9.3 The various maxima of the standing wave pattern of Fig.
1 are nearly equal in magnitude. Thus V
max
(x) is very nearly a
straight, horizontal line. The minimum microphone voltages,
however, form a V
min
(x) locus with a noticeable slope. It is not
the absorption at the sample face but rather the attenuation
within the tube itself that causesV
min
(x) to exhibit this slope.
Indeed, if there were no attenuation of incident and reflected
waves as they propagated back and forth in the tube, V
min
(x)
and V
max
(x) could both be represented as horizontal lines and
SWR(x)would be the same everywhere along the length of the
tube. Attenuation within the tube, however, while having only
a slight effect on the individual maxima, causes the individual
voltage minima to increase with increasing distance from the
face of the specimen.
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