Description
Applications which use wireless sensors are increasing in number. The emergence of wireless sensor networks has also motivated the integration of a large number of small and lightweight nodes which integrate sensors, processors, and wireless transceivers. Existing books on wireless sensor networks mainly focus on protocols and networks and pay little attention to the sensors themselves which the author believes is the main focus. Without adequate knowledge of sensors as well as how they can be designed, realized and used, books on wireless sensor networks become too theoretical and irrelevant. The purpose of this book is to intimately acquaint readers with the technique of sensing (resistive, capacitive, inductive, magnetic, inertial, etc.) and existing sensor technologies. It also discusses how the sensors are used in a wide application domain and how new sensors can be designed and used in a novel way.
Table of Contents
Preface xiii
About the Companion Website xv
List of Abbreviations xvii
1 Introduction 1
1.1 System Overview 2
1.1.1 Sensing System 2
1.1.2 Conditioning System 3
1.1.3 Analogue-to-digital Signal Conversion 3
1.1.4 Processor 4
1.2 Example: AWireless Electrocardiogram 4
1.3 Organisation of the Book 7
2 Applications 9
2.1 Civil Infrastructure Monitoring 9
2.1.1 Bridges and Buildings 10
2.1.2 Water Pipelines 17
2.2 Medical Diagnosis and Monitoring 21
2.2.1 Parkinson’s Disease 21
2.2.2 Alzheimer’s Disease 25
2.2.3 Sleep Apnea and Medical Journalling 26
2.2.4 Asthma 28
2.2.5 Gastroparesis 31
2.3 Water-quality Monitoring 34
References 39
3 Conditioning Circuits 44
3.1 Voltage and Current Sources 44
3.2 Transfer Function 45
3.3 Impedance Matching 51
3.4 Filters 56
3.5 Amplification 61
3.5.1 Closed-loop Amplifiers 63
3.5.2 Difference Amplifier 65
References 70
4 Electrical Sensing 72
4.1 Resistive Sensing 73
4.2 Capacitive Sensing 78
4.3 Inductive Sensing 84
4.4 Thermoelectric Effect 91
References 94
5 Ultrasonic Sensing 96
5.1 UltrasonicWave Propagation 100
5.2 Wave Equation 106
5.3 Factors Affecting UltrasonicWave Propagation 108
References 111
6 Optical Sensing 114
6.1 Photoelectric Effect 116
6.2 Compton Effect 120
6.3 Pair Production 126
6.4 Raman Scattering 127
6.5 Surface Plasmon Resonance 131
References 133
7 Magnetic Sensing 136
7.1 Superconducting Quantum Interference Devices 136
7.1.1 DC-SQUID 139
7.1.2 RF-SQUID 141
7.2 Anisotropic Magnetoresistive Sensing 142
7.3 Giant Magnetoresistance 148
7.4 Tunnelling Magnetoresistance 151
7.5 Hall-effect Sensing 155
References 157
8 Medical Sensing 160
8.1 Excitable Cells and Biopotentials 161
8.1.1 Resting Potential 162
8.1.2 Channel Current 166
8.1.3 Action Potentials 166
8.1.4 Propagation of Action Potentials 167
8.1.5 Measuring Action Potentials 171
8.2 Cardiac Action Potentials 175
8.2.1 Propagation of Cardiac Action Potentials 177
8.2.2 The Electrocardiogram 180
8.2.2.1 Re-entry 181
8.2.2.2 Loss of Membrane Potential 182
8.2.2.3 Afterdepolarisations 183
8.3 Brain Action Potentials 185
8.3.1 Electroencephalography 188
8.3.2 Volume Conduction 193
8.3.3 Electrode Placement 195
References 198
9 Microelectromechanical Systems 202
9.1 Miniaturisation and Scaling 202
9.1.1 Physical Properties 203
9.1.2 Mechanical Properties 203
9.1.3 Thermal Properties 204
9.1.4 Electrical and Magnetic Properties 205
9.1.5 Fluid Properties 205
9.1.6 Chemical Properties 206
9.1.7 Optical Properties 206
9.2 Technology 206
9.2.1 Growth and Deposition 207
9.2.2 Photolithography 207
9.2.3 Etching 209
9.3 Micromachining 209
9.3.1 Surface Micromachining 210
9.3.2 Bulk Micromachining 211
9.3.2.1 Reactive Ion Etching 212
9.3.2.2 Micromolding 215
9.3.2.3 Non-silicon Micromolding 216
9.3.2.4 Plastic Micromolding 217
9.4 System Integration 218
9.5 Micromechanical Sensors 220
9.5.1 Pressure and Force Sensors 220
9.5.1.1 Piezoelectric Effect 222
9.5.1.2 Piezoresistance 226
9.5.1.3 Fabrication of a Piezoresistive Sensor 227
9.5.2 Flow Sensors 227
9.5.2.1 Floating Plate 228
9.5.2.2 Artificial Hair Cell 231
9.5.3 Accelerometers 234
9.5.3.1 Fabrication of an Accelerometer 235
9.5.4 Gyroscopes 236
9.5.4.1 Fabrication of a Gyroscope 246
References 249
10 Energy Harvesting 253
10.1 Factors Affecting the Choice of an Energy Source 253
10.1.1 Sensing Lifetime 254
10.1.2 Sensor Load 254
10.1.3 Energy Source 255
10.1.4 Storage 256
10.1.5 Regulation 257
10.2 Architecture 263
10.3 Prototypes 265
10.3.1 Microsolar Panel 265
10.3.2 Microgenerator 269
10.3.3 Piezoelectricity 272
References 275
11 Sensor Selection and Integration 278
11.1 Sensor Selection 278
11.1.1 Accuracy 278
11.1.2 Sensitivity 280
11.1.3 Zero-offset 280
11.1.4 Reproducibility 280
11.1.5 Span 281
11.1.6 Stability 281
11.1.7 Resolution 282
11.1.8 Selectivity 282
11.1.9 Response Time 282
11.1.10 Self-heating 282
11.1.11 Hysteresis 283
11.1.12 Ambient Condition 283
11.1.13 Overload Characteristics 283
11.1.14 Operating Life 284
11.1.15 Cost, Size, andWeight 284
11.2 Example: Temperature Sensor Selection 284
11.2.1 Resistance Temperature Detectors 284
11.2.2 Thermistors 285
11.2.3 Thermocouples 286
11.2.4 Infrared 286
11.3 Sensor Integration 287
11.3.1 Dead Volume 287
11.3.2 Self-heating 287
11.3.3 Internal Heat Sources 294
11.3.3.1 External Heat and Radiation Sources 296
References 296
12 Estimation 298
12.1 Sensor Error as a Random Variable 299
12.2 Zero-offset Error 303
12.3 Conversion Error 305
12.4 Accumulation of Error 309
12.4.1 The Central LimitTheorem 313
12.5 Combining Evidence 315
12.5.1 Weighted Sum 316
12.5.2 Maximum-likelihood Estimation 322
12.5.3 Minimum Mean Square Error Estimation 325
12.5.4 Kalman Filter 328
12.5.5 The Kalman Filter Formalism 334
References 335
Index 337
