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EM THEORY

EM THEORY. Amrutha Harichandran Assistant Professor ECE Dept., ASE. Area of interest EM Theory and related subject Difficulties. WAVES:. Transfer energy from one place to another. Eg: Water and sound waves. Speed of electromagnetic waves = 300,000,000 m/s

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EM THEORY

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

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

  3. WAVES: • Transfer energy from one place to another 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. 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. • 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.

  10. 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.

  11. 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)

  12. X- RAYS • Shorter wavelength and higher frequency than UV-rays • Carry a great amount of energy • Can penetrate most matter. • Bones and teethabsorb 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.

  13. 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.

  14. Using the EM waves to view the Sun • At different wavelengths

  15. 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.

  16. 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

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

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

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

  20. Transmission Lines • Carry EM energy • Eg: Coaxial cable • Low frequency and high frequency

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

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

  23. Q.1 • A plane wave propagating in a lossless dielectric medium has n electric field given as E= 10 cos(1.5x 1010 t- 61.6 z). Determine the wavelength , phase velocity and wave impedance for this wave and the dielectric constant of the medium.

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

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

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

  27. 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 = 307.8 Ω

  28. 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?

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

  30. 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.

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

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

  33. 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

  34. 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)

  35. 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

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