This presentation is about Propagation of Electromagnetic Waves and covers the following topics:
-Introduction to EM Waves
-Electromagnetic Wave Spectrum
-Wave Propagation in Lossy Dielectrics
-Plane Waves in Free Space
-Properties of EM Waves
This presentation is as per the course of DAE Electronics ELECT-212.
2. Contents
Introduction to EM Waves.
Electromagnetic Spectrum
Wave Propagation in Lossy Dielectrics
Plane Waves in Free Space
Plane Waves in Good Conductors
3. Introduction to EM-Waves
Electromagnetic Waves, also abbreviated as EM-Waves, are the waves
which consist of both Electric and Magnetic Fields and travel at a speed
same as that of light, i.e. 3x108 m/sec
All forms of electromagnetic radiation consist of perpendicular oscillating
electric and magnetic fields.
4. Properties of EM-Waves
Invisible
Travel at speed of light
Consist of Electric and Magnetic fields
Electric Field, Magnetic Field and Direction of Propagation of an EM wave
are all perpendicular to each other
Their Electric and Magnetic fields cannot be separated from each other
The total energy of an EM wave is equally divided between Electric and
Magnetic fields
When they pass through a metallic conductor they produce voltage across
the conductor
5. Properties of EM-Waves
They don’t need any medium to travel
Their intensity is same all around in free space
When they travel from one place to another their power (intensity) is
reduced, i.e. they suffer from attenuation
When they enter from one medium to another:
Their form of energy changes, i.e. they suffer from Absorption
They are diverted from their path, this process is called refraction
When they pass through a hole they bent along sides when leaving the
hole, this process is called Deflection
7. Electromagnetic Spectrum
EM Spectrum is the range of wavelengths or frequencies over which
electromagnetic radiation extends.
It consists of different frequency bands which are basically groups of
certain frequency ranges.
9. Waves
Longitudinal Waves Transverse Waves
Electromagnetic Waves
Electromagnetic Spectrum
Radiowave
Microwave
Infra-Red
Light
Ultra-Violet
X-ray
Gamma ray
Applications
Sound waves
Classified into
Comprises of
10. Some tips to help you to remember:
EM Spectrum
Raja’s Mother Is Visiting Uncle Xavier’s Garden
Visible Light Spectrum
Run Off You Girls Boys In View
Radio
wave
Micro
wave
Infra-red
Rays
Visible
light
Ultra-violet
ray
X-rays Gamma
rays
red orange yellow green blue indigo violet
11. Wave Propagation in Lossy Dielectrics
A Lossy Dielectric is basically a medium which reduce the power of EM
waves, due to its “Poor Condition”, when they travel through it.
In other words, a Lossy Dielectric is a practical conducting medium that is
neither a good conductor nor a good insulator.
The following terms are used to describe the losses in a propagating wave:
Attenuation Coefficient 𝛼
Phase Coefficient 𝛽
12. Attenuation Coefficient is measured in Neper Per Meter (Np/m) or Decibel
Per Meter (dB/m)
1Np = 20log(e) = 8.686 dB
Formulas for Velocity and Wavelength of a wave are:
Wave Propagation in Lossy Dielectrics
Formulas for Attenuation and Phase coefficients are:
𝜎 = sigma = Conductivity
𝜇 = mu = Permeability
𝜔 = omega = Angular velocity
ε = epsilon = Permittivity
13. Plane Waves in Free Space
This is a special case for which:
Permeability 𝜇 = 𝜇𝑜 (Permeability of free space) = µ0 = 4π × 10−7 H
Conductivity 𝜎 = 0
Permittivity ε = εo (Permittivity of free space) = 8.85 x 10-12 F/m
Editor's Notes
The permeability constant (µ0), also known as the magnetic constant or the permeability of free space, is a measure of the amount of resistance encountered when forming a magnetic field in a classical vacuum. The magnetic constant has the exact (defined) value (µ0 = 4π × 10−7 H.
Permittivity: the ability of a substance to store electrical energy in an electric field.
Skin depth is a measure of how far electrical conduction takes place in a conductor, and is a function of frequency. At DC (0 Hz) the entire conductor is used, no matter how thick it is. The skin depth is a measure of the penetration of a plane electromagnetic wave into a material.