Page 83 - Electrical Engineering Dictionary

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

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2000 by CRC Press LLC