Electromagnetic waves have different wavelengths and frequencies depending on their position in the electromagnetic spectrum. They all travel at the same speed of 300 million meters per second in a vacuum. Waves with longer wavelengths have lower frequencies while those with shorter wavelengths have higher frequencies. The higher the frequency, the higher the energy carried by the electromagnetic wave.

1. PROPAGATION OF
ELECTRO MAGNETIC
WAVES
Dr. C. Saritha
Lecturer in
Electronics
S.S.B.N. College
ANANTAPUR

2. DEFINITION OF E.M.WAVES:
 The wave of the electric field and the wave of the magnetic field
are propagated perpendicularly to the direction of propagation and to
each other. At extremely low frequencies, the electric field and the
magnetic field are specified separately. At higher frequencies, electric
and magnetic fields are not separable, and are named
"electromagnetic waves" or "electromagnetic fields".

3. Nature of Electromagnetic Waves
They are Transverse waves without a medium.
(They can travel through empty space)
They travel as vibrations in electrical and
magnetic fields.
Have some magnetic and some electrical properties
to them.
Speed of electromagnetic waves = 300,000,000
meters/second (Takes light 8 minutes to move from
the sun to earth {150 million miles} at this speed.)

4. Ground-Wave Propagation
At frequencies up to about 2 MHz, the most
important method of propagation is by ground
waves which are vertically polarized. They follow
the curvature of the earth to propagate far beyond
the horizon. Relatively high power is required.
Direction of wave travel
Increasing
Tilt
Earth

5. SPACE WAVE PROPAGATION
The EM wave that propagates from the transmitter to
the receiver in the earth’s troposphere is called “Space
Wave”.
Troposphere is the region of the atmosphere with in
15km above the surface of the earth.
The Maximun line of sight distance between two
antenns depends on the height of each antenna.

6. SKYWAVE PROPAGATION
Sky wave propagation is also called Ionospheric wave
propagation. E.M waves directed upward at some
angle from the earth’s Surface are called Skywaves.
Sky wave propagation is usefull in the frequency
range of 2 to 30 MHz and for long distance
communication
Ionosphere is the upper portion of the atmosphere
between 50km and 350km above the earth,which is
ionoised by absorbing large quantities of radiation
energy from the Sun.
The Major ionisation is from α,β and γ radiation from
the Sun and cosmic rays and meter

8. Reflection
Refraction
Diffraction
Polarization
Scattering

9. Reflection:
Reflection is when waves, whether physical or electromagnetic, bounce from a
surface back toward the source. A mirror reflects the image of the observer.

10. Polarization:
The polarization of an electromagnetic wave indicates the plane
in which it is vibrating. As electromagnetic waves consist of an
electric and a magnetic field vibrating at right angles to each
other it is necessary to adopt a convention to determine the
polarization of the signal. For this purpose the plane of the
electric field is used.

11. Refraction:
Refraction is the bending of light as it passes between materials of
different optical density
Refraction of a material is the ratio of the speed of light in vacuum to the speed
of light in that material:
n=

12. Diffraction:
When a travelling water wave hits an obstacle, the wave fronts spreads out round
the edge and becomes curved. This phenomenon refers to diffraction

13. Scattering:
The change in direction of a particle or photon because of a collision with another
particle or a system.

14. FADING:
Fading effect is nothing but the fluctuation in
received signal strength at the receiver that is, any
random variation in the received signal can be termed
as fading.
While the microwave signal travel in the medium due
to different parameters there is reduction in signal
strength, according to that signal fading is divided
into seven types: (1) Slow fading (2)Fast fading
(3) Interference fading (4)Absorption fading
(5)Selective fading (6) Polarization fading
(7)Skip fading

15. Waves or Particles
 Electromagnetic radiation has properties of waves
but also can be thought of as a stream of
particles.
 Example: Light
 Light as a wave: Light behaves as a transverse
wave which we can filter using polarized lenses.
 Light as particles (photons)
 When directed at a substance light can knock
electrons off of a substance (Photoelectric effect)

16. Waves of the Electromagnetic Spectrum
Electromagnetic Spectrum—name for the range of
electromagnetic waves when placed in order of increasing
frequency
ULTRAVIOLET GAMMA
RADIO INFRARED
RAYS RAYS
WAVES RAYS
MICROWAVES X-RAYS
VISIBLE LIGHT

17. RADIO WAVES
A. Have the longest wavelengths and lowest
frequencies of all the electromagnetic waves.
B. A radio picks up radio waves through an antenna
and converts it to sound waves.
C. Each radio station in an area broadcasts at a
different frequency. # on radio dial tells frequency.
D. MRI (MAGNETIC RESONACE IMAGING)
Uses Short wave radio waves with a magnet to create an
image

19. MICROWAVES
Microwaves—have the shortest wavelengths and the
highest frequency of the radio waves.
Used in microwave ovens.
 Waves transfer energy to the water in the food causing them to
vibrate which in turn transfers energy in the form of heat to the
food.
Used by cell phones and pagers.
RADAR (Radio Detection and Ranging)
 Used to find the speed of an object by sending out radio waves and
measuring the time it takes them to return.

21. Infrared= below red
Shorter wavelength and higher frequency than
microwaves.
You can feel the longest ones as warmth on your skin
Heat lamps give off infrared waves.
Warm objects give off more heat energy than cool
objects.
Thermogram—a picture that shows regions of
different temperatures in the body. Temperatures are
calculated by the amount of infrared radiation given
off. Therefore people give off infrared rays.

22. VISIBLE LIGHT
Shorter wavelength and higher frequency than infrared
rays.
Electromagnetic waves we can see.
Longest wavelength= red light
Shortest wavelength= violet (purple) light
When light enters a new medium it bends (refracts). Each
wavelength bends a different amount allowing white light
to separate into it’s various colors ROYGBIV.

24. ULTRAVIOLET RAYS
Shorter wavelength and higher frequency than visible
light
Carry more energy than visible light
Used to kill bacteria. (Sterilization of equipment)
Causes your skin to produce vitamin D (good for teeth
and bones)
Used to treat jaundice ( in some new born babies.
Too much can cause skin cancer.
Use sun block to protect against (UV rays)

25. X- RAYS
Shorter wavelength and higher frequency than UV-rays
Carry a great amount of energy
Can penetrate most matter.
Bones and teeth absorb x-rays. (The light part of an x-
ray image indicates a place where the x-ray was absorbed)
Too much exposure can cause cancer
 (lead vest at dentist protects organs from unnecessary exposure)
Used by engineers to check for tiny cracks in structures.
 The rays pass through the cracks and the cracks appear dark on
film.

27. GAMMA RAYS
Shorter wavelength and higher frequency than X-rays
Carry the greatest amount of energy and penetrate the
most.
Used in radiation treatment to kill cancer cells.
Can be very harmful if not used correctly.

28. Brief SUMMARY
A. All electromagnetic waves travel at the same
speed. (300,000,000 meters/second in a vacuum.
B. They all have different wavelength and different
frequencies.
Long wavelength-lowest frequency
Short wavelength highest frequency
The higher the frequency the higher the energy.

30. Power in a wave
A wave carries power and transmits it
wherever it goes
The power density per
area carried by a wave
is given by the Pointing
vector.