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  1. 1. Chapter 1IntroductionAbstract In this chapter a general overview regarding sensors will be presented.Some of the fundamental terminologies, which are frequently encountered in thesensor field, will be described. The importance and applications of sensors will behighlighted.1.1 Sensors and TransducersThe word sensor has a Latin root “sentire,” which means “to perceive,” originated in1350–1400, the Middle English era. A sensor is a device which responds to stimuli—or an input quality—by generating processable outputs. These outputs are function-ally related to the input stimuli which are generally referred to as measurands.Transducer is the other term that is sometimes interchangeably used instead ofthe term sensor, although there are subtle differences. A transducer is a device thatconverts one type of energy to another. The origin is “transduce,” which means “totransfer” that was first coined in 1525–1535. A transducer is a term that can be usedfor the definition of many devices such as sensors, actuators, or transistors.Schematic diagram of a sensor is depicted in Fig. 1.1. A sensor is commonlymade of two major components: a sensitive element and a transducer. The sensitiveelement has the capability to interact with a target measurand and cause a change inthe operation of the transducer. Affected by this change, the transducer produces asignal, which is translated into readable information by a data acquisition system.It is important to note that for devices such as transistors and actuators, theconversion efficiency is generally an important factor. However, in addition to theconversion efficiency, a sensor should have many other qualities such as selectivityand sensitivity, which will be explained later.Other common definition is to use the term sensor for the sensing element itselfand transducer for the sensing element plus any associated peripherals (the overallsystem). For example, a temperature sensor is called a sensor, while together withthe data acquisition circuit (to convert the signal into a measurable electricalvoltage) is called a transducer.K. Kalantar-zadeh, Sensors: An Introductory Course,DOI 10.1007/978-1-4614-5052-8_1, # Springer Science+Business Media New York 20131
  2. 2. Most of the man-made systems acquire data from their surrounding environments,process them, and consequently translate the data into useful functions. Sensors’ rolesin such systems are the acquisition of data. Using sensors, direct contact with thesurrounding world is more possible. Sensors enable systems to interact with theirenvironments and receive desired information. This information is then sent to aprocessing system, where it is processed into meaningful information. The processedinformation can be either directly deciphered as the sought after output or further fedinto another system for additional processing or producing signals for actuators. Themore complex the system, the larger number of sensors is required for its operation.1.2 Sensors QualitiesSensors should be sensitive to their target measurands, and insensitive to any otherinput quantities, which might impact on their performance. As a universal rule,sensors should provide reliable, accurate, stable, and generally low cost sensing.A good sensor should not affect the measurand. For instance, if a sensor is usedfor measuring temperature, the size of the sensor should be much smaller than size ofthe monitored object (e.g., micro-/nano-sized objects) or the measurement should beconducted remotely (infrared temperature measuring systems). A sensor life time isimportant—some should last for a long time—such as smoke detectors for houses—some are disposable—such as pregnancy test sensors (which should be kept freshand intact in sealed packaging until their applications). Response behavior of a senorshould be well-understood by users: parameters such as linearity and repeatability,which will be discussed in detail in Chap. 2. These parameters are presented in thedata sheet of a sensor and a good sensor must have a comprehensive and clear datasheet. A senor has to be well calibrated before the application. This means an extracost for the manufacturer. Interferences of signals other than the measurand shouldMeasurandMeasurand affecting thesensitive interface and/orthe bulk of the transducerTransducerSensitive interfaceTo data acquisition systemSensorFig. 1.1 Schematic depiction of a sensing system2 1 Introduction
  3. 3. be minimal for a good sensor. Sensors resolution, which will also be discussed inChap. 2, should be well presented to the consumers via the data sheet.A sensor’s fabrication cost should be as small as possible. Economy alwaysgoverns the engineering and design, and a lower cost is always a winner. A sensorshould be environmentally friendly. Many types of sensors are disposable and allsensors have limited life span. After the end of their lives, they should be able to bereturn to nature safely. For instance, in the past many sensors were using mercury intheir structure, which are now mostly banned from the manufacturing. Selectivityof the sensor is also an important issue. A good sensor is selective to the targetmeasurand. A discussion on selectivity will also be presented in Chap. 2. In addition,a sensor’s power consumption should be manageable and always considered in thedesign and fabrication. One of the main hurdles of sensor networks is the sensors’,and their circuits, demand for power. In a network, sensors can be scattered all over afield and they should be individually supplied with sufficient power. This alwaysposes a challenge. Stand-alone sources, such as batteries, have limited lifetime.Renewable sources, such as solar cells, have their own complexity of operation andadd to the costs. Providing the energy form a central source requires expensive andcomplicated wiring matrix. Another issue is the communications between thecentral data acquisition system and sensors in the nodes of such sensor networks.The discussion on sensor networks is outside the contents of this book though and theauthor advice readers to refer to excellent available textbooks in the field.1.3 Types of TransducersSince the conversion of energy from one form to another is an essential character-istic that governs the sensing process, it is important to be familiar with differentforms of energies. The list is presented in Table 1.1.A general schematic of a sensing system is shown in Fig. 1.2. As can be seen, theinput energy is entered via an input interface, goes through a transduction process,and is released as a signal processable for a user via an output interface.Table 1.1 Various forms of energies and their occurrenceType of energy OccurrenceGravitational Gravitational attractionMechanical Motion, displacement, mechanical forces, etc.Thermal Thermal energy of an object increases with temperature. In thermodynamics,thermal energy is the internal energy present in a system in a state ofthermodynamic equilibrium because of its temperatureElectromagnetic Electric charge, electric current, magnetism, electromagnetic wave energy(including the high frequency waves such as infrared, visible, UV, etc.)Chemical Energy released or absorbed during chemical reactionsNuclear Binding energy between nuclei—binds the subatomic particles of a matter1.3 Types of Transducers 3
  4. 4. A two-dimensional representation of the direct transduction, from one form ofenergy to another, is shown in Fig. 1.3. The primary energy input to the system isrepresented by one axis and the energy output by the other axis. With the 6 forms ofenergy, we have 6 Â 6 ¼ 36 possibilities.Physical and chemical effects are involved in signal transductions. Physicaleffects involve those that couple a material’s thermal, mechanical, electromagnetic(including optical), gravitational, and nuclear properties. These effects togetherwith the chemical effects are utilized within sensors. Table 1.2 shows examples ofeffects that are obtained when these properties are coupled with each other or withthemselves.GravitationalMechanicalThermalElectromagneticNuclearChemicalGravitationalMechanicalThermalElectromagneticNuclearChemicalTransductionprocessInput OutputFig. 1.2 Schematic depiction of a sensing system interacting with various possible input andoutput energiesGravitationalMechanicalThermalElectromagneticNuclearChemicalGravitationalMechanicalThermalElectromagneticNuclearChemicalFig. 1.3 A two-dimensional representation of possible direct transductions from one form toanother4 1 Introduction
  5. 5. Table1.2ExamplesofsomephysicalandchemicaleffectsNuclearGravitationalThermalMechanicalElectromagnetic(includingoptical)ChemicalThermalFusion,fission–HeattransferThermalexpansionThermoresistanceEndothermicreactionMechanical––FrictionAcousticeffectsinmusicalinstrumentsMagnetostriction–Electromagnetic(includingoptical)Synchrotron–PeltiereffectPiezoelectricityHallandFaradayeffectsElectrodepositionChemicalNuclearreactions–ExothermicreactionHeatenginesBatteriesandfuelcellsChemicalinteractionsGravitationalSunpower–––Accelerationbygravity–NuclearNuclearreactions–NuclearpowerplantsShockwavesinnuclearexplosion––1.3 Types of Transducers 5
  6. 6. A transduction system can be more complicated than the ones shown in Fig. 1.2.The procedure might consist of the transduction of energy via several consecutivesteps. For instance, the input signal can be in the form of a mechanical stimulant,which generates heat (e.g., via friction) and this heat is then transformed into avoltage (electromagnetic energy), which is a measurable signal for a user. In thiscase, we have an extra intermediate transduction process. This adds extradimensions to the transduction plane representation of Fig. 1.3. In this case anextra intermediate step, we are dealing with a space with 6 Â 6 Â 6 possibilities.Surely for more complicated systems the number of possibilities increases, if thenumber of in-between transduction steps increases. Such systems can be morecomplex and costly but in return can increase the reliability and performance.1.4 Sensors ApplicationsIn recent years the development of operational systems has become progressivelyimportant and sensors have become an ever-present part of such systems. Sensorsare playing a greater than ever role in our day-to-day interactions and are becomingan integral part of the modern technological growth and development. Each appli-cation places various requirements on a sensor and its integrated sensing system.However, regardless of the type of application all sensors have the same object: toachieve accurate and stable monitoring of target measurands.Sensor technology has flourished as the need for physical, chemical, andbiological recognition has grown. Nowadays sensors are finding a more prominentrole, as strong needs on devices aimed at making lives better, easier, and safer areobserved. They are employed in applications ranging from environmental monitor-ing, medical diagnostics and health care, automotive and industrial manufacturing,home appliance, defense and security, and even toys. In recent times, however, theimportance of sensors has grown significantly due to increasing automation andmore use of microelectronics, both of which require more sensors. Parallel to thisdevelopment, the capabilities of sensors are increasing and sensors prices areshrinking. Application of sensors can be categorized as follows:• Health and biomedical.• Defense and military industries.• Industrial applications: aerospace, agriculture, nuclear, automation, automotive,transportations, building technology, machine control, power generation, textile,chemical, and food industries.• Homeland security and safety.• Environmental surveillance and climate parameters measurements.• Consumer products: electronic systems and household appliances.6 1 Introduction
  7. 7. Sensors are found commonly around the household. For example, they arelocated in gas cook tops, where they determine whether or not the pilot is on, andif not, halt the gas flow preventing the room from being filled with gas. They are inelectrical devices from surge protectors to automatic light switches, refrigeratorsand climate control appliances, toasters, and of course in smoke detectors (Fig. 1.4).We encounter sensors in everyday life: entering a department store with auto-matically opening doors, or when light is automatically turned on and off uponentering or leaving an office.Sensors are also an integral part of health care and diagnostics. They candetermine whether or not biological systems are functioning correctly and mostimportantly, direct us to act without delay when something is wrong. For instanceglucose meters are playing a crucial role in determining the amount of sugar levelsin people diagnosed with diabetes. They are incorporated in off-the-shelf bloodpressure and oxygen content monitoring as well as in pregnancy tests systems.The functions of senors are generally not so noticeable, yet millions of them arecontained within central processing units of computers and microcontrollers. Inaddition to these internally integrated electronic devices, electronic systems have alarge number of external sensors for interacting with their users. Touch screen pads,mouse, and voice recognition systems all use sensors in their operations.Fig. 1.4 Examples of sensors incorporated in a typical house1.4 Sensors Applications 7
  8. 8. Nowadays almost all engineering machines incorporate sensors. Sensors arewidely used in automotive industry. An average vehicle can have hundreds ofindividual sensors for different functions (Fig. 1.5). This includes: sensors fordoors, wipers, several temperature and exhaust sensors around engine and exhaustpipes, and gas flow sensors. Aircraft are riddled with them as they monitor position,wind speed, air pressure, altitude, etc. Another important use is for industrial andprocess control, where the sensors continually monitor to ensure that efficiency ismaximized, production costs are minimized, and that waste is reduced.The choice of a senor for a specific task is a process that should be well-thoughtduring the design and implementation process. The question of “which sensorshould be used in what application” might have several answers, depending onthe circumstances. For instance, for measuring “seat position in a car” a variety ofdifferent sensors such as Hall effect, capacitor, inductor, and magnetoresistor-basedsensors can be used (the operation of these types of sensors will be explained inlater chapters of this book). There is no limitation and no real rule in the choice ofthe most suitable sensor for this task. it can depend on many different parameterssuch as design of the sensors, design of the seat, the size of the vehicle, theavailability of the power supply, the total cost of the vehicle, and many moreother parameters. A good sensor engineer is the person who always finds the bestsolution considering the circumstances and opportunities.Essential drive sensorsPressureMass air flowAtmospheric pressureOxygenCO2Rotational speedPetrol levelPedal positionAngular positionEngine temperatureOil levelCrankshaft positionSafety sensorsSafety distanceTiltTorqueSteering wheel angleAccelerationBeltConvenience sensorsAir qualityHumidityTemperatureRainSeat positionFig. 1.5 Example of sensors incorporated into a typical vehicle8 1 Introduction
  9. 9. 1.5 About this BookIn this book, firstly the basic terminologies and fundamentals of sensorcharacteristics will be described. Physical transduction effects will be presentednext and sensor templates will be explained and their peculiarities be highlighted.Organic sensors, with an emphasis on biosensors, will be presented in the finalchapter and readers will become familiar with the operation of such sensors andtheir applications.The sensor field is multidisciplinary by nature. Therefore, the book where it isneeded, presents the basic background knowledge regarding the physics, chemistry,and biology of sensors.The book will cover the most applied sensors in the market and will highlighttheir conventional and advanced applications. Technical information is followed byin-depth discussions and relevant practical examples in each chapter.This book can be utilized as a text for students who are entering the field ofsensors for the first time. It is written in a manner that early-year university studentsin the fields of chemistry, physics, electronics, biology, biotechnology, mechanicalengineering, and bioengineering can benefit. It can also serve as a reference forengineers already working in this field.1.5 About this Book 9