Page 87 - The Illustrated Dictionary of Electronics

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72 bifilar electrometer • bimorphous cell

plied, the fibers separate by a distance propor-
tional to the voltage.
bifilar resistor A wirewound resistor with two op- R1 R3 R1
positely wound filaments. The nature of the wind-
ing tends to cancel the inductance, making the R2 R2
device useful at a much higher frequency than an
ordinary wirewound resistor.
bifilar transformer A transformer in which unity R1 R3 R1
coupling is approached by interwinding the pri-
mary 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 reac-
tance. C1 C2 C1

L1 L1

bifilar winding

bifurcated contact A forked contact whose parts
act as two contacts in parallel for increased relia- bilateral network
bility.
bilateral amplifier An amplifier that transmits or
receives in either direction equally well (i.e., the half-wave dipole. But they can be at varying an-
input and output can be exchanged at will). gles, as in a long-wire antenna.
bilateral antenna A bidirectional antenna, such as bimetal A union of two dissimilar metals—espe-
a loop antenna or a half-wave dipole. cially those having a different temperature coeffi-
bilateral element A circuit element or component cient of expansion. The two are usually welded
(as a capacitor, resistor, or inductor) that trans- together over their entire surface.
mits energy equally well in either direction. Com- bimetallic element A strip or disk of bimetal.
pare UNILATERAL ELEMENTS. When the element is heated, it bends in the di-
bilateral network A network, usually passive and rection of the metal that has the lower tempera-
either balanced or unbalanced, that has BILAT- ture coefficient of expansion; when cooled, it
ERAL SYMMETRY. Thus, the input and output unbends. Usually, an electrical contact is made
terminals can be exchanged without affecting the at one extreme or the other so that the element
performance of the network in any way. can serve as a thermostat.
bilateral symmetry 1. Exhibiting symmetry, with bimetallic switch A temperature-sensitive switch
respect to a vertical line or plane. 2. For a net- based on a bimetallic element.
work, having the property that if the input and bimetallic thermometer A thermometer based on
output are reversed, the circuit behavior remains a bimetallic element that is mechanically coupled
precisely the same. See BILATERAL NETWORK. (as through a lever and gear system) to a pointer
3. For an amplitude-versus-frequency response that moves over a temperature scale.
curve, having the property that the right-hand bimetallic thermostat A thermostat in which a
and left-hand halves are mirror images of each bimetallic element closes or opens a pair of
other. switch contacts.
billboard antenna A phased group of dipole anten- bimorphous cell A piezoelectric transducer that
nas that lie in one plane. A reflector might be consists of two crystal plates, such as Rochelle
used behind the entire array. salt, bound intimately face to face. In a crystal
bilobe pattern An antenna radiation pattern con- microphone, vibration of the transducer results
sisting of two major lobes in a given plane, usu- in a voltage output; in a crystal headphone, an ac
ally the horizontal plane. Often the lobes exist in signal voltage impressed on the transducer
opposite directions relative to each other, as in a causes vibratory mechanical motion.