Mie scatter

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3D representation of the Mie scattering of red light (633 nm) on a spherical particle with a diameter of 2 µm. The particle is in the middle at , the light is emitted from the left. The different expansion of the surface corresponds to the intensity of the scattering in this direction ( logarithmic plot). The intensity of the scattered light depends on the scattering angle.

When Mie scattering or Lorenz-Mie scattering (after the physicists Gustav Mie and Ludvig Lorenz ) is defined as the elastic scattering of electromagnetic waves of spherical objects whose diameter is approximately the wavelength corresponding to the radiation. This scatter can be described physically with the Lorenz-Mie theory .

description

Court formation during the full moon , also known as corona , caused by the classical geometric scattering of small drops.
The Tyndall effect created by Mie scattering makes the area around the tower appear brighter. The apparent "shadow" arises from a lack of the effect within the shadow volume of the tower.

The Mie scattering creates the Tyndall effect . This arises from scattering on objects in which the particle diameter corresponds approximately to the wavelength.

The scattering on the molecules of the air is called Rayleigh scattering, the falling raindrops and floating fog dripping as classic scattering and only the emulsified fat droplets as Mie scattering, although all cases are exactly described by the Lorenz-Mie theory become. In practice, these cases can be easily separated from one another by the different degrees of polarization and the scatter distribution:

Type of dispersion Dependence on
the wavelength		 polarization Scatter distribution
Rayleigh strong with vertical scattering:
linear		 symmetrically forward and backward
Mie light with vertical scattering:
light to medium		 slightly asymmetrical to complex
classic (geometric)
on small droplets		 weak without mainly forward (visible through the formation of a courtyard ), but also
complex (no longer detectable through variation of the droplet size)
classic (geometric)
on large drops		 with transparent material ( Tyndall effect ): very narrow and weakly forward, so that no halo formation occurs;
additionally with transparent material (Tyndall effect): at a large angle
weak weak

Significance in radio technology

Mie scattering is also important in radio technology . In this way, the reflection and the radar cross-section of metallic bodies can be calculated whose circumference is in the order of magnitude of the wavelength of the radio waves. The effective reflective surface of a metal sphere with a diameter of a third of the wavelength is almost four times what would be expected according to classical scattering. Further, smaller maxima occur with integer multiples of the circumference to the wavelength.

literature

  • Gustav Mie: Contributions to the optics of cloudy media, especially colloidal metal solutions. Annalen der Physik , Volume 4, Vol. 25, 1908, pp. 377–445, doi: 10.1002 / andp.19083300302 .
  • Julius Adams Stratton : Electromagnetic Theory. McGraw-Hill, New York NY 1941.
  • Milton Kerker: The scattering of light and other electromagnetic radiation (= Physical Chemistry. Vol. 16, ISSN  0079-1881 ). Academic Press, New York NY et al. 1969.
  • Hendrik C. van de Hulst : Light scattering by small particles. Unabridged and corrected republication of the work originally published in 1957. Dover, 1981, ISBN 0-486-64228-3 .
  • Craig F. Bohren, Donald R. Huffman: Absorption and scattering of light by small particles. Wiley, 1983, ISBN 0-471-29340-7 .
  • Peter W. Barber, Steven C. Hill: Light scattering by particles. Computational Methods (= Advanced Series in Applied Physics. 2). World Scientific, Singapore 1990, ISBN 9971-5-0832-X .
  • Thomas Wriedt: Mie theory 1908, on the mobile phone 2008. Journal of Quantitative Spectroscopy & Radiative Transfer 109, 2008, pp. 1543–1548, doi: 10.1016 / j.jqsrt.2008.01.009 .

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