18WuD2x

72 bifilar electrometer • bimorphous cell
plied, the fibers separate by a distance proportional
to the voltage.
bifilar resistor A wirewound resistor with two oppositely
wound filaments. The nature of the winding
tends to cancel the inductance, making the
device useful at a much higher frequency than an
ordinary wirewound resistor.
bifilar transformer A transformer in which unity
coupling is approached by interwinding the primary
and secondary coils (i.e., the primary and
secondary turns are wound side by side and in
the same direction).
bifilar winding 1. A method of winding a coil (such
as a resistor coil) in the shape of a coiled hairpin
so that the magnetic field is self-canceling and
the inductance is minimized. 2. A method of
winding transformers to minimize leakage reactance.
R1
R2
R1
C1
R3
R3
C2
R2
R1
R1
C1
L1
L1
bifilar winding
bifurcated contact A forked contact whose parts
act as two contacts in parallel for increased reliability.
bilateral amplifier An amplifier that transmits or
receives in either direction equally well (i.e., the
input and output can be exchanged at will).
bilateral antenna A bidirectional antenna, such as
a loop antenna or a half-wave dipole.
bilateral element A circuit element or component
(as a capacitor, resistor, or inductor) that transmits
energy equally well in either direction. Compare
UNILATERAL ELEMENTS.
bilateral network A network, usually passive and
either balanced or unbalanced, that has BILAT-
ERAL SYMMETRY. Thus, the input and output
terminals can be exchanged without affecting the
performance of the network in any way.
bilateral symmetry 1. Exhibiting symmetry, with
respect to a vertical line or plane. 2. For a network,
having the property that if the input and
output are reversed, the circuit behavior remains
precisely the same. See BILATERAL NETWORK.
3. For an amplitude-versus-frequency response
curve, having the property that the right-hand
and left-hand halves are mirror images of each
other.
billboard antenna A phased group of dipole antennas
that lie in one plane. A reflector might be
used behind the entire array.
bilobe pattern An antenna radiation pattern consisting
of two major lobes in a given plane, usually
the horizontal plane. Often the lobes exist in
opposite directions relative to each other, as in a
bilateral network
half-wave dipole. But they can be at varying angles,
as in a long-wire antenna.
bimetal A union of two dissimilar metals—especially
those having a different temperature coefficient
of expansion. The two are usually welded
together over their entire surface.
bimetallic element A strip or disk of bimetal.
When the element is heated, it bends in the direction
of the metal that has the lower temperature
coefficient of expansion; when cooled, it
unbends. Usually, an electrical contact is made
at one extreme or the other so that the element
can serve as a thermostat.
bimetallic switch A temperature-sensitive switch
based on a bimetallic element.
bimetallic thermometer A thermometer based on
a bimetallic element that is mechanically coupled
(as through a lever and gear system) to a pointer
that moves over a temperature scale.
bimetallic thermostat A thermostat in which a
bimetallic element closes or opens a pair of
switch contacts.
bimorphous cell A piezoelectric transducer that
consists of two crystal plates, such as Rochelle
salt, bound intimately face to face. In a crystal
microphone, vibration of the transducer results
in a voltage output; in a crystal headphone, an ac
signal voltage impressed on the transducer
causes vibratory mechanical motion.