Japan IT Week 2024 Brochure by 47Billion (English)
Sensors
1. Chapter 1
Introduction
Abstract In this chapter a general overview regarding sensors will be presented.
Some of the fundamental terminologies, which are frequently encountered in the
sensor field, will be described. The importance and applications of sensors will be
highlighted.
1.1 Sensors and Transducers
The word sensor has a Latin root “sentire,” which means “to perceive,” originated in
1350–1400, 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 of
the term sensor, although there are subtle differences. A transducer is a device that
converts one type of energy to another. The origin is “transduce,” which means “to
transfer” that was first coined in 1525–1535. A transducer is a term that can be used
for 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 commonly
made of two major components: a sensitive element and a transducer. The sensitive
element has the capability to interact with a target measurand and cause a change in
the operation of the transducer. Affected by this change, the transducer produces a
signal, which is translated into readable information by a data acquisition system.
It is important to note that for devices such as transistors and actuators, the
conversion efficiency is generally an important factor. However, in addition to the
conversion efficiency, a sensor should have many other qualities such as selectivity
and sensitivity, which will be explained later.
Other common definition is to use the term sensor for the sensing element itself
and transducer for the sensing element plus any associated peripherals (the overall
system). For example, a temperature sensor is called a sensor, while together with
the data acquisition circuit (to convert the signal into a measurable electrical
voltage) 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 2013
1
2. Most of the man-made systems acquire data from their surrounding environments,
process them, and consequently translate the data into useful functions. Sensors’ roles
in such systems are the acquisition of data. Using sensors, direct contact with the
surrounding world is more possible. Sensors enable systems to interact with their
environments and receive desired information. This information is then sent to a
processing system, where it is processed into meaningful information. The processed
information can be either directly deciphered as the sought after output or further fed
into another system for additional processing or producing signals for actuators. The
more complex the system, the larger number of sensors is required for its operation.
1.2 Sensors Qualities
Sensors should be sensitive to their target measurands, and insensitive to any other
input 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 used
for measuring temperature, the size of the sensor should be much smaller than size of
the monitored object (e.g., micro-/nano-sized objects) or the measurement should be
conducted remotely (infrared temperature measuring systems). A sensor life time is
important—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 fresh
and intact in sealed packaging until their applications). Response behavior of a senor
should 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 the
data sheet of a sensor and a good sensor must have a comprehensive and clear data
sheet. A senor has to be well calibrated before the application. This means an extra
cost for the manufacturer. Interferences of signals other than the measurand should
Measurand
Measurand affecting the
sensitive interface and/or
the bulk of the transducer
Transducer
Sensitive interface
To data acquisition system
Sensor
Fig. 1.1 Schematic depiction of a sensing system
2 1 Introduction
3. be minimal for a good sensor. Sensors resolution, which will also be discussed in
Chap. 2, should be well presented to the consumers via the data sheet.
A sensor’s fabrication cost should be as small as possible. Economy always
governs the engineering and design, and a lower cost is always a winner. A sensor
should be environmentally friendly. Many types of sensors are disposable and all
sensors have limited life span. After the end of their lives, they should be able to be
return to nature safely. For instance, in the past many sensors were using mercury in
their structure, which are now mostly banned from the manufacturing. Selectivity
of the sensor is also an important issue. A good sensor is selective to the target
measurand. 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 the
design 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 a
field and they should be individually supplied with sufficient power. This always
poses a challenge. Stand-alone sources, such as batteries, have limited lifetime.
Renewable sources, such as solar cells, have their own complexity of operation and
add to the costs. Providing the energy form a central source requires expensive and
complicated wiring matrix. Another issue is the communications between the
central 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 the
author advice readers to refer to excellent available textbooks in the field.
1.3 Types of Transducers
Since 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 different
forms 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, the
input 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 occurrence
Type of energy Occurrence
Gravitational Gravitational attraction
Mechanical 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 of
thermodynamic equilibrium because of its temperature
Electromagnetic 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 reactions
Nuclear Binding energy between nuclei—binds the subatomic particles of a matter
1.3 Types of Transducers 3
4. A two-dimensional representation of the direct transduction, from one form of
energy to another, is shown in Fig. 1.3. The primary energy input to the system is
represented by one axis and the energy output by the other axis. With the 6 forms of
energy, we have 6 Â 6 ¼ 36 possibilities.
Physical and chemical effects are involved in signal transductions. Physical
effects involve those that couple a material’s thermal, mechanical, electromagnetic
(including optical), gravitational, and nuclear properties. These effects together
with the chemical effects are utilized within sensors. Table 1.2 shows examples of
effects that are obtained when these properties are coupled with each other or with
themselves.
Gravitational
Mechanical
Thermal
Electromagnetic
Nuclear
Chemical
Gravitational
Mechanical
Thermal
Electromagnetic
Nuclear
Chemical
Transduction
process
Input Output
Fig. 1.2 Schematic depiction of a sensing system interacting with various possible input and
output energies
Gravitational
Mechanical
Thermal
Electromagnetic
Nuclear
Chemical
Gravitational
Mechanical
Thermal
Electromagnetic
Nuclear
Chemical
Fig. 1.3 A two-dimensional representation of possible direct transductions from one form to
another
4 1 Introduction
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 consecutive
steps. 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 a
voltage (electromagnetic energy), which is a measurable signal for a user. In this
case, we have an extra intermediate transduction process. This adds extra
dimensions to the transduction plane representation of Fig. 1.3. In this case an
extra 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 the
number of in-between transduction steps increases. Such systems can be more
complex and costly but in return can increase the reliability and performance.
1.4 Sensors Applications
In recent years the development of operational systems has become progressively
important and sensors have become an ever-present part of such systems. Sensors
are playing a greater than ever role in our day-to-day interactions and are becoming
an 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: to
achieve accurate and stable monitoring of target measurands.
Sensor technology has flourished as the need for physical, chemical, and
biological recognition has grown. Nowadays sensors are finding a more prominent
role, as strong needs on devices aimed at making lives better, easier, and safer are
observed. 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, the
importance of sensors has grown significantly due to increasing automation and
more use of microelectronics, both of which require more sensors. Parallel to this
development, the capabilities of sensors are increasing and sensors prices are
shrinking. 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. Sensors are found commonly around the household. For example, they are
located in gas cook tops, where they determine whether or not the pilot is on, and
if not, halt the gas flow preventing the room from being filled with gas. They are in
electrical devices from surge protectors to automatic light switches, refrigerators
and 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 upon
entering or leaving an office.
Sensors are also an integral part of health care and diagnostics. They can
determine whether or not biological systems are functioning correctly and most
importantly, direct us to act without delay when something is wrong. For instance
glucose meters are playing a crucial role in determining the amount of sugar levels
in people diagnosed with diabetes. They are incorporated in off-the-shelf blood
pressure and oxygen content monitoring as well as in pregnancy tests systems.
The functions of senors are generally not so noticeable, yet millions of them are
contained within central processing units of computers and microcontrollers. In
addition to these internally integrated electronic devices, electronic systems have a
large 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 house
1.4 Sensors Applications 7
8. Nowadays almost all engineering machines incorporate sensors. Sensors are
widely used in automotive industry. An average vehicle can have hundreds of
individual sensors for different functions (Fig. 1.5). This includes: sensors for
doors, wipers, several temperature and exhaust sensors around engine and exhaust
pipes, 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 and
process control, where the sensors continually monitor to ensure that efficiency is
maximized, 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-thought
during the design and implementation process. The question of “which sensor
should be used in what application” might have several answers, depending on
the circumstances. For instance, for measuring “seat position in a car” a variety of
different sensors such as Hall effect, capacitor, inductor, and magnetoresistor-based
sensors can be used (the operation of these types of sensors will be explained in
later chapters of this book). There is no limitation and no real rule in the choice of
the most suitable sensor for this task. it can depend on many different parameters
such as design of the sensors, design of the seat, the size of the vehicle, the
availability of the power supply, the total cost of the vehicle, and many more
other parameters. A good sensor engineer is the person who always finds the best
solution considering the circumstances and opportunities.
Essential drive sensors
Pressure
Mass air flow
Atmospheric pressure
Oxygen
CO2
Rotational speed
Petrol level
Pedal position
Angular position
Engine temperature
Oil level
Crankshaft position
Safety sensors
Safety distance
Tilt
Torque
Steering wheel angle
Acceleration
Belt
Convenience sensors
Air quality
Humidity
Temperature
Rain
Seat position
Fig. 1.5 Example of sensors incorporated into a typical vehicle
8 1 Introduction
9. 1.5 About this Book
In this book, firstly the basic terminologies and fundamentals of sensor
characteristics will be described. Physical transduction effects will be presented
next and sensor templates will be explained and their peculiarities be highlighted.
Organic sensors, with an emphasis on biosensors, will be presented in the final
chapter and readers will become familiar with the operation of such sensors and
their applications.
The sensor field is multidisciplinary by nature. Therefore, the book where it is
needed, 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 highlight
their conventional and advanced applications. Technical information is followed by
in-depth discussions and relevant practical examples in each chapter.
This book can be utilized as a text for students who are entering the field of
sensors for the first time. It is written in a manner that early-year university students
in the fields of chemistry, physics, electronics, biology, biotechnology, mechanical
engineering, and bioengineering can benefit. It can also serve as a reference for
engineers already working in this field.
1.5 About this Book 9
