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5.9 Noise in Sensors and Circuits 215 Fig. 5.51. Equivalent circuit of a capacitor. supply impedance can be quite high.As the frequency increases, the inductive parasitic becomes troublesome and may result in circuit oscillation or ringing effects. Even if the circuit operates at lower frequencies, the bypass capacitors are still important, as high-frequency noise may be transmitted to the circuit and power-supply conductors from external sources, (e.g., radio stations). At high frequencies, no power supply or regulator has zero output impedance. What type of capacitor to use is determined by the application, frequency range of the circuit, cost, board space, and some other considerations. To select a bypass capacitor, one must remember that a practical capacitor at high frequencies may be far from the idealized capacitor described in textbooks.’ Ageneralized equivalent circuit of a capacitor is shown in Fig. 5.51. It is composed of a nominal capacitance C, leakage resistance r l , lead inductances L, and resistances R. Further, it includes dielectric absorption terms r and c a , which are manifested in the capacitor’s “memory”. In many interface circuits, especially amplifiers, analog integrators, and current (charge)-to-voltage converters, dielectric absorption is a major cause for errors. In such circuits, film capacitors should be used whenever possible. In bypass applications, r l and dielectric absorption are second-order terms, but series R and L are of importance. They limit the capacitor’s ability to damp transients and maintain a low-power supply output impedance. Often, bypass capacitors must be of large values (10 µF or more) so they can absorb longer transients; thus, electrolytic capacitors are often employed. Unfortunately, these capacitors have large series R and L. Usually, tantalum capacitors offer better results; however, a combination of aluminum electrolytic with nonpolarized (ceramic or film) capacitors may offer even further improvement. A combination of the wrong types of bypass capacitor may lead to ringing, oscillation, and cross-talk between data communication channels. The best way to specify a correct combination of bypass capacitors is to first try them on a breadboard. 5.9.5 Magnetic Shielding Proper shielding may dramatically reduce noise resulting from electrostatic and electrical fields. Unfortunately, it is much more difficult to shield against magnetic fields because it penetrates conducting materials.Atypical shield placed around a conductor and grounded at one end has little, if any, effect on the magnetically induced voltage in that conductor. As a magnetic field B 0 penetrates the shield, its amplitude drops exponentially (Fig. 5.52B). The skin depth δ of the shield is the depth required for the field attenuation by 37% of that in the air. Table 5.5 lists typical values of δ for
216 5 Interface Electronic Circuits (A) (B) Fig. 5.52. Reduction of a transmitted magnetic noise by powering a load device through a coaxial cable (A); Magnetic shielding improves with the thickness of the shield (B). Table 5.5. Skin Depth, δ, (in mm) Versus Frequency Frequency Copper Aluminum Steel 60 Hz 8.5 10.9 0.86 100 Hz 6.6 8.5 0.66 1 kHz 2.1 2.7 0.20 10 kHz 0.66 0.84 0.08 100 kHz 0.2 0.3 0.02 1 MHz 0.08 0.08 0.008 Source: Adapted from Ref. [15]. several materials at different frequencies. At high frequencies, any material may be used for effective shielding; however, at a lower range, steel yields a much better performance. For improving low-frequency magnetic field shielding, a shield consisting of a high-permeability magnetic material (e.g., mumetal) should be considered. However, mumetal effectiveness drops at higher frequencies and strong magnetic fields. An effective magnetic shielding can be accomplished with thick steel shields at higher frequencies. Because magnetic shielding is very difficult, the most effective approach at low frequencies is to minimize the strength of magnetic fields, minimize the magnetic loop area at the receiving end, and select the optimal geometry of conductors. Some useful practical guidelines are as follows: • Locate the receiving circuit as far as possible from the source of the magnetic field. • Avoid running wires parallel to the magnetic field; instead, cross the magnetic field at right angles. • Shield the magnetic field with an appropriate material for the frequency and strength. • Use a twisted pair of wires for conductors carrying the high-level current that is the source of the magnetic field. If the currents in the two wires are equal and opposite, the net field in any direction over each cycle of twist will be zero. For this
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HANDBOOK OF MODERN SENSORS PHYSICS,
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HANDBOOK OF MODERN SENSORS PHYSICS,
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To the memory of my father
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Preface Seven years have passed sin
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Contents Preface ..................
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Contents XI 4.5 Lenses ............
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Contents XIII 7.7.1 Micropower Impu
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Contents XV 15 Radiation Detectors
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Contents XVII Table A.9 Physical Pr
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1 Data Acquisition “It’s as lar
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1.1 Sensors, Signals, and Systems 3
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1.1 Sensors, Signals, and Systems 5
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1.2 Sensor Classification 7 oscillo
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1.3 Units of Measurements 9 Table 1
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Table 1.7. SI Basic Units Reference
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2 Sensor Characteristics “O, what
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2.2 Span (Full-Scale Input) 15 Fig.
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2.4 Accuracy 17 2.4 Accuracy Avery
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2.6 Calibration Error 19 To compute
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2.8 Nonlinearity 21 Fig. 2.4. Trans
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2.12 Resolution 23 (A) (B) Fig. 2.7
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2.16 Dynamic Characteristics 25 2.1
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2.16 Dynamic Characteristics 27 Sub
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2.17 Environmental Factors 29 2.17
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2.18 Reliability 31 guide. For inst
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2.20 Uncertainty 33 • Thermal sho
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Table 2.2. Uncertainty Budget for T
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3 Physical Principles of Sensing
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3.1 Electric Charges, Fields, and P
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3.2 Capacitance 45 The capacitor ma
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3.2 Capacitance 47 (A) (B) Fig. 3.6
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3.2 Capacitance 49 h 0 (A) (B) Fig.
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3.3 Magnetism 51 N S S N (A) (B) Fi
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3.3 Magnetism 53 electric charge ca
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3.3 Magnetism 55 3.3.3 Toroid Anoth
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3.4 Induction 57 • Changing the o
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3.5 Resistance 59 Fig. 3.16. Voltag
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3.5 Resistance 61 For pure resistan
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3.5 Resistance 63 resistor) and the
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3.5 Resistance 65 Fig. 3.19. Strain
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3.6 Piezoelectric Effect 67 (A) (B)
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3.6 Piezoelectric Effect 69 Another
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3.6 Piezoelectric Effect 71 Another
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3.6 Piezoelectric Effect 73 absorpt
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3.6 Piezoelectric Effect 75 that en
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3.7 Pyroelectric Effect 77 circuit
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3.7 Pyroelectric Effect 79 through
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3.7 Pyroelectric Effect 81 Fig. 3.2
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3.8 Hall Effect 83 Fig. 3.30. Hall
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Table 3.2. Typical Characteristics
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3.9 Seebeck and Peltier Effects 87
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3.10 Sound Waves 93 If we consider
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3.11 Temperature and Thermal Proper
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3.11 Temperature and Thermal Proper
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3.12 Heat Transfer 99 to about 35
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3.12 Heat Transfer 101 (A) (B) Fig.
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3.12 Heat Transfer 103 Fig. 3.41. S
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3.12 Heat Transfer 105 Fig. 3.42. S
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3.12 Heat Transfer 107 Fig. 3.44. W
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3.12 Heat Transfer 109 (A) (B) Fig.
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3.13 Light 111 [38] whose emissivit
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3.14 Dynamic Models of Sensor Eleme
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References 119 specified and three
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References 121 34. Thomson, W. On t
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124 4 Optical Components of Sensors
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150 Optical Components of Sensors 1
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5 Interface Electronic Circuits 5.1
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5.1 Input Characteristics of Interf
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5.1 Input Characteristics of Interf
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5.2 Amplifiers 157 (A) (B) Fig. 5.5
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5.2 Amplifiers 159 Fig. 5.7. Voltag
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5.2 Amplifiers 161 (A) (B) Fig. 5.9
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5.2 Amplifiers 163 Fig. 5.11. An eq
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Page 188 and 189: 5.3 Excitation Circuits 169 Fig. 5.
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Page 194 and 195: 5.4 Analog-to-Digital Converters 17
Page 196 and 197: Table 5.2. Binary Bit Weights and R
Page 206 and 207: 5.5 Direct Digitization and Process
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Page 210 and 211: 5.6 Ratiometric Circuits 191 (A) (B
Page 212 and 213: 5.7 Bridge Circuits 193 determine t
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Page 216 and 217: 5.7 Bridge Circuits 197 Fig. 5.39.
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Page 242 and 243: 5.10 Batteries for Low Power Sensor
Page 244 and 245: References 225 nickel-metal hydrate
Page 246 and 247: 6 Occupancy and Motion Detectors Se
Page 248 and 249: 6.2 Microwave Motion Detectors 229
Page 250 and 251: 6.2 Microwave Motion Detectors 231
Page 252 and 253: 6.3 Capacitive Occupancy Detectors
Page 254 and 255: 6.3 Capacitive Occupancy Detectors
Page 256 and 257: 6.4 Triboelectric Detectors 237 6.4
Page 258 and 259: 6.5 Optoelectronic Motion Detectors
Page 262 and 263: and the facet pitch is 6.5 Optoelec
Page 270 and 271: References 251 Fig. 6.17. Calculate
Page 272 and 273: 7 Position, Displacement, and Level
Page 274 and 275: 7.1 Potentiometric Sensors 255 (A)
Page 276 and 277: 7.2 Gravitational Sensors 257 (A) (
Page 278 and 279: 7.3 Capacitive Sensors 259 (A) (B)
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7.4 Inductive and Magnetic Sensors
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7.5 Optical Sensors 275 Therefore,
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7.5 Optical Sensors 277 (A) (B) (C)
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7.5 Optical Sensors 279 (A) (B) Fig
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7.5 Optical Sensors 281 Fig. 7.32.
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7.5 Optical Sensors 283 (A) (B) (C)
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7.5 Optical Sensors 285 is proporti
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7.6 Ultrasonic Sensors 287 (A) (B)
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7.7 Radar Sensors 289 (A) (B) Fig.
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7.7 Radar Sensors 291 (A) (B) Fig.
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7.8 Thickness and Level Sensors 293
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References 299 8. Dakin, J. P., Wad
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8 Velocity and Acceleration Acceler
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8.1 Accelerometer Characteristics 3
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8.2 Capacitive Accelerometers 305 a
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8.3 Piezoresistive Accelerometers 3
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8.5 Thermal Accelerometers 309 Fig.
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8.5 Thermal Accelerometers 311 forc
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8.6 Gyroscopes 313 8.6 Gyroscopes N
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8.6 Gyroscopes 315 (A) (B) Fig. 8.1
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8.6 Gyroscopes 317 Products Company
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8.7 Piezoelectric Cables 319 (A) (B
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References 321 (A) (B) Fig. 8.16.Ap
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9 Force, Strain, and Tactile Sensor
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9.1 Strain Gauges 325 (A) (B) Fig.
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9.2 Tactile Sensors 327 9.2 Tactile
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9.2 Tactile Sensors 329 (A) (B) Fig
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9.2 Tactile Sensors 331 Fig. 9.7. P
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9.2 Tactile Sensors 333 Fig. 9.9. T
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9.3 Piezoelectric Force Sensors 335
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References 337 14. Karrer, E. and L
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10 Pressure Sensors “To learn som
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10.3 Mercury Pressure Sensor 341 1
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10.4 Bellows, Membranes, and Thin P
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10.5 Piezoresistive Sensors 345 Fig
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10.5 Piezoresistive Sensors 347 bri
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10.6 Capacitive Sensors 349 (A) (B)
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10.7 VRP Sensors 351 (A) (B) Fig. 1
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10.8 Optoelectronic Sensors 353 Fig
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10.9 Vacuum Sensors 355 (A) (B) Fig
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References 357 (A) (B) (C) Fig. 10.
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11 Flow Sensors It’s a simple tas
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11.2 Pressure Gradient Technique 36
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11.3 Thermal Transport Sensors 363
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11.3 Thermal Transport Sensors 365
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11.4 Ultrasonic Sensors 367 A senso
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11.4 Ultrasonic Sensors 369 Fig. 11
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induced in the liquid. The magnitud
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11.6 Microflow Sensors 373 (A) (B)
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11.7 Breeze Sensor 375 (A) (B) Fig.
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11.9 Drag Force Flow Sensors 377 Wi
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References 379 11. Philip-Chandy, R
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12 Acoustic Sensors “Your ears wi
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12.3 Fiber-Optic Microphone 383 (A)
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12.4 Piezoelectric Microphones 385
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12.5 Electret Microphones 387 Fig.
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12.6 Solid-State Acoustic Detectors
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References 391 References 1. Hohm,
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13 Humidity and Moisture Sensors 13
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13.1 Concept of Humidity 395 Table
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13.2 Capacitive Sensors 397 Fig. 13
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13.3 Electrical Conductivity Sensor
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13.4 Thermal Conductivity Sensor 40
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13.6 Oscillating Hygrometer 403 chi
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References 405 9. Jachowicz, R. S.
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14 Light Detectors “There is noth
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14.1 Introduction 409 Table 14.1. B
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14.2 Photodiodes 411 Maximum revers
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14.2 Photodiodes 413 when i = 0), w
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14.2 Photodiodes 415 (A) (B) (C) Fi
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14.2 Photodiodes 417 Fig. 14.9. Res
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14.3 Phototransistor 419 Fig. 14.12
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14.4 Photoresistors 421 (A) (B) Fig
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14.5 Cooled Detectors 423 (A) (B) F
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14.6 Thermal Detectors 425 Table 14
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14.6 Thermal Detectors 427 Fig. 14.
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Table 14.3. Typical Specifications
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14.6 Thermal Detectors 431 A dual e
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14.6 Thermal Detectors 433 Fig. 14.
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14.6 Thermal Detectors 435 (A) (B)
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14.6 Thermal Detectors 437 Section
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14.7 Gas Flame Detectors 439 P = V
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References 441 housing assures wide
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15 Radiation Detectors Figure 3.41
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15.1 Scintillating Detectors 445 Fi
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15.2 Ionization Detectors 447 emitt
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15.2 Ionization Detectors 449 Fig.
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15.2 Ionization Detectors 451 parti
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15.2 Ionization Detectors 453 There
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References 455 the pure intrinsic t
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16 Temperature Sensors When a scien
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16 Temperature Sensors 459 from whi
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16.1 Thermoresistive Sensors 461 2.
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16.1 Thermoresistive Sensors 463 Ta
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16.1 Thermoresistive Sensors 465 Fi
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16.1 Thermoresistive Sensors 467 pr
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16.1 Thermoresistive Sensors 475 (m
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16.2 Thermoelectric Contact Sensors
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16.3 Semiconductor P-N Junction Sen
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16.4 Optical Temperature Sensors 49
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16.4 Optical Temperature Sensors 49
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16.5 Acoustic Temperature Sensor 49
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References 497 plate—the so-calle
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17 Chemical Sensors 1 Chemical sens
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17.3 Classification of Chemical-Sen
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17.4 Direct Sensors 503 17.4 Direct
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17.4 Direct Sensors 505 voltage e.
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17.4 Direct Sensors 507 This reacti
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17.4 Direct Sensors 509 (A) (B) Fig
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17.4 Direct Sensors 511 µm thick a
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17.5 Complex Sensors 513 Fig. 17.11
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17.5 Complex Sensors 515 Fig. 17.12
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17.5 Complex Sensors 517 frequency
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Table 17.1. SAW Chemical Sensors 17
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17.6 Chemical Sensors Versus Instru
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References 531 13. LaCourse, W.R. P
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18 Sensor Materials and Technologie
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18.1 Materials 535 etching is a key
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18.1 Materials 537 Fig. 18.3. The a
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18.1 Materials 539 The following is
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18.1 Materials 541 should be consid
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18.2 Surface Processing 543 sensor
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18.2 Surface Processing 545 On a co
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18.3 Nano-Technology 547 6000-Å la
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18.3 Nano-Technology 549 exposed to
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18.3 Nano-Technology 551 Fig. 18.10
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18.3 Nano-Technology 553 (A) (B) Fi
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References 555 Fig. 18.17. Bonding
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Appendix Table A.1. Chemical Symbol
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Table A.4. SI Conversion Multiples
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Table A.4 Continued Light cd/in. 2
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Table A.4 Continued Cup 2.36588 ×
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Appendix 565 Table A.7. Some Materi
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Appendix 567 Table A.11. Thermoelec
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Table A.14. Mechanical Properties o
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Appendix 571 Table A.18. Typical Em
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Table A.20. Characteristics of C-Zn
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Table A.23 Continued Manufacturer P
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Table A.25. Properties of Glasses S
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Index α-particles, 443 A/D, 175, 1
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Index 581 Coulomb’s law, 40 cross
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Index 583 H 2 O, 108 Hall, 82 Hall
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Index 585 occupancy sensors, 227 od
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Index 587 SAW, 75, 388, 404, 496, 5
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Index 589 velocity sensor, 302 vert
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