Difference between revisions of "Microwave" - New World Encyclopedia
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"Microwaves can be used to study the Universe, communicate with satellites in Earth orbit, and cook popcorn." | "Microwaves can be used to study the Universe, communicate with satellites in Earth orbit, and cook popcorn." | ||
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+ | == Historical work == | ||
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+ | [[James Clerk Maxwell]], using his famous "[[Maxwell's equations]]*," predicted the existence of invisible electromagnetic waves, of which microwaves are a part, in 1865. In 1888, [[Heinrich Hertz]] became the first to demonstrate the existence of such waves by building an apparatus that produced and detected microwaves in the [[ultra high frequency]] region. Hertz recognized that the results of his experiment validated Maxwell's prediction, but he did not see any practical applications for these invisible waves. Later work by others led to the invention of wireless communications, based on microwaves. Contributors to this work included [[Nikola Tesla]], [[Guglielmo Marconi]], [[Samuel F. B. Morse|Samuel Morse]], Sir [[William Thomson, 1st Baron Kelvin|William Thomson]] (later Lord Kelvin), [[Oliver Heaviside]]*, [[Lord Rayleigh]]*, and [[Oliver Lodge]]*. | ||
+ | |||
+ | Specific significant areas of research and work developing microwaves and their applications: | ||
+ | |||
+ | {| class="wikitable" | ||
+ | |+Specific work on microwaves | ||
+ | !Work carried out by!!Area of work | ||
+ | |- | ||
+ | |[[Barkhausen]]* and Kurz||Positive grid [[oscillator]]*s | ||
+ | |- | ||
+ | |Hull||Smooth bore [[magnetron]]* | ||
+ | |- | ||
+ | |Varian Brothers||Velocity modulated electron beam → [[klystron]]* tube | ||
+ | |- | ||
+ | |Randall and Boot||Cavity magnetron | ||
+ | |} | ||
+ | |||
+ | Microwave integrated devices called [[Monolithic Microwave Integrated Circuit|MMIC]]* (Monolithic Microwave Integrated Circuit) are manufactured by using mostly [[gallium arsenide]]* (GaAs) wafers. | ||
==Generation== | ==Generation== | ||
− | Microwaves can be generated by | + | Microwaves can be generated by various means, generally placed in two categories: solid state devices and vacuum-tube based devices. Solid state microwave devices are based on semiconductors such as [[silicon]] or [[gallium]] arsenide. They include field-effect transistors (FETs), bipolar junction transistors (BJTs), Gunn diodes, and IMPATT diodes. Specialized versions of standard transistors, developed for higher speed, are commonly used in microwave applications. |
− | Microwave devices based on the [[vacuum tube]]* operate on the ballistic motion of electrons in a vacuum chamber under the influence of electric or magnetic fields. They include the [[magnetron]]*, [[klystron]]*, [[traveling wave tube]]* (TWT), and [[gyrotron]]*. | + | Microwave devices based on the [[vacuum tube]]* operate on the ballistic motion of electrons in a vacuum chamber, under the influence of electric or magnetic fields. They include the [[magnetron]]*, [[klystron]]*, [[traveling wave tube]]* (TWT), and [[gyrotron]]*. |
==Uses== | ==Uses== | ||
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* A [[microwave oven]] uses a magnetron microwave generator to produce microwaves at a frequency of approximately 2.45 GHz for the purpose of cooking food. Microwave ovens cook food by causing [[molecule]]s of [[water]] and other compounds in the food to vibrate or rotate. The vibrations generate heat, which warms the food. Given that food contains moisture, it is easily cooked by this method. | * A [[microwave oven]] uses a magnetron microwave generator to produce microwaves at a frequency of approximately 2.45 GHz for the purpose of cooking food. Microwave ovens cook food by causing [[molecule]]s of [[water]] and other compounds in the food to vibrate or rotate. The vibrations generate heat, which warms the food. Given that food contains moisture, it is easily cooked by this method. | ||
− | * Microwaves pass easily through the [[ | + | * Microwaves pass easily through the [[Earth's atmosphere]] with less interference than longer wavelengths. For this reason, microwaves are used in [[broadcasting]] transmissions. In addition, the microwave spectrum covers much more [[bandwidth]]* than the rest of the radio spectrum. Typically, microwaves are used in [[television]] news coverage, to transmit signals from a remote location to a television station from a specially equipped van. |
− | * [[ | + | * The technology known as [[radar]] also uses microwave radiation to detect the range, speed, and other characteristics of remote objects. |
* Wireless communications between various devices—such as computers, printers, digital cameras, and personal digital assistants (PDAs)—rely on microwaves, often in the 900 megahertz (MHz), 2.4 GHz, or 5.0 GHz bands. This type of short-range network is known as WLAN (Wireless Local Area Network). | * Wireless communications between various devices—such as computers, printers, digital cameras, and personal digital assistants (PDAs)—rely on microwaves, often in the 900 megahertz (MHz), 2.4 GHz, or 5.0 GHz bands. This type of short-range network is known as WLAN (Wireless Local Area Network). | ||
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* Large, wireless computer networks covering a university [[campus]] or [[city]] also communicate by microwave transmissions. The communications protocol (standard for data transfer) is known as a wireless MAN (Metropolitan Area Network) protocol, such as WiMAX (Worldwide Interoperability for Microwave Access). For commercial applications, these microwave communications are in the 2.5 GHz, 3.5 GHz and 5.8 GHz ranges. | * Large, wireless computer networks covering a university [[campus]] or [[city]] also communicate by microwave transmissions. The communications protocol (standard for data transfer) is known as a wireless MAN (Metropolitan Area Network) protocol, such as WiMAX (Worldwide Interoperability for Microwave Access). For commercial applications, these microwave communications are in the 2.5 GHz, 3.5 GHz and 5.8 GHz ranges. | ||
− | * [[Cable | + | * [[Cable television]]* and [[Internet]] access on coax cable as well as [[broadcast television]] use some of the lower microwave frequencies. Several mobile phone networks, such as GSM (Global System for Mobile Communications), also use the lower microwave frequencies. |
* Microwaves are used to generate [[plasma physics|plasma]] for many semiconductor processing techniques, such as [[reactive ion etching]]* and plasma-enhanced [[chemical vapor deposition]]* (PECVD). | * Microwaves are used to generate [[plasma physics|plasma]] for many semiconductor processing techniques, such as [[reactive ion etching]]* and plasma-enhanced [[chemical vapor deposition]]* (PECVD). | ||
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* Microwaves can theoretically be used for wireless power transmission through outer space and the atmosphere. In the 1970s and early 1980s, [[NASA]] worked to research the possibilities of using solar power satellite (SPS) systems with large [[solar array]]*s that would beam power down to the [[Earth]]'s surface via microwaves. | * Microwaves can theoretically be used for wireless power transmission through outer space and the atmosphere. In the 1970s and early 1980s, [[NASA]] worked to research the possibilities of using solar power satellite (SPS) systems with large [[solar array]]*s that would beam power down to the [[Earth]]'s surface via microwaves. | ||
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== Subdivisions of microwave frequencies == | == Subdivisions of microwave frequencies == | ||
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The term "P band" is sometimes used for ultra high frequencies below the L-band. For other definitions, see [http://www.jneuhaus.com/fccindex/letter.html Letter Designations of Microwave Bands] | The term "P band" is sometimes used for ultra high frequencies below the L-band. For other definitions, see [http://www.jneuhaus.com/fccindex/letter.html Letter Designations of Microwave Bands] | ||
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==References== | ==References== |
Revision as of 03:43, 24 July 2006
- This page is about the radiation; for the appliance, see microwave oven.
The term microwaves is used for electromagnetic radiation in the approximate wavelength range of 1 millimeter (mm) (frequency of 300 gigahertz (GHz)) to 1 meter (m) (frequency of 0.3 GHz). They are part of the radio-wave region of the spectrum and lie at the higher frequency end of radio waves. Compared to visible light, microwaves have longer wavelengths and are therefore invisible to the human eye.
- It should, however, be noted that the boundaries between far infrared light, Terahertz radiation, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and used variously between different fields of study.
"Microwaves can be used to study the Universe, communicate with satellites in Earth orbit, and cook popcorn."
Historical work
James Clerk Maxwell, using his famous "Maxwell's equations," predicted the existence of invisible electromagnetic waves, of which microwaves are a part, in 1865. In 1888, Heinrich Hertz became the first to demonstrate the existence of such waves by building an apparatus that produced and detected microwaves in the ultra high frequency region. Hertz recognized that the results of his experiment validated Maxwell's prediction, but he did not see any practical applications for these invisible waves. Later work by others led to the invention of wireless communications, based on microwaves. Contributors to this work included Nikola Tesla, Guglielmo Marconi, Samuel Morse, Sir William Thomson (later Lord Kelvin), Oliver Heaviside, Lord Rayleigh, and Oliver Lodge.
Specific significant areas of research and work developing microwaves and their applications:
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 |
Microwave integrated devices called MMIC (Monolithic Microwave Integrated Circuit) are manufactured by using mostly gallium arsenide (GaAs) wafers.
Generation
Microwaves can be generated by various means, generally placed in two categories: solid state devices and vacuum-tube based devices. Solid state microwave devices are based on semiconductors such as silicon or gallium arsenide. They include field-effect transistors (FETs), bipolar junction transistors (BJTs), Gunn diodes, and IMPATT diodes. Specialized versions of standard transistors, developed for higher speed, are commonly used in microwave applications.
Microwave devices based on the vacuum tube operate on the ballistic motion of electrons in a vacuum chamber, under the influence of electric or magnetic fields. They include the magnetron, klystron, traveling wave tube (TWT), and gyrotron.
Uses
- A microwave oven uses a magnetron microwave generator to produce microwaves at a frequency of approximately 2.45 GHz for the purpose of cooking food. Microwave ovens cook food by causing molecules of water and other compounds in the food to vibrate or rotate. The vibrations generate heat, which warms the food. Given that food contains moisture, it is easily cooked by this method.
- Microwaves pass easily through the Earth's atmosphere with less interference than longer wavelengths. For this reason, microwaves are used in broadcasting transmissions. In addition, the microwave spectrum covers much more bandwidth than the rest of the radio spectrum. Typically, microwaves are used in television news coverage, to transmit signals from a remote location to a television station from a specially equipped van.
- The technology known as radar also uses microwave radiation to detect the range, speed, and other characteristics of remote objects.
- Wireless communications between various devices—such as computers, printers, digital cameras, and personal digital assistants (PDAs)—rely on microwaves, often in the 900 megahertz (MHz), 2.4 GHz, or 5.0 GHz bands. This type of short-range network is known as WLAN (Wireless Local Area Network).
- Large, wireless computer networks covering a university campus or city also communicate by microwave transmissions. The communications protocol (standard for data transfer) is known as a wireless MAN (Metropolitan Area Network) protocol, such as WiMAX (Worldwide Interoperability for Microwave Access). For commercial applications, these microwave communications are in the 2.5 GHz, 3.5 GHz and 5.8 GHz ranges.
- Cable television and Internet access on coax cable as well as broadcast television use some of the lower microwave frequencies. Several mobile phone networks, such as GSM (Global System for Mobile Communications), also use the lower microwave frequencies.
- Microwaves are used to generate plasma for many semiconductor processing techniques, such as reactive ion etching and plasma-enhanced chemical vapor deposition (PECVD).
- A maser is a device in which atoms or molecules are stimulated to amplify and emit a highly focused, coherent beam of microwave radiation. The term maser is an acronym for "microwave amplification by stimulated emission of radiation." Masers are used in atomic clocks and as amplifiers in radio telescopes.
- Microwaves can theoretically be used for wireless power transmission through outer space and the atmosphere. In the 1970s and early 1980s, NASA worked 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.
Subdivisions of microwave frequencies
Microwave signals are often divided into three categories:
- ultra high frequency (UHF) (0.3-3 GHz);
- super high frequency (SHF) (3-30 GHz); and
- extremely high frequency (EHF) (30-300 GHz).
In addition, microwave frequency bands are designated by specific letters. The designations by the Radio Society of Great Britain are given below.
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 |
Ku band | 12 to 18 GHz |
K band | 18 to 26.5 GHz |
Ka band | 26.5 to 40 GHz |
Q band | 30 to 50 GHz |
U band | 40 to 60 GHz |
V band | 50 to 75 GHz |
E band | 60 to 90 GHz |
W band | 75 to 110 GHz |
F band | 90 to 140 GHz |
D band | 110 to 170 GHz |
The term "P band" is sometimes used for ultra high frequencies below the L-band. For other definitions, see Letter Designations of Microwave Bands
ReferencesISBN links support NWE through referral fees
- Pozar, David M. (1993). Microwave Engineering Addison-Wesley Publishing Company. ISBN 0-201-50418-9.
See also
- Cosmic microwave background radiation
- Electron cyclotron resonance
- Home appliances
- Microwave ovens
- Microwave auditory effect
- Radio
- Optics
- Microwave chemistry
- Microwave radio relay
Radio spectrum | ||||||||||
ELF | SLF | ULF | VLF | LF | MF | HF | VHF | UHF | SHF | EHF |
3 Hz | 30 Hz | 300 Hz | 3 kHz | 30 kHz | 300 kHz | 3 MHz | 30 MHz | 300 MHz | 3 GHz | 30 GHz |
30 Hz | 300 Hz | 3 kHz | 30 kHz | 300 kHz | 3 MHz | 30 MHz | 300 MHz | 3 GHz | 30 GHz | 300 GHz |
|
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