magnetrons definition of magnetrons in the Free Online Encyclopedia.

magnetron (măg`nĭtrŏn'), vacuum tube oscillator (see electron tube electron tube, device consisting of a sealed enclosure in which electrons flow between electrodes separated either by a vacuum (in a vacuum tube) or by an ionized gas at low pressure (in a gas tube).
..... Click the link for more information. ) that generates high-power electromagnetic signals in the microwave microwave, electromagnetic wave having a frequency range from 1,000 megahertz (MHz) to 300,000 MHz, corresponding to a wavelength range from 300 mm (about 12 in.) to 1 mm (about 0.04 in.). Like light waves, microwaves travel essentially in straight lines.
..... Click the link for more information. frequency range. Its operation is based on the combined action of a magnetic field applied externally and the electric field between its electrodes. The tube is a diode diode (dī`ōd), two-terminal electronic device that permits current flow predominantly in only one direction.
..... Click the link for more information. having a cathode and an anode and is surrounded by an external magnet. Without this external magnetic field, the tube would work much like a simple diode, with the electrons flowing directly from the cathode to the anode. The magnetic field forces the cathode-emitted electrons to assume a curved path and thus creates a rotating electron cloud about the tube axis. The magnetron is noted for its high efficiency (ability to convert electrical power input to microwave power output). Magnetrons are available for generating microwave energies ranging from a few kilowatts to a few megawatts and are used extensively in radar radar, system or technique for detecting the position, movement, and nature of a remote object by means of radio waves reflected from its surface. Although most radar units use microwave frequencies, the principle of radar is not confined to any particular frequency
..... Click the link for more information. systems and microwave ovens microwave oven, device that uses microwaves to rapidly cook food. The microwaves cause water molecules in the food to vibrate, producing heat, which is distributed through the food by induction. A special electron tube called a magnetron produces the microwaves.
..... Click the link for more information. .

A type of vacuum tube used as the frequency source in microwave ovens, radar systems and other high-power microwave circuits. In radar, magnetrons can be used as the signal source to feed the power stage of the radar transmitter, typically a klystron tube.

A magnetron is a type of diode vacuum tube in which the filament also serves as the cathode. Rather than being used as a diode, the physical structure of the elements causes the magnetron to act as an oscillator in the UHF or microwave frequency ranges. This is accomplished through the placement of permanent magnets within a series of resonating chambers that are tuned to the center frequency of the oscillation. These resonating chambers comprise the anode of the magnetron.

In operation, as the electrons are released from the cathode, they are directed toward the anode. However, since the electrons are influenced by the magnets in the resonant cavities, they flow circularly through the resonant chambers and set up an oscillation based upon their speed through the chambers. One or more chambers contain collecting antennas that let the generated RF signal flow outside the tube. See klystron and diode.

Magnetron

The oldest of a family of crossed-field microwave electron tubes wherein electrons, generated from a heated cathode, move under the combined force of a radial electric field and an axial magnetic field. By its structure a magnetron causes moving electrons to interact synchronously with traveling-wave components of a microwave standing-wave pattern in such a manner that electron potential energy is converted to microwave energy with high efficiency. Magnetrons have been used since the 1940s as pulsed microwave radiation sources for radar tracking. Because of their compactness and the high efficiency with which they can emit short bursts of megawatt peak output power, they have proved excellent for installation in aircraft as well as in ground radar stations. In continuous operation, a magnetron can produce a kilowatt of microwave power which is appropriate for rapid microwave cooking.

The magnetron is a device of essentially cylindrical symmetry (see illustration). On the central axis is a hollow cylindrical cathode. The outer surface of the cathode carries electronemitting materials, primarily barium and strontium oxides in a nickel matrix. Such a matrix is capable of emitting electrons when current flows through the heater inside the cathode cylinder.

At a radius somewhat larger than the outer radius of the cathode is a concentric cylindrical anode. The anode serves two functions&colon; (1) to collect electrons emitted by the cathode and (2) to store and guide microwave energy. The anode consists of a series of quarter-wavelength cavity resonators symmetrically arranged around the cathode.

A radial dc electric field (perpendicular to the cathode) is applied between cathode and anode. This electric field and the axial magnetic field (parallel and coaxial with the cathode) introduced by pole pieces at either end of the cathode provide the required crossed-field configuration.

Magnetron (redirected from magnetrons)

Magnetron
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