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magnetostriction • main memory 431
Charged cosmic
particle
Magnetosphere
evated temperature) inside the body, as in heating
a cancerous tumor for therapeutic purposes.
magnetron A microwave vacuum tube consisting
of a diode (with a cylindrical anode) through
which the field of a powerful external permanent
magnet passes. The magnetic field causes electrons
leaving the cathode to travel in spiral paths
between the electrodes. This action gives the tube
a negative-resistance characteristic, resulting in
oscillation when the tube is connected in an appropriate
circuit. Some magnetrons have a builtin
resonant cavity.
magnetosphere
comparable to piezoelectric vibration in a quartz
crystal.
magnetostriction filter See ULTRASONIC FIL-
TER, 1.
magnetostriction oscillator An oscillator whose
frequency is controlled by a magnetostrictive rod
(see MAGNETOSTRICTION). The dimensions of
the rod and the type of metal it contains determine
its vibration frequency and, accordingly, the
operating frequency of the oscillator.
+
−
magnetostriction oscillator
Output
Magnetostrictive
rod
magnetostrictive delay line A delay line in which
the signal is propagated through a magnetostrictive
rod. Also see MAGNETOSTRICTION.
magnetostrictive microphone A microphone in
which sound vibrations produce changes in a
magnetostrictive element, which, in turn, are
converted into output-voltage changes. Also see
MAGNETOSTRICTION.
magnetostrictive transducer A transducer in
which some phenomenon, such as vibration or
pressure, produces changes in a magnetostriction
element, which in turn are converted into outputvoltage
changes. Also see MAGNETOSTRICTION.
magnet protector See KEEPER.
magnetrode The trademark of a radio-frequency
device for externally producing hyperthermia (el-
S
Plate
Plate
Magnets
Cathode
N
2nd
plate
1st
plate
magnetron
Cathode
Β− Β+
magnet steel A high-retentivity alloy of chromium,
cobalt, manganese, steel, and tungsten,
used in the manufacture of permanent magnets.
magnet tester An instrument used to measure the
flux of a magnet. Also see FLUXMETER.
magnet wire Insulated wire (usually solid copper)
of 14 to 40 gauge, so called because of its original
major use in winding the coils of electromagnets.
magnitude 1. General expression for degree, size,
or extent. 2. Signal strength (amplitude). 3. For a
number or vector quantity, the absolute value or
length. 4. A measure of the relative or absolute
brightness of celestial objects.
mAh Abbreviation of milliampere-hour.
main British expression for the alternating-current
(ac) utility power available in a house or building.
main bang 1. In a radar display, the pip or pulse
resulting from the actual transmitted signal. This
pulse is blanked out. 2. In a spectrum analyzer,
the pip corresponding to a frequency of zero, and
caused by the local oscillator.
mainframe 1. The chassis containing the central
processor and arithmetic and logic circuits for a
large computer. 2. The general term for a large,
powerful computer.
main lobe Also called major lobe. In a directional
antenna system, the portion of the directivity pattern
representing the greatest transmitted signal
gain and/or the greatest received signal response.
Also see MINOR LOBE, SIDE LOBE.
main memory The principal (immediate process)
memory unit in a digital computer or dataprocessing
system.