E N C Y C L O P E D I A

Microwave

Microwaves are electromagnetic waves with a wavelength longer than infrared light, but shorter than radio waves.

Microwaves, also known as Super High Frequency (SHF) signals, have wavelengths approximately in the range of 30 cm (1 GHz) to 1 mm (300 GHz). However, the boundaries between far infrared light, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used variously between different fields of study. Microwaves were discovered by James Clerk Maxwell in 1864.

Note: above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that the atmosphere is effectively opaque to higher frequencies of electromagnetic radiation, until the atmosphere becomes transparent again in the so-called infrared and optical window frequency ranges.

Uses

A microwave oven uses a magnetron microwave generator to produce microwaves at a frequency of approximately 2.4 GHz for the purpose of cooking food. Microwaves cook food by causing water molecules to vibrate - heating them, and the rest of the food, up. Since organic life is made up primarily of water, food is easily cooked by this method.

A maser is a device similar to a laser, except that it works at microwave frequencies. Microwaves are also used in satellite transmissions because this frequency passes easily through the earth's atmosphere with less interference than higher wavelengths.

Radar also uses microwave radiation.

Wireless LAN communication protocols such as IEEE 802.11 and bluetooth also use microwaves in the 2.4 GHz ISM band.

Cable TV and Internet access on coax cable.

Research into power transmission via microwaves occurred during the late 70's and early 80's - during the Kuwait oil crisis - by NASA, called Microwave Power Transmission (mpt), or Solar Power Satellite (SPS).

The microwave spectrum is defined as electromagnetic energy ranging from approximately 300 MHz to 1000 GHz in frequency. Most common applications are within the 1 to 40 GHz range.

Microwave Frequency Bands are defined below:

Letter Designation Frequency Range

L Band 1 to 2 GHz S Band 2 to 4 GHz C Band 4 to 8 GHz X Band 8 to 12 GHz K_u 12 to 18 GHz K Band 18 to 26 GHz K_a 26 to 40 GHz Q Band 30 to 50 GHz U Band 40 to 60 GHz V Band 46 to 56 GHz W Band 56 to 100 GHz

For some of the history in the development of electromagnetic theory applicable to modern microwave applications see the following figures: Michael Faraday, James Clerk Maxwell, Heinrich Hertz, Guglielmo Marconi, Samuel Morse, Sir William Thomson later Lord Kelvin, Oliver Heaviside, Lord Rayleigh, Oliver Lodge.

Microwave specific work:

Barkhausen and Kurz - Positive grid oscillators
Hull - Smooth bore magnetron
Varian Brothers - Velocity modulated electron beam --> klystron tube
Randall and Boot - Cavity magnetron