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3.9 Seebeck and Peltier Effects 87 (A) (B) Fig. 3.34. (A) Seebeck experiment; (B) the varying temperature along a conductor is a source of a thermoelectric e.m.f. in incremental voltage: dT dV a = α a dx, (3.87) dx where dT is the temperature gradient across a small length, dx, and α a is the absolute Seebeck coefficient of the material [30]. If the material is homogeneous, α a is not a function of length and Eq. (3.87) reduces to dV a = α a dT. (3.88) Equation (3.88) is a principle mathematical expression of a thermoelectric effect. Figure 3.34B shows a conductor having nonuniform temperature T along its length x. A temperature gradient between any arbitrary points defines an electromotive force (e.m.f.) between these points. Other possible temperatures between the selected points (temperatures T 3 , T 4 and T 5 , for example) have no effect whatsoever on the value of e.m.f. between points 1 and 2. To measure the e.m.f., we connect a voltmeter to the conductor as shown in Fig. 3.34B; this is not as simple as may first look. To measure thermally induced e.m.f., we would need to attach the voltmeter probes. However, the probes are also made of conductors which may be different from the conductor we observe. Let us consider a simple measurement electric circuit where a current loop is formed. In such a loop, a meter is connected in series with the wire (Fig. 3.35A). If the loop is made of a uniform material, say cooper, then no current will be observed, even if the temperature along the conductor is not uniform. Electric fields in the left and right arms of the loop produce equal currents i a = i b , which cancel each other, resulting in a zero net current. A thermally induced e.m.f. exists in every thermally nonhomogeneous conductor, but it cannot be directly measured. In order to observe thermoelectricity, it is, in fact, necessary to have a circuit composed of two different materials, 11 and we can then measure the net difference between their thermoelectric properties. Figure 3.35B shows a loop of two dissimilar metals which produces net current i = i a − i b . The actual current depends on many factors, including the shape and size of the conductors. If, on the other hand, instead 11 Or perhaps the same material in two different states—for example, one under strain, and the other not.
88 3 Physical Principles of Sensing (A) (B) Fig. 3.35. Thermoelectric loop: (A) joints of identical metals produce zero net current at any temperature difference; (B) joints of dissimilar metals produce net current i. of current we measure the net voltage across the broken conductor, the potential will depend only on the materials and the temperature difference. It does not depend on any other factors. A thermally induced potential difference is called the Seebeck potential. What happens when two conductors are joined together Free electrons in metal may behave as an ideal gas. The kinetic energy of electrons is a function of the material temperature. However, in different materials, energies and densities of free electrons are not the same. When two dissimilar materials at the same temperature are brought into a contact, free electrons diffuse through the junction [30]. The electric potential of the material accepting electrons becomes more negative at the interface, and the material emitting electrons becomes more positive. Different electronic concentrations across the junction set up an electric field which balances the diffusion process, and the equilibrium is established. If the loop is formed and both junctions are at the same temperature, the electric fields at both junctions cancel each other, which is not the case when the junctions are at different temperatures. Asubsequent investigation [40] has shown the Seebeck effect to be fundamentally electrical in nature. It can be stated that the thermoelectric properties of a conductor are, in general, just as much bulk properties as are the electrical and thermal conductivities. Coefficient α a is a unique property of a material. When a combination of two dissimilar materials (A and B) is used, the Seebeck potential is determined from a differential Seebeck coefficient: and the net voltage of the junction is α AB = α A − α B , (3.89) dV AB = α AB dT. (3.90) Equation (3.90) can be used to determine a differential coefficient: α AB = dV AB dT . (3.91)
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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
Page 56 and 57: 3 Physical Principles of Sensing
Page 58 and 59: 3.1 Electric Charges, Fields, and P
Page 64 and 65: 3.2 Capacitance 45 The capacitor ma
Page 66 and 67: 3.2 Capacitance 47 (A) (B) Fig. 3.6
Page 68 and 69: 3.2 Capacitance 49 h 0 (A) (B) Fig.
Page 70 and 71: 3.3 Magnetism 51 N S S N (A) (B) Fi
Page 72 and 73: 3.3 Magnetism 53 electric charge ca
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Page 76 and 77: 3.4 Induction 57 • Changing the o
Page 78 and 79: 3.5 Resistance 59 Fig. 3.16. Voltag
Page 80 and 81: 3.5 Resistance 61 For pure resistan
Page 82 and 83: 3.5 Resistance 63 resistor) and the
Page 84 and 85: 3.5 Resistance 65 Fig. 3.19. Strain
Page 86 and 87: 3.6 Piezoelectric Effect 67 (A) (B)
Page 88 and 89: 3.6 Piezoelectric Effect 69 Another
Page 90 and 91: 3.6 Piezoelectric Effect 71 Another
Page 92 and 93: 3.6 Piezoelectric Effect 73 absorpt
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Page 96 and 97: 3.7 Pyroelectric Effect 77 circuit
Page 98 and 99: 3.7 Pyroelectric Effect 79 through
Page 100 and 101: 3.7 Pyroelectric Effect 81 Fig. 3.2
Page 102 and 103: 3.8 Hall Effect 83 Fig. 3.30. Hall
Page 104 and 105: Table 3.2. Typical Characteristics
Page 108 and 109: 3.9 Seebeck and Peltier Effects 89
Page 110 and 111: 3.9 Seebeck and Peltier Effects 91
Page 112 and 113: 3.10 Sound Waves 93 If we consider
Page 114 and 115: 3.11 Temperature and Thermal Proper
Page 116 and 117: 3.11 Temperature and Thermal Proper
Page 118 and 119: 3.12 Heat Transfer 99 to about 35
Page 120 and 121: 3.12 Heat Transfer 101 (A) (B) Fig.
Page 122 and 123: 3.12 Heat Transfer 103 Fig. 3.41. S
Page 124 and 125: 3.12 Heat Transfer 105 Fig. 3.42. S
Page 126 and 127: 3.12 Heat Transfer 107 Fig. 3.44. W
Page 128 and 129: 3.12 Heat Transfer 109 (A) (B) Fig.
Page 130 and 131: 3.13 Light 111 [38] whose emissivit
Page 132 and 133: 3.14 Dynamic Models of Sensor Eleme
Page 138 and 139: References 119 specified and three
Page 140 and 141: References 121 34. Thomson, W. On t
Page 142 and 143: 124 4 Optical Components of Sensors
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138 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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5.3 Excitation Circuits 165 5.3.1 C
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5.3 Excitation Circuits 167 (A) (B)
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5.3 Excitation Circuits 169 Fig. 5.
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5.3 Excitation Circuits 171 atures.
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5.3 Excitation Circuits 173 (A) (B)
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5.4 Analog-to-Digital Converters 17
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Table 5.2. Binary Bit Weights and R
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5.5 Direct Digitization and Process
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5.5 Direct Digitization and Process
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5.6 Ratiometric Circuits 191 (A) (B
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5.7 Bridge Circuits 193 determine t
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5.7 Bridge Circuits 195 Fig. 5.38.
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5.7 Bridge Circuits 197 Fig. 5.39.
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It can be solved for the temperatur
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5.8 Data Transmission 201 (A) (B) (
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5.8 Data Transmission 203 wire meth
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5.9 Noise in Sensors and Circuits 2
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5.10 Batteries for Low Power Sensor
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References 225 nickel-metal hydrate
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6 Occupancy and Motion Detectors Se
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6.2 Microwave Motion Detectors 229
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6.2 Microwave Motion Detectors 231
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6.3 Capacitive Occupancy Detectors
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6.3 Capacitive Occupancy Detectors
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6.4 Triboelectric Detectors 237 6.4
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6.5 Optoelectronic Motion Detectors
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and the facet pitch is 6.5 Optoelec
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References 251 Fig. 6.17. Calculate
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7 Position, Displacement, and Level
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7.1 Potentiometric Sensors 255 (A)
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7.2 Gravitational Sensors 257 (A) (
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7.3 Capacitive Sensors 259 (A) (B)
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7.3 Capacitive Sensors 261 Fig. 7.7
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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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