Transcript Electromagnetic radiation

ERT247:GEOMATIC
ENGGINEERING
Electromagnetic
radiation
GROUP A2:
WAN MOHD ALIF
NUR SALWANA
KER LEE SHIANG
SITI AFIQAH
HUZAIFAH
INTAN LIANA
Definition of electromagnetic
radiation
•
Electromagnetic = the process of formation of a
free electromagnetic field
•
Radiation = used to design the free that is radiated electromagnetic
field itself
•
So in physics electromagnetic radiation is regarded as the emission
of electromagnetic waves by electric charge that are moving under
acceleration (current)
•
Electromagnetic radiation is emitted in discrete units known as
photons that travel at the speed of light as electromagnetic waves.
Electromagnetic energy is classified by increasing energy or
decreasing wavelength into radio waves, microwaves, infrared,
visible light, ultraviolet, X-rays and gamma-rays (Figure 1).
• Electromagnetic radiation (often
abbreviated E-M radiation or EMR) is a form
of energy exhibiting wave-like behavior as it
travels through space. EMR has both electric
and magnetic field components,
which oscillate in phase perpendicular to each
other and perpendicular to the direction of
energy propagation.
• Electromagnetic radiation is classified according
to the frequency of its wave. In order of
increasing frequency and decreasing wavelength,
these are radio waves, microwaves, infrared
radiation, visible light, ultraviolet radiation, Xrays and gamma rays. The eyes of
various organisms sense a small and somewhat
variable window of frequencies called the visible
spectrum. The photon is the quantum of the
electromagnetic interaction and the basic "unit" of
light and all other forms of electromagnetic
radiation and is also the force carrier for the
electromagnetic force. EM radiation
carries energy and momentum that may be
imparted to matter with which it interacts.
THEORY OF ELECTROMAGNETIC
RADIATION
• Shows the relative wavelengths of the
electromagnetic waves of three
different colors of light (blue, green
and red) with a distance scale in
micrometres along the x-axis.
• The theory that prove electromagnetic radiation:
Classical radiation theory (Maxwell`s
theory) the theory of electromagnetic
radiation was developed by James
Clerk Maxwell and published in 1865. He
showed that the speed of propagation
of electromagnetic radiation should be
identical with that of light , about
186,000 mi (300,000 km) per
• James Clerk Maxwell first formally
postulated electromagnetic waves. These were
subsequently confirmed by Heinrich Hertz. Maxwell
derived a wave form of the electric and magnetic equations,
thus uncovering the wave-like nature of electric and
magnetic fields, and their symmetry. Because the speed of
EM waves predicted by the wave equation coincided with
the measured speed of light, Maxwell concluded
that light itself is an EM wave.
• According to Maxwell's equations, a time-varying electric
field generates a time-varying magnetic field and vice versa.
Therefore, as an oscillating electric field generates an
oscillating magnetic field, the magnetic field in turn
generates an oscillating electric field, and so on. These
oscillating fields together form a propagating
electromagnetic wave.
• A quantum theory of the interaction between
electromagnetic radiation and matter such as electrons is
described by the theory of quantum electrodynamics.
The propagation direction of a
light wave
V=EXB
RIGHT- HAND SCREW
RULE
Electromagnetic wave
• Electromagnetic waves can be
imagined as a self-propagating
transverse oscillating wave of electric
and magnetic fields. This diagram
shows a plane linearly polarized wave
propagating from right to left. The
electric field is in a vertical plane and
the magnetic field in a horizontal
plane.
• The physics of electromagnetic radiation
is electrodynamics. Electromagnetism is the physical
phenomenon associated with the theory of
electrodynamics. Electric and magnetic fields obey the
properties of superposition. Thus, a field due to any
particular particle or time-varying electric or magnetic
field contributes to the fields present ing the same space
due to other causes. Further, as they are vector fields, all
magnetic and electric field vectors add together
according to vector addition. For example, in optics two
or more coherent lightwaves may interact and by
constructive or destructive interference yield a resultant
irradiance deviating from the sum of the component
irradiances of the individual lightwaves.
• Since light is an oscillation it is not affected by travelling
through static electric or magnetic fields in a linear medium
such as a vacuum. However in nonlinear media, such as
some crystals, interactions can occur between light and static
electric and magnetic fields — these interactions include
the Faraday effect and the Kerr effect.
• n refraction, a wave crossing from one medium to another of
different density alters its speed and direction upon entering
the new medium. The ratio of the refractive indices of the
media determines the degree of refraction, and is summarized
by Snell's law. Light disperses into a visible spectrum as light
passes through a prism because of the wavelength
dependent refractive index of the prism material (Dispersion
• EM radiation exhibits both wave properties
and particle properties at the same time (see waveparticle duality). Both wave and particle characteristics
have been confirmed in a large number of experiments.
Wave characteristics are more apparent when EM
radiation is measured over relatively large timescales
and over large distances while particle characteristics
are more evident when measuring small timescales and
distances. For example, when electromagnetic radiation
is absorbed by matter, particle-like properties will be
more obvious when the average number of photons in
the cube of the relevant wavelength is much smaller
than 1. Upon absorption of light, it is not too difficult to
experimentally observe non-uniform deposition of
energy. Strictly speaking, however, this alone is not
evidence of "particulate" behavior of light, rather it
reflects the quantum nature of matter
• There are experiments in which the wave and
particle natures of electromagnetic waves
appear in the same experiment, such as the
self-interference of a
single photon.True single-photon experiments
(in a quantum optical sense) can be done today
in undergraduate-level labs.[2] When a single
photon is sent through an interferometer, it
passes through both paths, interfering with
itself, as waves do, yet is detected by
a photomultiplier or other sensitive detector
only once.
Particle Model
• Because energy of an EM interaction is quantized, EM waves are
emitted and absorbed as discrete packets of energy, or quanta,
called photons. Because photons are emitted and absorbed by
charged particles, they act as transporters of energy, and are
associated with waves with frequency proportional to the energy
carried. The energy per photon can be related to the frequency via
the Planck–Einstein equation:[4]
• where E is the energy, h is Planck's constant, and f is frequency. The
energy is commonly expressed in the unit of electronvolt (eV). This
photon-energy expression is a particular case of the energy levels of
the more general electromagnetic oscillator, whose average energy,
which is used to obtain Planck's radiation law, can be shown to
differ sharply from that predicted by the equipartition principle at
low temperature, thereby establishes a failure of equipartition due to
quantum effects at low temperature.
• As a photon is absorbed by an atom,
it excites the atom, elevating an electron to a
higher energy level. If the energy is great
enough, so that the electron jumps to a high
enough energy level, it may escape the positive
pull of the nucleus and be liberated from the
atom in a process called photoionisation.
Conversely, an electron that descends to a
lower energy level in an atom emits a photon
of light equal to the energy difference. Since
the energy levels of electrons in atoms are
discrete, each element emits and absorbs its
own characteristic frequencies.
• Together, these effects explain the emission and absorption
spectra of light. The dark bands in the absorption spectrum are
due to the atoms in the intervening medium absorbing different
frequencies of the light. The composition of the medium
through which the light travels determines the nature of the
absorption spectrum. For instance, dark bands in the light
emitted by a distant star are due to the atoms in the star's
atmosphere. These bands correspond to the allowed energy
levels in the atoms. A similar phenomenon occurs
for emission. As the electrons descend to lower energy levels,
a spectrum is emitted that represents the jumps between the
energy levels of the electrons. This is manifested in
the emission spectrum of nebulae. Today, scientists use this
phenomenon to observe what elements a certain star is
composed of. It is also used in the determination of the
distance of a star, using the red shift.
SPEED OF PROPAGATION
• Any electric charge which accelerates, or any changing magnetic
field, produces electromagnetic radiation. Electromagnetic
information about the charge travels at the speed of light.
Accurate treatment thus incorporates a concept known
as retarded time (as opposed to advanced time, which is not
physically possible in light ofcausality), which adds to the
expressions for the electrodynamic electric field and magnetic
field. These extra terms are responsible for electromagnetic
radiation. When any wire (or other conducting object such as
an antenna) conducts alternating current, electromagnetic
radiation is propagated at the same frequency as the electric
current. At the quantum level, electromagnetic radiation is
produced when the wavepacket of a charged particle oscillates or
otherwise accelerates. Charged particles in a stationary state do
not move, but a superposition of such states may result in
oscillation, which is responsible for the phenomenon of radiative
transition between quantum states of a charged particle.
• Depending on the circumstances, electromagnetic radiation may behave as
a wave or as particles. As a wave, it is characterized by a velocity
(the speed of light),wavelength, and frequency. When considered as
particles, they are known as photons, and each has an energy related to the
frequency of the wave given by Planck'srelation E = hν, where E is the
energy of the photon, h = 6.626 × 10−34 J·s is Planck's constant, and ν is the
frequency of the wave.
• One rule is always obeyed regardless of the circumstances: EM radiation in
a vacuum always travels at the speed of light, relative to the observer,
regardless of the observer's velocity. (This observation led to Albert
Einstein's development of the theory of special relativity.)
• In a medium (other than vacuum), velocity factor or refractive index are
considered, depending on frequency and application. Both of these are
ratios of the speed in a medium to speed in a vacuum.
Thermal radiation and
electromagnetic radiation as a form
of heat
•
The basic structure of matter involves charged particles bound together in many
different ways. When electromagnetic radiation is incident on matter, it causes the
charged particles to oscillate and gain energy. The ultimate fate of this energy
depends on the situation. It could be immediately re-radiated and appear as
scattered, reflected, or transmitted radiation. It may also get dissipated into other
microscopic motions within the matter, coming tothermal equilibrium and
manifesting itself as thermal energy in the material. With a few exceptions such
as fluorescence, harmonic generation,photochemical reactions and the photovoltaic
effect, absorbed electromagnetic radiation simply deposits its energy by heating the
material. This happens both for infrared and non-infrared radiation. Intense radio
waves can thermally burn living tissue and can cook food. In addition to
infrared lasers, sufficiently intense visible and ultraviolet lasers can also easily set
paper afire. Ionizing electromagnetic radiation can create high-speed electrons in a
material and break chemical bonds, but after these electrons collide many times
with other atoms in the material eventually most of the energy gets downgraded to
thermal energy, this whole process happening in a tiny fraction of a second. That
infrared radiation is a form of heat and other electromagnetic radiation is not, is a
widespread misconception in physics. Any electromagnetic radiation can heat a
material when it is absorbed.
• The inverse or time-reversed process of absorption is
responsible for thermal radiation. Much of the thermal
energy in matter consists of random motion of charged
particles, and this energy can be radiated away from the
matter. The resulting radiation may subsequently be
absorbed by another piece of matter, with the deposited
energy heating the material. Radiation is an important
mechanism of heat transfer.
• The electromagnetic radiation in an opaque cavity at
thermal equilibrium is effectively a form of thermal
energy, having maximum radiation entropy.
Thethermodynamic potentials of electromagnetic
radiation can be well-defined as for matter. Thermal
radiation in a cavity has energy density .
Types of Electromagnetic Wave
• Light, microwaves, x-rays, and TV
and radio transmissions are all
kinds of electromagnetic waves.
They are all the same kind of wavy
disturbance that repeats itself over
a distance called the wavelength.
• Electromagnetic waves can be
described in terms of three basic
parameters:
1. Velocity (c)
2. Wavelength (λ)
3. Frequency (f)
• The following relationship exists
between the above three parameters:
• λf = c = 3.8 x108m/sec
• Where λ is in metres and f is in hertz.
• Electromagnetic radiation effects
approach in a wide range of
wavelengths. This electromagnetic
radiation range is broken behind
aware keen on a numeral of dissimilar
group, every of that divide definite
possessions.
Wave
Wavelength
Radiation Uses
Long Wave Radio
1500 m
Broadcasting
ave Radio
300 m
Broadcasting
Short Wave Radio
25 m
Broadcasting
FM Radio
3m
Broadcasting and communication
UHF Radio
30 cm
TV transmissions
Microwaves
3 cm
Communication
Infra red
3 mm
Communication in optical fibres
Light
200 - 600 nm
Seeing
Ultra violet
100 nm
Sterilising
X-ray
5 nm
Shadow pictures of bones
Gamma rays
<0.01 nm
Scientific research
Long radio waves:
• That include the deprived occurrence
with uses of wavelength at times contain
occurrence smaller amount than 1 Hertz
with wavelengths during surplus of 1
kilometre.
Short radio waves:
• That have privileged occurrence with
also minute wavelength. Frequently uses
in extremely short-range broadcasting
communication.
Microwaves:
• That is difficult event influence
hypocritical approximately among
broadcasting with infrared waves.
Infrared radiation:
• That radiation is the part of the
electromagnetic spectrum use
immediately under scarlet beam within
conditions of occurrence.
Ultraviolet light:
• That is further than violet beam during
situation of occurrence. Its major use of
organization is the sun also further leading
light. It is formed through electric-curve
light for technological function.
Different Types of Radiation:
X rays:
• That also recognized are divided keen on two
categories: soft also hard X rays. Soft X rays
consist of lengthy wavelengths and are
quicker to the ultraviolet group of the
spectrum. Hard X rays are faster toward the
gamma-ray collection of the spectrum with
comprising a lot undersized wavelengths.
Gamma rays:
• That is the small wavelength, high event
category of electromagnetic energy. They
are fundamentally uses equal toward X rays
during their consequence, excluding are
formed through energized basis as a
substitute of internal electrons.
Electromagnetic Spectrum
Application of ER in remote
sensing:
• An Ideal remote sensing system shown
in Figure 1, consists of the following
basic stages:
1. Electromagnetic energy source
2. Energy propagation
3. Energy interaction\Return signal
4. Recording
5. Supply of information in the desired
form.
Figure 1: Remote Sensing System
• The source of energy produces
electromagnetic energy and it
propagates from the source to a
homogeneous target.
• In ideal case, produced electromagnetic
energy contains all wavelengths and
there is no loss of energy during
propagation.
• When the energy interacts with the
target, depending upon the
characteristics of the target, the energy is
transmitted, absorbed scattered emitted,
or reflected from the target to the sensor.
• The energy from the target to the sensor
is in the form of return signal, reaching a
linear sensor which responds linearly to
electromagnetic energy of all
wavelengths and intensity. The return
signal is recorded and processes in real
time by the data recorder. The data is
then processed into a format which is
useful for interpretation. T
• he information about the target
collected is made available to the users
in the desired form.
Radar
• Radar, like sonar and seismology, uses
a man-made pulse of radio energy to
map distance based on the length of
time it takes the pulse to return from
the source.
• Radar (short for "Radio Detection and
Ranging"), which can be airborne or
spaceborne, has greatly changed
the way we see the land and ocean
surfaces.
• Radar is based on the principle of sending very
long wavelength radiation (called microwaves)
from an antenna, and then detecting that
energy after it bounces off a remote target.
• The wavelength of the microwave, its
polarization (vertical or horizontal orientation)
and strength can be controlled at the source
and measured when it returns.
• Many common land-cover types and materials
affect the polarity and strength of the radar
return differently, which helps in their
identification
Electromagnetic radiation and
health
• Electromagnetic radiation can be classified
into ionizing radiation and non-ionizing radiation,
based on whether it is capable of ionizing atoms
and breaking chemical bonds. Ultraviolet and
higher frequencies, such as X-rays or gamma
rays are ionizing. These pose their own special
hazards: see radiation and radiation poisoning.
• Non-ionizing radiation, discussed here, is
associated with two major potential hazards:
electrical and biological. Additionally,
induced electric current caused by radiation can
generate sparks and create a fire or explosive
hazard.
Types of hazards
• the oscillating electric and magnetic fields in
electromagnetic radiation will induce an electric
current in any conductor through which it passes.
Strong radiation can induce current capable of
delivering an electric shock to persons or animals. It
can also overload and destroy electrical equipment.
The induction of currents by oscillating magnetic fields
is also the way in which solar storms disrupt the
operation of electrical and electronic systems, causing
damage to and even the explosion of power
distribution transformers,[1] blackouts (as in 1989), and
interference with electromagnetic signals (e.g. radio,
TV, and telephone signals).[2]
• Fire hazards
• Extremely high power electromagnetic radiation can cause
electric currents strong enough to create sparks (electrical
arcs) when an induced voltage exceeds the breakdown
voltage of the surrounding medium (e.g. air). These sparks
can then ignite flammable materials or gases, possibly leading
to an explosion.
• This can be a particular hazard in the vicinity
of explosives or pyrotechnics, since an electrical overload
might ignite them. This risk is commonly referred to
as HERO (Hazards of Electromagnetic Radiation to
Ordnance). MIL-STD-464A mandates assessment of HERO in
a system, but Navy document OD 30393 provides design
principles and practices for controlling electromagnetic
hazards to ordnance.
• On the other hand, the risk related to fueling is known
as HERF (Hazards of Electromagnetic Radiation to Fuel).
NAVSEA OP 3565 Vol. 1 could be used to evaluate HERF,
which states a maximum power density of 0.09 W/m² for
frequencies under 225 MHz (i.e. 4.2 meters for a 40 W
emitter).
Biological hazards
• The best understood biological effect of electromagnetic fields is to cause
dielectric heating. For example, touching or standing around
an antenna while a high-power transmitter is in operation can cause severe
burns. These are exactly the kind of burns that would be caused inside
a microwave oven.
• This heating effect varies with the power and the frequency of the
electromagnetic energy. A measure of the heating effect is thespecific
absorption rate or SAR, which has units of watts per kilogram (W/kg).
The IEEE[3] and many national governments have established safety limits
for exposure to various frequencies of electromagnetic energy based on
SAR, mainly based onICNIRP Guidelines,[4] which guard against thermal
damage.
• There are publications which support the existence of complex biological
effects of weaker non-thermal electromagnetic fields
(see Bioelectromagnetics), including weak ELF magnetic fields.[5][6] and
modulated RF and microwave fields[7] Fundamental mechanisms of the
interaction between biological material and electromagnetic fields at nonthermal levels are not fully understood.[8]
• DNA fragmentation. A 2009 study at the University of Basel in Switzerland
found that intermittent (but not continuous) exposure of human cells to a
50 Hz electromagnetic field at a flux density of 1 mT (or 10 G) induced a
slight but significant increase of DNA fragmentation in the Comet
assay.[9] However that level of exposure is already above current
established safety exposure limits.
Positions of governments and scientific bodies
• World Health Organization
• "The Task Group concluded that there are no substantive health
issues related to ELF electric fields at levels generally encountered
by members of the public.... [O]n balance, the evidence
[about magnetic fields being] related to childhood leukaemia is not
strong enough to be considered causal.... A number of other adverse
health effects have been studied for possible association with ELF
magnetic field exposure. These include other childhood cancers,
cancers in adults, depression, suicide, cardiovascular disorders,
reproductive dysfunction, developmental disorders, immunological
modifications, neurobehavioural effects and neurodegenerative
disease. The WHO Task Group concluded that scientific evidence
supporting an association between ELF magnetic field exposure and
all of these health effects is much weaker than for childhood
leukaemia. In some instances (i.e. for cardiovascular disease or
breast cancer) the evidence suggests that these fields do not cause
them."[10]
• Mobile phone radiation and health concerns have been
raised, especially following the enormous increase in the use
of wireless mobile telephony throughout the world (as of
August 2005, there were more than 2 billion users
worldwide). Mobile phones use electromagnetic radiation in
the microwave range, and some[39][unreliable medical source?] believe
this may be harmful to human health. These concerns have
induced a large body of research (both epidemiological and
experimental, in non-human animals as well as in humans).
Concerns about effects on health have also been raised
regarding other digital wireless systems, such as data
communication networks.
• The World Health Organization, based upon the consensus
view of the scientific and medical communities, states that
health effects (e.g. headaches or promotion of cancer) are
unlikely to be caused by cellular phones or their base
stations,[40][41] and expects to make recommendations about
mobile phones in the third quarter of 2010 at the earliest, or
the first quarter of 2011 at the latest.[42]
U.S. military definition
• In Federal Standard 1037C, the United
States government adopts thefollowing definition:
• Electromagnetic radiation hazards (RADHAZ or EMR
hazards): Hazards caused by a transmitter/antenna
installation that generates electromagnetic radiation in
the vicinity of ordnance, personnel, or fueling operations
in excess of established safe levels or increases the
existing levels to a hazardous level; or a personnel,
fueling, or ordnance installation located in an area that is
illuminated by electromagnetic radiation at a level that is
hazardous to the planned operations or occupancy.
• These hazards will exist when an
electromagnetic field of sufficient intensity is
generated to: (a) induce or otherwise couple
currents and/or voltages of magnitudes large
enough to initiate electroexplosive devices or
other sensitive explosive components of weapon
systems, ordnance, or explosive devices; (b)
cause harmful or injurious effects to humans and
wildlife; (c) create sparks having sufficient
magnitude to ignite flammable mixtures of
materials that must be handled in the affected
area. —Department of Defense Dictionary of
Military and Associated Terms
CONELRAD (Contal
Electromagnetic Radiation)
• CONELRAD (Control
of ElectromagneticRadiation) was a method
of emergencybroadcasting to the public of
the United States in the event of enemy
attack during the Cold War. It was intended to
serve two purposes; to
prevent Soviet bombers from homing in on
American cities by usingradio or TV stations
as beacons, and to provide essential civil
defense information.U.S. President Harry S.
Trumanestablished CONELRAD in 1951.
• After the development of intercontinental ballistic
missiles reduced the likelihood of a bomber
attack, CONELRAD was replaced by
the Emergency Broadcast System on August 5,
1963, which was later replaced with
the Emergency Alert System in 1997; all were
administered by the Federal Communications
Commission(FCC).[1]
• Unlike its successors, the EBS and EAS,
CONELRAD was never used for nor intended to
be used for severe weather warnings or local
civil emergencies.
• ONELRAD concept was originally known
as theKey Station System. According to an
FCC document created during the
"Informal Government - Industry Technical
Conference" on March 26, 1951
• In the event of an emergency, all United
States television and FM radio stationswere required to
stop broadcasting. Upon alert, most AM medium
wave stations shut down. The stations that stayed on the
air would transmit on either 640 or 1240 kHz. They
would transmit for several minutes, and then go off the
air and another station would take over on the same
frequency in a "round robin" chain. This was to confuse
enemy aircraft who might be navigating using Radio
Direction Finding. By law, radio sets manufactured
between 1953 and 1963 had these frequencies marked
by the triangle-in-circle ("CD Mark") symbol of Civil
Defense.
• In the event of an emergency, all United
States television and FM radio stationswere required to stop
broadcasting. Upon alert, most AM medium wave stations shut
down. The stations that stayed on the air would transmit on either
640 or 1240 kHz. They would transmit for several minutes, and then
go off the air and another station would take over on the same
frequency in a "round robin" chain. This was to confuse enemy
aircraft who might be navigating using Radio Direction Finding. By
law, radio sets manufactured between 1953 and 1963 had these
frequencies marked by the triangle-in-circle ("CD Mark") symbol
of Civil Defense.[3]
•
"CD Mark" symbols like this (though generally shown as simple white triangles)
were on every radio sold in the U.S., at the 640 kHz and 1240 kHz frequency
points, to help listeners find the CONELRAD stations.