18WuD2x

FE-EL • ferrite limiter 279
FE-EL Abbreviation of ferroelectric-electroluminescent.
feeler 1. A wire or blade contact (e.g., a finger that
senses holes in a punched card). 2. The wire portion
of a point-contact diode.
Felici mutual-inductance balance An inductive
null circuit for determining mutual inductance
(M x ) in terms of a standard mutual inductance
(M s ). The secondary coils of two mutual-inductance
circuits are connected in phase opposition.
The standard mutual inductor, which is variable,
is adjusted for null. At null, M x = M s .
Generator
M x
Primary Secondary Null
detector
Secondary
Primary
M s
Felici mutual-inductance balance
female plug A plug whose contacts are separated
by a recess into which the prongs of a mating
male plug are inserted. Compare HERMA-
PHRODITE PLUG and MALE PLUG.
femto- Abbreviation, f. A prefix meaning quadrillionth
(10 –15 ).
femtoampere Abbreviation, fA. A unit of extremely
low current; 1 fA equals 10 –15 A.
femtofarad Abbreviation, fF. A unit of extremely
low capacitance; 1 fF equals 10 –15 F.
femtovolt Abbreviation, fV. A unit of extremely low
voltage; 1 fV equals 10 –15 V.
fence A system or string of early warning radar
stations.
Fermat’s principle The principle that the path of a
ray of radiant energy between two points in any
medium is the shortest distance between those
points in that medium. This path is also the path
of least propagation time. This might not necessarily
be a straight line. On a flat plane, the path
of least time between any two points is always a
straight line, assuming constant velocity of propagation.
However, on a sphere, the path of least
time between two points is represented by a great
circle.
fermi Abbreviation, F. An extremely small unit of
length and wavelength, equal to one quadrillionth
(10 –15 ) of a meter.
Fermi-Dirac distribution function The probability
that an electron will be in a certain quantum
state under conditions of thermal equilbrium.
This is determined as the probability that the
electron will be in a given energy band at a particular
instant of time.
fermium Symbol, Fm. A radioactive metallic element
that is artificially produced. Atomic number,
100. Atomic weight, 257.
ferpic Acronym for ferroelectric ceramic picture device.
An image-storing device containing a photoconductive
film, transparent electrodes, and a
ferroelectric ceramic, in layers.
ferreed A form of magnetic switching device, similar
to a reed relay, that maintains its position indefinitely
without the need for a continuous
current.
ferret A vehicle or craft equipped for determining
the locations of enemy radar transmitters.
ferri- A prefix used to denote magnetic properties.
ferric oxide Formula, Fe 2 O 3 . A red oxide of iron
used to coat magnetic recording tape.
ferristor A high-frequency magnetic amplifier using
a ferroresonant circuit.
ferrite A high-resistance magnetic material consisting
principally of ferric oxide and one or more
other metals. After being powdered and sintered,
ferrites exhibit low eddy-current loss at high frequencies
and make ideal core material for inductors
and switching elements. Also used in
television deflection yokes and in miniature antennas.
Also see FERROSPINELS.
ferrite antenna See FERRITE-ROD ANTENNA.
ferrite bead 1. A magnetic storage device in the
form of a bead of ferrite powder fused onto the
signal conductors of a memory matrix. 2. A tiny
ring of ferrite that can be slipped over a wire or
cable to choke off radio-frequency (RF) currents.
Ferrite
bead
ferrite bead
Cable
ferrite core A coil or switching-element core made
from a ferrite; specifically, in a core memory, a
small magnetic toroid that can retain its polarity
when charged by a pulse.
ferrite core memory A magnetic memory in which
ferrite cores are interconnected by a network of
input and output wires.
ferrite isolator A microwave device that permits
energy to pass with negligible loss in one direction
through a waveguide or coaxial line, while absorbing
energy passing in the opposite direction.
ferrite limiter A device used in the antenna circuit
or front end of a receiver, to prevent overload
while maintaining a linear response. Used mostly
at ultra-high and microwave frequencies.