The atrium magnetron is a activating exhaustion tube that generates microwaves application the alternation of a beck of electrons with a alluring field. The 'resonant' atrium magnetron alternative of the beforehand magnetron tube was invented by John Randall and Harry Boot in 1940 at the University of Birmingham, England.1 The top ability of pulses from the atrium magnetron fabricated centimeter-band alarm practical, with beneath amicableness radars acceptance apprehension of abate objects. The bunched atrium magnetron tube acutely bargain the admeasurement of alarm sets2 so that they could be installed in anti-submarine aircraft3 and escort ships.2 At present, atrium magnetrons are frequently acclimated in bake ovens and in assorted alarm applications.4
Thursday, February 16, 2012
Construction and operation
All atrium magnetrons abide of a hot cathode with a top (continuous or pulsed) abrogating abeyant by a high-voltage, direct-current ability supply. The cathode is congenital into the centermost of an evacuated, lobed, annular chamber. A alluring acreage alongside to the fiber is imposed by a abiding magnet. The alluring acreage causes the electrons, admiring to the (relatively) absolute alien allotment of the chamber, to circling apparent in a annular aisle rather than affective anon to this anode. Spaced about the rim of the alcove are annular cavities. The cavities are accessible forth their breadth and affix the accepted atrium space. These cavities act just like actual awful able acquainted circuits. As electrons ambit accomplished these openings, they abet a resonant, high-frequency radio acreage in the cavity, which in about-face causes the electrons to agglomeration into groups. The assumption is actual agnate to alarming a beck of air beyond the accessible top of a canteen pop bottle. The cavities resonate, and afford a able radio-frequency activity output. A allocation of this acreage is extracted with a abbreviate antenna that is affiliated to a waveguide (a metal tube usually of ellipsoidal cantankerous section). The waveguide directs the extracted RF activity to the load, which may be a affable alcove in a bake oven or a high-gain antenna in the case of radar.
A cross-sectional diagram of a beating atrium magnetron. Alluring curve of force are alongside to the geometric arbor of this structure.
The sizes of the cavities actuate the beating frequency, and thereby the abundance of emitted microwaves. However, the abundance is not absolutely controllable. The operating abundance varies with changes in amount impedance, with changes in the accumulation current, and with the temperature of the tube.5 This is not a botheration in uses such as heating, or in some forms of alarm area the receiver can be synchronized with an estimated magnetron frequency. Area absolute frequencies are needed, added accessories such as the klystron are used.
The magnetron is a self-oscillating accessory acute no alien elements added than a ability supply. A categorical beginning anode voltage have to be activated afore cadence will body up; this voltage is a action of the ambit of the beating cavity, and the activated alluring field. In pulsed applications there is a adjournment of several cycles afore the oscillator achieves abounding aiguille power, and the accession of anode voltage have to be accommodating with the accession of oscillator output.5
The magnetron is a adequately able device. In a bake oven, for instance, a 1.1 kilowatt ascribe will about actualize about 700 watt of bake power, an ability of about 65%. (The high-voltage and the backdrop of the cathode actuate the ability of a magnetron.) Large S-band magnetrons can aftermath up to 2.5 megawatts aiguille ability with an boilerplate ability of 3.75 kW.5 Large magnetrons can be baptize cooled. The magnetron charcoal in boundless use in roles which crave top power, but area absolute abundance ascendancy is unimportant.
A cross-sectional diagram of a beating atrium magnetron. Alluring curve of force are alongside to the geometric arbor of this structure.
The sizes of the cavities actuate the beating frequency, and thereby the abundance of emitted microwaves. However, the abundance is not absolutely controllable. The operating abundance varies with changes in amount impedance, with changes in the accumulation current, and with the temperature of the tube.5 This is not a botheration in uses such as heating, or in some forms of alarm area the receiver can be synchronized with an estimated magnetron frequency. Area absolute frequencies are needed, added accessories such as the klystron are used.
The magnetron is a self-oscillating accessory acute no alien elements added than a ability supply. A categorical beginning anode voltage have to be activated afore cadence will body up; this voltage is a action of the ambit of the beating cavity, and the activated alluring field. In pulsed applications there is a adjournment of several cycles afore the oscillator achieves abounding aiguille power, and the accession of anode voltage have to be accommodating with the accession of oscillator output.5
The magnetron is a adequately able device. In a bake oven, for instance, a 1.1 kilowatt ascribe will about actualize about 700 watt of bake power, an ability of about 65%. (The high-voltage and the backdrop of the cathode actuate the ability of a magnetron.) Large S-band magnetrons can aftermath up to 2.5 megawatts aiguille ability with an boilerplate ability of 3.75 kW.5 Large magnetrons can be baptize cooled. The magnetron charcoal in boundless use in roles which crave top power, but area absolute abundance ascendancy is unimportant.
Applications
In alarm devices, the waveguide is affiliated to an antenna. The magnetron is operated with actual abbreviate pulses of activated voltage, consistent in a abbreviate beating of top ability bake activity getting radiated. As in all alarm systems, the radiation reflected off a ambition is analyzed to aftermath a alarm map on a screen.
Several characteristics of the magnetron's ability achievement cabal to accomplish alarm use of the accessory somewhat problematic. The aboriginal of these factors is the magnetron's inherent alternation in its transmitter frequency. This alternation is acclaimed not alone as a abundance about-face from one beating to the next, but aswell a abundance about-face aural an alone transmitted pulse. The additional agency is that the activity of the transmitted beating is advance over a advanced abundance spectrum, which makes all-important its receiver to accept a agnate advanced selectivity. This advanced selectivity permits ambient electrical babble to be accustomed into the receiver, appropriately abashing somewhat the accustomed alarm echoes, thereby abbreviation all-embracing alarm performance. The third factor, depending on application, is the radiation hazard acquired by the use of top ability electromagnetic radiation. In some applications, for archetype a abyssal alarm army on a recreational vessel, a alarm with a magnetron achievement of 2 to 4 application is generally begin army actual abreast an breadth active by aggregation or passengers. In applied use, these factors accept been overcome, or alone accepted, and there are today bags of magnetron aerodynamics and abyssal alarm units in service. Recent advances in aerodynamics acclimate abstention alarm and in abyssal alarm accept auspiciously implemented semiconductor transmitters that annihilate the magnetron entirely.
edit Heating
In bake ovens, the waveguide leads to a radio frequency-transparent anchorage into the affable chamber.
edit Lighting
In microwave-excited lighting systems, such as a sulfur lamp, a magnetron provides the bake acreage that is anesthetized through a waveguide to the lighting atrium absolute the light-emitting actuality (e.g., sulfur, metal halides, etc.)
Several characteristics of the magnetron's ability achievement cabal to accomplish alarm use of the accessory somewhat problematic. The aboriginal of these factors is the magnetron's inherent alternation in its transmitter frequency. This alternation is acclaimed not alone as a abundance about-face from one beating to the next, but aswell a abundance about-face aural an alone transmitted pulse. The additional agency is that the activity of the transmitted beating is advance over a advanced abundance spectrum, which makes all-important its receiver to accept a agnate advanced selectivity. This advanced selectivity permits ambient electrical babble to be accustomed into the receiver, appropriately abashing somewhat the accustomed alarm echoes, thereby abbreviation all-embracing alarm performance. The third factor, depending on application, is the radiation hazard acquired by the use of top ability electromagnetic radiation. In some applications, for archetype a abyssal alarm army on a recreational vessel, a alarm with a magnetron achievement of 2 to 4 application is generally begin army actual abreast an breadth active by aggregation or passengers. In applied use, these factors accept been overcome, or alone accepted, and there are today bags of magnetron aerodynamics and abyssal alarm units in service. Recent advances in aerodynamics acclimate abstention alarm and in abyssal alarm accept auspiciously implemented semiconductor transmitters that annihilate the magnetron entirely.
edit Heating
In bake ovens, the waveguide leads to a radio frequency-transparent anchorage into the affable chamber.
edit Lighting
In microwave-excited lighting systems, such as a sulfur lamp, a magnetron provides the bake acreage that is anesthetized through a waveguide to the lighting atrium absolute the light-emitting actuality (e.g., sulfur, metal halides, etc.)
History
The aboriginal simple, two-pole magnetron was developed in 1920 by Albert Hull6 at General Electric's Research Laboratories (Schenectady, New York), as an bulge of his plan on the alluring ascendancy of exhaustion tubes in an attack to plan about the patents captivated by Lee De Forest on electrostatic control.
Hull's magnetron was not originally advised to accomplish VHF (very-high-frequency) electromagnetic waves. However, in 1924, Czech physicist August Žáček7 (1886–1961) and German physicist Erich Habann8 (1892–1968) apart apparent that the magnetron could accomplish after-effects of 100 megahertz to 1 gigahertz. Žáček, a assistant at Prague's Charles University, appear first; however, he appear in a account with a baby apportionment and appropriately admiring little attention.9 Habann, a apprentice at the University of Jena, advised the magnetron for his doctoral argument of 1924.10 Throughout the 1920s, Hull and added advisers about the apple formed to advance the magnetron.111213 Most of these aboriginal magnetrons were bottle exhaustion tubes with assorted anodes. However, the two-pole magnetron, aswell accepted as a split-anode magnetron, had almost low efficiency. The atrium adaptation (properly referred to as a resonant-cavity magnetron) accepted to be far added useful. An aboriginal multi-cavity adaptation of the magnetron was appear by Bucharest University Assistant Theodor V. Ionescu. and followed in 1937-1940 by a agnate multi-cavity magnetron congenital by the British physicist, Sir John Turton Randall, FRSE calm with a aggregation of British coworkers for the British and American, aggressive alarm installations in WWII.14
While alarm was getting developed during Apple War II, there arose an burning charge for a high-power bake architect that formed at beneath wavelengths (around 10 cm (3 GHz)) rather than the 150 cm (200 MHz) that was accessible from tube-based generators of the time. It was accepted that a multi-cavity beating magnetron had been developed and patented in 1935 by Hans Hollmann in Berlin,15 and independently, in 1935, by physicist Theodor V. Ionescu in Romania. However, the German aggressive advised the abundance alluvion of Hollman's accessory to be undesirable, and based their alarm systems on the klystron instead. But klystrons could not at that time accomplish the top ability achievement that magnetrons eventually reached. This was one acumen that German night fighter radars were not a bout for their British counterparts.16
Hull's magnetron was not originally advised to accomplish VHF (very-high-frequency) electromagnetic waves. However, in 1924, Czech physicist August Žáček7 (1886–1961) and German physicist Erich Habann8 (1892–1968) apart apparent that the magnetron could accomplish after-effects of 100 megahertz to 1 gigahertz. Žáček, a assistant at Prague's Charles University, appear first; however, he appear in a account with a baby apportionment and appropriately admiring little attention.9 Habann, a apprentice at the University of Jena, advised the magnetron for his doctoral argument of 1924.10 Throughout the 1920s, Hull and added advisers about the apple formed to advance the magnetron.111213 Most of these aboriginal magnetrons were bottle exhaustion tubes with assorted anodes. However, the two-pole magnetron, aswell accepted as a split-anode magnetron, had almost low efficiency. The atrium adaptation (properly referred to as a resonant-cavity magnetron) accepted to be far added useful. An aboriginal multi-cavity adaptation of the magnetron was appear by Bucharest University Assistant Theodor V. Ionescu. and followed in 1937-1940 by a agnate multi-cavity magnetron congenital by the British physicist, Sir John Turton Randall, FRSE calm with a aggregation of British coworkers for the British and American, aggressive alarm installations in WWII.14
While alarm was getting developed during Apple War II, there arose an burning charge for a high-power bake architect that formed at beneath wavelengths (around 10 cm (3 GHz)) rather than the 150 cm (200 MHz) that was accessible from tube-based generators of the time. It was accepted that a multi-cavity beating magnetron had been developed and patented in 1935 by Hans Hollmann in Berlin,15 and independently, in 1935, by physicist Theodor V. Ionescu in Romania. However, the German aggressive advised the abundance alluvion of Hollman's accessory to be undesirable, and based their alarm systems on the klystron instead. But klystrons could not at that time accomplish the top ability achievement that magnetrons eventually reached. This was one acumen that German night fighter radars were not a bout for their British counterparts.16
klystron
In 1940, at the University of Birmingham in the United Kingdom, John Randall and Harry Boot produced a alive ancestor agnate to Hollman's atrium magnetron, but added aqueous cooling and a stronger cavity. Randall and Boot anon managed to access its ability achievement 100 fold. Instead of abandoning the magnetron due to its abundance instability, they sampled the achievement arresting and synchronized their receiver to whatever abundance was in fact getting generated. In 1941, the botheration of abundance alternation was apparent by coupling alternating cavities aural the magnetron.
Because France had just collapsed to the Nazis and Britain had no money to advance the magnetron on a massive scale, Churchill agreed that Sir Henry Tizard should action the magnetron to the Americans in barter for their banking and automated advice (the Tizard Mission). An aboriginal 6 kW version, congenital in England by the General Electric Aggregation Research Laboratories, Wembley, London (not to be abashed with the analogously called American aggregation General Electric), was accustomed to the US government in September 1940. At the time the a lot of able agnate bake ambassador accessible in the US (a klystron) had a ability of alone ten watts. The atrium magnetron was broadly acclimated during World War II in bake alarm accessories and is about accustomed with giving Allied alarm a ample achievement advantage over German and Japanese radars, appropriately anon influencing the aftereffect of the war. It was after declared by America as "the a lot of admired burden anytime brought to our shores".17
The Bell Telephone Laboratories fabricated a producible adaptation from the magnetron delivered to America by the Tizard Mission, and afore the end of 1940, the Radiation Laboratory had been set up on the campus of the Massachusetts Institute of Technology to advance assorted types of alarm application the magnetron. By aboriginal 1941, carriageable centimetric aerial radars were getting activated in American and British planes.18 In backward 1941, the Telecommunications Research Establishment in Great Britain acclimated the magnetron to advance a advocate airborne, ground-mapping alarm codenamed H2S. The H2S alarm was in allotment developed by Alan Blumlein and Bernard Lovell.
Centimetric radar, fabricated accessible by the atrium magnetron, accustomed for the apprehension of abundant abate altar and the use of abundant abate antennas. The aggregate of small-cavity magnetrons, baby antennas, and top resolution accustomed small, top superior radars to be installed in aircraft. They could be acclimated by amphibian convoying aircraft to ascertain altar as baby as a abysmal periscope, which accustomed aircraft to advance and abort abysmal submarines which had ahead been ephemeral from the air. Centimetric curve mapping radars like H2S bigger the accurateness of Allied bombers acclimated in the cardinal bombing campaign. Centimetric gun-laying radars were additionally far added authentic than the earlier technology. They fabricated the big-gunned Allied battleships added baleful and, forth with the anew developed adjacency fuze, fabricated anti-aircraft accoutrements abundant added alarming to advancing aircraft. The two accompanying calm and acclimated by anti-aircraft batteries, placed forth the flight aisle of German V-1 aerial bombs on their way to London, are accustomed with antibacterial abounding of the aerial bombs afore they accomplished their target.
Since then, abounding millions of atrium magnetrons accept been manufactured; while some accept been for alarm the all-inclusive majority accept been for bake ovens. The use in alarm itself has dwindled to some extent, as added authentic signals accept about been bare and developers accept confused to klystron and traveling-wave tube systems for these needs.
Because France had just collapsed to the Nazis and Britain had no money to advance the magnetron on a massive scale, Churchill agreed that Sir Henry Tizard should action the magnetron to the Americans in barter for their banking and automated advice (the Tizard Mission). An aboriginal 6 kW version, congenital in England by the General Electric Aggregation Research Laboratories, Wembley, London (not to be abashed with the analogously called American aggregation General Electric), was accustomed to the US government in September 1940. At the time the a lot of able agnate bake ambassador accessible in the US (a klystron) had a ability of alone ten watts. The atrium magnetron was broadly acclimated during World War II in bake alarm accessories and is about accustomed with giving Allied alarm a ample achievement advantage over German and Japanese radars, appropriately anon influencing the aftereffect of the war. It was after declared by America as "the a lot of admired burden anytime brought to our shores".17
The Bell Telephone Laboratories fabricated a producible adaptation from the magnetron delivered to America by the Tizard Mission, and afore the end of 1940, the Radiation Laboratory had been set up on the campus of the Massachusetts Institute of Technology to advance assorted types of alarm application the magnetron. By aboriginal 1941, carriageable centimetric aerial radars were getting activated in American and British planes.18 In backward 1941, the Telecommunications Research Establishment in Great Britain acclimated the magnetron to advance a advocate airborne, ground-mapping alarm codenamed H2S. The H2S alarm was in allotment developed by Alan Blumlein and Bernard Lovell.
Centimetric radar, fabricated accessible by the atrium magnetron, accustomed for the apprehension of abundant abate altar and the use of abundant abate antennas. The aggregate of small-cavity magnetrons, baby antennas, and top resolution accustomed small, top superior radars to be installed in aircraft. They could be acclimated by amphibian convoying aircraft to ascertain altar as baby as a abysmal periscope, which accustomed aircraft to advance and abort abysmal submarines which had ahead been ephemeral from the air. Centimetric curve mapping radars like H2S bigger the accurateness of Allied bombers acclimated in the cardinal bombing campaign. Centimetric gun-laying radars were additionally far added authentic than the earlier technology. They fabricated the big-gunned Allied battleships added baleful and, forth with the anew developed adjacency fuze, fabricated anti-aircraft accoutrements abundant added alarming to advancing aircraft. The two accompanying calm and acclimated by anti-aircraft batteries, placed forth the flight aisle of German V-1 aerial bombs on their way to London, are accustomed with antibacterial abounding of the aerial bombs afore they accomplished their target.
Since then, abounding millions of atrium magnetrons accept been manufactured; while some accept been for alarm the all-inclusive majority accept been for bake ovens. The use in alarm itself has dwindled to some extent, as added authentic signals accept about been bare and developers accept confused to klystron and traveling-wave tube systems for these needs.
Health hazards
Among added abstract hazards, at atomic one in accurate is able-bodied accepted and documented. As the lens of the eye has no cooling claret flow, it is decidedly decumbent to overheating if apparent to bake radiation. This heating can in about-face advance to a college accident of amaurosis in after life.19 A bake oven with a angled aperture or poor bake sealing can be hazardous.
There is aswell a ample electrical hazard about magnetrons, as they crave a top voltage ability supply.
Some magnetrons accept beryllium oxide (beryllia) bowl insulators, which are alarming if ashamed and inhaled, or contrarily ingested. Single or abiding acknowledgment can advance to berylliosis, an cureless lung condition. In addition, beryllia is listed as a accepted animal carcinogen by the IARC; therefore, torn bowl insulators or magnetrons should not be anon handled.
There is aswell a ample electrical hazard about magnetrons, as they crave a top voltage ability supply.
Some magnetrons accept beryllium oxide (beryllia) bowl insulators, which are alarming if ashamed and inhaled, or contrarily ingested. Single or abiding acknowledgment can advance to berylliosis, an cureless lung condition. In addition, beryllia is listed as a accepted animal carcinogen by the IARC; therefore, torn bowl insulators or magnetrons should not be anon handled.
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