Electromagnetic Waves

Electromagnetic Wave is the oscillation which has moving field of electric and magnetic forces, which propagate with the velocity of light in free space. This waves are transverse in nature i.e., oscillations are perpendicular to the direction of propagation of wave.

Electromagnetic Spectrum

The electromagnetic spectrum from VLF to UHF range gives rise to the following waves.

i) Sonar waves
ii) Radio Waves
iii) Infrared waves

Major propagation from VLF to UHF include the following :

i) Ground wave or surface wave propagation.
ii) Sky wave propagation or ionospheric propagation.
iii) Space wave or tropospheric wave propagation.

When electrons move, they create electromagnetic waves that can propagate through free space even in a vacuum. By attaching an antenna of the appropriate size to an electrical circuit, the electromagnetic waves can be broadcast efficiently and received by a receiver some distance away. All wireless communication is based on this principle. The electromagnetic spectrum is shown in the following figure. The radio, microwave, infrared and visible light portion of the spectrum can all be used for transmitting information by modulating the amplitude, frequency, or phase of the wave. Ultraviolet light, X- Ray and gamma rays would be even better, due to their higher frequencies but they are hard to produced and modulate, do not propagate well through buildings and are dangerous to living things. The bands listed below at the bottom of electromagnetic spectrum are the official ITU names and based on the ware lengths. So the LF band goes from 1km to 10 km (approximately 30 KHz to 300 KHz). The terms LF, MF and HF refer to low, medium and high frequency respectively. The amount of information that an electromagnetic wave can carry is related to its bandwidth.

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