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The term backscattering is used for transmission in optical waveguides and in RF technology. In optical waveguides, it is a matter of a fraction of the light that has been deflected from its transmission direction by scattering being reflected within the optical waveguide and transmitted back in the direction of the light source. In RF technology, especially in WiFi, one selects and detects the backscattered RF signals and uses them to feed the low- power components.

Backscattering in optical fibers

In optical transmission technology, backscattering methods are used to determine irregularities, increased attenuation values or mismatches in optical fibers or FO connectors. Using the time course of the backscattered light, it is possible to measure not only the length and attenuation of an installed optical fiber from one end, but also local irregularities caused by too tight bending radii, manufacturing errors, bad splices or FO connectors. This technique is implemented in optical time domain reflectometry( OTDR).

Reflectivity of backscatter

Reflectivity of backscatter

There are several types of backscatter: Rayleigh scattering, Brillouin scattering, and Raman scattering. The best known is Rayleigh scattering, which is caused in optical waveguides by changes in the core glass. Whereby the core glass itself contributes to the backscattering by cross-sectional changes as well as by micro- and macro-curvatures. Microcurvatures refer to manufacturing tolerances in the position of the core glass relative to the cladding glass; macrocurvatures, on the other hand, occur during cable laying due to non- compliance with the bending radius.

The measure of backscatter is backscatter attenuation, the logarithm of the ratio of radiated to reflected energy. The backscatter attenuation is an important quality criterion for fiber optic connectors and splices.

Backscattering in RF technology

In RF technology, backscattering is used, for example, in WiFi and in RFID to extract energy from reflective radio frequencies to power low-power( LP) components, or RFID tags. The former technique is used in Wireless Sensor Networks(WSN) and Wireless Sensor and Actor Networks(WSAN), in machine-to-machine( M2M) communications, and in the Wireless Internet of Things(WIoT). WiFi networks often require much less energy than is transmitted. Because they have their own carrier signal, the reflective RF signals can be selectively detected and used to provide a supply voltage for low-power components such as sensors. The voltage from the WiFi backscattering can be used to charge the batteries of the LP components or to power them without batteries. The reflective radio frequencies are called backscatter and vary in level. Sometimes they are stronger, other times less so.

The further development of backscattering leads to interscattering, where radio signals from different technologies are transformed into another technology during transmission.

Englisch: backscattering
Updated at: 26.11.2018
#Words: 434
Links: transmission, indium (In), light, scattering, waveguide
Translations: DE

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