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doohickey • dot 207
doohickey A usually unnamed device—especially
one used to achieve some significant modification
of circuit performance.
doorknob capacitor A high-voltage fixed capacitor,
so called from its round package, which
somewhat resembles a doorknob.
doorknob tube A special UHF vacuum tube, so
called from its characteristic shape. The unique
design provides short electron-transit time and
low interelectrode capacitance. Largely replaced
in recent years by semiconductor devices.
dopant An impurity added in controlled amounts
to a semiconductor to make it an n-type or p-type
material. Also see ACCEPTOR and DONOR.
dope To add impurities to a semiconductor material.
Doping allows the manufacture of n-type or
p-type semiconductors with varying degrees of
conductivity. In general, the greater the extent of
doping, the higher the conductivity.
doped junction In a semiconductor device, a junction
produced by adding a dopant to the semiconductor
melt.
doping Adding a dopant to a semiconductor to alter
the way it conducts current.
doping agent See DOPANT.
doping compensation Opposite doping (i.e., adding
a donor impurity to p-type semiconductor
material or adding an acceptor impurity to n-type
semiconductor material).
doping gas A gas diffused into a semiconductor
material to dope it. For example, phosphorus
pentoxide gas can be used to create an n-type region
in a p-type silicon chip.
doping level The relative concentration of impurity
added to a semiconductor material to obtain a
certain resistivity and polarity. The greater the
doping level, the lower the resistivity.
Doppler broadening In a spectrum, the spreading
out or blurring of a spectral line caused by
DOPPLER EFFECT, in turn resulting from motion
of molecules, atoms, or other particles in the
medium.
Doppler cabinet A loudspeaker enclosure with
which a vibrato effect is achieved by rotating or
reciprocating either the loudspeaker or a baffle
board; the length of the sound path is altered
cyclically.
Doppler effect A change in the frequency of a wave
that occurs when the source and observer are in
relative motion. The frequency of the wave increases
(the wavelength shortens) as the source
and observer approach each other; the frequency
decreases (the wavelength becomes greater) as
the source and observer recede from each other.
This effect is often observed with sound waves, as
when the pitch of an automobile horn seems to
rise as the car approaches and to fall as the car
passes. The effect is also observable in electromagnetic
radiation at all wavelengths. It affects
satellite communication and space communication.
Doppler enclosure See DOPPLER CABINET.
Doppler radar A radar that uses the change in carrier
frequency of the signal returned by a moving
target (approaching or receding) to measure its
velocity. Used by law enforcement officers to determine
the speed of moving vehicles. Also used
by meteorologists to evaluate air circulation patterns
in thunderstorms, and to determine wind
speeds in hurricanes and tornadoes.
Doppler ranging See DORAN.
Doppler shift The extent to which the frequency or
wavelength of a signal changes because of
DOPPLER EFFECT. Can be measured in Hertz
(for frequency) or in meters (for wavelength). In
astronomy, the shift is also measured as displacement
of absorption or emission lines in an
infrared, visible, or ultraviolet spectrum.
Doppler’s principle See DOPPLER EFFECT.
doran A continuous-wave trajectory-measuring
system utilizing Doppler shift (see DOPPLER EF-
FECT). The name is a contraction of doppler ranging.
dorsal column stimulator Abbreviation, DCS. A
machine that generates radio-frequency energy
that is applied to human tissues for the temporary
relief of pain.
dosage meter See DOSIMETER.
dose The total quantity of radiation received upon
exposure to nuclear radiation or X-rays.
dosimeter An instrument for measuring the
amount of exposure to nuclear radiation or
X-rays.
dot 1. The shorter of the two characters (dot and
dash) of the telegraph code. The dot, a short
sound, mark, or perforation, is one-third the