beam toroid
a device used for measur-
ing beam intensities by measuring the mag-
netic field fluctuations produced by the pass-
ing beam. The magnetic field fluctuations
produce a current in a coil, that is wound
around a closed circular ring (torus) through
which the beam passes.
beam waist
position at which a beam is
most highly confined; for Gaussian beams in
real media the position at which the phase
fronts are flat.
beamformers
system commonly used for
detecting and isolating signals that are prop-
agating in a particular direction.
beamforming
a form of filtering in spatial
rather than time domain to obtain a desired
spatial impulse response in order to suppress
or to reject signal components coming from
certain directions. The technique involves
directing one or more beams in certain di-
rections by adjusting, for example, the ele-
ment excitation of an array antenna. Used
in communications applications to suppress
other signals than the desired source signal.
Also termed spatial filtering.
beamline
a series of magnets placed
around a vacuum pipe that carry the proton
beam from one portion of the accelerator to
another. Also known as transport line.
beamsplitter
any of a number of passive
optical devices that divide an optical wave-
front into two parts. Wavefront division may
be according to intensity, polarization, wave-
length, spatial position, or other optical prop-
erties.
beamwidth
the angular width of the ma-
jor lobe of a radiation pattern. It is usually
at the half-power level, i.e., 3 dB below the
peak of the major lobe. It can also be speci-
fied as the width between the nulls on either
side of the major lobe (BWFN).
bearing currents
current flow in the
bearings of electrical machines, because of
electromagnetic unbalance in the machine
or from using high
dv
dt
inverters. The lat-
ter is able to charge up the stray capacitance
present between the stator and rotor and be-
tween the rotor and shaft and thus allows mo-
tor bearing currents to flow, with resulting
bearing damage.
beat frequencies
the two frequencies,
sum and difference frequencies, generated
during the heterodyning process or during the
amplitude-modulating process. For exam-
ple, if a 500 kHz carrier signal is amplitude-
modulated with a 1 kHz frequency, the beat
frequencies are 499 kHz and 501 kHz.
beat frequency oscillator
an adjustable
oscillator used in superheterodyne receivers
generating a frequency when combined with
the final IF produces a difference or beat fre-
quency in audio range.
becky
a knot used to secure a handline.
bed of nails
a test fixture for automated
circuit qualification in which a printed wiring
board is placed in contact with a fixture that
contacts the board at certain nodes required
for exercising the assembly.
bel
See
decibel
.
Bell, Alexander Graham
(1847–1922)
Born: Edinburgh, Scotland
Bell is best know as the first patent holder
for a device to electronically transmit human
speech. Bell’s early interest in the mecha-
nisms of speech come from living with his
grandfather, a London speech tutor. Work
with the deaf was to be a lifelong vocation
for Bell. Bell’s inventions were not limited
to the telephone. He was the first person to
transmit speech without wires, he invented
the gramophone, an early tape recorder, an
air-cooling system, an iron lung, and he had
several patents in telegraphy.
c
2000 by CRC Press LLC