18WuD2x

280 ferrite loopstick • fetch
ferrite loopstick See FERRITE-ROD ANTENNA.
ferrite memory A static memory using ferrite
cores. See CORE MEMORY.
ferrite-rod antenna Also called loopstick antenna.
A small antenna that can be used for wireless reception
at frequencies below approximately
20 MHz. This antenna consists of a coil wound
on a solenoidal, high-permeability, powderediron
core, usually less than 20 centimeters (cm)
long and 1 cm in diameter. A series or parallel
capacitor, in conjunction with the coil forms a
tuned circuit. The operating frequency is determined
by the resonant frequency of the inductance-capacitance
(LC) combination. Response
is maximum off the sides of the coil, and a sharp
null occurs off the ends. This antenna has narrow
bandwidth. The null can be oriented to minimize
system response to undesired local signals
or humanmade noise. Compare SMALL LOOP
ANTENNA.
ferrite switch A device that regulates the flow of
power through a waveguide. The electric-field
vector is rotated, resulting in a high degree of attenuation
when actuated, but little or no attenuation
when not activated.
ferroelectric 1. Producing ferroelectricity. 2. A ferroelectric
material.
ferroelectric amplifier See DIELECTRIC AMPLI-
FIER.
ferroelectric capacitor A capacitor in which a ferroelectric
material is the dielectric.
ferroelectric cell See FERROELECTRIC CAPACI-
TOR.
ferroelectric crystal A crystal of ferroelectric material.
ferroelectric flip-flop A flip-flop based on the hysteresis
of a ferroelectric capacitor. Compare FER-
RORESONANT FLIP-FLOP.
ferroelectricity Electric polarization in certain
crystalline materials. The effect is analogous to
the magnetization of a ferromagnetic material by
a magnetic field.
ferroelectric-luminescent Pertaining to a ferroelectric
cell that emits light.
ferroelectric material A nonlinear dielectric material
capable of producing ferroelectricity. Examples:
barium titanate, barium strontium titanate,
potassium dihydrogen phosphate, guanadine
aluminum sulfate hexahydrate (GASH), Rochelle
salt, and triglycene sulfate.
ferromagnetic 1. Pertaining to a substance that
conducts a magnetic field with relative ease. 2.
Pertaining to a material in which a magnetic-field
change causes a voltage, which in turn results in
a measurable current flow.
ferromagnetic-core inductor A coil of wire designed
to introduce inductive reactance into a circuit
or system, wound around a core consisting of
ferromagnetic material that greatly increases the
inductance for a given number of turns. With
proper design and choice of core material, the Q
factor (selectivity attainable) can be extremely
high. The core confines much of the magnetic
flux within itself. When the coil current exceeds
a certain level, core saturation occurs, and further
increases in the current will not produce a corresponding
increase in magnetic flux. This decreases
the effective inductance, and reduces the
efficiency because power is dissipated as heat in
the core.
ferromagnetic material A substance that concentrates
magnetic lines of flux relative to their concentration
in free space. Iron, powdered iron, and
ferrite are common examples.
ferromagnetic resonance The point at which the
permeability of a magnetic material peaks at a
microwave frequency.
ferromagnetic spinels Highly permeable and resistive
ceramic-like materials. The low eddycurrent
losses and high permeability of these
materials suit them for use as cores in radiofrequency
(RF) transformers and inductors. Also
see FERRITE.
ferromagnetic tape Magnetic tape used for winding
closed transformer cores.
ferrometer An instrument for testing hysteresis
and permeability in steel and iron.
Ferron detector See IRON-PYRITES DETECTOR.
ferroresonant circuit An inductance-capacitance
(LC) circuit in which the coil is a saturable reactor.
Because of coil nonlinearity, the circuit is resonant
at only one value of alternating-current (ac)
voltage, and exhibits both negative resistance
and bistable operation.
ferroresonant counter A digital counter using ferroresonant
flip-flops, rather than semiconductor
devices.
ferroresonant flip-flop A flip-flop using one or two
ferroresonant circuits instead of semiconductor
devices. See BISTABLE MULTIVIBRATOR. Compare
FERROELECTRIC FLIP-FLOP.
ferroresonant shift register A shift register using
ferroresonant circuits instead of semiconductor
devices.
ferrosoferric oxide See MAGNETITE.
ferrospinels See FERROMAGNETIC SPINELS.
ferrous Pertaining to a substance that contains
iron and is magnetizable.
Ferroxcube A nonmetallic ferromagnetic material
having high permeability and resistivity, and a
Curie point near room temperature. These characteristics
make the material suitable for the
cores of radio-frequency (RF) inductors and
transformers, and for high-frequency magnetic
shields.
Fessenden oscillator In underwater communications,
a transmitter of acoustic waves.
FET Abbreviation of FIELD-EFFECT TRANSISTOR.
fetch An operation in a computer run in which the
location of the next instruction is taken from
memory and changed if necessary; it then goes to
the control register.