Electro Magnetic Wave Propagation
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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.
Electro Magnetic Wave Propagation
- 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
- 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.
Editor's Notes
- #31: Dr. S. Cruz-Pol, INEL 4152-Electromagnetics Electrical Engineering, UPRM