signal with respect to a
selected baseline that is not zero pressure—for example, to the atmospheric
pressure.
3. Another way to look at a sensor is to consider some of its properties that may be
of a speciﬁc interest [3]. Below are the lists of various sensor characteristics and
properties (Tables 1.1, 1.2, 1.3, 1.4, and 1.5).
Table 1.1 Sensor
specifications
Sensitivity Stimulus range (span)
Stability (short and long term) Resolution
Accuracy Selectivity
Speed of response Environmental conditions
Overload characteristics Linearity
Hysteresis Dead band
Operating life Output format
Cost, size, weight Other
Table 1.2 Sensing
element material
Inorganic Organic
Conductor Insulator
Semiconductor Liquid gas or plasma
Biological substance Other
Table 1.3 Conversion phenomena
Physical Thermoelectric
Photoelectric
Photomagnetic
Magnetoelectric
Electromagnetic
Thermoelastic
Electroelastic
Thermomagnetic
Thermo-optic
Photoelastic
Other
Chemical Chemical transformation
Physical transformation
Electrochemical process
Spectroscopy
Other
Biological Biochemical transformation
Physical transformation
Effect on test organism
Spectroscopy
Other

Table 1.4 Field of applications
Agriculture Automotive
Civil engineering, construction Domestic, appliances
Distribution, commerce, finance Environment, meteorology, security
Energy, power Information, telecommunication
Health, medicine Marine
Manufacturing Recreation, toys
Military Space
Scientific measurement Other
Transportation (excluding automotive)
Table 1.5 Stimuli
Stimulus Stimulus
Acoustic
Wave amplitude, phase
Spectrum polarization
Wave velocity
Other
Biological
Biomass (types, concentration states)
Other
Chemical
Components (identities, concentration, states)
Other
Electric
Charge, current
Potential, voltage
Electric field (amplitude, phase, polarization,
spectrum)
Conductivity
Permittivity
Other
Magnetic
Magnetic field (amplitude, phase, polarization,
spectrum)
Magnetic flux
Permeability
Other
Optical
Wave amplitude, phase, polarization, spectrum
Wave velocity
Refractive index
Emissivity, reflectivity, absorption
Other
Mechanical Position (linear, angular)
Acceleration
Force
Stress, pressure
Strain
Mass, density
Moment, torque
Speed of flow, rate of
mass transport
Shape, roughness,
orientation
Stiffness, compliance
Viscosity
Crystallinity, structural
integrity
Other
Radiation Type
Energy
Intensity
Other
Thermal Temperature
Flux
Specific heat
Thermal conductivity
Other
1.2 Sensor Classification 9

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of her best cap, and holding by the hand a little girl with very red
eyes, and a red nose, who kept up a suspicious little sniffing, as
though it was only by great effort she refrained from bursting into
fresh tears. Grandma walked straight toward her daughter, and said,
“Mamma, we have come to ask you if you will not forgive poor little
Nannie, who is very sorry, and let her go to-day, for Grandma’s sake
—not for hers at all, but for Grandma’s.”
And the handsome mother, with a sudden glad light flashing in
her gray eyes, stooped and kissed the cheek of her sweet old
mother, and then of her own little daughter, as she said, “Dear
mother, you know what you ask for your own sake I could certainly
never refuse.”
The years have rolled on since then, enough of them to make
little Nannie twenty-six, and the mother of one Rosamond, who has
golden hair like the dollie, her namesake, but who is mischievous, as
Rosamond of old never was. And I heard the sweet mother say, last
Thanksgiving morning, after having told this story of her past for the
benefit of some young mothers, “I am thankful for two things: that I
had a mother who taught me that wrong-doing must bring
unhappiness, not only to myself, but to others; and that I had a dear
Grandmother who taught me what it was to have a powerful friend
to come between me and Justice, and say, ‘For my sake.’“
Pansy.

PAPA’S CHOICE.
HERE stands my baby,
On two little feet;
With her bushy brown head,
And her dimples so sweet.
Her arms are all ready
To give me a hug;
So give me my baby,
And you keep your pug.
R.

WHAT is thy mission, November,
Thou link ’twixt the living and dead?
What message would’st have us remember,
Writ on thy dried leaves, to be read
As lessons to youth and to age,
To the simple, the student, the sage?
Stern duty, thy scepter of power,
The husbandman readily sees;
And takes up the tasks of the hour
As the limbs bear the buds on the trees;
For he sows not, ploughs not, nor reaps;
He laughs not, he frowns not, nor weeps.
The frosts, without cost, starch the ground;
Spread a mirror o’er river and lakes;
While nuts scattered thickly around,
More treasured than apples and cakes,
The children may gather with ease,
With the squirrels which hide in the trees.
The apples are now in the bins,
The pumpkins upon the barn floor,
Save those which, bereft of their skins,
Hang to dry on the biggest barn door;
The banking’s high piled ’gainst the house,
To keep it as snug as a mouse.
Thou wast wisely ordained for man,
For time was much needed, we see,
In which for cold winter to plan,
And prepare for the storms which must be;
So, while few may sing of thy praise,
We will welcome and treasure thy days.
N t ll th b t thi f thi d ld th

Not all the best things of this grand old earth,
Not all the hours of the year around,
Are welcomed here with the songs of mirth,
Nor in fields of pleasure are ever found,
For cloudy are the days of welcome rain,
And sharp the sickle for the golden grain.
G. R. A.
The soul that perpetually overflows with kindness
and sympathy will always be cheerful.

BABY’S CORNER.
WHAT MADE BABY LAUGH?
ABY DALE’S mamma had a great many pictures of her
little boy, but they were not pretty.
The trouble was, he would not sit still even for one
little minute. He was always jumping or clapping his
fat hands, or saying “Baa, baa!”
One of his pictures had three eyes, and one had no nose.
One funny one had his mouth wide open like a big O, for he was
crying.
And there was one where he had his mouth shut, but he looked
very cross. He had a frown between his eyes. Mamma said she
would not know it was her sunny boy.
But by and by a man came who could take pictures whether
babies kept still or not.
One day little Dale was in his high chair by the window. Outdoors
it was snowing.
Baby thought the snowflakes were pretty white feathers coming
down from the sky. Mamma and he played with a feather once that
came out of his pillow. It was nice.
Such a lot of feathers! They made pretty white caps on the fence
posts. And there were great heaps of them on the ground!
“Some day,” thought Baby, “I will go out that door, and I will
creep right down the steps, and I will go to that big pile of feathers,

and I will get my hand full, and I will throw them away up, up, back
into the sky!”
Then baby laughed, and the man who had come to take his
picture touched a button on a queer little box he had, and there was
Baby just as you see him.
That is how Baby Dale came to have a picture that mamma loved.
All the aunties, when they saw it, said, “Oh! how sweet.”
“I WILL GET MY HAND FULL.”
Mamma sent a picture to the grandma down in Flor-i-da, and one
to the grandma up in Maine. One went over the ocean to Uncle John
who loves Baby Dale very dearly. One went out West to Auntie Lou,
and one went to Boston, to be printed for you.

Mrs. C. M. Livingston.
SOMETIMES in the early springtime,
The sunbeams floating ’round
Are caught out in the showers,
And are washed into the ground.
But, ere the summer’s over,
They take root in the sod,
And grow up with fresh brightness
In the form of Golden Rod.
—Selected.

LORA’S SERMON.
T was Sunday morning, and all the family except Lora
and her mother had gone to church. As a rule they, or
at least Lora, were the first to be tucked into the
sleigh; but on this particular morning Mrs. Wheeler
had said she was not going; that she had a little cold,
she believed, and was “all tuckered out” with the week’s work, and
just in condition to get more cold very easily; and Lora’s coat did
look too ridiculous to wear to church, so she had better stay at home
with her.
“By next Sunday you will have your new coat,” she said, to
console the child, “and be all in order for church for the rest of the
winter.”
Lora looked sober for a few minutes; she was very fond of riding
to church tucked in among the great soft robes, and she did not
mind the service so very much, though the sermon was pretty long.
However, she was naturally a sunny little girl, and her face soon
cleared as she buttoned her somewhat shabby coat, and went out to
watch the snowbirds, who were gathering in great numbers near the
barn doors.
Lora and the snowbirds were friends; indeed she made friends
with all sorts of dumb animals, and had queer little ideas about
them.
“You will fall,” she said gravely, addressing a fat bird who swung
on a tiny branch almost at her side; “you have picked out a very
slimsy branch; it looks as though it was almost broked off; maybe it
will break while you are swinging on it—I most know it will—then
you will fall down in the snow and hurt yourself. I falled off of a limb
once, and it hurted.”

The bird paid not the slightest attention to this friendly warning,
but Lora continued to stand still, looking at the swaying bush, her
face full of earnest thought. She had already turned from the bird,
and was thinking about the verse sister Nannie had taught her that
morning. It was a long verse for a little girl, with some hard words in
it; but Lora had mastered them, and said them over in her mind,
revolving, meanwhile, the explanation which Nannie had made of
them. “If a man abide not in me he is cast forth as a branch, and is
withered.” “Branches do wivver as soon as they are broked off,” said
Lora. “I’ve seen them; and papa and Moses burn them up—that is
what it said.
“This stick is broked off,” she continued, carefully examining the
one which she grasped with both chubby hands; “it used to grow,
but it won’t ever any more. All the leaves have wivvered off it, and
some day it will get burned up, I s’pose; it isn’t good for much.”
Words stopped just here, but that little Lora’s brain went on with
the great thoughts which she could not express, was evident from
the look on her face. The Bible verse and Nannie’s careful
explanation of it had taken deep root in her heart. She went into the
house presently; the thoughts had grown so large that she felt as
though she must ask some more questions.
As a usual thing, Sunday quiet reigned in Mrs. Wheeler’s kitchen
at this hour of the day. But this day was an exception. Mrs. Wheeler,
bustling about doing up the last things connected with the morning
work, had come across a bowl of mince meat and a lump of dough
evidently left from pie crust. “I declare for it!” she exclaimed, “I
thought Kate made up all the pies yesterday. What a careless thing,
to leave this bowl of mince meat here over Sunday! It would make
two good pies, and if all the folks come for Thanksgiving we may fall
short; they set such store by my pies. I wonder what Kate was
about? It must have got dark before she finished. These must be
made up the first thing to-morrow—but there is pretty near
everything to do to-morrow, too; it makes a great deal of work
getting ready for such a house full; and pie crust is none the better

for standing, either; I declare, I’ve a mind to slap this on to a couple
of tins and set them in the oven; there is fire enough to bake them
nicely, and it won’t take five minutes, hardly, and there are so many
ways to turn to-morrow.”
There were more thoughts about it not put into words, but it
ended in the moulding board being spread out on the table, and the
flour jar and rolling-pin and pastry knife being laid beside it. I
wonder they did not all blush for shame, for such a thing had never
happened to them before on a Sabbath. Mrs. Wheeler’s cheeks were
rather red, and she felt what she would have called “kind of queer”;
but she flew about very fast, and meant to be soon seated in the
best room in her Sunday dress.
It was just at that moment that Lora pushed open the kitchen
door and entered, her eyes large with the thoughts about which she
wanted to question. They grew larger as she took in the situation.
Her mother rolling out pie crust! And it was Sunday! Such a thing
had never happened in Lora’s experience. Nobody knows why the
queer little brain put together the thoughts which had come to her
outside, and the pie crust in the kitchen; but it did, and there came,
presently, this question: “Did you get broked off, muvver?”
“Did I what?” said Mrs. Wheeler, her cheeks very red. There was
something in Lora’s look and tone which made them redder.
“Get broked off. That is what Nannie said. She said folks that got
broked off did things that Jesus did not want done; and kept doing
them. Does he want you to make pies to-day, muvver?”
“If I ever saw such a child!” said Mrs. Wheeler, making the rolling-
pin revolve over the board at railroad speed. “What does Nannie
mean putting such notions into your head? Go into the other room,
child, and take off your coat; I’ll be there in a few minutes. I’m not
going to make pies; I shall wad up this dough and keep it until to-
morrow.”
And she did.

THAT RAINY DAY.
HE Stautenbergers were not rich, neither were they
poor. Their house was not large, neither was it very
little; but there was none too much room in it.
Mrs. Stautenberger was dead; had “fallen asleep,”
as the father called it, that very autumn; so when he went to the
shop for his day’s work, Pauline, the eldest, had to be both sister
and mother to her three sisters, and one little brother.
The teacher of the school in their district was very kind, and after
her first call at the “home without a mother,” she said to Pauline, “Do
not stay at home to care for baby sister; bring her with you, and we
will manage in some way. I think she will be a good little girl.”
Then Pauline felt sure she should love the teacher very much.
When her father came home she told him what Miss Gilbert had
said, and as he wiped a tear away, he, too, thought she would be a
nice teacher, and must have a good heart to be so willing to help his
motherless ones.
There are a great many things I would like to tell you about this
little family and their splendid teacher, but all I will have time for
now, is the story of one rainy day, and what they did about it.
The storm was so hard they could none of them venture out;
certainly little Gretchen must not be taken out, so there seemed a
prospect for a dull, dreary, lonesome day.
The few dishes were soon put away, and all were hungry for
school.
“I know what to do,” said Pauline; “let’s play school. We can read
and spell and make numbers, and maybe we can study geography a

little; then when we go to school to-morrow teacher will be so
s’prised to see how much we have learned; and then she’ll smile,
and maybe she will kiss us, every one! Won’t that be fun?”
She didn’t try to rhyme, but in her eagerness it came of itself.
So they had school, and Metza played teacher, and Pauline sat by
little Gretchen, and Fritz and Mary sat with them on the long lounge,
and they had such a nice time they forgot that it was storming
outside, and were much astonished when at noon papa came home
to lunch, and so sorry they had forgotten to heat the water for his
coffee.
But when they told him what a nice time they had had, he smiled,
and said, “My Pauline has been a good mother to-day.” And she
thought, “I have the best papa in the world.”
G. R. A.

“THIS STICK IS BROKED OFF,” SAID LORA.

P
PERFUMED GLOVES.
ERFUMED gloves were brought from Italy by Edward Vere, Earl
of Oxford, after his exile, and his present to Queen Elizabeth of a
pair with embroidered roses is mentioned in history. But the
refinement of perfumed gloves had been known for three centuries
in France before the days of the Virgin Queen, and in Spain the
gloves were famous for the scent imparted to them long before her
day. The luxurious court of Charles the Second used perfumed
gloves, and those “trimmed and laced as fine as Nell’s,” you have no
doubt read about. Louis the Fourteenth also issued letter patents of
his “marchands maitres gantiers parfeumeurs.” In Venice, where the
love of dress was conspicuous, perfumed gloves were introduced by
a dogess as early as 1075.—Selected.
QUEEN ELIZABETH WHEN A PUPIL.

That day is best wherein we give
A thought of others’ sorrows;
Forgetting self, we learn to live,
And blessings born of kindly deeds
Make golden our to-morrows.

A SABBATH IN A BOARDING-
SCHOOL IN TURKEY.
I.
T was the dawn of a winter morning. Ding-dong-ding
clanged the chapel bell. I sprang up and began to
dress, while Marta went to the mission-house for a
cup of coffee. As I fastened the last button, there was
a rap at the door. “Come,” I called, and in walked the
dear little maid with a cup of coffee carefully covered to keep in the
steam, and a roll done up in a napkin, which the cook had insisted
upon her bringing.
Ding-dong began the bell again. “Tell the girls not to wait for me,”
I said; and soon the clatter of many feet on the stairs indicated their
departure. The coffee must be swallowed, and the little roll must not
be wholly neglected; then putting on bonnet and ulster, I started to
follow. Fido, our little spaniel, was standing disconsolate in the hall
below. Her eyes were full of entreaty, and wagging her tail
persuasively, she accompanied me to the door.
“Go back, Fido. Can’t take little dogs to church!” I exclaimed. She
knew it was no use to tease, and stood watching me as I opened the
heavy door with difficulty, and slammed it after me—it would not
latch unless slammed. As I reached the church door, I heard the
organ—that meant the service had begun, and I was late! something
I never meant to be, but this was so early to go to church! The
Armenians are all accustomed in the Gregorian Church to a service
even earlier, and when they become Protestant, or Evangelical, they
still cling to the old way of making worship the first thing in the
morning, and giving breakfast the second place.

Instead, then, of going up the men’s aisle, and sitting at the
further end where we missionaries usually do, I went on to the door
at the left—the women’s—and slipped into a back seat. A little girl
just in front of me passed me her hymn book, so that I could join
with the congregation in singing “Garode yem, voh garode yem”—“I
need Thee, O, I need Thee.” Just as the hymn closed, the sun’s rays
struck the eastern window and streamed in; then the preacher arose
and read the epistle to Philemon, and also 1 Cor. vii. 22....
The benediction was pronounced, and the congregation slowly
streamed out. The walk from the chapel to the street is narrow, and
as it is not proper for women to crowd in among the men, we waited
till they had mostly passed on. While standing outside, Shushan, one
of our day pupils, came along with her mother; both were
completely enveloped in the white crapy wrap which is worn by the
Armenian women in this section. Shushan’s bright-colored dress
showed through, and at the same time set off the figure in the wrap.
“Par-ee loo-is, Shushan; are you of the same mind as yesterday
about going to Kozloo?”
She returned my good-morning, and said she was; yes, indeed!
“Why should we change our minds?” said her mother. “Are we not
also Christ’s servants?” referring to the sermon we had just heard.
You see, Shushan’s brother was bitterly opposed to her going
away to teach, and I thought it quite possible that he had influenced
her to give it up. It was years after girls’ schools were opened before
people were willing to send their children to a woman teacher—I
mean a native—still worse if she was “only a girl.” They would far
rather send them to a man, however ignorant and incapable. That
long struggle has ended at last in victory, and we have no more
trouble in finding work for our girls; but we have another difficulty
now. Well-to-do parents and brothers consider it a disgrace—at least
many of them do—to have their daughters and sisters work as
though they were obliged to earn their support.

“Haven’t you food and clothes?” they ask indignantly, when a girl,
filled with a desire to do something for her people, intimates a
purpose to teach. Perhaps I may as well complete this little tale here
and now, although it does not belong to the incident of the Sabbath
I have been describing.
A few days later the (native) pastor came to me and asked
anxiously, “Can’t you persuade Shushan, for the sake of peace, to
give up going to Kozloo? Her brother is very violent, and talks
terribly, declaring that even if she were mounted, and going through
the most public street, he would drag her off the horse; if she should
by any chance succeed in carrying out her plan, she should never
come home again—he would never again acknowledge her as his
sister.” The pastor went on to say that he thought the brother had
offered to send her away to school if she would give up “this crazy
scheme,” as he called it.
I sent for Shushan, and finding that her brother had made the
offer referred to, advised her to accept it. The sacrifice of her will for
the sake of avoiding scandal, would, I was sure, be as acceptable to
the Master as the service she had intended. In less than a week
thereafter, she was on her way to a distant school.
We passed out through the arched gateway, and then parted with
a mutual “yer-tak par-rov”—“good-by.” How the sun sparkled on the
snowy street, on the mountains which seemed to stand across it, so
near they looked, and reared their dazzling summits into the brilliant
blue of the winter sky.
The girls with their shawls modestly over their heads, crossed the
street in a straggling little procession. Fido appeared in the window
which she had pried open with her little black nose—windows are
hung like doors—gave an eager and joyful bark or two, and rushed
down to welcome them home. Then they sat down to their breakfast
of tea and bread. The former was seasoned with white lump sugar
(brown sugar is unknown), but there was no butter for the bread.

I doubt whether my readers would have recognized the thin,
whity-brown sheets, or the rags placed before one of the girls who
had elected to take the pieces, as bread, but so it was. They have
many kinds in Turkey, and this thin kind, a little thicker than blotting-
paper, is very popular here. In the autumn it is a very common thing
for a girl to come and say, “Teacher, mother says will you please
excuse me from school to-day?” And she explains that they are
baking bread, and need her help.
“But why doesn’t your mother get some woman to help her?”
Then I find that it is a regular “bee”—a bread bee! The neighbors
are already there, and they will work all night—it is no small job to
roll it out so thin. There will be no more baking till the worst of the
winter is over. It is stacked away in a dry place, and when wanted
the requisite number of sheets (about two feet long by one wide) is
taken, sprinkled as you would clothes for ironing, and after a few
moments, folded once lengthwise and laid around the edge of the
table. If, instead of being sprinkled, the bread is held over the fire a
moment, it becomes crisp and really nice; but this is seldom done.
After the housework was done we had prayers, and then the girls
were dismissed with a charge not to hang about the halls or
stairways, as the boys were coming over again to sing, and to keep
their doors closed. “Not ajar as last Sunday, to my mortification and
your disgrace; most likely the boys thought you left them open on
purpose so that they could look in.” Somehow the boys and girls are
wonderfully interesting to each other all the world over.
Soon the young fellows filed in, looking half-pleased, half-shy—
big, six-foot Isaac, and clever little Bo-ghos; Sumpad, with his
bright, frank smile; poor, awkward Deekran, the best writer in
school, and his brother Arsen. We practiced “Hold the Fort”; there
were two bad mistakes with which we struggled for a while. Then
we sang “What a Friend we have in Jesus,” “Sweet By and by,”
“Almost Persuaded,” “Go Bury thy Sorrow,” “The Ninety and Nine,”
and others—all in Armenian, of course.

Then I said just a word to Deekran about money I entrusted to
him—merely a caution to be careful to return any money that might
be left over. It was hardly the thing for the Sabbath, but I was not
likely to see him for some days, and I wanted to prevent any
carelessness—it is so important for boys that they learn to be careful
and business-like.
Harriet G. Powers, in the Evangelist.

M
THE HARD TEXT.
(Matt. xii. 31, 32.)
ANY have been troubled over this text. Some have been in
despair of being saved because they thought they had
committed this unpardonable sin.
Probably many are mistaken. Any one that truly feels sorrow for
his sins, and really longs for forgiveness and hungers for holiness,
shows some of the best signs that he has not committed this. God
will not cast out such a person, if he comes in Jesus’ name.
But there is a sin against the Holy Ghost so great that it cannot
be forgiven, and probably when one has committed it he is so
desperately wicked, so hard in heart, that he never asks to be
forgiven.
You will wish to know what this awful sin is, so that you may
never commit it. The thought of being doomed never to see heaven
and Christian friends after death fills you with horror.
But then, why should you not tremble at committing any sin? One
little sin leads to another, and so on, until the sin of sins is the end
of it all. Take care!

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