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Handbook of Modern Sensors

Fourth Edition

Jacob Fraden

Handbook of Modern Sensors

Physics, Designs, and Applications

Fourth Edition

Jacob Fraden jacob@fraden.com

ISBN 978-1-4419-6465-6 e-ISBN 978-1-4419-6466- DOI 10.1007/978-1-4419-6466- Springer New York Heidelberg Dordrecht London

Library of Congress Control Number: 2010932807

Springer ScienceþBusiness Media, LLC 2010

All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer Science+Business Media, LLC, 233 Spring Street, New York, NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights.

Printed on acid-free paper

Springer is part of Springer Science+Business Media (www.springer.com)

catalogues and websites. However, the information is scattered over many publica- tions, and almost every question I was pondering required substantial research work. Little by little, I have been gathering practical information on everything, which in anyway was related to various sensors and their applications to scientific and engineering measurements. Soon, I realized that the information I collected might be quite useful to more than one person. This idea prompted me to write this book and this 4th edition is the proof that I was not mistaken. In setting my criteria for selecting various sensors for the 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 (immodestly 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 those who look for a convenient reference. It is the author’s intention to present a comprehensive and up-to-date account of the theory (physical principles), design, and practical implementations of various (especially, the newest) sensors for scientific, industrial, and consumer applications. The topics included in the book reflect the author’s own preferences and interpreta- tions. Some may find a description of a particular sensor either too detailed or too broad or, on the contrary, too brief. In most cases, the author tried to strike a balance between a detailed description and simplicity of coverage. It is clear that one book cannot embrace the whole variety of sensors and their applications, even if it would be called something like “The Encyclopedia of Sensors.” This is a different book and the author’s task was much less ambitious. Here, an attempt has been made to generate 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 and/or design sensors for practical systems. The prior editions of this book have been used quite extensively as desktop references and textbooks for the related college courses. Comments and suggestions from the sensor designers, professors, and students prompted me to implement several changes and 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 Drs. Todd E. Mlsna and Sanjay V. Patel for their invaluable contribution to the chapter on chemical sensors. Even though the book is intended for the scientific and engineering communities, as a rule, technical descriptions and mathematic treatments do not require a background beyond a high school curriculum. Simplicity of description and intui- tive approach were the key requirements that I set for myself while working on the manuscript. My true goal was not to pile up a collection of information but rather to entice the reader into a creative process. As Plutarch said nearly two millennia ago, “The mind is not a vessel to be filled but a fire to be kindled.. .”

San Diego, California Jacob Fraden April, 2010

vi Preface

Contents

• 1 Data Acquisition
  • 1.1 Sensors, Signals, and Systems
  • 1.2 Sensor Classification
  • 1.3 Units of Measurements
  • References
• 2 Sensor Characteristics
  • 2.1 Transfer Function
    • 2.1.1 Mathematical Model
    • 2.1.2 Functional Approximations
    • 2.1.3 Polynomial Approximations
    • 2.1.4 Sensitivity
    • 2.1.5 Linear Piecewise Approximation
    • 2.1.6 Spline Interpolation
    • 2.1.7 Multidimensional Transfer Functions
  • 2.2 Calibration
    • 2.2.1 Computation of Transfer Function Parameters
    • 2.2.2 Linear Regression
  • 2.3 Computation of Stimulus
    • 2.3.1 Computation from Linear Piecewise Approximation
    • 2.3.2 Iterative Computation of Stimulus (Newton Method)
  • 2.4 Span (Full-Scale Full Scale Input)
  • 2.5 Full-Scale Output
  • 2.6 Accuracy
  • 2.7 Calibration Error
  • 2.8 Hysteresis
  • 2.9 Nonlinearity
  • 2.10 Saturation
  • 2.11 Repeatability
  • 2.12 Dead Band
  • 2.13 Resolution
  • 2.14 Special Properties
  • 2.15 Output Impedance
  • 2.16 Output Format
  • 2.17 Excitation
  • 2.18 Dynamic Characteristics
  • 2.19 Environmental Factors
  • 2.20 Reliability
  • 2.21 Application Characteristics
  • 2.22 Uncertainty
  • References
• 3 Physical Principles of Sensing
  • 3.1 Electric Charges, Fields, and Potentials
  • 3.2 Capacitance
    • 3.2.1 Capacitor
    • 3.2.2 Dielectric Constant
  • 3.3 Magnetism
    • 3.3.1 Faraday Law
    • 3.3.2 Solenoid
    • 3.3.3 Toroid
    • 3.3.4 Permanent Magnets
  • 3.4 Induction
  • 3.5 Resistance
    • 3.5.1 Specific Resistivity
    • 3.5.2 Temperature Sensitivity
    • 3.5.3 Strain Sensitivity
    • 3.5.4 Moisture Sensitivity
  • 3.6 Piezoelectric Effect
    • 3.6.1 Ceramic Piezoelectric Materials
    • 3.6.2 Polymer Piezoelectric Films
  • 3.7 Pyroelectric Effect
  • 3.8 Hall Effect
  • 3.9 Thermoelectric Effects
    • 3.9.1 Seebeck Effect
    • 3.9.2 Peltier Effect
  • 3.10 Sound Waves
  • 3.11 Temperature and Thermal Properties of Materials
    • 3.11.1 Temperature Scales
    • 3.11.2 Thermal Expansion
    • 3.11.3 Heat Capacity
  • 3.12 Heat Transfer
    • 3.12.1 Thermal Conduction
    • 3.12.2 Thermal Convection
    • 3.12.3 Thermal Radiation
  • 3.13 Light - 3.13.1 Light Polarization - 3.13.2 Light Scattering
  • 3.14 Dynamic Models of Sensor Elements - 3.14.1 Mechanical Elements - 3.14.2 Thermal Elements - 3.14.3 Electrical Elements - 3.14.4 Analogies
  • References
• 4 Optical Components of Sensors
  • 4.1 Radiometry
  • 4.2 Photometry
  • 4.3 Windows
  • 4.4 Mirrors
  • 4.5 Lenses
  • 4.6 Fresnel Lenses
  • 4.7 Fiber Optics and Waveguides
  • 4.8 Concentrators
  • 4.9 Coatings for Thermal Absorption
  • 4.10 Nano-optics
  • References
• 5 Interface Electronic Circuits
  • 5.1 Input Characteristics of Interface Circuits
  • 5.2 Amplifiers
    • 5.2.1 Operational Amplifiers
    • 5.2.2 Voltage Follower
    • 5.2.3 Instrumentation Amplifier
    • 5.2.4 Charge Amplifiers
  • 5.3 Light-to-Voltage Converters
  • 5.4 Excitation Circuits
    • 5.4.1 Current Generators
    • 5.4.2 Voltage References
    • 5.4.3 Oscillators
    • 5.4.4 Drivers
    • 5.4.5 Optical Drivers
  • 5.5 Analog-to-Digital Converters
    • 5.5.1 Basic Concepts
    • 5.5.2 V/F Converters
    • 5.5.3 Dual-Slope Converters
    • 5.5.4 Successive Approximation Converter
    • 5.5.5 Resolution Extension
  • 5.6 Direct Digitization
  • 5.7 Capacitance-to-Voltage Converters
  • 5.8 Integrated Interfaces
  • 5.9 Ratiometric Circuits
  • 5.10 Differential Circuits
  • 5.11 Bridge Circuits - 5.11.1 General Concept - 5.11.2 Disbalanced Bridge - 5.11.3 Null-Balanced Bridge - 5.11.4 Bridge Amplifiers
  • 5.12 Data Transmission - 5.12.1 Two-Wire Transmission - 5.12.2 Four-Wire Sensing - 5.12.3 Six-Wire Sensing
  • 5.13 Noise in Sensors and Circuits - 5.13.1 Inherent Noise - 5.13.2 Transmitted Noise - 5.13.3 Electric Shielding - 5.13.4 Bypass Capacitors - 5.13.5 Magnetic Shielding - 5.13.6 Mechanical Noise - 5.13.7 Ground Planes - 5.13.8 Ground Loops and Ground Isolation - 5.13.9 Seebeck Noise
  • 5.14 Calibration
  • 5.15 Batteries for Low-Power Sensors - 5.15.1 Primary Cells - 5.15.2 Secondary Cells
  • References
• 6 Occupancy and Motion Detectors
  • 6.1 Ultrasonic Detectors
  • 6.2 Microwave Motion Detectors
  • 6.3 Capacitive Occupancy Detectors
  • 6.4 Triboelectric Detectors
  • 6.5 Optoelectronic Motion Detectors
    • 6.5.1 Sensor Structures
    • 6.5.2 Visible and Near IR Light Motion Detectors
    • 6.5.3 Far-Infrared Motion Detectors
  • 6.6 Optical Presence Sensors
  • 6.7 Pressure-Gradient Sensors
  • References
• 7 Position, Displacement, and Level
  • 7.1 Potentiometric Sensors
  • 7.2 Capacitive Sensors
  • 7.3 Inductive and Magnetic Sensors
    • 7.3.1 LVDT and RVDT
    • 7.3.2 Eddy Current Sensors
    • 7.3.3 Transverse Inductive Sensor
    • 7.3.4 Hall Effect Sensors
    • 7.3.5 Magnetoresistive Sensors
    • 7.3.6 Magnetostrictive Detector
  • 7.4 Optical Sensors
    • 7.4.1 Optical Bridge
    • 7.4.2 Proximity Detector with Polarized Light
    • 7.4.3 Fiber-Optic Sensors
    • 7.4.4 Fabry-Perot Sensors
    • 7.4.5 Grating Sensors
    • 7.4.6 Linear Optical Sensors
  • 7.5 Ultrasonic Sensors
  • 7.6 Radar Sensors
    • 7.6.1 Micropower Impulse Radar
    • 7.6.2 Ground Penetrating Radars
  • 7.7 Thickness and Level Sensors
    • 7.7.1 Ablation Sensors
    • 7.7.2 Thin Film Sensors
    • 7.7.3 Liquid Level Sensors
  • 7.8 Pointing Devices
    • 7.8.1 Optical Pointing Devices
    • 7.8.2 Magnetic Pickup
    • 7.8.3 Inertial and Gyroscopic Mice
  • References
• 8 Velocity and Acceleration
  • 8.1 Accelerometer Characteristics
  • 8.2 Capacitive Accelerometers
  • 8.3 Piezoresistive Accelerometers
  • 8.4 Piezoelectric Accelerometers
  • 8.5 Thermal Accelerometers
    • 8.5.1 Heated Plate Accelerometer
    • 8.5.2 Heated Gas Accelerometer
  • 8.6 Gyroscopes
    • 8.6.1 Rotor Gyroscope
    • 8.6.2 Monolithic Silicon Gyroscopes
    • 8.6.3 Optical (Laser) Gyroscopes
  • 8.7 Piezoelectric Cables
  • 8.8 Gravitational Sensors
  • References
  • 9 Force, Strain, and Tactile Sensors
    • 9.1 Strain Gauges
    • 9.2 Tactile Sensors
      • 9.2.1 Switch Sensors
      • 9.2.2 Piezoelectric Sensors
      • 9.2.3 Piezoresistive Sensors
      • 9.2.4 MEMS Sensors
      • 9.2.5 Capacitive Touch Sensors
      • 9.2.6 Acoustic Touch Sensors
      • 9.2.7 Optical Sensors
    • 9.3 Piezoelectric Force Sensors
    • References
• 10 Pressure Sensors - 10.1 Concepts of Pressure - 10.2 Units of Pressure - 10.3 Mercury Pressure Sensor - 10.4 Bellows, Membranes, and Thin plates - 10.5 Piezoresistive Sensors - 10.6 Capacitive Sensors - 10.7 VRP Sensors - 10.8 Optoelectronic Pressure Sensors - 10.9 Indirect Pressure Sensor - 10.10 Vacuum Sensors - 10.10.1 Pirani Gauge - 10.10.2 Ionization Gauges - 10.10.3 Gas Drag Gauge - 10.10.4 Membrane Vacuum Sensors - References
• 11 Flow Sensors - 11.1 Basics of Flow Dynamics - 11.2 Pressure Gradient Technique - 11.3 Thermal Transport Sensors - 11.3.1 Hot-Wire Anemometers - 11.3.2 Three-Part Thermoanemometer - 11.3.3 Two-Part Thermoanemometer - 11.3.4 Microflow Thermal Transport Sensors - 11.4 Ultrasonic Sensors - 11.5 Electromagnetic Sensors - 11.6 Breeze Sensor - 11.7 Coriolis Mass Flow Sensors - 11.8 Drag Force Sensors - 11.9 Dust and Smoke Detectors - 11.9.1 Ionization Detector - 11.9.2 Optical Detector
  • References
• 12 Acoustic Sensors
  • 12.1 Resistive Microphones
  • 12.2 Condenser Microphones
  • 12.3 Fiber-Optic Microphone
  • 12.4 Piezoelectric Microphones
  • 12.5 Electret Microphones
  • 12.6 Dynamic Microphones
  • 12.7 Solid-State Acoustic Detectors
  • References
• 13 Humidity and Moisture Sensors
  • 13.1 Concept of Humidity
  • 13.2 Capacitive Sensors
  • 13.3 Electrical Conductivity Sensors
  • 13.4 Thermal Conductivity Sensor
  • 13.5 Optical Hygrometer
  • 13.6 Oscillating Hygrometer
  • References
• 14 Light Detectors
  • 14.1 Introduction
  • 14.2 Photodiodes
  • 14.3 Phototransistor
  • 14.4 Photoresistors
  • 14.5 Cooled Detectors
  • 14.6 Image Sensors
    • 14.6.1 CCD Sensor
    • 14.6.2 CMOS-Imaging Sensors
  • 14.7 Thermal Detectors
    • 14.7.1 Golay Cells
    • 14.7.2 Thermopile Sensors
    • 14.7.3 Pyroelectric Sensors
    • 14.7.4 Bolometers
    • 14.7.5 Active Far-Infrared Sensors
  • 14.8 Optical Design
  • 14.9 Gas Flame Detectors
  • References
• 15 Radiation Detectors
  • 15.1 Scintillating Detectors
    • 15.2 Ionization Detectors
      • 15.2.1 Ionization Chambers
      • 15.2.2 Proportional Chambers
      • 15.2.3 Geiger–Mu¨ller Counters
      • 15.2.4 Semiconductor Detectors
    • 15.3 Cloud and Bubble Chambers
    • References
• 16 Temperature Sensors - 16.1 Coupling with Object - 16.2 Temperature Reference Points - 16.3 Thermoresistive Sensors - 16.3.1 Resistance Temperature Detectors - 16.3.2 Silicon Resistive PTC Sensors - 16.3.3 Thermistors - 16.4 Thermoelectric Contact Sensors - 16.4.1 Thermoelectric Laws - 16.4.2 Thermocouple Circuits - 16.4.3 Thermocouple Assemblies - 16.5 Semiconductor pn-Junction Sensors - 16.6 Optical Temperature Sensors - 16.6.1 Fluoroptic Sensors - 16.6.2 Interferometric Sensors - 16.6.3 Thermochromic Solution Sensor - 16.7 Acoustic Temperature Sensor - 16.8 Piezoelectric Temperature Sensors - References
• 17 Chemical Sensors - 17.1 Overview - 17.2 History - 17.3 Chemical Sensor Characteristics - 17.4 Classes of Chemical Sensors - 17.4.1 Electrical and Electrochemical Transducers - 17.4.2 Elastomer Chemiresistors - 17.4.3 Photoionization Detector - 17.4.4 Physical Transducers - 17.4.5 Optical Transducers
  • 17.5 Biochemical Sensors - 17.5.1 Enzyme Sensors
  • 17.6 Multisensor Arrays
  • 17.7 Electronic Noses and Tongues
  • 17.8 Specific Difficulties
  • References
• 18 Sensor Materials and Technologies
  • 18.1 Materials
    • 18.1.1 Silicon as Sensing Material
    • 18.1.2 Plastics
    • 18.1.3 Metals
    • 18.1.4 Ceramics
    • 18.1.5 Glasses
    • 18.1.6 Optical Glasses
    • 18.1.7 Nanomaterials
  • 18.2 Surface Processing
    • 18.2.1 Deposition of Thin and Thick Films
    • 18.2.2 Spin Casting
    • 18.2.3 Vacuum Deposition
    • 18.2.4 Sputtering
    • 18.2.5 Chemical Vapor Deposition
    • 18.2.6 Electroplating
  • 18.3 Microtechnology
    • 18.3.1 Photolithography
    • 18.3.2 Silicon Micromachining
  • References
• Appendix
• Index

electrochemical 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 that are used in the artificial systems must speak the same language as the devices with which they are inter- faced. This language is electrical in its nature and a man-made sensor should be capable of responding with 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 sensors, 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 under- stood. The stimulus is the quantity, property, or condition that is received and converted into an electrical signal. Some texts (for instance, [2]) use a different term, measurand which has the same meaning, however with the stress on quanti- tative characteristic of sensing.

Fig. 1.1 Level control system. A sight tube and operator’s eye form a sensor, a device which converts information into an 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

The purpose of a sensor is to respond to some kind of an input physical property (stimulus) and to convert it into an electrical signal that is compatible with ele- ctronic circuits. We may say that a sensor is a translator of a generally nonelectrical value into an electrical value. When we say “electrical,” we mean a signal, which can be channeled, amplified, and modified by electronic devices. The sensor’s output signal may be in the form of voltage, current, or charge. These may be further described in terms of amplitude, polarity, frequency, phase, or digital code. This set of 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 from the object of measurement to the sensor. The process of sensing is a particular case of information transfer, and any transmission of information requires transmission of energy. Of course, one should not be confused by an 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 an object to the sensor or from the sensor to the object. A special case is when the net energy flow is zero, which also carries information about existence of that particular case. 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) or the voltage is 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 the same temperature, the flux is zero and the output voltage is zero. This carries a message that the temperatures are the same. The term sensor should be distinguished from transducer. The latter is a converter of any one type of energy into another, whereas the former converts any type of energy into electrical energy. An example of a transducer is a loud- speaker, 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 an 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. Transducers may be parts of complex sensors (Fig. 1.2). For example, a chemical sensor may have a part, which converts the energy of a chemical reaction into heat (transducer) and another part, a thermopile, which converts heat into an electrical signal. The combination of the two makes a 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 one direct-type sensor and a

(^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