66165646 Cavity Magnetron

7/28/2019 66165646 Cavity Magnetron

1/19

- Kim Couthinho

-Theon Couthinho- Neil Crasto- Frigen Dabre- Zelem Dabre


2/19

A magnetron is a high-poweredvacuum tube that generates nonconsistent microwaves with built-inresonators or by special oscillators orsolid-state devices to control thefrequency.

The electromagnetic energy createdfrom a magnetron can travel at thespeed of light and is the same type ofenergy used in radio and televisionbroadcasting.


3/19

CONSTRUCTION

ADVANTAGES &

DISADVANTAGES


4/19

CONSTRUCTION & OPERATIONCONSTRUCTION & OPERATION


5/19

e-

B

Fm

e-

B

Effect of electric fieldEffect of electric field Effect of magneticEffect of ma

gnetic

fieldfield

E

e-

Effect of Crossed-FieldsEffect of Crossed-Fields


6/19

As shown in the figure, a cavity magnetronsAs shown in the figure, a cavity magnetrons

consist of a hot filament (consist of a hot filament (cathodecathode) kept at, or) kept at, orpulsed to, a high negative potential by a high-pulsed to, a high negative potential by a high-voltage, direct-current power supply. Thevoltage, direct-current power supply. The

cathode is built into the center of an evacuated,cathode is built into the center of an evacuated,lobed, circular chamber.lobed, circular chamber.A magnetic field parallel to the filament isA magnetic field parallel to the filament is

imposed by a electro-magnet. The magneticimposed by a electro-magnet. The magneticfield causes the electrons, attracted to thefield causes the electrons, attracted to the(relatively) positive outer part of the chamber,(relatively) positive outer part of the chamber,to spiral outward in a circular path rather thanto spiral outward in a circular path rather than

moving directly to thismoving directly to this anodeanode..


7/197

E

B


8/19

Spaced around the rim of the chamber areSpaced around the rim of the chamber are

cylindrical cavities. The cavities are opencylindrical cavities. The cavities are open

along their length and connect thealong their length and connect thecommon cavity space. As electrons sweepcommon cavity space. As electrons sweep

past these openings, they induce apast these openings, they induce a

resonant, high-frequency radio field in theresonant, high-frequency radio field in the

cavity, which in turn causes the electronscavity, which in turn causes the electrons

to bunch into groups.to bunch into groups.

A portion of this field is extracted with aA portion of this field is extracted with a

short antenna that is connected to ashort antenna that is connected to awaveguidewaveguide (a metal tube usually of(a metal tube usually of

rectangular cross section). The waveguiderectangular cross section). The waveguide

directs the extracted RF energy to thedirects the extracted RF energy to the

load, which may be a cooking chamber inload, which may be a cooking chamber in


9/19


10/19

APPLICATIONSAPPLICATIONS

RADAR In radar devices thewaveguide is connected toan antenna. Themagnetron is operatedwith very short pulses ofapplied voltage, resultingin a short pulse of high

power microwave energybeing radiated. As in allradar systems, theradiation reflected off a

target is analyzed to
http://en.wikipedia.org/wiki/Radarhttp://en.wikipedia.org/wiki/Antenna_(electronics)http://en.wikipedia.org/wiki/Antenna_(electronics)http://en.wikipedia.org/wiki/Radar


11/19


HEATING

In microwave ovens the

waveguide leads to a radiofrequency-transparent portinto the cooking chamber.It is important that there is

food in the oven when it isoperated so that thesewaves are absorbed,rather than reflecting into

the waveguide where theintensity ofstanding waves can causearcing. The arcing, ifallowed to occur for long
http://en.wikipedia.org/wiki/Microwave_ovenhttp://en.wikipedia.org/wiki/Standing_waveshttp://en.wikipedia.org/wiki/Standing_waveshttp://en.wikipedia.org/wiki/Microwave_oven


12/19


LIGHTING In microwave-excitedlighting systems, suchas Sulphur Lamps, a

magnetron providesthe microwave fieldthat is passed through

a waveguide to thelighting cavitycontaining the light-emitting substance(e.g. Sulfur, metal
http://en.wikipedia.org/wiki/Sulfur_lamphttp://en.wikipedia.org/wiki/Sulfur_lamphttp://en.wikipedia.org/wiki/Sulfur_lamphttp://en.wikipedia.org/wiki/Sulfur_lamp


13/19

HISTORYHISTORY

The oscillation of magnetrons was firstobserved and noted by Augustin ek,professor at the Charles University, Prague inthe Czech Republic.

The first magnetron developed was the two-pole magnetron, also known as a

split-anode magnetron, which hadrelatively low efficiency. The cavityversion (properly referred to as a

resonant-cavity magnetron) proved to


14/19

ADVANTAGESADVANTAGES

The magnetron is a fairly efficient device. In amicrowave oven, for instance, an 1100 wattinput will generally create about 700 watts ofmicrowave energy, an efficiency of around65%.

The combination of the small-cavity

magnetron, small antennas, and high resolutionallowed small, high quality radars to beinstalled in aircraft.


15/19

DISADVANTAGESDISADVANTAGES

hey are costly and hence limited in use.

lthough cavity magnetron are used because theygenerate a wide range of frequencies , thefrequency is not precisely controllable.

he use in radar itself has reduced to some extent,

as more accurate signals have generally been


16/19

HEALTH HAZARDS due to

microwave radiations

As the lens of the eye has no cooling blood

flow, it is particularly prone to overheatingwhen exposed to microwave radiation. Thisheating can in turn lead to a higher incidence of

cataracts in later life.


17/19

A microwave oven with a warped dooror poor microwave sealing can behazardous.

There is also a considerable electricalhazard around magnetrons, as they

require a high voltage power supply.Operating a magnetron with theprotective covers removed and

interlocks bypassed should therefore


18/19

www.answers.com

www.wikipedia.com
http://www.answers.com/http://www.wikipedia.com/http://www.wikipedia.com/http://www.answers.com/


19/19

he sizes of the cavities determine the resonantfrequency, and thereby the frequency of emittedmicrowaves.

he voltage applied and the properties of the

cathode determine the power of the device.

ven though the magnetron is widely used at places

which require high power it is avoided where

66165646 Cavity Magnetron

Documents

Transcript of 66165646 Cavity Magnetron