In the microstructure of a Transmission medium, a site at which electromagnetic waves are scattered.

Note 1: Examples of Scattering centers are vacancy defects; interstitial defects; inclusions, such as a gas molecules, hydroxide ions, iron ions, and trapped water molecules; and microcracks or fractures in Dielectric waveguides. Note 2: Scattering centers are frozen in the medium when it solidifies and may not necessarily cause Rayleigh scattering, which varies inversely as the fourth power of the wavelength. For example, in Glass optical fibers, there is a high Attenuation band at 0.95 m, primarily caused by scattering and Absorption by OH (hydroxyl) ions.