Page 336 - Electrical Engineering Dictionary

half-life the average time needed for half halogen one of the halide atoms known
the nuclei of a radioactive element to decay. for being highly reactive.

half-power bandwidth the frequency at halt instruction an instruction (typically
which a lowpass filter amplitude response privileged) that causes a microprocessor to
1
falls to √ of the DC response is known as the stop execution.
2
half-power point. The two-sided half-power
Hamming code an encoding of binary
bandwidth is twice the half-power point.
numbers that permit error detection and cor-
rection first discovered by Richard Hamming
half-wave rectifier a device that passes
at Bell Laboratories.
positive polarity portions of a signal and
A Hamming code is a perfect codes with
blocks negative polarity portions of an AC m
codewordlengthn = 2 −1andsourceword
signal. Ideally, for a sinusoidal input v i (t) =
length k = n−m for any m> 2. A Hamming
V m cos(ωt), the output equals the input while
code can correct an error involving a single
the input is positive and is zero while the in-
bit in the binary number. It can also detect
put is negative.
an error involving two bits. See also parity.
half-wave symmetry a periodic function Hamming distance the number of digit
that satisfies x(t) =−x(t − T/2). positions in which the corresponding digits
of two binary words of the same length dif-
half-wave voltage the voltage required to fer. The minimum distance of a code is the
produceanamountofrefractiveindexchange smallest Hamming distance between any pair
in a medium that will retard the phase of a of code words. For example, if the sequences
traversing optical wave. are 1010110 and 1001010, then the Ham-
ming distance is 3.
halftone technique of simulating continu-
Hamming net a pattern recognition net-
ous tones by varying the amount of area cov-
work that has a set of prototype patterns
ered by the colorant. Typically accomplished
by varying the size of the printed dots in re- stored in its weights. A given input pattern
lation to the desired intensity. is identified with the prototype whose Ham-
ming distance from the input pattern is least.
Hall effect the phenomenon whereby
Hamming weight the number of nonzero
charge carriers are displaced perpendicularly
symbols in a given sequence of symbols.
to their drift velocity when current flows in
the presence of a magnetic field. The re-
Hamming window a tapering function
sulting shift in carriers inside the conductor
used to truncate functions spectrally or in the
or semiconductor produces a transverse Hall
time domain (i.e., in frequency it is a specifi-
voltage that is proportional to the strength of
cally formed low pass filter). It is defined as
the magnetic field (for constant current).
w(x) = 0.54+0.46∗cos(2∗π ∗x/x o )|x| <
x o /2. The Hamming window sacrifices fil-
Hallmeasurement asemiconductorchar- ter sharpness at the cutoff frequency for a
acterization that uses a crossed electric and smoother stop band behavior.
magnetic field to yield information on the
conductivity of a test sample. hand See end-effector.

Hall probe a device with a Hall effect hand-held computer a small lightweight
transducer to sense a magnetic field. computer that performs functions such as

c
2000 by CRC Press LLC