Electrical Engineering Dictionary - part 24

breakaway points of the root loci

break-

away points on the root loci correspond to
multiple-order roots of the equation.

breakaway torque

minimum torque

needed to begin rotating a stationary load.
Breakaway torque represents the absolute
minimum starting torque specification for a
motor used to drive the load.

breakdown

as applied to insulation (in-

cluding air), the failure of an insulator or in-
sulating region to prevent conduction, typi-
cally because of high voltage.

breakdown strength

voltage gradient at

which the molecules of medium break down
to allow passage of damaging levels of elec-
tric current.

breakdown torque

maximum torque that

can be developed by a motor operating at
rated voltage and frequency without expe-
riencing a significant and abrupt change in
speed. Sometimes also called the stall torque
or pull-out torque.

breakdown voltage

the reverse biased

voltage across a device at which the current
begins to dramatically deviate and increase
relative to the current previously observed at
lower voltages close to the breakdown volt-
age. This effect is attributed to avalanche or
zener breakdown. It is usually specified at a
predetermined value of current.

In a diode, applying a voltage greater than

the breakdown voltage causes the diode to
operate in the reverse breakdown region.

breakpoint

(1) an instruction address at

which a debugger is instructed to suspend the
execution of a program.

(2) a critical point in a program, at which

execution can be conditionally stopped to
allow examination if the program variables
contain the correct values and/or other ma-
nipulation of data. Breakpoint techniques are
often used in modern debuggers, which pro-

vide nice user interfaces to deal with them.
See also

breakpoint instruction

breakpoint instruction

a debugging in-

struction provided through hardware support
in most microprocessors. When a program
hits a break point, specified actions occur that
save the state of the program, and then switch
to another program that allows the user to ex-
amine the stored state. The user can suspend
the execution of a program, examine the reg-
isters, stack, and memory, and then resume
the program’s execution, which is very help-
ful in a program’s debugging.

breath noise

the noise that is commonly

produced when talking at the microphone. It
is due to breathing.

breeder reactor

a nuclear reactor in

which a non-fissile isotopes are converted to
fissile isotopes by irradiation. Ideally, such
a reactor produces more fissile products than
it consumes.

Bremsstrahlung

electromagnetic radia-

tion, usually in the X-ray region of the spec-
trum produced by electrons in a collision with
the nucleus of an atom. Bremsstrahlung ra-
diation is produced in regions of high electric
potential such as areas surrounding electro-
static septa and RF cavities. Bremsstrahlung
is German for breaking.

Brewster angle

the angle from normal at

which there is no reflection at a planar inter-
face between two media. The Brewster an-
gles for perpendicular and parallel polariza-
tions are different. For nonmagnetic media,
in which the relative permeability is unity,
the Brewster angle for perpendicular polar-
ization does not exist.

Brewster mode

a bound radiative sur-

face mode when one of the media is a plasma
medium and has a positive dielectric func-
tion.

2000 by CRC Press LLC

Brewster window

transmission window

oriented at Brewster’s angle with respect to
an incident light beam; light polarized in the
plane of incident experiences no reflection.

bridge

a simple device that connects

two or more physical local-area networks
(LANs). It forwards packets of data from
one LAN segment to another without chang-
ing it, and the transfer is based on physical
addresses only. The separate LAN segments
bridged this way must use the same protocol.

bridge balance condition

represents the

relationship between bridge circuit compo-
nents when the current in the balance indica-
tor is absent. Most of the technically useful
bridges include a regular connection (series,
parallel, series-parallel, or parallel-series) of
two two-ports. The condition of balance can
be reformulated in terms of two-port param-
eters, so that depending on structure, the sum
of two forward transfer parameters or the sum
of one forward and another backward transfer
parameter is equal to zero.

bridge calibration

used in bridge trans-

ducer applications. It is achieved connect-
ing two auxiliary circuits to the bridge. One
circuit including two resistors and a poten-
tiometer is connected in parallel to the bridge
power supply diagonal, and the potentiome-
ter tap and one end of detector are connected
to the same bridge node. Sliding the tap,
one can eliminate the bridge offset.

An-

other circuit, usually including a constant
and a variable resistor, is connected in series
with power supply. This circuit allows one
to change the voltage applied to the bridge,
and to establish the correspondence between
the maximal deflection of the detector and
maximum of the physical variable applied to
the bridge resistors playing the role of active
gauges.

bridge circuit

the circuit that includes

four lateral impedances,

, a

diagonal impedance

, and a voltage source

of the output impedance

is an exam-

ple of the so-called bridge circuit. This and
other similar circuits are characterized by the
bridge balance condition, which represents
a relationship between the bridge elements
when the current in the diagonal impedance
is absent (in the case shown this condition is
Z

= Z

). The bridge circuits find ap-

plication in instrumentation and transducers.

bridge linearization

necessary design

concern in transducer application of the
bridge circuits. It is achieved by reduction
of the bridge sensitivity in the bridges where
only one arm is a transducer. Linearization
can also be achieved with two transducers
providing the signals of opposite signs and
connected in the opposite arms of the bridge
or using a current source instead of the volt-
age source as a bridge power supply.

bridge rectifier

a full-wave rectifier to

convert ac to dc, that contains four rectifying
elements for single phase, and six elements
for three phase, connected as the arm of a
bridge circuit.

bridge sensitivity

the ratio of the vari-

ation of the voltage or the current through
the detector to the variation of the compo-
nent that causes the disbalance of the bridge
circuit.

bridge-controlled multivibrators

using

switches in a two-operational amplifier or in
an amplifier-comparator multivibrator so that
the bridge is “rotated” each half of the period,
one can obtain control of the oscillation fre-
quency by detuning a resistive bridge. The
circuit can be applied in sensors with limited
number of access wires.

bridging

using bridges for local-area net-

works.

brightness

the perceived luminance or ap-

parent intensity of light. This is often differ-
ent from the actual (physical) luminance, as
demonstrated by brightness constancy, Mach
band, and simultaneous contrast.

2000 by CRC Press LLC

brightness adaptation

the ability of the

human visual system (HVS) to shift the nar-
row range in which it can distinguish differ-
ent light intensities over a large span of lumi-
nances. This permits the overall sensitivity
of the HVS to gray levels to be very large
even though the number of gray levels that
it can simultaneously differentiate is fairly
small.

See also

brightness constancy

the perception that

an object has the same brightness despite
large changes in its illumination.

Thus a

piece of paper appears to be approximately
as white in moonlight as in sunlight, even
though the illumination from the sun may
be one million times greater than that from
the moon. See also

Brillouin flow

a stream of electron beam

emitted from an electron gun that is not ex-
posed to a focusing magnetic field.

Brillouin frequency shift

the frequency

shift that a wave experiences in undergoing
Brillouin scattering. The shift can be to either
lower or higher frequency, and typically has
a value in the range 0.1 to 10 GHz. See also

Stokes scattering

anti-Stokes scattering

Brillouin laser

acoustic maser in which

the amplification mechanism is considered to
be Brillouin scattering.

Brillouin scattering

the scattering of

light from sound waves. Typically in Bril-
louin scattering the sound waves have fre-
quencies in the range 0.1 to 10 GHz, whereas
in acousto-optics the sound waves have fre-
quencies

<0.1 GHz. Brillouin scattering can

be either spontaneous or stimulated.

See

also

acousto-optic effect

spontaneous light

scattering

stimulated light scattering

broadband

a service or system requiring

transmission channels capable of supporting
bit rates greater than 2 Mbit/s.

broadband antenna

an antenna whose

characteristics (such as input impedance,
gain, and pattern) remain almost constant
over a wide frequency band. Two such types
of antennas are the log periodic and the bi-
conical.

broadband emission

an emission having

a spectral distribution sufficiently broad in
comparison to the response of a measuring
receiver.

broadband integrated services digital net-
work (B-ISDN)

a generic term that gen-

erally refers to the future network infrastruc-
ture that will provide ubiquitous availability
of integrated voice, data, imagery, and video
services.

broadband system

a broadband commu-

nication system is one that employs a high
data transmission rate. In radio terminology
it implies that the system occupies a wide ra-
dio bandwidth.

broadcast

(1) the transfer of data to multi-

ple receiver units simultaneously rather than
to just one other subsystem.

(2) a bus-write operation intended to be

recognized by more than one attached device.

broadcast channel

a single transmit-

ter, multiple receiver system in which iden-
tical information is transmitted to each re-
ceiver, possibly over different channels. See
also

interference channel

multiple access

channel

broadcast channel allocations

a fre-

quency of a width prescribed by a nation’s
communications governing agency that are
standardized throughout the country for use
in one-way electronic communication.

2000 by CRC Press LLC

broadcast picture quality

the accept-

able picture performance for NTSC terres-
trial telecast signals. A panel of untrained
observers subjectively evaluates the NTSC
received picture and sound quality as signal
impairments are inserted into the broadcast
signal.

The evaluation scores are used to

determine the values for objectionable sig-
nal impairment levels. The signal impair-
ments tested are the video and audio signal-
to-noise ratios, the interference due to adja-
cent channel signals, the interference due to
co-channel signals, and the echoes (ghosts)
caused by multipath signals effects.

broadcasting

sending a message to mul-

tiple receivers.

broadside

when the pattern factor is

maximum in the H plane (for a dipole an-
tenna along the z axis this is the plane where
theta=90 degrees).

broadside array

an array where the main

beam of the array is directed perpendicular
to the array axis. In many applications it is
desirable to have the maximum radiation of
an array directed normal to the axis of the
array.

broadside coupled microstrip lines

mi-

crostrip lines that share the same ground
plane but separated from each other in normal
direction to the ground plane. Both the mi-
crostrip lines are aligned at their centers along
the normal direction to the ground plane.

Brown book

See

IEEE Color Books

Brownian motion

a stochastic process

with independent and stationary increments.
The derivative of such a process is a white
noise process. A Brownian motion process
X

is the solution to a stochastic differential

equation of the form

= b(t, X

) + σ (t, X

) · W

where

is a white noise process.

brownout

an intentional lowering of util-

ity voltage to reduce loading on the system.

brush

a conductor, usually carbon or a

carbon–copper mixture, that makes sliding
electrical contact to the rotor of an electri-
cal machine. Brushes are used with sliprings
on a synchronous machine to supply the DC
field and are used with a commutator on a DC
machine.

brush rigging

the components used to

hold the brushes of a rotating machine in
place, and to insure proper brush tension is
applied.

brush tension

the force required on the

brushes of a rotating machine to insure proper
contact between the brush and the commuta-
tor or slipring. Proper brush tension is usu-
ally provided by springs, and is specified in
the manufacturer’s technical manual of the
machine.

brushless DC motor

See

electronically

commutated machine

brushless exciter

See

rotating-rectifier

exciter

brushless rotary flux compressor

a ro-

tating machine designed to deliver pulsed
output (1 MJ in 100

µs). The stator coils are

excited by an external capacitor bank. The
rotor is a salient structure that compresses
the flux resulting in amplification of the elec-
tric pulse, by converting the rotating kinetic
energy of the rotor to electrical energy.

BSO

abbreviation for bismuth silicon ox-

ide, Bi

SiO

. A photoconductive insulat-

ing crystal that exhibits photorefractive ef-
fects. Useful in applications such as multi-
beam coupling and phase conjugation.

BTB

See

branch target buffer

BTC

See

block truncation coding

2000 by CRC Press LLC

Content .. 22 23 24 25 ..