handbook of modern sensors

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15 Radiation Detectors Figure 3.41 of Chapter 3 shows a spectrum of the electromagnetic waves. On its lefthand side, there is a region of the γ -radiation. However, this is not the shortest possible length of the electromagnetic waves. In addition, a spontaneous radiation from the matter is not necessarily electromagnetic: There is the so-called nuclear radiation which is the emission of particles from the atomic nuclei. It can be of two types: the charged particles (α and β particles and protons) and uncharged particles, which are the neutrons. Some particles are complex like the α-particles, which are nuclei of helium atoms consisting of two neutrons; other particles are generally simpler, like the β-particles, which are either electrons or positrons. The γ - and X-rays belong to the nuclear type of electromagnetic radiation. In turn, X-rays depending on the wavelengths are divided into hard, soft, and ultrasoft rays. Ionizing radiations are given that name because as they pass through various media which absorb their energy, additional ions, photons, or free radicals are created. Certain naturally occurring elements are not stable but slowly decompose by throwing away a portion of their nucleus. This is called radioactivity. It was discovered in 1896 by Henry Becquerel when he found that uranium atoms (Z = 92) 1 give off radiation which fogs photographic plates. In addition to the naturally occurring radioactivity, there are many man-made nuclei which are radioactive. These nuclei are produced in nuclear reactors, which may yield highly unstable elements. Regardless of the sources or ages of radioactive substances, they decay in accordance with the same mathematical law. The law is stated in terms of the number N of nuclei still undecayed and dN, the number of nuclei which decay in a small interval dt.Itwas proven experimentally that dN =−λN dt, (15.1) where λ is a decay constant specific for a given substance. From Eq. (15.1), it can be defined as the fraction of nuclei which decays in unit time: 1 Z is the atomic number. λ =− 1 N dN dt . (15.2)
444 15 Radiation Detectors The SI unit of radioactivity is the becquerel (Bq) which is equal to the activity of a radionuclide decaying at the rate of one spontaneous transition per second. Thus, the becquerel is expressed in a unit of time: Bq = s −1 . To convert to the old historical unit, the curie, the becquerel should be multiplied by 3.7 × 10 10 (Table A.4). The absorbed dose is measured in grays (Gy). A gray is the absorbed dose when the energy per unit mass imparted to matter by ionizing radiation is 1 joule per kilograms; that is, Gy = J/kg. When it is required to measure exposure to X- and γ -rays, the dose of ionizing radiation is expressed in coulombs per kilogram, which is an exposure resulting in the production of 1Cofelectric charge per 1 kg of dry air. In SI, the unit C/kg replaces the older unit roentgen. The function of any radiation detector depends on the manner in which the radiation interacts with the material of the detector itself. There are many excellent texts available on the subject of detecting radioactivity—for instance, Refs. [1] and [2]. There are three general types of radiation detector: the scintillation detector, the gaseous detector, and the semiconductor detector. Further, all detectors can be divided into two groups according to their functionality: the collision detector and the energy detector. The former merely detect the presence of a radioactive particle, whereas the latter can measure the radiative energy; that is, all detectors can be either quantitative or qualitative. 15.1 Scintillating Detectors The operating principle of these detectors is based on the ability of certain materials to convert nuclear radiation into light. Thus, an optical photon detector in combination with a scintillating material can form a radiation detector. It should be noted, however, that despite the high efficiency of the conversion, the light intensity resulting from the radiation is extremely small. This demands photomultipliers to magnify signals to a detectable level. The ideal scintillation material should possess the following properties: 1. It should convert the kinetic energy of charged particles into detectable light with a high efficiency. 2. The conversion should be linear; that is, the light produced should be proportional to the input energy over a wide dynamic range. 3. The postluminescence (the light decay time) should be short to allow fast detection. 4. The index of refraction of the material should be near that of glass to allow efficient optical coupling of the light to the photomultiplier tube. The most widely used scintillators include the inorganic alkali halide crystals (of which sodium iodine is the favorite) and organic-based liquids and plastics. The inorganics are more sensitive, but generally slow, whereas organics are faster, but yield less light. One of the major limitations of scintillation counters is their relatively poor energy resolution. The sequence of events which leads to the detection involves many
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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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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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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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