1. Amrutha Harichandran Assistant Professor ECE Dept., ASE
EM THEORY
Amrutha Harichandran
Assistant Professor
ECE Dept., ASE

2. EM Theory and related subject
Area of interest
EM Theory and related subject
Difficulties

3. WAVES: Transfer energy from one place to another
Mechanical
Electromagnetic
Require a medium
Not Require a medium
Eg: Water and sound waves
Speed of electromagnetic waves = 300,000,000 m/s
8 minutes to move from the sun to earth {150 million miles}

4. When an electric field changes, so does the magnetic field
When an electric field changes, so does the magnetic field. The changing magnetic field causes the electric field to change. When one field vibrates—so does the other.
electromagnetic wave.

5. Importance of EM Waves
Each wavelength of electro-magnetic radiation (light) brings us unique information
Almost everything we know about the Universe comes from the study of the electromagnetic radiation emitted or reflected by objects in space
Objects in space send out electromagnetic radiation at all wavelengths - from gamma rays to radio waves.

6. Electromagnetic Spectrum
EM waves when placed in order of increasing frequency
Band width and frequency

7. RADIO WAVES Longest wavelengths and lowest frequencies
A radio picks up radio waves through an antenna and converts it to sound waves
Each radio station in an area broadcasts at a different frequency

8. MICROWAVES Used in microwave ovens. Used by cell phones and pagers
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.

9. INFRARED RAYS 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.

11. 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.

14. 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)

15. 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
Used by engineers to check for tiny cracks in structures.

16. 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.

17. Using the EM waves to view the Sun
At different wavelengths

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

21. Electromagnetic Spectrum Quiz
Which of the following is correct in order of lowest to highest frequency?
[A] X-rays, Visible Light, Microwave [B] Ultraviolet, Visible Light, Gamma-rays [C] Microwave, Visible Light, Gamma-rays
Answer: C

22. Gas in space emits radio waves.
[A] True
[B] False
Answer: A

23. This type of emission can come from radioactive materials.
[A] Radio [B] X-rays [C] Gamma-rays
Answer: C

24. Applications of EM Waves
Transmission Lines
High frequency circuits
Satellite Communication
Antenna
Fiber Optic Communication
Mobile Communication
EMI and EMC

25. Transmission Lines Carry EM energy Eg: Coaxial cable
Low frequency and high frequency
LOW Freq
HIGH Freq
. Discrete Components-RLC
.Physical size has no effect
.KVL KCL
.V and I
. Distributed
.Length of the connecting wire
.Maxwell
.Waves

26. High frequency circuits
Discontinuity in ckt path – Radiation
Computer
Satellite Communication
C band (6/4 GHz)
Remote sensing
Antenna
EMI/EMC
Tempest

27. Transmission Media Twisted Pair Coaxial Cable Wave Guide Low Data Rate
Telephone lines-avoid common interference
Coaxial Cable
Few Mbps
LAN
Wave Guide
High frequency
Center conductor loss- Skin effect

31. Q.1
A plane wave propagating in a lossless dielectric medium has n electric field given as E= 10 cos(1.5x 1010 t z). Determine the wavelength , phase velocity and wave impedance for this wave and the dielectric constant of the medium.

32. E=E0 cos(wt-kz)
Angular velocity w=
Wavenumber / Phase constant k=

33. E=E0 cos(wt-kz)
Angular velocity w=1.5x 1010 rad/sec
Wavenumber / Phase constant k= 61.6 m-1

34. Wave length λ = 2π/k
Phase Velocity Vp= w/k
εr = (c/ Vp )2
η= η0 / √εr

35. Wave length λ = 2π/k =0.102 m
Phase Velocity Vp= w/k = 2.45 x 108 m/sec
εr = (c/ Vp )2= 1.5
η= η0 / √εr = Ω

36. Q. 2
A plane wave incident on a medium having εr = 9 and incident power is 45 w/m2.Find reflection coefficient reflected power and power transmitted through the medium?

37. Reflection coefficient, R= (1- √εr )/(1+ √εr )
Reflected Power=lRl2 x Incident Power
Transmitted Power= (1-lRl2 )x Incident Power

38. Q. 3
A radio transmitter is connected to an antenna having an impedance 80+j40 Ω with a 50 Ω coaxial cable. If the 50 Ω transmitter can deliver 30 W when connected to a 50 Ω load, how much power is delivered to the antenna.

39. R= (Zl - Zo)/ (Zl +Zo)
PLoad =PIncident – Preflected
Pload = (1-lRl2 )x PIncident

40. R= (Zl - Zo)/ (Zl +Zo) = 0.367<360
PLoad =PIncident – Preflected
Pload = (1-lRl2 )x PIncident =25.9 W

41. Q. 4
A transmission line has the following per unit length parameters: L=0.2 µ H/m, C= 300 pF/m, R= 5 Ω/m and G=0.01 S/m. Calculate the propagation constant and characteristic impedance of this line at 500 MHz. Recalculate these quantities in the absence of loss

42. r = √((R+jwL)(G+jwC)) = α + j β Zo = √((R+jwL)/(G+jwC))
Propagation Constant
r = √((R+jwL)(G+jwC)) = α + j β
Zo = √((R+jwL)/(G+jwC))
Absence of loss (R=G=0)
α=0
r =w √(LC)
Zo = √(L/C)

43. r = √((R+jwL)(G+jwC)) = α + j β =0.23+j24.3 rad/m
Propagation Constant
r = √((R+jwL)(G+jwC)) = α + j β =0.23+j24.3 rad/m
Zo = √((R+jwL)/(G+jwC)) = 25.8+j 0.03 Ω
Absence of loss (R=G=0)
α=0
r =w √(LC)=24.3 rad/m
Zo = √(L/C)=25.8 Ω