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fr:Micro-onde ja:マイクロ波 zh:微波
This page is about the radiation; for the appliance, see microwave oven.
Microwave image of 3C353 galaxy at 8.4 GHz (3.6 cm). The overall linear size of the radio structure is 120
Kpc.
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. The existence of electromagnetic waves, of which microwaves are part of the higher frequency spectrum, was predicted by James Clerk Maxwell in 1864 from his famous Maxwell's equations. In 1888, Heinrich Hertz was the first to demonstrate the existence of electromagnetic waves by building apparatus to produce radio waves.
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 molecules of water and other compounds to vibrate. The vibration creates heat which warms the food. Since organic matter 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 to detect the range, speed, and other characteristics of remote objects.
Wireless LAN communication protocols such as IEEE 802.11 and bluetooth also use microwaves in the 2.4 GHz ISM band, although some variants use a 5 GHz band for communication.
Cable TV and Internet access on coax cable as well as broadcast television use some of the lower microwave frequencies. Some cellphone networks also uses the lower microwave frequences as well.
Microwaves can be used to transmit power over long distances, and post-World War II research was done to examine possibilities. NASA worked in the 1970s and early 1980s to research the possibilities of using Solar Power Satellite (SPS) systems with large solar arrays that would beam power down to the Earth's surface via microwaves.
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 in the table below:
For some of the history in the development of electromagnetic theory applicable to modern microwave applications see the following figures:
Specific significant areas of research and work developing microwaves and their applications:
Specific work on microwaves
| Work carried out by | Area of work
|
| Barkhausen and Kurz | Positive grid oscillators
|
| Hull | Smooth bore magnetron
|
| Varian Brothers | Velocity modulated electron beam → klystron tube
|
| Randall and Boot | Cavity magnetron
|
The Microwave integrated devices which are called MMIC (Monolithic Microwave Integrated Circuit)are manufactured by using mostly Gallium Arsenide(GaAs)wafers.
See also
External links
- How Microwaves Work (http://www.colorado.edu/physics/2000/microwaves) Article by Professor Lee, Colorado University
- How Microwaves Work (http://www.repairclinic.com/0088_6_3.asp) Article by RepairClinic
- How Microwaves Work (http://www.gallawa.com/microtech/how_work.html) Article by Microtech
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