Standing Wave - Opposing Waves

Opposing Waves

Standing waves

  • Standing wave in stationary medium. The red dots represent the wave nodes.

  • A standing wave (black) depicted as the sum of two propagating waves traveling in opposite directions (red and blue).

  • Electric force vector (E) and magnetic force vector (H) of a standing wave.

  • Standing waves in a string — the fundamental mode and the first 6 overtones.

  • A two-dimensional standing wave on a disk; this is the fundamental mode

  • A higher harmonic standing wave on a disk with two nodal lines crossing at the center.

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 of the same frequency 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. The failure of the line to transfer power at the standing wave frequency will usually result in attenuation distortion.

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 traveling wave. The degree to which the wave resembles either a pure standing wave or a pure traveling wave is measured by the standing wave ratio (SWR).

Another example is standing waves in the open ocean formed by waves with the same wave period moving in opposite directions. These may form near storm centres, or from reflection of a swell at the shore, and are the source of microbaroms and microseisms.

Read more about this topic:  Standing Wave

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