Standing wave
A
standing wave, also known as a
stationary wave, is a
wave that remains in a constant position. This phenomenon can occur because the medium is moving in the opposite direction to the wave, or it can arise in a stationary medium as a result of
interference between two waves traveling in opposite directions.
As an example of the first type, under certain meteorological conditions standing waves form in the atmosphere in the
lee of mountain ranges. Such waves are often exploited by
glider pilots.
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Standing wave in stationary medium. The red dots represent the wave nodes |
As an example of the second type, a
standing wave in a
transmission line is a wave in which the distribution of
current,
voltage, or
field strength is formed by the
superposition of two waves propagating in opposite directions. The effect is a series of nodes (zero
displacement) and anti-nodes (maximum
displacement) at fixed points along the transmission line. Such a standing wave may be formed when a wave is transmitted into one end of a transmission line and is reflected from the other end by an
impedance mismatch,
i.e.,
discontinuity, such as an
open circuit or a
short.
In practice, losses in the transmission line and other components mean that a perfect reflection and a pure standing wave are never achieved. The result is a partial standing wave, which is a superposition of a standing wave and a travelling wave. The degree to which the wave resembles either a pure standing wave or a pure travelling wave is measured by the
standing wave ratio (SWR).
Standing waves are also observed in physical media such as strings and columns of air. Any waves travelling along the medium will reflect back when they reach the end. This effect is most noticeable in musical instruments where, at various multiples of a string or air column's
natural frequency, a standing wave is created, allowing
harmonics to be identified. Nodes occur at fixed ends and antinodes at open ends. If fixed at only one end, only odd-numbered harmonics are available.
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List of wave topics :
Wave,
Amphidromic point,
Voltage standing wave ratio,
Trumpet,
Longitudinal mode,
Modelocking,
Seiche*
List of electronics topics :
Impedance,
Federal Standard 1037C,
Normal mode,
Cavity resonator,
Characteristic impedance,
Cymatics*
People:
Nikola Tesla*
Vibrations and Waves - a chapter from an online textbook
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Standing Waves experiment Shows how the point moves with frequency change.
