This is intended to give a basic idea of electromagnetic radiation and their role in the everyday world.

1. THE PHYSICS OF RADIATION
AROUND US
PREPARED BY
S.VENKATRAMAN
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2. This is intended to give a basic idea of electromagnetism and
radiation.
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3. AC AND EM
INTRODUCTION: We live in a world wherein radiations are
omnipresent. The world we see everyday is just the reflection of
visible light from the objects around us. Rest of the radiations in
the spectrum are invisible to us. And these group of invisible
radiations get the job done for us.
BASIC ELEMENT: Charges are the basic elements mainly
responsible for the various phenomena around us. Falling under
positive and negative categories, their properties of attraction,
repulsion, drift, excitation, reflection, diffraction and so on play a
major role.
ELECTRONS: Negatively charged and exhibit the above
properties according to the environments they face.
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4. PROTONS : Positively charged. Heavier than the electrons (mass).
CURRENT: The flow of charges (electrons) constitute electric current.
Flow of electrons in a conductor can be visualized as the flow of
water in a pipe.
The flow of water from a pipe. The flow of electrons in a
metal conductor.
CURRENT
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5. The above analogy works well only with lower frequencies up to
radio and microwave frequency ranges.
AC : Alternating Current Electrons switch their direction back
and forth or, they periodically reverse their direction. In AC, the
electrons don’t move in only one direction. Instead, they hop
from atom to atom in one direction for a while, and then turn
around and hop from atom to atom in the opposite direction.
A given length of a metal contains certain amount of atoms. In
this way, hopping can be visualized.
The most widely used representation of AC is the sine wave.
Square waves, saw-tooth waves, however, are also used.
DC : Direct Current, on the other hand, flows only in one
direction.
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6. PRODUCTION OF EM WAVES
ELECTRON
BACK AND FORTH MOVEMENT OF AN
ELECTRON, FORMING WAVY LINES OF FORCE
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7. The wavy pattern is a disturbance caused to the earlier viewed
lines of force. The EM waves are produced by accelerated
charges.
Maximum
Amplitude A
-A
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8. A charged particle produces an electric field.
Accelerated charged particles produce electromagnetic fields
Wherein changing electric fields produce magnetic fields and
changing magnetic fields produce electric fields. This continues
and an “electromagnetic wave” is produced. The E & H fields are
Perpendicular to the direction of propagation of the EM Wave.
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9. ELECTROMAGNETIC SPECTRUM
The various frequencies are listed in the order of increasing
frequencies or, decreasing wavelengths.
These are two important relations.
c = speed of light , f is the frequency. E is the energy
and h is the Planck’s constant. h=6.62607004 × 10-34 m2 kg / s
Nu ( ) also refers to frequency.
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10. LEARNING ABOUT EM WAVES THAT AREN’T VISIBLE TO US?
We generally don’t believe things until we see them.
Unfortunately, this isn’t the case with EM waves.
Why can’t we see them then?
In our eyes, we have rods and cones. They are responsible for
our perception of colors during all parts of a day. They are two
general classes of photoreceptors in the human retina. One class
is specialized for discriminating between very low levels of light
(night vision). The receptors are long and thin, and are called
rods. The second class is specialized for discriminating between
high light levels (day vision), and also between different spectra.
These are the cones since their shape is conical.
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11. VISIBLE RADIATION
Wavelength: 4000 Å to 7000 Å
Radiation or the visible light ranging only from these wavelength
ranges will excite these rods and cones and help us see the world
around us. Our eyes are attuned only to these range of
wavelengths. This isn’t the case with birds and insects.
Any range of frequencies or wavelengths above or below this
however, can be viewed using Spectroscopic techniques.
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12. CARRIER WAVE AND MODULATED WAVE
In communication systems, the information in the form of image,
text, audio, video and numbers is carried by a carrier wave. This
Carrier wave is a radio wave or microwave. The modulating
wave
carries your information. The carrier wave should have high
frequency than the modulating wave. Why?
Consider this toddler to be the modulating
wave. Now this toddler is trying to climb up
the sofa. He mayn’t have the power or stamina
to climb up independently.
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13. Then how?
His/her parent comes to the scene and helps him to reach the
sofa.
Here, Carrier wave = Parent
Toddler = Modulating wave
The toddler (Modulating wave), if transmitted alone as such,
will eventually fade out due to lack of power/ strength and
destination is not reached. Hence, it is necessary to set the
frequency of carrier wave higher than the input wave. The
carrier wave (RF/ Microwave) is imposed with the modulating
wave and the resultant is called as a whole as “RF Signal” for
radio frequency. The carrier wave is modulated according to the
input have and the carrier doesn’t carry any data.
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14. ENCODING TEXT DURING TRANSMISSION
The messages we send to people are often encoded and then
transmitted to the destination. The original text message we
send is actually encoded in a format. This is done for security
purpose. Decoding is done at the receiving end.
Some of the encoding formats used are
GSM 7bit encoding
UCS 2 encoding
Base-64 encoding
Your actual text is converted to some other format and that is
transmitted to the base station of receiver where decoding is
done.
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15. THE COAXIAL CABLE
The coaxial cable is a transmission line.
APPLICATIONS
Wireless and antenna application(connecting from dish to
television through co-axial cable. Example: Tata sky) RF and
Microwave transmission, Video distribution, Cable television and
cable internet.
The coaxial cable is shown here.
Since both the inner and outer
conductors share the same axis,
it is named “co-axial”
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16. EM WAVES IN A COAXIAL CABLE
The EM waves travel in between the inner and outer conductor.
The outer conductor is meant to shield the EM waves from
getting radiated outward due to high frequency effects. Skin
effect is one such effect.
inner conductor
outer conductor
Dielectric
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17. INNER CONDUCTOR ( CLAD WITH SOME 35-40% STEEL )
- carriers current due to presence of electron, as it a metal-
alloy structure.
OUTER CONDUCTOR (BRAIDS OF COPPER)
- carrier current in the direction opposite to that of the inner
conductor
DIELECTRIC
- The energy carried in the E & H Fields are carried here.
Dielectrics aren’t complete insulators. They carry the EM
waves.
So, EM Waves don’t propagate inside the conductors however,
in between them. The electrons in both the conductors serve
to pass the EM wave from the source to the load.
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18. ANTENNA AND THE FM RANGE
Antenna or the aerial is a transducer that radiates and receives
Electromagnetic waves. Antennas work only with Alternating
Current. Antennas come in different geometry. Half-wave dipole, patch
antenna, reflector antenna etc., are some of the types.
The FM range used in our mobile phones is from 87 Mhz to
108 Mhz. Suppose that we’re listening to 92.7 (Big FM) Mhz
channel.
MEANING: Now the frequency of operation is 92.7 Mhz. This
means that wavelength is 3.23m. The size of an antenna
depends on the wavelength used. The generally used size is
half wave and quarter wave dipole. So physical dimension of
antenna gets reduced.
Folding is done in case of microstrip / patch antennas for
compactness.
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19. WHY STUDY EM Waves?
Unintentional generation, propagation and reception of
electromagnetic energy may cause unwanted effects such
as electromagnetic interference (EMI) or even physical damage
in operational equipment.
The interference should be avoided and the government
provides preferred EMC Standards that a product should
comply with.
Different electronic product is desired to operate within it’s own
desired range and not have any mutual interference with other
devices.
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20. NATURE
Not everything present in the nature can be explained to the
fullest extent. Indeed nature is mysterious.
The study of radiation is theoretically satisfying and practical
simulations have also been carried out with good results.
Still, waves and particles still seem to be a mystery.
All these seemingly mysterious things are the building blocks
of the universe!
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21. REFERENCES
Images : emaze.com
xtide.ldeo.columbia.edu
www.gify.com
Some of the websites useful for encoding schemes
http://smstools3.kekekasvi.com/topic.php?id=288
http://base64-encoding.online-domain-tools.com
http://www.smartposition.nl/resources/sms_pdu.html
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22. AUTHOR
Electronics and Communication engineer from
Sri Sairam Engineering College, Tamilnadu
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23. THANK YOU
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