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6.5 Optoelectronic Motion Detectors 247 object on the surface of one part of the sensor only, which is occupied by a single pair of electrodes. The element generates a charge only across the electrode pair subjected to a heat flux. When the thermal image moves from one electrode to another, the current i flowing from the sensing element to the bias resistor R (Fig. 6.14B) changes form zero, to positive, then to zero, to negative, and again to zero (Fig. 6.14A lower portion). A JFET transistor Q is used as an impedance converter. The resistor R value must be very high. For example, a typical alternate current generated by the element in response to a moving person is on the order of 1 pA (10 −12 A). If a desirable output voltage for a specific distance is v = 50 mV, according to Ohm’s law the resistor value is R = v/i = 50 G (5 × 10 10 ). Such a resistor can not be directly connected to a regular electronic circuit; hence, transistor Q serves as a voltage follower (the gain is close to unity). Its typical output impedance is on the order of several kilohms. Table A.9 lists several crystalline materials which possess a pyroelectric effect and can be used for the fabrication of sensing elements. The most often used are the ceramic elements, thanks to their low cost and ease of fabrication. The pyroelectric coefficient of ceramics to some degree may be controlled by varying their porosity (creating voids inside the sensor’s body).An interesting pyroelectric material is a polymer film polyvinylidene fluoride (PVDF) which, although not as sensitive as most of the solid-state crystals, has the advantages of being flexible and inexpensive. In addition, it can be produced in any size and may be bent or folded in any desirable fashion. In addition to the sensing element, an infrared motion detector needs a focusing device. Some detectors employ parabolic mirrors, but the Fresnel plastic lenses (Section 4.6 of Chapter 4) become more and more popular because they are inexpensive, may be curved to any desirable shape, and, in addition to focusing, act as windows, protecting the interior of the detector from outside moisture and pollutants. To illustrate how a plastic Fresnel lens and a PVDF film can work together, let us look at the motion detector depicted in Fig. 6.15A. It uses a polyethylene multifaceted curved lens and a curved PVDF film sensor [7]. The sensor design combines two methods described earlier: a facet lens and a complex electrode shape. The lens and the film are curved with the same radii of curvature equal to one-half of the focal distance f , thus assuring that the film is always positioned in the focal plane of the corresponding facet of the lens. The film has a pair of large interdigitized electrodes which are connected to the positive and negative inputs of a differential amplifier located in the electronic module. The amplifier rejects common-mode interference and amplifies a thermally induced voltage. The side of the film facing the lens is coated with an organic coating to improve its absorptivity in the far-infrared spectral range. This design results in a fine resolution (detection of small displacement at a longer distance) and a very small volume of the detector (Fig. 6.15B). Small detectors are especially useful for the installation in devices where overall dimensions are critical. For instance, one application is a light switch where the detector must be mounted into the wall plate of a switch. 6.5.3.2 PIR Sensor Efficiency Analysis Regardless of the type of optical device employed, all modern PIR detectors operate on the same physical effect—pyroelectricity. To analyze the performance of such a
248 6 Occupancy and Motion Detectors (A) (B) Fig. 6.15. Far-infrared motion detector with a curved Fresnel lens and a pyroelectric PVDF film: (A) internal structure of the sensor; (B) external appearance of the sensor. sensor, first we must calculate the infrared power (flux), which is converted into an electric charge by the sensing element. The optical device focuses thermal radiation into a miniature thermal image on the surface of the sensor. The energy of an image is absorbed by the sensing element and is converted into heat. That heat, in turn, is converted by the pyroelectric crystalline element into a minute electric current. To estimate a power level at the sensor’s surface, let us make some assumptions. We assume that the moving object is a person whose effective surface area is b (Fig. 6.16) and the temperature along this surface (T b ) is distributed uniformly and is expressed in Kelvin. The object is assumed to be a diffuse emitter (radiates uniformly within the hemisphere having a surface area of A = 2πL 2 ). Also, we assume that the focusing device makes a sharp image of an object at any distance. For this calculation,
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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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Page 244 and 245: References 225 nickel-metal hydrate
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Page 270 and 271: References 251 Fig. 6.17. Calculate
Page 272 and 273: 7 Position, Displacement, and Level
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7.8 Thickness and Level Sensors 297
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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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