Fernfeldannahmen

Fernfeldannahmen refers to a set of assumptions used in physics and engineering, particularly in the study of waves and radiation. These assumptions simplify the mathematical analysis of electromagnetic fields, acoustic waves, or other wave phenomena when the observer or receiver is located at a significant distance from the source. The term "Fernfeld" is German for "far field."

The core of the fernfeldannahmen is that at great distances, the curvature of the wavefront originating from a point source can be approximated as planar. This simplification allows for the application of techniques that are more manageable than those required for spherical waves. For instance, in antenna theory, the far field approximation allows for the characterization of antenna radiation patterns without needing to consider the complex near-field interactions. Similarly, in acoustics, it simplifies the analysis of sound propagation over long distances.

Key aspects of the fernfeldannahmen include the assumption that the amplitude of the wave decays inversely with distance from the source and that the phase varies linearly with distance. This implies that interference effects and diffraction phenomena become less significant or exhibit predictable patterns in the far field. The specific distance at which these assumptions become valid depends on the wavelength of the radiation and the dimensions of the source. Generally, the far field is considered to begin at a distance that is a multiple of the wavelength or a characteristic dimension of the source, whichever is larger. Violations of these assumptions can lead to inaccuracies in calculations, especially in close proximity to the source.